Assessment of Climate Indices in Drylands of Colombia

ASSESSMENT OF CLIMATE INDICES IN DRYLANDS OF COLOMBIA

Fredy Hernando NEIRA MENDEZ

“Con el apoyo del Programa Alßan, Programa de becas de alto nivel de la Unión Europea para América Latina, beca nº E04M034769CO”

“Supported by the Programme Alßan, the European Union Programme of High Level Scholarships for Latin America, scholarship No.(E04M034769CO)”.

Al artífice de mi existencia, A Mery y Ricardo los Autores de mis días A Ada, Julian y Juan

ACKNOWLEDGEMENTS

This work has been possible thanks to the contributions of many people.

First I owe my special gratitude to the ALBAN programme for the funding to develop this Master Programme in Europe. I wish to gratefully acknowledge the invaluable help of my promoter Prof. Dr. ir. Donald Gabriels for his guidance and supervision and his interest in study desertification in Latin America.

I want to give special thanks to the IDEAM, University of Valle in Colombia and the PHI-LAC project for supporting me with data of meteorological stations. Specially thanks to Yesid Carvajal and Martha Liliana in Cali, Colombia.

I also want to give my thanks to my friends Wim Verstraete and Vernon Dabalos for their help and support.

The support, love and sacrifice of my family and friends from Colombia.

ABSTRACT

Climate indices are used to determine drylands in seven different geographical zones of Colombia. These zones are selected from previous studies as the areas with land degradation and desertification problems. With secondary information of 391 stations the following indices are evaluated: Lang (1915), Thornthwaite (1948), De Martonne (1926), Emberger (1930), UNEP (1997) and Bagnouls-Gaussen (1957). From those, only the Lang, UNEP and Thornthwaite indices show drylands in Colombia although all of them result in different classification for each region.

Aggressivity of rainfall is evaluated using the Modified Fournier Index (MFI) (Arnoldus, 1980). The Caribbean, Magdalena, Santanderes and Nariño are the zones with higher aggressivity of rainfall. The Guajira zone however has index values between low and very low aggressivity.

Seasonality of rainfall is evaluated using the Precipitation Concentration Index (PCI) (Oliver, 1980). For almost all the zones, the areas with high seasonality are those classified as dry lands, and the areas with low seasonality are the more humid ones.

The Erosivity index (ErIn) is estimated using the CORINE (1995) methodology. The Caribbean zone shows a high erosivity index. Santanderes, Nariño and Magdalena zones have moderate to high values. The Guajira and Cauca zones have dominant moderate values and the Cundiboyacense between low to moderate erosivity.

SAMENVATTING

Klimaatindexen worden gebruikt voor het bepalen van ‘droge gebieden’ in verschillende geografische zones van Colombia. Deze zones werden geselekteerd uit vroegere studies als gebieden onderhevig aan landdegradatie en desertificatie problemen. Met meteorologische gegevens van 391 weerstations worden de volgende indexen berekend: Lang (1915), Thornthwaite (1948), De Martonne (1926), Emberger (1930), UNEP (1997) en Bagnouls-Gaussen (1957). Enkel de Lang, UNEP en Thornthwaite indexen toonden de ‘droge gebieden’ in Colombia aan, alhoewel met al de indexen verschillende ariditeitsklassen werden bekomen.

De aggresiviteit van de neerslag werd geëvalueerd met de ‘Aangepaste Fournier Index (Modified Fournier Index MFI) (Arnoldus, 1980). De Caribbean, Magdalena, Santanderes en Nariño zijn de zones met de hoogste neerslagaggressiviteit. De Guarjira zone heeft evenwel een lage tot zeer lage neerslagaggressiviteit.

De seizoensverdeling van de neerslag werd geëvalueerd door middel van de Neerslag Concentratie Index (Precipitation Concentration Index PCI) (Oliver, 1980). Voor nagenoeg al de zones werden de gebieden met de hoogste seizoensverdeling geklasseerd als ‘droge gebieden’, de zones met weinig (laag) seizoensverdeling zijn dan meer humied.

De erosiviteitsindex (ErIn) werd bepaald volgens de CORINE (1995) methode. De Caribbean zone heeft een hoge erosiviteitsindex. Santanderes, Nariño en Magdalena hebben middelmatige tot hoge waarden. Ook de Guajira en Cauca zones hebben overwegend middelmatige waarden terwijl in de Cundiboyacense zone er een laag tot middelmatige erosivitiet heerst.

ILLUSTRATIONS

LIST OF FIGURES

Figure 1. Location of Colombia in South America...... 15 Figure 2. Main Natural Regions of Colombia (IGAC, 1999) ...... 15 Figure 3. Micro Regions of Colombia (IGAC, 1999)...... 16 Figure 4. Lang climate classification of Colombia (IDEAM, 2001) ...... 21 Figure 5. De Martonne classification of Colombia (IDEAM, 2001)...... 22 Figure 6. Thornthwaite classification of Colombia (IDEAM, 2001)...... 23 Figure 7. Average Annual Precipitation Distribution in Colombia (IDEAM, 2001) ...... 24 Figure 8. Land use and cover in Colombia (IGAC, 2003)...... 28 Figure 9. Main processes of soil degradation in Colombia (IDEAM 2001)...... 29 Figure 10. Zones with potential of desertification in Colombia (IDEAM, 2001)...... 32 Figure 11. Location of the study zones...... 34 Figure 12. Location of meteorological stations and precipitation distribution in the Guajira zone...... 43 Figure 13. Location of climate stations and precipitation distribution in the Caribbean plateaus ...... 45 Figure 14. Precipitation distribution and meteorological stations in the Santanderes and Cesar zone...... 46 Figure 15. Precipitation distribution and climate stations in the Cundiboyacense high plateau ...... 47 Figure 16. Precipitation distribution and meteorological stations in the High Magdalena River basin ...... 48 Figure 17. Precipitation distribution and meteorological stations in the Cauca valley ...... 49 Figure 18. Precipitation distribution and climate stations in Nariño and Popayan high plateaus ...... 50

i Figure 19. Climate classifications of the Guajira peninsula ...... 52 Figure 20. Omberothermic curves for the Guajira peninsula ...... 54 Figure 21. Climate classifications of the Caribbean plateaus...... 58 Figure 22. Bagnouls - Gaussen Index distribution in the Caribbean plateaus...... 59 Figure 23. Omberothermic curves for some stations of the Caribbean plateaus ...... 60 Figure 24. Climate classifications of the Santanderes and Cesar zone...... 63 Figure 25. Bagnouls - Gaussen Index distribution in the Santanderes and Cesar zone...... 64 Figure 26. Omberothermic curves different stations in the Santanderes and Cesar ...... 65 Figure 27. Climate classifications of the Cundiboyacense high plateau ...... 68 Figure 28. Bagnouls - Gaussen Index distribution in the Cundiboyacense High plateau...... 69 Figure 29. Omberothermic curves for the Cundiboyacense high plateau...... 70 Figure 30. Tatacoa named “desert”...... 73 Figure 31. Climate zones of the High Magdalena River basin...... 74 Figure 32. Bagnouls - Gaussen Index distribution in the High Magdalena River basin ...... 75 Figure 33. Omberothermic curves for the Magdalena river basin ...... 76 Figure 34. Climate classifications of the Cauca valley...... 78 Figure 35. Bagnouls - Gaussen Index distribution in the Cauca valley...... 79 Figure 36. Omberothermic curve for the Cauca valley...... 80 Figure 37. Climate classifications of the Nariño and Popayan high plateaus...... 83 Figure 38. Bagnouls - Gaussen Index of Nariño and Popayan...... 84 Figure 39. Omberothermic curves for the Nariño and Popayan high plateaus...... 85 Figure 40a -40b. Linear relationship between PCI1 and PCI2 in the study zones ...... 87 Figure 41. Seasonal and Temporal Rainfall Distribution of the Guajira peninsula...... 88 Figure 42. Seasonal and Temporal Rainfall Distribution in the Caribbean plateaus...... 89 Figure 43. PCI Distribution in the Santanderes and Cesar zone...... 90 Figure 44. PCI Distribution in the Cundiboyacense high plateau ...... 90 Figure 45. PCI Distribution in the High Magdalena River Basin...... 91 Figure 46. Distribution of the PCI in the Cauca valley...... 91 Figure 47. Distribution of the PCI in the Nariño and Popayan high plateaus ...... 92 Figure 48. Linear relationship between MFI1 and MFI2 for all the regions ...... 93 Figure 49. Distribution of the MFI in the Guajira peninsula ...... 94

ii Figure 50. Distribution of the MFI in the Caribbean plateaus...... 95 Figure 51. Distribution of the MFI in the Santanderes and Cesar zone...... 95 Figure 52. Distribution of the MFI in the Cundiboyacense high plateau ...... 96 Figure 53. Distribution of the MFI in the High Magdalena River Basin...... 96 Figure 54. Distribution of the MFI in the Cauca valley...... 97 Figure 55. Distribution of the MFI in the Nariño and Popayan high plateaus...... 97 Figure 56. Distribution of “ErIn” for the Guajira and Caribbean zones...... 99 Figure 57. Distribution of “ErIn” for the Santanderes and Magdalena zones ...... 99 Figure 58. Distribution of “ErIn” for the Cundiboyacense and Cauca zones...... 100 Figure 59. Distribution of “ErIn” for the Nariño and Popayan high plateaus ...... 100

LIST OF FIGURES

Table 1. Distribution of Soil Orders in Colombia (IGAC, 2000)...... 27 Table 2. Percentage of area affected by erosion in Colombia (IDEAM, 2001)...... 30 Table 3. Degree of land degradation by aridity and erosion in Colombia (MinAmbiente, 2000) ...... 31 Table 4. Climate types proposed by Richard Lang (1915) ...... 36 Table 5. Climate types proposed by De Martonne (1923)...... 37 Table 6. Climate types of Emberger (1932)...... 38 Table 7. Thornthwaite climate classification (1948) ...... 38 Table 8. UNEP (1997) Climate classification...... 39 Table 9. BGI climate classification (1952)...... 40 Table 10. Precipitation Concentration Index classification ...... 41 Table 11. Modified Fournier Index scale...... 41 Table 12. Variability class of Modified Fournier Index ...... 42 Table 13. Aridity class of BGI...... 42 Table 14. Erosivity Index (ErIn)...... 42 Table 15. Aridity indices of Guajira peninsula...... 51 Table 16. Bagnouls - Gaussen climate classification for the Guajira peninsula...... 54

iii Table 17. Aridity indices of Caribbean Plateaus ...... 55 Table 18. Climate classification using Bagnouls - Gaussen index ...... 59 Table 19. Climate classifications of the Santanderes and Cesar zone ...... 61 Table 20. Climate classification using Bagnouls - Gaussen...... 64 Table 21. Climate indices of the Cundiboyacense high plateau ...... 66 Table 22. Climate classification using Bagnouls - Gaussen...... 69 Table 23. Climate classifications of the Low Magdalena basin ...... 71 Table 24. Bagnouls - Gaussen classification of the High Magdalena River basin ...... 75 Table 25. Climate classifications of the Cauca valley ...... 77 Table 26. Climate classification using Bagnouls - Gaussen...... 79 Table 27. Climate classifications of the Nariño and Popayan High plateaus ...... 82 Table 28. Bagnouls – Gaussen climate classification...... 84 Table 29. Relationship between PCI1 and PCI2...... 86 Table 30. Climate classification using Bagnouls - Gaussen...... 92 Table 31. Areas (ha) and percentage of drylands per study zone according to different climate indices ...... 103

TABLE OF CONTENTS

1. INTRODUCTION 1 1.1. OBJECTIVES 2 1.2. LIMITATIONS 3 2. LITERATURE REVIEW 4 2.1. DRYLANDS 4 2.1.1. Hyperarid environments 5 2.1.2. Arid areas 6 2.1.3. Semiarid areas 6 2.1.4. Dry Subhumid areas 6 2.2. EROSION 7 2.2.1. Types of soil erosion 8 2.2.2. Universal Soil Loss Equation (USLE) 9 2.2.3. Erosivity indices 12 3. GENERAL DESCRIPTION OF COLOMBIA 14 3.1. NATURAL REGIONS OF COLOMBIA 14 3.1.1. Caribe Region 17 3.1.2. Pacific Region 18 3.1.3. Andes Region 18 3.1.4. Orinoquia Region 19 3.1.5. Amazonas region 19 3.1.6. Insular region 19 3.2. CLIMATE OF COLOMBIA 20 3.3. SOILS OF COLOMBIA 25 3.4. LAND USE 27 3.5. LAND DEGRADATION IN COLOMBIA 28 3.5.1. Erosion 29

v 3.5.2. Desertification 31 4. METHODOLOGY 33 4.1. STUDY AREAS 33 4.2. DATA SOURCES 35 4.3. DELINEATION OF ARID ZONES 35 4.3.1. Lang climate classification (1915) 36 4.3.2. Aridity index of De Martonne (1923) 37 4.3.3. Aridity index of Emberger (1932) 37 4.3.4. Thornthwaite classification (1948) 38 4.3.5. UNEP Arid Index (1997) 38 4.3.6. Bagnouls – Gaussen classification method (1952) 39 4.4. RAIN EROSIVITY AND CONCENTRATION INDICES 40 4.4.1. Precipitation Concentration Index (PCI) 40 4.4.2. Modified Fournier Index (MFI) 41 4.4.3. Erosivity Index (ErIn) 42 5. DESCRIPTION OF THE STUDY ZONES 43 5.1. GUAJIRA PENINSULA 43 5.2. CARIBBEAN PLATEAUS 44 5.3. SANTANDER AND CESAR VERTIENTES 45 5.4. CUNDIBOYACENSE HIGH PLATEAU 46 5.5. HIGH MAGDALENA RIVER BASIN 48 5.6. CAUCA VALLEY 49 5.7. NARIÑO AND POPAYAN HIGH PLATEAUS 50 6. CLIMATE TYPES AND ARIDITY INDICES 51 6.1. GUAJIRA PENINSULA 51 6.2. CARIBBEAN PLATEAUS 55 6.3. SANTANDERES AND CESAR ZONE 60 6.4. CUNDIBOYACENSE HIGH PLATEAU 66 6.5. HIGH MAGDALENA BASIN 71 6.6. CAUCA VALLEY 77 6.7. NARIÑO AND POPAYAN HIGH PLATEAUS 81

vi 7. RAINFALL AGGRESSIVITY INDICES 86 7.1. PRECIPITATION CONCENTRATION INDEX (PCI) 86 7.2. MODIFIED FOURNIER INDEX (MFI) 92 7.3. EROSIVITY INDEX of CORINE (1995) 98 8. CONCLUSIONS 101 9. REFERENCES 106

vii Introduction

1. INTRODUCTION

In Colombia drylands have been estimated using different climate classifications. Most of them have been applied in different latitudes and are very accurate for temperate regions. As Colombia is located in the equatorial and tropical zones it is necessary to evaluate the most accurate indices to determine drylands in this latitudes.

Drylands are related to land degradation processes which make them susceptible to desertification. When erosion occurs in drylands becomes into desertification, which can be a serious problem due to the irreversibility of the process. Water erosion is the main soil degradation process in Colombia, reducing the productive capacity of the soils and the irreversible loss of other natural resources.

The magnitude of the erosion problem and the degree of development depends of factors such as slope, soil cover, management practices and soil type and rainfall which determine erodibility and erosivity respectively.

This study is done in order to analyse relationships between different arid indices applied for Colombia, using meteorological data of some of the main areas considered “dry” by the National Institute of Meteorology and Environment “IDEAM”. Drylands differ from one to another classification system, but in most of them cover approximately one fourth of the country as drylands. For this study seven zones are selected from those which are declared “in process of desertification” by the Ministry of Environment in Colombia. The study zones are “The Guajira Peninsula”, “The Caribbean plateaus”, “Santander and Cesar”, “The Cundiboyacense high plateau”, “The High Magdalena river basin”, “The Cauca valley” and ·the Nariño and Popayan high plateaus”.

Climate data of those regions was collected from secondary studies, using 391 meteorological stations from the years 1971 to 2000.

1 Introduction

The climate indices used to determine drylands are: Lang (1915), Thornthwaite (1948), De Martonne (1923), Emberger (1932), UNEP (1997) and Bagnouls - Gaussen (1952).

Aggressivity of rainfall or erosivity will be evaluated using the Modified Fournier Index (MFI). The Precipitation Concentration Index (PCI) will be used to estimate the temporal variation of the monthly rainfall.

Finally, the Erosivity index will be estimated using CORINE methodology (1995), which is based on the Modified Fournier Index and the Bagnouls - Gaussen Index.

1.1. OBJECTIVES

The main objective of this study is to determine an arid index showing the best representation for different regions in Colombia.

A comparison is made between the climate indices of De Martonne (1923), UNEP (1997), Thornthwaite (1948), Lang (1915), Emberger (1932) and Bagnouls-Gaussen (1952) for delineating the climate zones.

An evaluation is made of the erosivity of the rainfall using the Modified Fournier Index (MFI), the rain distribution using the Precipitation Concentration Index (PCI) and the erosivity index proposed by the CORINE project (1995) methodology.

A delineation of drylands prone to desertification is made at a regional level in Colombia using different aridity indices.

2 Introduction

1.2. LIMITATIONS

Although there are more climate data available, only the meteorological stations that record data from three decades were used. Different events as El Niño and La Niña were not analyzed.

Drylands in Colombia are not really delineated. Several studies show different areas which are considered dry but all of them vary according to the methodology or the classification system used. In this study the boundaries of the drylands were selected from the micro regions study, which was done at a national scale, and those regions are not completely homogeneous in climate characteristics.

Delineation of climate has been done using an interpolation method but the effect of relief and winds over precipitations is not studied.

3 Literature review

2. LITERATURE REVIEW

2.1. DRYLANDS

The term “drylands” refers to lack of water or water deficit in the soil to support primary production and nutrient cycling. The definition implies that the moisture input given by precipitation is lower than the moisture losses through evapotranspiration during one part of the year or even all the year around and in successive years.

Drylands can experience large in between-year variability in precipitation and they are not uniform. They differ in degree of moisture limitation and in the period they experience. Drylands can be classified based on climate and environmental attributes but their boundaries are neither static nor abrupt due to the high inter-annual variability in mean rainfall and to the occurrence of droughts that can last for several years (Gabriels, 2006).

The United Nations Convention to Combat Desertification UNCCD approach recognized four drylands subtypes: dry-subhumid, semiarid, arid and hyperarid drylands, based on an increasing level of aridity or moisture deficit. The level of aridity is given by the ratio of the mean annual precipitation to the mean annual potential evapotranspiration which is the amount of moisture that, if it were available, would be removed from a given land area by evaporation and transpiration. The long-term mean of this ratio is termed the "Aridity Index" (AI). Drylands are areas with an AI value of less than 0.65 (UNEP, 1997).

Susceptible drylands are those other than polar and sub polar with an AI between 0.05 and 0.65 which are arid, semiarid and dry-subhumid areas susceptible to desertification (Gabriels, 2006).

4 Literature review

Drylands occurs in 40 percent of the earth’s surface with 20 percent of the global population (UNEP, 1997). Drylands are vulnerable to degradation and to natural droughts which induce stresses on plant, animal and human population. Land degradation processes occurring in drylands, induced by both human activities and climate changes, called “desertification”.

In Latin America, the population living in drylands, as reported by UNDP/UNSO in 1997 was about 120 million or 29% of the total population. The same source reports for that time 103 million ha classified as arid (5%); 285 million ha as semiarid (14%) and 150 million ha as dry subhumid (7.5%) of a total of 538 million ha (26.5%) classified as drylands.

For Latin America, Dregne (1991) reports a total area of 306 million ha affected by desertification, which is approximately 17% of the total land area and around 72% of all used drylands. For the same sub-continent, the project UNEP/GLASOD reports in 1997 that about 79 million ha of drylands are affected by human-induced soil degradation, 4.5% of total Latin American land area.

2.1.1. Hyperarid environments

These zones are considered “the true deserts” and are not considered prone to desertification, with a very limited and highly variable rainfall amounts (up to 100%) on a monthly basis without seasonal inter annual rainfall regime. Those areas have year-long periods without rainfall. The aridity index (P/ETP) is less than 0.05 (AI<0.05). The annual precipitation in winter rainfall is less than 50 mm and in summer rainfall less than 100 mm. Perennial vegetation is largely confined to river beds, with some growth of annual plants in favourable sites. Grazing is severely restricted or impossible and irrigation must be practiced.

5 Literature review

2.1.2. Arid areas

Those areas are characterized by a mean annual precipitation between 50 - 200 mm per year in winter rainfall areas and 100 - 300 mm in summer rainfall areas. Inter annual variability is between 50 to 100 % range. Use of underwater resources is highly susceptible to climate variability and pastoralism is possible but without mobility (AI = 0.03-0.2). The vegetation includes woody shrubs, succulents, some perennial grasses and many annual grasses. Grazing and irrigation is practiced, rainfed cropland does not occur.

2.1.3. Semiarid areas

Those areas have high seasonal rainfall regimes and mean values up to 600 mm in summer rainfall areas and 500 mm in winter regimen. Interannual variability is between 25 to 50 %. Grasslands and sedentary agriculture are susceptible to seasonal and inter annual moisture deficiency. AI = 0.2 – 0.5. The main land use is grazing, extensive rainfed cropland in wetter parts. Typical coverage are grasslands, shrubs and woodlands.

2.1.4. Dry Subhumid areas

Areas with highly seasonal rainfall regimes and with less than 25% of inter annual variability. Those areas are also susceptible to degradation caused by seasonality of the rainfall, drought periods and intensive with human use. AI = 0.2 – 0.65. Typical vegetations are grasslands, savannahs, woodlands, with rainfed cropland and grazing. Mean precipitation values of 500-850 during winter rainfall and from 600 to 1000 in the summer rainfall.

6 Literature review

2.2. EROSION

Soil erosion is the detachment and movement of soil particles by the erosive forces of wind or water. Soil detached and transported away from one location is often deposited at some other place. While soil erosion can be controlled, it is almost impossible to stop completely. The process may be natural or accelerated by human activity. Depending on the local landscape and weather conditions, erosion may be very slow or very rapid (Soil Survey Staff, 1993).

Soil erosion can be natural or of human origin. Erosion that takes place naturally, without the influence of human activity, is termed geological or natural erosion (Brady, 2002). Accelerated erosion is largely the consequence of human activity. The primary causes are tillage, grazing, and cutting of timber.

Water erosion results from the removal of soil material by flowing water. A part of the process is the detachment of soil material by the impact of raindrops. The soil material is suspended in runoff water and carried away. Four kinds of accelerated water erosion are commonly recognized: sheet, rill, gully, and tunnel (piping).

The mechanics of soil erosion by water occurs in three steps (Brady, 2002):

- Detachment of soil particles from the soil mass by raindrop impact - Transportation of the detached particles downhill by floating, rolling, dragging and splashing. - Deposition of the transported particles at some lower place in the landscape.

7 Literature review

2.2.1. Types of soil erosion

Natural erosion

Natural erosion is a process that transforms soils into sediment. Soil erosion that takes place naturally, without the influence of human activity, is termed geological erosion (Brady, 2002). It is a natural levelling process. Natural erosion has sculptured landforms on the uplands and built landforms on the lowlands. Its rate and distribution in time controls the age of land surfaces and many of the internal properties of soils on the surfaces.

Accelerated erosion

Accelerated erosion is largely the consequence of human activity. The primary causes are tillage, grazing, and cutting of timber. The rate of erosion can be increased by activities other than those of humans. Fire that destroys vegetation and triggers erosion has the same effect. The spectacular episodes of erosion, such as the soil blowing on the Great Plains of the Central United States in the 1930s, have not all been due to human habitation. Frequent dust storms were recorded on the Great Plains before the region became a grain- producing area. "Natural" erosion is not easily distinguished from "accelerated" erosion on every soil. A distinction can be made by studying and understanding the sequence of sediments and surfaces on the local landscape, as well as by studying soil properties (USDA, 1993).

Erosion can be accelerated through the activities of human beings such as the removal of surface vegetation and residue cover in agricultural cultivation, forest harvesting, rangeland grazing, surface mining, urban and highway construction. Tillage

8 Literature review implements, forest harvesting equipment, mining activities, and construction equipment all disturb the soil structure, which can also reduce the soil's resistance to detachment.

2.2.2. Universal Soil Loss Equation (USLE)

Several methods and equations to estimate and predict soil erosion by water have been proposed. Most common worldwide applied is the Universal Soil Loss Equation (USLE). The equation development started with Zing’s equation (1940), and the final form was defined by Wischmeier and Smith (1978). This equation was modified into the Revised Universal Soil Loss Equation (Renard, 1997). This equation is a model to predict sheet and rill erosion based on six major factors: rainfall erosivity (R), soil erodibility (K), slope length factor (L), the slope steepness (S) and the erosion control practices (P). The product of those factors is equal to the total soil loss (A) written in the equation: A = R x K x L x S x C x P Where soil loss (A) is expressed in tons per hectares.

The Rainfall Erosivity Factor (R)

R is defined as the aggressivity of the rainfall to induce soil erosion or the potential ability of rain to cause erosion. R is equal to the product of kinetic energy (E) of a rainstorm. Raindrops parameters necessary to quantify rainfall erosivity are the size, distribution and terminal velocity of individual raindrops (Gabriels, 2006).

Wischmeier and Smith (1958), based in an extensive statistical analysis that the best correlation with soil loss is given by a storm’s maximum intensity of 30 minute duration

(EI30). The factor R is the calculated by the equation:

R = EI30 Where R = Erosion index of the storm (MJ.mm/ha.h) E = total kinetic energy of the storm (MJ/ha)

I30= Maximum intensity during 30 min of the storm (mm/h)

9 Literature review

The erosive power of the raindrops is determined by the kinetic energy of the rainfall, which is determined by the distribution and the fall velocity of the raindrops (Poessen, 1992).

Kinetic Energy (E)

The energy supplied by falling drops to produce erosion is the kinetic energy (E), calculated by Morgan (1980) as follows:

KE = 1 mv2 2 Where m = mass of the falling raindrops (kg) V = terminal velocity of the falling raindrops (ms-1)

Kinetic energy is considered the major factor initiating soil detachment (Lal, 1988) and the other soil erosion process depend on the rate of particle detachment which increases with heavy rains, large drops and kinetic energy.

Rainfall intensity (I)

Rainfall intensity is defined as the instantaneous rate of rainfall occurring at a point. Precipitation intensity is defined by WMO as the amount of precipitation, collected per unit time interval. According to this definition, precipitation intensity data can be derived by the measurement of precipitation amount using an ordinary precipitation gauge.

The Soil Erodibility Factor (K)

K is the soil erodibility factor which represents susceptibility of soil to erosion measured under a standard unit plot condition. Main soils properties influencing this factor are: texture, organic matter, soil structure and permeability of the soil profile.

10 Literature review

The Topographic Factor (LS)

L is the slope length factor, representing the effect of slope length on erosion. It is the ratio of soil loss from the field slope length to that from a 22.1 meter length on the same soil type and gradient. Slope length is the distance from the origin of overland flow along its flow path to the location of either concentrated flow or deposition. Fortunately, computed soil loss values are not especially sensitive to slope length and differences in slope length of more or less 10% are not important on most slopes, especially flat landscapes.

S represents the effect of slope steepness on erosion. Soil loss increases more rapidly with slope steepness than it does with slope length. It is the ratio of soil loss from the field gradient to that from a 9% slope under otherwise identical conditions. The relation of soil loss to gradient is influenced by density of vegetative cover and soil particle size.

The Crop Management Factor (C)

C is the cover-management factor. The C-factor is used to reflect the effect of cropping and management practices on erosion rates. It is the factor used most often to compare the relative impacts of management options on conservation plans. The C-factor indicates how the conservation plan will affect the average annual soil loss and how that soil-loss potential will be distributed in time during construction activities, crop rotations or other management schemes.

The Conservation Practice Factor (P)

P is the support practice factor. The RUSLE P-factor reflects the impact of support practices and the average annual erosion rate. It is the ratio of soil loss with contouring and/or strip-cropping to that with straight row farming up-and-down slope. P-factor

11 Literature review differentiates between cropland and rangeland or permanent pasture. Both options allow for terracing or contouring, but the cropland option contains a strip-cropping routine whereas the rangeland/permanent-pasture option contains an "other mechanical disturbance" routine (Renard et al 1995).

2.2.3. Erosivity indices

The EI30 index has been used in many places but for tropical conditions it is not entirely satisfactory. Lal (1976) reported that this index might underestimate the kinetic energy of tropical storms and Hudson & Jackson (1959) found in Zimbabwe that this index was not efficient.

As a result, other indices have been proposed by different authors. Erosivity indices are used to assess a storm or the rainfall pattern which describes its capacity to erode soil from unprotected field (Wischmeier, 1959).

Hudson (1971) defined the KE > 1 index as the sum of the kinetic energies in storms with intensities greater than 1 in.h-1 (25.4 min.h-1). This index was based on the concept that there is a threshold value of intensity at which rain starts soil erosion. This index could be more adequate for tropical soils with well structured profiles and high infiltration rates.

Lal (1976) proposed the AIm index to assess rainfall erosivity. The AIm index is defined as the product of total rainfall (A) in cm and maximum intensity (Im) in cm.h-1 for a minimum duration of 7.5 minutes.

Fournier (1960) defined a rainfall distribution index (FI), as the ratio between main rainfall for the wettest month of the year (pm) and the annual precipitation (P) using the formulae: p2 FI = m P

12 Literature review

Arnoldus (1980) determined that the Fournier index (FI) and EI30 were poorly correlated (r2=0.55) and he proposed a Modified Fournier Index (MFI), considering the rainfall of all the months. The new index proposed was:

2 p MFI = ∑ P Where p : monthly rainfall P : annual rainfall

Precipitation Concentration Index (PCI) was proposed by Oliver (1980), and it expresses the seasonal and annual rainfall variability in %. Low values of PCI indicate a uniform rainfall distribution and high values represents a high concentration of rainfall or seasonality. PCI index can be estimated using rainfall concentration of a mean year (PCI1) and using multi-annual data (PCI2). Oliver (1980) and Michiels (1992) demonstrated that PCI was appropriate to evaluate and compare concentration of rainfall between stations.

The formulae to calculate PCI proposed by Oliver (1980) is: ∑ p2 ∑ p2 PCI = 100. = 2 P2 ∑()p Where p : monthly rainfall P : annual rainfall

The CORINE (1995) project applied in Europe an erosivity index (ErIn) based in the Modified Fournier index which gives a variability class (Vc) and the Bagnouls – Gaussen Index which gives an aridity class (Ac). Both classes are combined to give the erosivity index, which is equal to the product of variability class and aridity class. ErIn = Vc x Ac

13 General Description of Colombia

3. GENERAL DESCRIPTION OF COLOMBIA

Colombia is located in the Northwest of South America, on the equatorial line with most of its land in the Northern hemisphere, between latitudes 12°26’46” N in the Guajira peninsula and 4° 12’30” S in the Amazon river and within 60° 50’54” W longitude on the Island of San José in the Negro river, limit between Colombia, Brazil and Venezuela and 79° 02’33” W longitude in Cabo Manglares in the Pacific Ocean (figure 1). The continental surface area of the country is 1141748 km2.

Colombia has no seasons, but due to its geographic location in the equatorial and tropical latitudes and topographic characteristics, Colombia has several kinds of climates. The temperature varies with altitude, from very hot in the lowlands to very cold in the high mountains. Moisture condition varies also from hyperarid in the Guajira desert to hyper humid regions in the Pacific region. Rainfall precipitation varies from less than 500 mm per year in the Guajira peninsula to more than 11000 mm in the Pacific region.

Colombia has also extra territories as the archipelagos of San Andrés, San Bernardo and El Rosario scattered in the Caribbean Sea, the islands of Barú and Tierra, in the Caribbean sea, and the islands of Malpelo, Gorgona and Gorgonilla in the Pacific Ocean.

3.1. NATURAL REGIONS OF COLOMBIA

Geographical, topographical and climate conditions make of Colombia a very heterogeneous country. Those differences are marked in six main natural regions: The Caribe, Pacific, Andes, Orinoquia, Amazonas and Insular (figure 2).

14 General Description of Colombia

Colombia

Figure 1. Location of Colombia in South America

6 1 1 Caribe

2 Pacific

4 3 Andes 3 2 4 Orinoquia 6 5 Amazonas 5 6 Insular

Figure 2. Main Natural Regions of Colombia (IGAC, 1999)

15 General Description of Colombia

1 3

REGION MICRO REGIONS 5 4 INSULAR 1 San Andres archipelago 6 2 Pacific cays and islands 3 Guajira Peninsula 33 4 Sierra Nevada de Santa Marta 5 Magdalena river delta 8 32 CARIBE 6 Caribean Savannahs 7 7 Sinu and San Jorge Valleys 9 8 Mompox depression 31 9 Uraba golf

26 17 30 41 12 24 29 37 38 13 28 23 36 39 34 11 25 40 2 22 27 47 45 18 42 14 3543 21 48 15 44 52 46 49 54 50 51

REGION MICROREGIONS 10 Northwest of Western Andes 11 Southwest of Western Andes PACIFICO 12 Baudo serrania REGION MICROREGIONS 13 Atrato and San Juan Valeys 14 Pacific plateaus 15 Nariño high plateau 16 Fosa del Patia 36 Piedemonte llanero 17 NororienteCordOcc 37 Llanuras dedesborde piedemonte 18 AltiplanodePopayan 38 Llanuras del rio Meta 19 Cauca valley ORINOQUIA 39 Llanuras del rio Orinoco 20 Cauca canyon 40 Llanuras rios Meta Guaviare 21 MacizoColombiano 41 Pantanos del rioArauca 22 CordCentralmeridional 42 Serrania dela Macarena 23 MacizoVolcanico 43 Piedemonte Amazonico 24 Montaña Antioquegna ANDES 44 Llanuras del rio Caqueta 25 Alto Magdalena 45 Llanuras Guaviare - Inirida 26 Magdalena medio 46 Putumayo Caqueta 27 VertMagdalenense C Or 47 Penillanuras sur pto Inirida 28 Altiplano Cundiboyacense 48 Llanuras Inirida -Yari 29 Montaña Santandereana AMAZONAS 49 Amazonas meridional 30 Fosa Suarez y Chicamocha 50 LlanurasdeIgaraParana Putumayo 31 Macizode Santurban 51 ConfluenciaApaporis Caqueta 32 Catatumbo 52 Serranias y montes isla 33 Serrania Motilones 53 Llanuras guaviare Inirida enOrinoco 34 Vert Llanera Cord Or 54 Llanuras deCaqueta,Yari,Miriti y Parana 35 Vert Amazonica Cord Or

Figure 3. Micro Regions of Colombia (IGAC, 1999)

16 General Description of Colombia

The main regions are divided in micro regions with topographic and climate characteristics. Figure 3 shows the 54 micro regions differentiated in Colombia by the Colombian Institute of Geography Agustin Codazzi (IGAC). From those, the driest micro regions will be selected in order to evaluate the arid indices using information of meteorological stations. The selected areas will be described later.

3.1.1. Caribe Region

The Caribe region with approximately 11 millions hectares is located in the North zone of the country to the Atlantic Ocean, from the Guajira peninsula to the Urabá gulf. This is a level region, crossed by main rivers as Magdalena, Cauca, San Jorge and Sinú, which form near the coast wetlands and marshy areas. This region with 1400 km of coast border, between Venezuela and Panama, presents varied geographic features as gulfs, bays and river deltas. The climate is very warm (27°C), with six months of rain and six dry months. Mostly 20% of the national population is located in this region (DANE, 2001) which makes this region as the second important in the country.

The Caribe region presents micro regions with very contrasting characteristics: the Guajira desert with less than 500 mm of water per year; the Mompox wetlands, under the sea level; the hills, savannah, the both marine and fluvial plateaus, with 1000 to 2000 mm of water per year (IDEAM, 2001); and finally the Sierra Nevada de Santa Martha, a group of mountains separated from the Andes but from the same genesis, characterized for high slope lands, different climate levels, from hot (24°C) to perpetual snow, and precipitations from 1000 to 3000 mm per year (IDEAM, 2001). In the driest zones the soils are neutral to slightly alkaline and the more humid zones soils are dominantly acid. The main activities are livestock and crops such as banana, sugar cane, cotton, tobacco and some fruits.

The Caribbean region is composed by the micro regions: Guajira peninsula, Sierra Nevada de Santa Marta, Magdalena River Delta, Caribbean Savannahs, Sinú and High San Jorge valleys, Momposina depression and Urabá golf.

17 General Description of Colombia

3.1.2. Pacific Region

Between the borders of Panama and Ecuador, with approximately 101000 km2 (10.1 millions ha) limited by the Pacific Ocean and the Western mountain range of the Andes, this region is a long plain interrupted to the north by small mountainous areas, crossed by infinity of rivers of torrential character, short, due to the proximity to the sea of the mountain range. The warm climate and the high rainfall amount make of this region a promise in flora subject and fauna. The population is very low due to the unfavourable healthy conditions caused by high temperature and rainfall.

This region is characterized by high precipitation with values from 4000 mm per year in the South to more than 11000 mm in the North (IDEAM, 2001). Although almost all the region still with native forest, the colonization processes in the latest years, due to the social internal conflict of the country, is changing the land use from native forest to agricultural lands in the southern part and wood extraction in the North.

3.1.3. Andes Region

This region occupies around 313000 km2 (31.3 millions ha), equal to 27.4% of the total area of the country. It is formed by three mountain ranges including plateaus and valleys. Geologically, it is formed by volcanic material, sedimentary and metamorphic rocks and quaternary sediments. Due to the variation of elevation, this region has different temperature levels, from the hottest valleys (Magdalena and Cauca) to the Paramus and Glaciers (more than 4800 meters above sea level). The precipitation is variable along this region, from 500 to 5000 mm per year (IDEAM, 2001).

The Andes is the main region of the country, with almost 70% of the population living there in activities as agriculture, livestock and industry. In the valleys of the rivers Cauca and Magdalena, with the warm climate and typically tropical vegetation, the agriculture is extensive. In the mountain ranges with tempered climate there is agricultural

18 General Description of Colombia development with coffee and plantain culture. The high plateaus with more fresh climate, are very favourable to the development of human activity, with abundant cattle, cereals, horticulture and potato.

3.1.4. Orinoquia Region

With 300263 km2, (26.3% of the national territory) and a density of 3.3 inhabitants by km2, it occupies a vast zone to the East of the Andes mountain range. It is an immense plateau, crossed by several rivers flowing to the Orinoco. The climate is warm and dry, with original natural savannah vegetation with grass. The flooding system caused by the rivers in the wet season made of this a very rich region in fauna. The population is low and the majority is dedicated to the livestock with low productivity. In the recent years new crops have been introduced such as oil palm. The precipitation in this region is from 2000 to 3000 mm per year with homogeneous temperatures around 27°C.

3.1.5. Amazonas region

Located in the South East of Colombia with 327315 km2 (almost 30% of the country). The Amazonas region consists of an immense plain, slightly to moderate undulated. The density of population is 0.6 inhabitants per km2, indicative of an uninhabited extension. Although its vegetation is mainly typical tropical rainforest, some crops have been introduced by the recently colonization process. This region presents precipitation values between 2500 and 5000 mm per year. The Amazonas region is considered a very fragile ecosystem.

3.1.6. Insular region

This region represents a complex of archipelagos, islands and cays in the Caribbean Sea and in the Pacific Ocean.

19 General Description of Colombia

3.2. CLIMATE OF COLOMBIA

Some climate classifications have been made for Colombia by the Institute of Meteorology and Environment “IDEAM”. The most common used are Caldas – Lang (1915), De Martonne (1928) and Thornthwaite (1948).

Using the Lang classification, Colombia shows all the climate types from desert to very humid. Desert occurs mainly in the North (in the Guajira peninsula) and some other small areas that are not shown at this scale. The arid areas are located mostly in the Caribe region: one part in the south of the Guajira peninsula and the other part to the west of Sierra Nevada de Santa Marta. The semiarid climate zone is mainly in a great part of the Caribe region and in part of the Andes, spread out in different localities. The semi humid climate is presented in a great part of the Andes and in the Orinoquia regions with the southern belt of the Caribe region and the Insular areas. Those four climate types are considered dry and they included more than 25% of the country as is shown in figure 4. The Amazonas region is completely humid and the Pacific region is between humid and very humid.

Using the classification of De Martonne, the country appears to be more humid. The desert climate is restricted to less than 1% of the country in the North, in one small plot of the Guajira peninsula, which in this case is the only arid region of the country. The semiarid climate corresponds almost to all the rest of the Caribe region and in some areas in the Andes, occupying 10% of its surface. The rest of the Andes, the Orinoquia, the Amazonas and the Insular regions are between humid and very humid and the Pacific region is very humid with no seasonal variation during the year. According to this classification, drylands in Colombia are reduced to almost 10 % of the country, mainly in the Caribe and small spots in the Andes (figure 5).

The classification of Thornthwaite climate classification based in water deficit and excess in mm per year is shown in figure 6. Although this classification does not show

20 General Description of Colombia desert regimes, it differs from de Martonne and is more similar with Lang for dry climates. The Guajira climate varies from arid to Semiarid, most of the Caribe region, Part of the Andes and the Insular region are considered dry.

77º 75º 73º 71º 69º

12ºN 12ºN

10ºN 10ºN

0 100 200 Km 8ºN 8ºN

6ºN 6ºN

4ºN 4ºN

2ºN 2ºN

0º 0º

Lang Factor Climatic class P/T Desertic < 20 2ºS Arid 20 – 40 Semiarid 40 – 60 Semi Humid 60 – 100 Humid 100 – 160 Very Humid > 160 4ºS 79º 77º 75º 73º 71º 69º

Figure 4. Lang climate classification of Colombia (IDEAM, 2001)

21 General Description of Colombia

77º75º 73º 71º 69º

12ºN

10ºN 10ºN

0 100 200 Km 8ºN 8ºN

6ºN 6ºN

4ºN 4ºN

2ºN 2ºN

0º 0º

Climatic class Arid index 2ºS Arid < 5 Semiarid 5 – 10 Sub Humid 10 – 20 Humid 20 – 35 Very Humid 35 – 100 Extremely Hum > 100 4ºS 79º 77º 75º 73º 71º 69º

Figure 5. De Martonne classification of Colombia (IDEAM, 2001)

22 General Description of Colombia

77º75º 73º 71º 69º

12ºN

10ºN 10ºN

0 100 200 Km 8ºN 8ºN

6ºN 6ºN

4ºN 4ºN

2ºN 2ºN

0º 0º

Water deficit Water excess Climatic class (mm/ year) (mm/ year) Arid > 1000 Semiarid 500 – 1000 Dry 0 – 500 2ºS Humid 0 – 500 Slightly Humid 500 – 1000 Mod Humid 1000 – 1500 Very Humid 1500 – 2000 Extremely Humid > 2000

4ºS 79º 77º 75º 73º 71º 69º

Figure 6. Thornthwaite classification of Colombia (IDEAM, 2001)

The precipitation in Colombia is determined by spatial and temporal variations of the Inter Tropical Convergence Zone joining the general circulation of the tropical and

23 General Description of Colombia subtropical winds and the interaction of these factors with the relief of the country. The distribution of the precipitation is heterogeneous and complex. In some regions the dry season is more predominant (more than six months) than the rainy season. Other regions have two dry and two rainy seasons during the year: In some areas as in the Pacific, the rainy season cover almost the whole year in contrast with the arid and desert zones with a dry season for almost the whole year around. Figure 7 shows the average annual precipitation distribution in Colombia (IDEAM, 2001).

Figure 7. Average Annual Precipitation Distribution in Colombia (IDEAM, 2001)

24 General Description of Colombia

3.3. SOILS OF COLOMBIA

Colombia has a great diversity of soils due to the different climate, geology, topography and vegetation but most of the soils are not suitable for agriculture. 50% of the soils of the country should be preserved in forest or natural reserve: the Paramus in the Andes region which play an important role in the maintenance and regulation of water resource for the population (Cortez, 1994). 30% of the soils are located on steep slopes with serious limitations for agriculture in the Andes region. Almost all the Amazonas and Pacific regions should be kept in forest due to the susceptibility of their soils to erosion and the high rainfall values, above 4000 mm of water per year (Malagón, 2003). Part of the Orinoquia and Caribe wetlands which act as water flooding regulators and also play an important role in the natural productivity of local fauna and migrating birds, which come from the northern part of America to the South in the winter season (Aguilera and Neira, 1998). Another restriction for agricultural use of the lands are water limitation as the Guajira desert and the presence of very acid and old soils with high aluminium content in the Orinoquia and Amazonas (IDEAM, 2001).

The fertile soils for agriculture use occupies only around 20% of the total area of the country, located mainly in the inter Andes valleys (Cauca and Magdalena rivers) and part in the Caribe and in the High Plateaus of the Andes regions (IDEAM, 2001).

Nowadays, Colombia is confronting serious problems of soil degradation, due to the deforestation, mismanagement, over grazing and pollution as main factors involved in the erosion and acidification of the soils. In mangroves and wetlands ecosystems oxidation problems occurs due to drainage practices.

In the Andes region the dominant soils are formed by volcanic ash. Those Andisols are present in slope lands and are characterized by moderate to good fertility but with very high susceptibility to soil erosion and landslides.

25 General Description of Colombia

In the Amazonas region (around 80% of the undulate landscape) and part of the Orinoquia (the well drained high plateau), the main soils are Ultisols and Oxisols, characterized by the high acidity. These soils have a poor fertility level, mainly Ultisols and Oxisols, with high aluminium contents being toxic for most crops.

The Amazonas is characterized by high temperatures and high precipitation well distributed along the year which determine the kind of ecosystem: tropical rain forest. In the Orinoquia, where the temperature is also high but the precipitation is distributed in one part of the year, the type of ecosystem is a tropical savannah with common occurrence of petroferric horizons. The Amazonas has high biomass productivity and the Orinoquia has very low biomass productivity (Malagón, 2003). The Orinoquia floodplain soils, originating from quaternary sediments and variable floods with aeolian influence is classified mainly as Spodosols.

The Caribe region is in contrast with the other three regions in climate, parent material and vegetation type. Soils in this region have 2/1 shrinking and swelling clays such as Vertisols, Mollisols, suitable for agriculture and livestock production and Aridisols in the Guajira peninsula, limited by the presence of salts and sodium. The natural savannah, with acid soils is also present in the western part of this region.

Entisols, Inceptisols and Alfisols occur all over the country in few amounts. Entisols occur predominantly in river floodplains and erosional landscapes, while the Inceptisols are in more slightly slopes and the Alfisols in high alluvial terraces.

Histosols occur in two main micro regions in the Andes zone: the Cucunuba lacustrae valley and the high Putumayo, in the South of the country.

26 General Description of Colombia

Table 1. Distribution of Soil Orders in Colombia (IGAC, 2000).

ORDER Hectares % of the country Entisols 22567734 19.8 Inceptisols 33624988 26.5 Mollisols 2741320 2.4 Alfisols 2534637 2.2 Andisols 8954567 7.8 Histosols 3041274 2.7 Vertisols 1615033 1.4 Ultisols 24613701 21.6 Oxisols 10879165 12.5 Aridisols 651248 0.6 Spodosols 718725 0.6 Others (water) 2232408 2.0

3.4. LAND USE

The IGAC (Geographic Institute Agustin Codazzi) reports for the year 2003 the coverage and land use in Colombia: forest land covers 50.7% of the total area of the country, grasslands 26.6% and savannah 10.8% (both used for cattle and livestock), agricultural lands 3.7%, lagoons and wetlands 2.6% and Paramus 1.9%.

According to IGAC, grassland is the land use which tends to increase while forest lands are decreasing considerably in the last fifty years.

The actual land use is affecting the biodiversity, the agricultural productivity and the environment producing erosion, affecting the quality of the natural resources and increasing socio economical conflicts (figure 8).

27 General Description of Colombia

Figure 8. Land use and cover in Colombia (IGAC, 2003)

3.5. LAND DEGRADATION IN COLOMBIA

There are several processes that express land degradation. Some of them are physical which refer to the loss of vegetal coverage, soils and water by deforestation, erosion or desertification. Others involve biochemical processes that reduce the quality of the resources in considerable way, such as the slow depletion of soil fertility through the loss of organic matter and micro organisms, compaction or nutrients lixiviation.

In Colombia, activities such as deforestation, burning, overgrazing, use of pesticides, excessive use of soluble fertilizers, mismanagement of irrigation water, excessive tillage with inadequate machinery, use of mono cultures, clean agricultural systems, among others are some factors that favours the development of land degradation processes. One of the main degradation processes is the soil erosion, which is the most dangerous and related with the decrease of quality level of the population involved (Leon, 2003). Erosion is also the most common degradation process due to the relief of the country, agricultural activities and human settlements which are located mainly in the Andes region. Other land degradation problems in Colombia are: desertification, mass movements, sedimentation, coastal and glacier erosion (IDEAM, 2001).

28 General Description of Colombia

DEGRADATION PROCESSES

Erosion by mining and constructions Complex erosion

Aeolian erosion

Gully Erosion River bed erosion

Sheet erosion Karstic erosion Marine Erosion

Sedimentation

Meteorization

Mass movement

Figure 9. Main processes of soil degradation in Colombia (IDEAM 2001)

3.5.1. Erosion

In Colombia, erosion has been estimated by three institutions. The National Institute of Natural Renewable Resources - INDERENA (former Ministry of Environment) made the first estimation in 1977. The IGAC made two studies, in 1987 using aerial photographs and in 1998 through satellite images. The IDEAM (Institute of Environmental Studies) made two estimations, in 1998 and in 2000 using models. Table 2 shows the erosion degree levels reported and the volume in hectares of soils affected.

29 General Description of Colombia

Table 2. Percentage of area affected by erosion in Colombia (IDEAM, 2001)

Degree of INDERENA IGAC IDEAM IGAC IDEAM erosion 1977 1987 1998 1998 2000 Without erosion 24.8 48.5 0 14.7 52 Not perceived 44.9 4.6 Slight 36.4 28.0 45.5 19.5 9.5 Moderate 12.8 12.9 11.1 11.3 8.9 Severe 0.6 7.8 7.8 3.3 10.8 Bad Lands 1.6 0.7 0.5 14.2 Others 23.8 2.1 35.6 5.8 TOTAL 100 100 100 100 100

The differences in the degrees of erosion calculated by these institutions may look confusing. This can be explained by the detail level of every study and the methodologies used. The IGAC determines the actual erosion using aerial photographs or satellite images. Depending on the scale and the time, the erosion evidences can not be shown in the remote sense images. The IDEAM, which is the official institution in charge of the meteorology and climatology affairs, has made some estimations or predictions using the precipitation data and soil characteristics.

While IDEAM reports for 2000 around 25% of the lands with severe erosion, the IGAC shows for the same year around 4% with the same erosion degree. Same divergences appears are shown for the slight class (19.5 % by IGAC and 9.5% by IDEAM) or zones without erosion (14.7% by IGAC and 52% by IDEAM).

In Colombia more than 2300000 hectares are affected by accelerated erosion because of land mismanagement, with an erosion rate higher than 1.8 tons per hectar per year.

30 General Description of Colombia

3.5.2. Desertification

Desertification is considered as a process of loss of the soil productivity in dry subhumid, semiarid and arid regions. The UNECCD (United Nation Convention to Combat Desertification and Drought) proposed an aridity index between 0.05 and 0.65 to delineated arid, semi arid and dry subhumid zones, defined as the ratio between total precipitation and potential evapotranspiration. A sample of 1409 meteorological stations was taken for this.

In Colombia, the areas with higher aridity index (AI), are La Guajira with the minimal AI value of 0.17 in Uríbia; Magdalena with AI of 0.29 in Santa Marta; Atlántico with AI 0.38 in Barranquilla; Bolivar with AI of 0.48 in Cartagena; all of them in the Caribe region. In the North Andes, close to Venezuela Norte de Santander with AI of 0.51 in Cúcuta; Santander with AI of 0.53 in Cepitá (Chicamocha river basin); Cundinamarca with AI of 0.54; Huila with AI of 0.60 in Baraya; Sucre with AI of 0.61 in San Pedro; Cesar with AI of 0.61 in Valledupar; Valle with 0.65 in Cali and Boyacá with AI of 0.65 in Villa de Leiva. The first report from the Ministry of Environment about desertification in Colombia appeared in 2000 using salinity and erosion in dry lands as indicators of desertification. In this report, 56.4% of the dry lands are affected with very high level of aridity and erosion.

Table 3. Degree of land degradation by aridity and erosion in Colombia (MinAmbiente, 2000)

Degree of aridity % of dry lands Area Km2 and erosion affected Very high 39677 20.5 High 69537 35.9 Moderate 50606 26.2 Low 33689 17.4 Total dry land 193510 16.9 of the country affected

The main areas in Colombia affected by current desertification processes are Guajira, Santander, Boyacá, Norte de Santander, Cauca, Nariño, Huila, Tolima, Atlántico,

31 General Description of Colombia

Magdalena, Sucre and Cesar, with around 4828875 affected hectares (4.1% of the country). From those 0.45% is very high, 0.19% high, 0.73% moderate, 1.77% low and 1.12% very low. This study suggests other 0.7% in desertification process (Leon, 2003).

Potential areas of land degradation by desertification in Colombia (IDEAM, 2001) were determined based on the susceptibility of soils to erosion, soil genesis, the arid index by UNCCD, xerophytic vegetation, ustic or arid soil moisture regime and evidence of erosion and salinization. The most susceptible soils to desertification are located mainly in the Caribe and Orinoquia regions, followed by some parts in the Andes and some local areas in the Amazonas region (figure 10). Those areas show an extension of approximated 15% of the country (Del Rosario, 2002).

Figure 10. Zones with potential of desertification in Colombia (IDEAM, 2001).

32 Methodology

4. METHODOLOGY

4.1. STUDY AREAS

The areas selected in this study are based on the results obtained by the Colombian Ministry of Environment and the report of Colombia for the UNCCD (IDEAM, 2001 and MinAmbiente, 2002). Those studies show the actual and potential land degradation and desertification areas in Colombia. Different maps were produced such as the erosion map, the actual and the potential desertification maps. Those maps were obtained from climate data, soil surveys, satellite images and vegetation maps.

The maps show the main areas that can be considered as dry, integrating not only climate but also criteria as vegetation, relief, soil and use. Although all of them are quite similar in the regions that are classified either dry or with desertification or with land degradation problems, it was necessary to select common areas, with similar conditions of relief and altitude which are also parameters influencing the weather conditions. Due to the complexity of environments in Colombia, the definition of micro regions by the IGAC was used to select and delineate the zones were land degradation and desertification of drylands at national scale were reported. In this way, the boundaries of the zones selected are natural allowing assess rainfall in more or less homogeneous geographic conditions of Colombia, with several climate regimes in terms of precipitation, moisture and temperature.

In total, seven study zones were selected. Two of them were selected from the Caribe natural region: the Guajira peninsula and the Caribbean plateaus, because they are geographically a mountainous micro region (Sierra Nevada de Santa Marta) dividing the two sectors, which is a prolongation of the Andes structure in the North of the country. Five zones were selected from the Andes natural region: two of them are located in lowlands and belong to the valleys of Cauca and Magdalena rivers. One zone is located at

33 Methodology the northeast of the country in a typical landscape of middle and high mountains “the Santanderes and Cesar Mountainous zone”. The other two are high plateaus, one in the centre of the country named “Cundiboyacense high plateau” and the other in the south “Nariño and Popayan high plateaus” including a deep valley of the Patía River and steep mountains. The figure 11 shows the location of the selected study zones. The selected zones are not completely drylands but include the most important areas with precipitation deficits and desertification processes such as land degradation and erosion with influence of human activities (mainly agricultural).

2 1 Guajira Peninsula 2 Caribbean plateaus 3 Santander and Cesar

3 4 Cundiboyacense High plateau 5 High Magdalena River Basin

4 5 6

6 Cauca valley 7 Nariño and Popayan High plateaus

Figure 11. Location of the study zones

34 Methodology

4.2. DATA SOURCES

Meteorological information was obtained from secondary information from FAO, CAZALAC, WMO database and from the programme PHI-LAC (Programa de Hidrología Internacional para Latino America y el Caribe) of the UNESCO in cooperation with CAZALAC (Centro para el Agua en Zonas Aridas y Semiáridas en Latino América y el Caribe). Information used was only multitemporal annual average values. All the information belongs to stations of the National Institute of Environmental Studies (IDEAM). Information of 391 meteorological stations covering the study zones was used, from 1971 to 2000. Missing data of precipitation and temperature was estimated using the multi-annual average for the same month. Additionally, multitemporal values of PCI and MFI were obtained from the project The list of the meteorological stations used is presented in the appendices.

4.3. DELINEATION OF ARID ZONES

Arid zones can be delineated using an Index of Moisture Deficit or Aridity Index. To calculate the aridity index it is necessary to determine the moisture loss or potential evapotranspiration (PET). This can be done in three ways: first, using lysimeters or evapotranspiration pans to obtain direct measurements. Although this is the most accurate procedure, at a global scale is impractical. Second, using Penman-Monteith (1948) empirical formula, but these calculations require a large input of direct meteorological data, which at a global scale is also impractical due to the lack of available data. The final and most practical approach is the Thornthwaite method (1948), based in the relationship between mean monthly temperatures and average number of daylight hours per month. This is more practical but also less accurate due to the underestimation of PET for drylands and overestimation for humid and cold environments.

To determine differences in climate types, five indices are used: Lang (1915), De Martonne (1923), Thornthwaite (1948) “Precipitation Effectiveness” and Emberger (1932).

35 Methodology

These indices require only the two general available climate parameters for almost all the meteorological stations: precipitation and temperature. Bagnouls-Gaussen classification method (1952) was used determining the number of dry and wet months, based also in monthly precipitation and temperature.

Spatial distribution for every region was determined with the “Inverse Distance Weighted” (IDW) interpolator method, using Arc/view software. This method assumes that each input point has a local influence that diminishes with distance. It weights the points closer to the processing cell than those farther away. A specified number of points, or optionally all points within a specified radius, can be used to determine the output value for each location. The climate zones were delineated using the boundary classes for each climate index and the surface area was calculated using the software Arc/view version 3.2.

4.3.1. Lang climate classification (1915)

Richard Lang (1915) established a climate classification based on a ratio factor between precipitation and temperature, from which six climate types are proposed. The Lang climate factor (L) is obtained with the relationship between the mean annual precipitation (P) in mm and the annual average temperature (T) in ºC, using the following formula: L = P/T Where, L : Lang Factor, P : Mean annual precipitation T: Mean annual temperature Table 4. Climate types proposed by Richard Lang (1915) Lang Factor P/T Climate type Symbol 0 – 20 Desert D 20.1 – 40 Arid A 40.1 – 60 Semiarid SA 60.1 – 100 Subhumid SH 100.1 – 160 Humid H > 160 Very humid VH

36 Methodology

4.3.2. Aridity index of De Martonne (1923)

De Martonne index is calculated using the mean annual precipitation (P) and the mean temperature (T). The basic of De Martonne formula gives an index of aridity (IM) which is expressed in the formula: P IM = t +10

P = Annual average rainfall (mm) t = Annual average temperature (°C)

Table 5. Climate types proposed by De Martonne (1923) Aridity Index (IM) Climate type 0 – 10 Arid 10 – 20 Semiarid 20 – 24 Mediterranean 24 – 28 Semi-humid 28 – 35 Humid 35 – 55 Very humid > 55 Extremely humid

4.3.3. Aridity index of Emberger (1932)

Emberger index is based in climate data associated with vegetation zones. He established a moisture quotient using the northern limit of his arid zone in north-west Africa. The Emberger index (IE) is obtained with the mean annual precipitation and mean temperature of both the coldest and hottest months and is determined using the formula: 100* P IE = M 2− m 2 Where, P = Annual average rainfall (mm) M = Average temperature of the hottest month (°C) m = Average temperature of the coldest month (°C)

37 Methodology

Table 6. Climate types of Emberger (1932) Aridity Index (IE) Climate type > 90 Humid 50 – 90 Subhumid 30 – 50 Semiarid < 30 Arid

4.3.4. Thornthwaite classification (1948)

Thornthwaite (1948) precipitation effectiveness index PE is based on temperature and precipitation, defined by the formula:

10 / 9 n=12 ⎛ P ⎞ PE = 115x⎜ ⎟ ∑ ⎜ ⎟ 1 ⎝ T −10 ⎠ where, P = Monthly precipitation (inches) T = Temperature (°F), n = months = 12

Table 7. Thornthwaite climate classification (1948) PE Index Climate type < 16 Arid 16 – 31 Semiarid 32 – 63 Subhumid 64 – 127 Humid > 127 Wet

4.3.5. UNEP Arid Index (1997)

UNEP (1997) has defined the aridity index as the ratio of precipitation (P) to potential evapotranspiration (ETo). ETo is determined by the Thornthwaite formula: 10×Tm ETo = 16× Nm × ( )a I where: ETo= monthly potential evapotranspiration (mm). Tm = mean monthly temperature (° C).

38 Methodology

Nm = adjustment factor related to hours of daylight. I = Heat annual index. This is calculated for every month (i):

12 I = ∑(Tm / 5)1.514 i=1

a is a parameter calculated using the equation:

3 2 a = 0.000000675 × I − 0.000071 × I + 0.01792 × I + 0.49239

Four climate types have been defined according to the annual ratio P/PET.

Table 8. UNEP (1997) Climate classification Index P/PET Climate type < 0.05 Hyper-arid zone 0.05 – 0.2 Arid 0.2 – 0.5 Semiarid 0.5 – 0.65 Dry subhumid 0.65 - 1 Subhumid > 1 Humid

4.3.6. Bagnouls – Gaussen classification method (1952)

This classification is based on the average monthly temperature and precipitation. It gives more precise climate classification and the climate identification is obtained by determining separately the numbers of dry and wet months. The Gaussen common aridity index is defined in the way as the dry, or arid month, corresponds to the month having the ratio between precipitation (P) and temperature (T) less than two. These two parameters are plotted as an omberothermic chart on the same graph doubling the values on the scale of precipitation. The dry months are those which the mean temperature curve is higher than the precipitation one. The Bagnouls-Gaussen Aridity index (BGI) is calculated as

12 BGI = ∑(2ti − pi ) * ki i=1 Where t is the average monthly air temperature, k is a coefficient indicating the number of months in which 2t>p and pi is the average rainfall of the month i (i=1 to 12).

39 Methodology

Table 9. BGI climate classification (1952) Index P/PET Climate type > 130 Very Dry 50 – 130 Dry 0 – 50 Moist 0 Humid

The Bagnouls – Gaussen index allows to determine dry periods along the year. Dry months here are considered when the monthly precipitation is lower than 2 times mean monthly temperature. The BGI dry period is compared with half the ETo, which is considered as the level sufficient to meet water requirements of dryland crops (FAO, 1983). Although ETo should be calculated using Penman’s method, in this case is calculated using Thornthwaite method due to the lack of available data.

4.4. RAIN EROSIVITY AND CONCENTRATION INDICES

Using the mean monthly and yearly precipitation data, the Precipitation Concentration Index and Climate aggressivity (Modified Fournier Index) (by Arnoldus, 1980) were evaluated. Through a geo-statistical method the interpolation of these variables was done in order to assess the spatial distribution. For this, IDW method of spatial analysis in Arc/view was used. First, the Precipitation Concentration Index (PCI) is estimated yearly and then monthly. The climate aggressivity was evaluated using the Modified Fournier Index (MFI).

4.4.1. Precipitation Concentration Index (PCI)

The Precipitation Concentration Index (PCI) was proposed by Oliver (1980) to define temporal aspects of the rainfall distribution within a year. It is expressed in % according to the formula:

2 ∑ pi PCI = 100 2 P

40 Methodology

Where, p = Monthly precipitation (mm) P = Annual precipitation (mm)

The PCI permits grouping of data sets according to the derived value, with increasing values indicating increasing monthly rainfall concentration

Table 10. Precipitation Concentration Index classification PCI Concept 8.3 – 10 Uniform 10 – 15 Moderately seasonal 15 – 20 Seasonal 20 – 50 Highly seasonal 50 - 100 Irregular

4.4.2. Modified Fournier Index (MFI)

Arnoldus (1980) modified the (FI) index into a Modified Fournier Index (MFI) considering the rainfall amounts of all months in the year.

12 p 2 MFI = ∑ i =1 P p is monthly precipitation and P is annual precipitation.

Table 11. Modified Fournier Index scale MFI Description Class < 60 Very low 1 60 – 90 Low 2 90 –120 Moderate 3 120-160 High 4 > 160 Very high 5

For every Index a linear and quadratic relationship was evaluated between the monthly average and the index estimated for the average yearly value.

41 Methodology

4.4.3. Erosivity Index (ErIn)

The erosivity index (ErIn) is estimated according to the CORINE project methodology (1995), which uses the modified Fournier index (MFI) and the Bagnouls- Gaussen index (BGI).

The Modified Fournier index is classified in variability classes and the Bagnouls- Gaussen index in aridity classes as follows:

Table 12. Variability class of Modified Fournier Index Variability Class Description Range (Vc) 1 Very low < 60 2 Low 60 to 90 3 Moderate 90 to 120 4 High 120 to 160 5 Very high > 160

Table 13. Aridity class of BGI Aridity Class Description Range (Ac) 1 Humid 0 2 Moist > 0 to 50 3 Dry > 50 to 130 4 Very dry > 130

Both classes are combined to give the erosivity index, which is equal to the product of variability class and aridity class. ErIn = Vc x Ac

Table 14. Erosivity Index (ErIn) Erosivity Index Description Range (ErIn) 1 Low < 4 2 Moderate 4 to 8 3 High > 8

42 Description of the study zones

5. DESCRIPTION OF THE STUDY ZONES

5.1. GUAJIRA PENINSULA

The Guajira Peninsula has an aeolian landscape located in the north-eastern top of Colombia, with an extension of 1136381 hectares, mainly flat and around sea level, with predominant wind erosion and partly xerophytic vegetation.

This region is considered the driest area of Colombia (IDEAM, 2001). The mean annual precipitation is less than 500 mm. According to the IDEAM, this region includes hyperarid, arid and semiarid moisture regimes. Mean temperatures during the whole year are between 28 and 32°C. The Guajira region is also considered a desertification region due to the erosion processes, which in this case is caused more by wind than by water. For the Guajira study zone climatologic information of 24 stations was used. Figure 12 shows the distribution of the precipitation and the location of the meteorological stations.

1150000 1200000 1250000 1300000 Precipitation (mm/year) < 200 200 - 300 300 - 400 $ 400 - 500 24 22 $ 500 - 600 20 $ 21 $ 18 17 19 $ 1850000$ Meteorological 1900000 $ $ $ 5 Stations 14 13 $1 $ $ 11 16 $ 10 $ $ 9 $ 12 8 $ 7 1800000 6 $ $ $ 5 4 $ 3 $ 2 $ 1 $ $

1750000 050100 Km

Figure 12. Location of meteorological stations and precipitation distribution in the Guajira zone

43 Description of the study zones

5.2. CARIBBEAN PLATEAUS

This zone is located in the Caribbean region, in the northern part of Colombia and includes wide plateaus relatively close to the sea level, with undulated surfaces and some hilly landscapes. This region is composed of the Sinú and High San Jorge Valleys, the Caribbean Savannahs and the Magdalena delta. The Mompox depletion is not considered here because this region forms a great wetland, flooded by the waters of San Jorge, Cauca and Magdalena rivers.

The Caribbean plateaus zone has a surface area of 5928835 hectares from which IDEAM (2001) reports around 5 million hectares as dry lands with soil degradation problems and susceptible to potential desertification.

The climate in this region is very hot all the year around, with mean temperatures above 27ºC due to the low altitudes (less than 500 m.a.s.l.). Mean annual precipitation varies from 750 to 2500 mm and most of the region lies between 1000 to 1500 mm per year. For this zone 93 meteorological stations were available, with data from 1971 to 2000.

This zone is very heterogeneous in precipitation. The lower values are found in the north, with less than 500 mm per year, increasing to the southwest. The highest values are in the Uraba Gulf, with more than 2000 mm per year (figure 13).

44 Description of the study zones

700000 800000 9000000 100000 1100000 50 51$$ $ $ 92 32$98 $ 107 33$ 96 97$ 82$

1700000 $ 95 94$ 116$$72$$ 91 29$ 0 50 100 Km $$90 $ 38$ 36 $37 87$$86$ $31 85 $26 $ 88 89 $46 30 $ 84 $$ $$ 49 83 2580 28 79 81$ $ 78$ $$77 $ 52 $76$115 $ 113 73 $ $ $114 $ $ 110$ 11274 111 $$ 1600000 70 67$$ 68 109 43$ 27 108$ 53$ $ 34 66 $ $$56 40$ $$63 57 6564 106 62$

1500000 $ 61 48$ 60$ 41$$$ $$ 104$ $$ 55 105 $$59584235$103 Precipitation 54 39$$ 37 102 100$ 101 (mm/year) 500 - 750 99$ 750 - 1000 1000 - 1500

1400000 $44 $45 1500 - 2000 2000 - 2500 47$ $ Climatic stations

1300000

Figure 13. Location of climate stations and precipitation distribution in the Caribbean plateaus

5.3. SANTANDER AND CESAR VERTIENTES

This zone is located in the northeast of the Andes Cordillera in Colombia. Formed by dry deep valleys, badlands and eroded high plateaus in mountain areas of the micro regions of Catatumbo, Suarez and Chicamocha Canyons, Santurban Macizo, Motilonia Serrania and Meseta of Bucaramanga with an area of 3680000 hectares from which around 587.400 are in desertification process. Severe erosion problems are present in some areas such as the Chicamocha valley and Bucaramanga mesa.

The precipitation varies from less than 1000 up to 2000 mm per year and the mean temperature varies with the altitude and lies between 27ºC in the lowest lands to around 14ºC in the highest lands. The 67 meteorological stations used are shown in the figure 14.

45 Description of the study zones

1000000 1100000 120 0000 1300000

00 168

00 175 Precipitation

17 184 (mm/year)

183 <500

0 182 0 500-750

0 129 181 750-1000 00

6 1 180 128 1000-1500 1500-2000 2000-2500

0 Climatic stations 0 0 0

0 5 1

179 0 127 178 00 177118 174 176 00 172 170124 173 125171123 167 169 130 165 166 121 162 163 164 014 122 159 00 161 158 160 155 126 157 156 153152151 30 0 148147 149 1 154 119 146 142 150 145 144 141 143 140 139 138 137 120 134 135 136

000 133 131 132 00 12

Figure 14. Precipitation distribution and meteorological stations in the Santanderes and Cesar zone

5.4. CUNDIBOYACENSE HIGH PLATEAU

This region is located in the central Andes Cordillera. Although the name is high plateau, it includes also hills and Island Mountains. The surface area of the zone selected is around 1061600 ha. Altitudes in this zone are between 1500 up to 3000 meters which result in moderate temperatures between 13 up to 21ºC. Precipitation in general is very

46 Description of the study zones heterogeneous, some areas can be very low (around 600 mm per year) but in other areas it can be higher (around 2400 mm per year).

This region is characterized by high intensity agricultural and industrial activities, which make the lands more susceptible to degradation by human impact. Water erosion is a common problem and some areas are affected by severe erosion turning them into badlands. The erosion is related to human influence although there are some parts considered as naturally dry such as “Candelaria semi-desert” in Villa de Leiva. Areas affected are non continuous and those have relatively high precipitations but only during a few months. Data was used from 40 climatic stations (figure 15).

1000000 1050000 1100000 1150000

0 50 100 Km $ 203 202$ 200$ 18$$ 6 199 207$ 224$ 193 $ $ $ $ 197 209 221$ 223 $ 22 2 21$ 2 219 220 $ 211$ 208 201 217 218 $ $ $$ 216$ 215$ 205$ 214$ 213$ 191 100000 1150000 $ Precipitation (mm/year) 188 $ 210$ 195$ 500-750 750-1000 204 $ $$192 1000-1500 $ 206$ 185 190 $ 194$ 198 196 $ Climatic stations $ 187$ 189$ 1000000 1050000 1 1000000 1050000 1

Figure 15. Precipitation distribution and climate stations in the Cundiboyacense high plateau

47 Description of the study zones

5.5. HIGH MAGDALENA RIVER BASIN

This zone is formed by intra mountain dry valleys located in Tolima, Huila and Cundinamarca departments and affluent of the Magdalena River, in the lower part of the Central and Eastern Andes Cordillera. The surface area of the selected zone is around 3964342 hectares. IDEAM (2001) reports that in Huila 572200 ha of lands with desertification processes and 769600 ha in Tolima. The temperature range in this region is between 18ºC and 27ºC, with altitudes lower than 300 up to 1700 m.a.s.l. Annual precipitation values vary from less than 800 mm per year in the driest areas up to almost 2000 mm per year. This region includes an arid area known as the “Tatacoa desert”, with an extension of around 304108 ha located at an average altitude of 440 m.a.s.l, and with average annual temperature of 28°C and less than 1000 mm of annual precipitation. Although Tatacoa is considered a desert, climate classifications or arid indices indicate that this is a semiarid or arid region (MinAmbiente, 2000). Data was available from 87 climate stations (figure 16). 700000 800000 900000 1000000

Precipitation (mm/year) 750-1000 $ 1000-1500 $ 1100000 1500-2000 $$ 2000-2500 $ $ $ $ Climatic stations $ $ $ $ $ $ $ $ $ $ 1000000 $ $$ $$$ $ $$$ $ $ $ $ $ $ $$$ $$ $ $ $ $ $ $ $ $$$ $ $ $$ $

900000 $ $ $ $$ $ $ $ $ $$ $ $$ $ $ $ $

800000 $ $$ $$ $ $ $ $$ $ $ $ $$ $ $ $ $

700000 $

Figure 16. Precipitation distribution and meteorological stations in the High Magdalena River basin

48 Description of the study zones

5.6. CAUCA VALLEY

This zone is located in the lowlands between the Western and Central Andes Cordilleras and corresponds with the Cauca River Valley micro region, characterized by temperatures above 19ºC, with altitudes lower than 1800 m.a.s.l. and a mean annual precipitation between 1000 and 2000 mm. The surface area of the Cauca valley is 1069330 ha, from which around 501100 ha are having desertification processes (IDEAM, 2001). Data was available from 32 climate stations.

700000 800000

Precipitation (mm/year) 750-1000 1000-1500 # #353 #35 1 352 1500-2000 2000-2500 35 0 34 9 # # 348 # Climatic stations #347# 346 1000000 # 345# 0 50 100 Km 34 4 # 343 #

342#

329#

324# 34# 1 323# 900000 #340 339#33# 2 ##338 328# 322 325# 326 # #331 # 327#337 336# 335# 334 33# 3 #

330#

Figure 17. Precipitation distribution and meteorological stations in the Cauca valley

49 Description of the study zones

5.7. NARIÑO AND POPAYAN HIGH PLATEAUS

This zone is located in the south of the Colombian Andes and includes the micro regions of Nariño high plateau, Popayan high plateau and the Patía valley with some hills and mountains associated to this landscape. This region shows moderate erosion to badlands, mainly in the Patía valley and slight to moderate erosion in the high plateaus. The area of the zone is 2015347 ha.

Temperatures of the zone vary from 10°C in the highlands of Nariño and Popayan to 24°C in the lower part of the Patía valley. The precipitation is higher in the high mountains, with values above 2000 mm per year, and lower values are found in the Patía valley, with less than 1000 mm per year. Altitude is from less than 600 up to around 3000 m.a.s.l.. Unfortunately, there is not many information available of the stations located in the dry Patía valley considered in great part having desertification process (MinAmbiente, 2002). Data was available for this zone from 38 climate stations.

450000 500000 550000 600000 650000 700000 Precipitation (mm/year) $ $ 500-750

750-1000 $ 1000-1500 $ 1500-2000 $ 2000-2500 $$ $ $ $ $$$ $ 2500-3000 $ 750000 800000 3000-4000 > 4000 $ $ $ Climatic Stations $ $$

$ $ $ $ $ $ $ $ $ $

$ $ $ $ $ $

600000 650000 700000 $ 0 50 100 Km $

Figure 18. Precipitation distribution and climate stations in Nariño and Popayan high plateaus

50 Climate types and aridity indices

6. CLIMATE TYPES AND ARIDITY INDICES

6.1. GUAJIRA PENINSULA

According to the Lang classification the Guajira has a “desert” climate in all the area, which is the driest class for this index. The Thornthwaite classification gives a dominant arid climate, which is also the driest class. The de Martonne and UNEP indices are quite similar, varying from arid to semiarid. With the Emberger index all the stations are classified as “humid” (table 15).

Table 15. Aridity indices of Guajira peninsula Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 1 19.8 Desert 15.0 Arid 14.4 Semiarid 0.32 Semiarid 658 Humid 2 19.1 Desert 14.4 Arid 13.9 Semiarid 0.30 Semiarid 634 Humid 3 10.4 Desert 7.8 Arid 7.5 Arid 0.17 Arid 344 Humid 4 18.9 Desert 14.2 Arid 13.7 Semiarid 0.30 Semiarid 626 Humid 5 19.2 Desert 14.5 Arid 13.9 Semiarid 0.31 Semiarid 636 Humid 6 18.2 Desert 13.8 Arid 13.2 Semiarid 0.29 Semiarid 605 Humid 7 8.7 Desert 6.6 Arid 6.3 Arid 0.14 Arid 290 Humid 8 10.1 Desert 7.6 Arid 7.3 Arid 0.16 Arid 334 Humid 9 11.3 Desert 8.5 Arid 8.2 Arid 0.18 Arid 373 Humid 10 7.1 Desert 5.4 Arid 5.2 Arid 0.11 Arid 237 Humid 11 8.2 Desert 6.2 Arid 5.9 Arid 0.13 Arid 272 Humid 12 7.4 Desert 5.6 Arid 5.3 Arid 0.12 Arid 245 Humid 13 16.8 Desert 12.7 Arid 12.2 Semiarid 0.27 Semiarid 557 Humid 14 17.8 Desert 13.4 Arid 12.9 Semiarid 0.28 Semiarid 589 Humid 15 17.2 Desert 13.1 Arid 12.5 Semiarid 0.27 Semiarid 571 Humid 16 8.9 Desert 6.7 Arid 6.5 Arid 0.14 Arid 220 Humid 17 11.0 Desert 8.3 Arid 7.9 Arid 0.17 Arid 364 Humid 18 8.2 Desert 6.2 Arid 5.9 Arid 0.13 Arid 272 Humid 19 17.5 Desert 13.2 Arid 12.6 Semiarid 0.28 Semiarid 579 Humid 20 12.5 Desert 9.5 Arid 9.1 Arid 0.20 Arid 416 Humid 21 17.8 Desert 13.5 Arid 12.9 Semiarid 0.28 Semiarid 591 Humid 22 14.7 Desert 11.1 Arid 10.6 Semiarid 0.23 Semiarid 487 Humid 23 9.0 Desert 6.8 Arid 6.5 Arid 0.14 Arid 299 Humid 24 8.7 Desert 6.6 Arid 6.3 Arid 0.14 Arid 289 Humid

51 Climate types and aridity indices

Using the IDW algorithm in Arc/view, it is possible to see the spatial arrangement between the Lang, Thornthwaite, de Martonne and UNEP classifications (figure 19). With the Emberger index all the stations are classified as humid, due to the fact that it considers the differences between the medium temperature of the hottest and the coldest months, and for this case is less than 5ºC, which is very low. It seems that this classification type is more adequate for temperate regions with high variations of temperature between seasons. Using the Lang factor the whole region is considered Desert with values from 7.1 to 19.2. With the Thornthwaite index, the zone is classified as arid with values from 5.4 to 14.5. Both classifications give the lowest value for all the stations.

1100000 1150000 1200000 1250000 1300000 1100000 1150000 1200000 1250000 1300000

Thornwaite Climatic Lang Climatic

1900000 1900000 Index type factor type <10 Arid <20 Desert

1850000 1850000

1800000 1800000

1750000 1750000 0 50 100 Km 050100 Km

1100000 1150000 1200000 1250000 1300000 1100000 1150000 1200000 1250000 1300000 De Martonne Climatic UNEP Climatic 1900000 1900000 Index type Index type

5 0 50 Klis t r <16 Arid 0.05-0.2 Arid 16-31 Semiarid 0.2-0.5 Semiarid

1850000 1850000

1800000 1800000

1750000 0 50 100 Km 1750000 050100 Km

Figure 19. Climate classifications of the Guajira peninsula

52 Climate types and aridity indices

With the de Martonne index, part of the region (59 %) is considered as the lower class “Arid” and the rest as “Semiarid”. The UNEP index is less marginal and considers 56% of the zone as “Arid”, which is not the lowest class for this Index. The remaining part is classified as Semiarid. The Lang and Thornthwaite indices are quite similar and differ from the de Martonne and the UNEP indices which are also similar between them. The Guajira zone is considered completely as “Dry-Land” due to the fact that all stations have been classified among the categories below the “subhumid” class for Lang, Martonne, Emberger and UNEP indices, except for the Emberger index which considers the region totally as Humid.

Using Bagnouls - Gaussen classification method the stations show in general a long dry season from nine to eleven dry months per year and a very short rainy season from less than three months in this zone. The driest months of the Guajira peninsula are from December to August and in almost half of the stations from November to September. October is the most humid month and September and November vary from arid to humid. In almost all the stations at least 9 months are considered arid. With the calculated annual BGI, all the stations are classified as “Moist”, even the station number 10 that has values of precipitation lower than 2 times temperature (2T) during all the year.

Table 16 resumes the results of the monthly classification comparing the precipitation value and the temperature. The months with mean monthly precipitation (in mm), lower than two times temperature (in °C) are represented as arid (A). Semihumid (S) are those with precipitation values between two and three times the temperature and humid (H) are those with precipitation values higher than three times the temperature.

Figure 20 shows the monthly relationship between precipitation and temperature for some stations of the Guajira zone. 0.5 ETo is showing that in all the stations, the level for dry period (DP) is higher than the calculated with BGI.

53 Climate types and aridity indices

Table 16. Bagnouls - Gaussen climate classification for the Guajira peninsula Code JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC BGI DESCRIPTION 1 A A A A S A A A H H H A 23 Moist 2 A A A A S A A A H H S A 26 Moist 3 A A A A A A A A A H A A 33 Moist 4 A A A A H A A A H H S A 25 Moist 5 A A A A S A A A H H S A 24 Moist 6 A A A A A A A A H H S A 28 Moist 7 A A A A A A A A A H A A 36 Moist 8 A A A A A A A A S H A A 34 Moist 9 A A A A A A A A A H A A 32 Moist 10 A A A A A A A A A A A A 37 Moist 11 A A A A A A A A A S A A 37 Moist 12 A A A A A A A A A S A A 37 Moist 13 A A A A A A A A S H S A 24 Moist 14 A A A A A A A A S H H A 26 Moist 15 A A A A A A A A A H H H 28 Moist 16 A A A A A A A A A S S A 35 Moist 17 A A A A A A A A A H S A 34 Moist 18 A A A A A A A A A S A A 36 Moist 19 A A A A A A A A S H H S 26 Moist 20 A A A A A A A A S H A A 31 Moist 21 A A A A A A A A A H H A 27 Moist 22 A A A A A A A A S H H S 29 Moist 23 A A A A A A A A A S S A 35 Moist 24 A A A A A A A A A S A A 36 Moist A = Arid, S = Semihumid, H = Humid

Station 11 Station 12 120 60 120 60 P 100 50 100 50

80 40 80 40 0.5 ETo 0.5 ETo 60 DP 30 2T 60 DP 30 2T Temp °C 40 20 P Temp °C BGI 40 20

Precipitation (mm) BGI

20 10 Precipitation (mm) 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months

Station 18 Station 22 120 60 120 60 P 100 50 100 50

80 P 40 80 40 0.5 ETo 0.5 ETo 60 DP 30 60 DP 30 2T 2T Temp °C 40 20 Temp °C 40 20 BGI BGI Precipitation (mm) Precipitation (mm) 20 10 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months Figure 20. Omberothermic curves for the Guajira peninsula

54 Climate types and aridity indices

From figure 20 it is clear that the mean temperature has no significant variation during the year and is more or less constant. With a dry period of nine months, and BGI indices between 23 and 37 for all the stations of the Guajira region, this zone is completely moist, using the BGI yearly classification range.

6.2. CARIBBEAN PLATEAUS

The different aridity indices show different results for this zone. Lang classification shows that the region is dominant dry with almost 90.5% of the area between “desert” to “semiarid” class. Using Thornthwaite index dry lands are reduced to 24.5%, the UNEP classified 16.4% and finally for the de Martonne only 4% of the area. Using the Emberger Index the whole zone is classified as humid, with very high values of aridity index. Table 17 shows the aridity indices estimated for every station. Figure 21 shows the spatial distribution for the same indices. The Emberger classification is not representative because the whole zone is considered as humid.

Table 17. Aridity indices of Caribbean Plateaus

Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 25 24.7 Arid 18.5 Semiarid 18.1 Semiarid 0.40 Semiarid 620 Humid 26 29.6 Arid 22.1 Semiarid 21.6 Mediterran 0.48 Semiarid 743 Humid 27 37.1 Arid 28.2 Semiarid 27.2 Semihumid 0.60 Dry subhumid 922 Humid 28 31.5 Arid 24.0 Semiarid 23.2 Mediterran 0.52 Dry subhumid 931 Humid 29 48.1 Semiarid 35.7 Subhumid 34.3 Humid 0.75 Subhumid 1607 Humid 30 35.4 Arid 26.4 Semiarid 25.6 Semihumid 0.56 Dry subhumid 1359 Humid 31 45.7 Semiarid 35.0 Subhumid 33.7 Humid 0.75 Subhumid 1755 Humid 32 31.6 Arid 23.7 Semiarid 23.1 Mediterran 0.51 Dry subhumid 833 Humid 33 36.0 Arid 26.7 Semiarid 25.6 Semihumid 0.56 Dry subhumid 1818 Humid 34 37.4 Arid 28.3 Semiarid 27.3 Semihumid 0.60 Dry subhumid 743 Humid 35 35.3 Arid 27.0 Semiarid 26.0 Semihumid 0.58 Dry subhumid 1254 Humid 36 52.5 Semiarid 39.3 Subhumid 37.9 Very Humid 0.83 Subhumid 1191 Humid 37 41.3 Semiarid 31.1 Subhumid 30.1 Humid 0.66 Subhumid 2304 Humid 38 42.3 Semiarid 31.7 Subhumid 30.6 Humid 0.67 Subhumid 2618 Humid 39 42.0 Semiarid 32.0 Subhumid 30.9 Humid 0.69 Subhumid 1490 Humid 40 42.5 Semiarid 31.8 Subhumid 30.7 Humid 0.68 Subhumid 965 Humid

55 Climate types and aridity indices

Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 41 42.6 Semiarid 32.5 Subhumid 31.3 Humid 0.69 Subhumid 1411 Humid 42 31.8 Arid 23.9 Semiarid 23.1 Mediterran 0.51 Dry subhumid 562 Humid 43 44.9 Semiarid 33.7 Subhumid 32.5 Humid 0.71 Subhumid 1019 Humid 44 94.5 Subhumid 71.0 Humid 68.5 1.51 Humid 3982 Humid Extremely 45 90.7 Subhumid 68.5 Humid 66.1 1.46 Humid 7568 Humid Humid 47 77.0 Subhumid 57.9 Subhumid 55.8 1.23 Humid 3245 Humid 46 35.8 Arid 26.9 Semiarid 25.9 Semihumid 0.57 Dry subhumid 812 Humid 48 57.0 Semiarid 43.2 Subhumid 41.8 Very Humid 0.93 Subhumid 1417 Humid 49 57.2 Semiarid 39.0 Subhumid 37.2 Very Humid 0.75 Subhumid 2358 Humid 50 30.2 Arid 22.9 Semiarid 22.3 Mediterran 0.49 Semiarid 839 Humid 51 17.2 Desert 12.6 Arid 12.1 Semiarid 0.26 Semiarid 955 Humid 52 27.6 Arid 20.8 Semiarid 20.3 Mediterran 0.45 Semiarid 872 Humid 53 31.7 Arid 23.7 Semiarid 22.9 Mediterran 0.50 Dry subhumid 720 Humid 54 35.4 Arid 26.7 Semiarid 25.8 Semihumid 0.57 Dry subhumid 627 Humid 55 46.8 Semiarid 35.2 Subhumid 34.0 Humid 0.75 Subhumid 828 Humid 56 45.1 Semiarid 34.0 Subhumid 32.8 Humid 0.72 Subhumid 798 Humid 57 42.0 Semiarid 31.4 Subhumid 30.3 Humid 0.67 Subhumid 953 Humid 58 40.5 Semiarid 30.5 Semiarid 29.5 Humid 0.65 Dry subhumid 717 Humid 59 54.0 Semiarid 40.6 Subhumid 39.3 Very Humid 0.87 Subhumid 956 Humid 60 53.9 Semiarid 40.3 Subhumid 38.9 Very Humid 0.85 Subhumid 1222 Humid 61 49.6 Semiarid 37.2 Subhumid 36.2 Very Humid 0.80 Subhumid 1308 Humid 62 50.7 Semiarid 38.2 Subhumid 36.9 Very Humid 0.81 Subhumid 898 Humid 63 44.5 Semiarid 33.4 Subhumid 32.5 Humid 0.72 Subhumid 1175 Humid 64 45.1 Semiarid 34.0 Subhumid 32.8 Humid 0.72 Subhumid 799 Humid 65 51.9 Semiarid 39.0 Subhumid 37.6 Very Humid 0.83 Subhumid 2186 Humid 66 52.4 Semiarid 39.6 Subhumid 38.1 Very Humid 0.84 Subhumid 927 Humid 67 45.7 Semiarid 35.1 Subhumid 33.8 Humid 0.75 Subhumid 1756 Humid 68 37.4 Arid 28.1 Semiarid 27.2 Semihumid 0.60 Dry subhumid 662 Humid 70 71.6 Subhumid 53.7 Subhumid 51.7 Very Humid 1.14 Humid 1624 Humid 72 38.7 Arid 29.2 Semiarid 28.1 Humid 0.62 Dry subhumid 684 Humid 73 47.4 Semiarid 35.5 Subhumid 34.2 Humid 0.75 Subhumid 1075 Humid 74 61.6 Subhumid 46.8 Subhumid 45.2 Very Humid 1.00 Humid 1531 Humid 76 64.3 Subhumid 49.2 Subhumid 47.5 Very Humid 1.05 Humid 2470 Humid 77 47.7 Semiarid 35.8 Subhumid 34.5 Humid 0.76 Subhumid 1082 Humid 78 50.3 Semiarid 38.0 Subhumid 36.9 Very Humid 0.82 Subhumid 1590 Humid 79 55.2 Semiarid 41.8 Subhumid 40.3 Very Humid 0.89 Subhumid 1456 Humid 80 41.3 Semiarid 31.6 Subhumid 30.5 Humid 0.68 Subhumid 1586 Humid 81 47.6 Semiarid 36.3 Subhumid 34.9 Humid 0.77 Subhumid 1182 Humid 82 33.0 Arid 24.5 Semiarid 23.5 Mediterran 0.51 Dry subhumid 1103 Humid 83 41.6 Semiarid 31.3 Subhumid 30.1 Humid 0.66 Subhumid 944 Humid 84 38.6 Arid 29.1 Semiarid 28.3 Humid 0.63 Dry subhumid 1219 Humid 85 37.2 Arid 27.9 Semiarid 26.9 Semihumid 0.59 Dry subhumid 843 Humid 86 31.4 Arid 23.7 Semiarid 23.1 Mediterran 0.51 Dry subhumid 994 Humid 87 38.7 Arid 29.1 Semiarid 28.1 Humid 0.62 Dry subhumid 1633 Humid 88 36.1 Arid 27.6 Semiarid 26.6 Semihumid 0.59 Dry subhumid 1385 Humid 89 50.6 Semiarid 38.2 Subhumid 36.8 Very Humid 0.81 Subhumid 895 Humid

56 Climate types and aridity indices

Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 90 45.6 Semiarid 34.2 Subhumid 33.0 Humid 0.72 Subhumid 1035 Humid 91 51.4 Semiarid 38.8 Subhumid 37.4 Very Humid 0.82 Subhumid 909 Humid 92 43.6 Semiarid 32.3 Subhumid 31.0 Humid 0.68 Subhumid 1455 Humid 93 42.4 Semiarid 32.0 Subhumid 30.8 Humid 0.68 Subhumid 751 Humid 94 39.0 Arid 29.3 Semiarid 28.2 Humid 0.62 Dry subhumid 885 Humid 95 39.8 Arid 30.1 Semiarid 29.0 Humid 0.64 Dry subhumid 705 Humid 96 47.3 Semiarid 35.1 Subhumid 33.7 Humid 0.73 Subhumid 1581 Humid 97 43.5 Semiarid 32.6 Subhumid 31.5 Humid 0.69 Subhumid 987 Humid 98 23.3 Arid 17.5 Semiarid 16.9 Semiarid 0.37 Semiarid 984 Humid 99 53.3 Semiarid 40.8 Subhumid 39.4 Very Humid 0.87 Subhumid 2048 Humid 100 53.5 Semiarid 40.0 Subhumid 38.6 Very Humid 0.85 Subhumid 1213 Humid 101 52.2 Semiarid 40.0 Subhumid 38.6 Very Humid 0.86 Subhumid 2005 Humid 102 62.9 Subhumid 47.1 Subhumid 45.5 Very Humid 1.00 Subhumid 1427 Humid 103 62.6 Subhumid 46.9 Subhumid 45.3 Very Humid 0.99 Subhumid 1421 Humid 104 50.5 Semiarid 38.7 Subhumid 37.3 Very Humid 0.83 Subhumid 1940 Humid 105 56.4 Semiarid 42.5 Subhumid 41.0 Very Humid 0.90 Subhumid 998 Humid 106 52.8 Semiarid 39.5 Subhumid 38.1 Very Humid 0.84 Subhumid 1197 Humid 107 12.9 Desert 9.7 Arid 9.4 Arid 0.21 Semiarid 545 Humid 108 32.6 Arid 24.3 Semiarid 23.4 Mediterran 0.51 Dry subhumid 1469 Humid 109 58.4 Semiarid 44.7 Subhumid 43.1 Very Humid 0.96 Subhumid 2241 Humid 110 54.3 Semiarid 41.0 Subhumid 39.9 Very Humid 0.88 Subhumid 1716 Humid 111 59.4 Semiarid 44.6 Subhumid 42.9 Very Humid 0.94 Subhumid 1347 Humid 112 45.4 Semiarid 34.6 Subhumid 33.5 Humid 0.74 Subhumid 1344 Humid 113 56.5 Semiarid 42.7 Subhumid 41.5 Very Humid 0.92 Subhumid 1785 Humid 114 60.9 Subhumid 46.0 Subhumid 44.3 Very Humid 0.98 Subhumid 1077 Humid 115 45.6 Semiarid 34.2 Subhumid 33.0 Humid 0.72 Subhumid 1035 Humid 116 40.5 Semiarid 30.7 Semiarid 29.5 Humid 0.65 Dry subhumid 718 Humid 117 41.8 Semiarid 31.6 Subhumid 30.4 Humid 0.67 Subhumid 740 Humid

The Thornthwaite and the UNEP indices are quite similar. Using Lang index the region is more dry and more humid using the de Martonne and the Emberger indices.

57 Climate types and aridity indices

700000 800000 9000000 100000 1100000 700000 800000 9000000 100000 1100000

0 50 100 Km 1700000 0 50 100 Km

1600000

1500000 Thornthwaite Climatic Lang Climatic Index type Factor type <16 Arid < 20 Desert 16-32 Semiarid

1400000 20-40 Arid 32-64 Subhumid 40-60 Semiarid 60-100 Subhumid

1300000 700000 800000 9000000 100000 1100000 700000 800000 9000000 100000 1100000

0 50 100 Km 1700000 0 50 100 Km

1600000

De Martonne Climatic

Index type 1500000 UNEP Climatic <10 Arid Index type 10-20 Semiarid 20-24 Mediterranean 0.2-0.5 Semi arid 24-28 Semihumid 0.5 – 0.65 Dry subhumid 28-35 Humid 1400000 Subhumid 35-55 Very humid 0.65 - 1 > 55 Extremely humid > 1 Humid

1300000 Figure 21. Climate classifications of the Caribbean plateaus

The Lang classification is the one that indicates more drylands in the Caribbean plateaus. Note that the de Martonne and UNEP classification show the southern part with the highest class while with the Lang index this zone is classified mostly as subhumid. This area is located close to the Uraba gulf where the precipitation is higher than in the rest of the Caribbean plateaus. With the Thornthwaite index this part is not shown as humid. In this case the Thornthwaite index does not indicate areas with more humid regimes.

58 Climate types and aridity indices

According to the Bagnouls - Gaussen classification there are 4 stations classified as “humid” and the remaining 89 as “Moist”, with BGI values from 3 to 28. There is not any station considered as Dry, although 85 of the 93 stations show a dominant dry period of four months: from December to March.

Table 18. Climate classification using Bagnouls - Gaussen index Dry months Number of BGI Area Class per year stations values (ha) 0 - 2 4 0 Humid 901864 3 - 5 85 3 - 19 Moist 5006971 6 - 10 4 20 - 28

The BGI values are lower, compared with the Guajira region. 89 stations have values lower than 20. Figure 22 shows the distribution of BGI values in the Caribbean plateaus. The highest values are in the North, which also corresponds to the stations with more dry months of the zone, BGI values decrease to the Southwest, where the amount of dry months per year decreases.

Figure 22. Bagnouls - Gaussen Index distribution in the Caribbean plateaus

59 Climate types and aridity indices

Figure 23 shows the omberothermic curves of precipitation (P), Temperature (2T) and 0.5 ETo. The dry period determined by the BGI, in all the stations is shorter than if 0.5 ETo is used.

Station 26 Station 51 180 90 120 60 160 P 80 140 70 100 50 P 120 60 80 40 100 50 0.5 ETo 80 40 60 DP 30 0.5 ETo Temp °C 2T 60 DP 30 Temp °C 2T 40 20 40 20 BGI Precipitation (mm)

BGI Precipitation (mm) 20 10 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months Station 87 Station 98

200 100 160 80 180 P 90 140 70 160 80 P 120 60 140 70 120 60 100 50 100 50 80 0.5 ETo 40 80 40 DP Temp °C Temp °C 60 30 0.5 ETo 2T 60 DP 2T 30 40 20 BGI Precipitation (mm)

Precipitation (mm) 40 20 BGI 20 10 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months Figure 23. Omberothermic curves for some stations of the Caribbean plateaus

6.3. SANTANDERES AND CESAR ZONE

In this zone there is a high difference between the Lang index with the UNEP Thornthwaite and de Martonne indices. These classifications consider respectively 53%, 9%, 7% and 2% “Dry-Lands”. The Lang and the de Martonne indices are in the extremes while the UNEP and Thornthwaite indices are quite similar. The Emberger index values are very high and all of the stations are classified as Humid.

60 Climate types and aridity indices

Table 19. Climate classifications of the Santanderes and Cesar zone

Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 118 57.1 Semiarid 38.9 Subhumid 37.6 Very Humid 0.76 Subhumid 2053 Humid 119 35.8 Arid 26.4 Semiarid 25.3 Semihumid 0.55 Dry subhumid 1620 Humid 120 28.8 Arid 20.5 Semiarid 19.6 Semiarid 0.41 Semiarid 1595 Humid 121 76.1 Subhumid 52.6 Subhumid 50.4 Very Humid 1.03 Humid 2562 Humid 122 57.7 Semiarid 39.7 Subhumid 38.1 Very Humid 0.78 Subhumid 1941 Humid 123 31.0 Arid 23.3 Semiarid 22.5 Mediterran 0.50 Semiarid 775 Humid 124 21.2 Arid 16.0 Arid 15.3 Semiarid 0.34 Semiarid 441 Humid 125 33.7 Arid 25.3 Semiarid 24.4 Semihumid 0.54 Dry subhumid 765 Humid 126 53.0 Semiarid 31.6 Subhumid 29.9 Humid 0.51 Dry subhumid 1931 Humid 127 52.4 Semiarid 36.3 Subhumid 34.8 Humid 0.71 Subhumid 2915 Humid 128 44.5 Semiarid 33.4 Subhumid 32.4 Humid 0.71 Subhumid 2232 Humid 129 56.0 Semiarid 42.5 Subhumid 40.5 Very Humid 0.89 Subhumid 712 Humid 130 32.6 Arid 24.8 Semiarid 23.8 Mediterran 0.53 Dry subhumid 606 Humid 132 63.2 Subhumid 39.3 Subhumid 37.4 Very Humid 0.68 Subhumid 2140 Humid 133 71.4 Subhumid 42.4 Subhumid 40.1 Very Humid 0.69 Subhumid 1448 Humid 131 110.1 Humid 62.9 Subhumid 59.5 0.97 Subhumid 5624 Humid 134 92.2 Subhumid 63.3 Humid 60.9 Extremely 1.24 Humid 3103 Humid 135 107.6 Humid 71.4 Humid 68.3 Humid 1.33 Humid 5331 Humid 138 114.6 Humid 71.1 Humid 67.6 1.22 Humid 3859 Humid 136 56.1 Semiarid 38.4 Subhumid 36.6 Very Humid 0.73 Subhumid 2005 Humid 137 60.3 Subhumid 42.8 Subhumid 41.0 Very Humid 0.86 Subhumid 2144 Humid 139 39.9 Arid 28.9 Semiarid 27.6 Semihumid 0.59 Dry subhumid 855 Humid 140 86.8 Subhumid 59.6 Subhumid 57.0 Extremely 1.15 Humid 4815 Humid 142 92.0 Subhumid 61.0 Subhumid 58.3 Humid 1.14 Humid 4556 Humid 141 82.2 Subhumid 50.0 Subhumid 47.5 Very Humid 0.84 Subhumid 3167 Humid 143 48.9 Semiarid 34.9 Subhumid 33.3 Humid 0.70 Subhumid 1001 Humid 144 65.1 Subhumid 46.3 Subhumid 44.4 Very Humid 0.93 Subhumid 3610 Humid 145 53.7 Semiarid 38.1 Subhumid 36.6 Very Humid 0.77 Subhumid 1440 Humid 146 148.0 Humid 83.1 Humid 78.4 Extremely 1.26 Humid 3785 Humid 149 102.5 Humid 70.4 Humid 67.3 Humid 1.36 Humid 5689 Humid 147 57.7 Semiarid 41.0 Subhumid 39.3 Very Humid 0.83 Subhumid 3201 Humid 148 46.3 Semiarid 33.1 Subhumid 31.7 Humid 0.67 Subhumid 1368 Humid 150 72.9 Subhumid 44.5 Subhumid 42.1 Very Humid 0.74 Subhumid 2808 Humid 151 57.3 Semiarid 33.4 Subhumid 31.2 Humid 0.52 Dry subhumid 1173 Humid 152 83.1 Subhumid 55.0 Subhumid 52.7 Very Humid 1.03 Humid 4114 Humid 153 46.3 Semiarid 32.7 Subhumid 31.4 Humid 0.66 Subhumid 977 Humid 154 65.1 Subhumid 46.9 Subhumid 45.0 Very Humid 0.96 Subhumid 2502 Humid 155 87.8 Subhumid 63.3 Humid 60.6 Extremely 1.29 Humid 3373 Humid 158 86.2 Subhumid 62.1 Subhumid 59.5 Humid 1.26 Humid 3312 Humid 156 66.0 Subhumid 47.6 Subhumid 45.6 Very Humid 0.97 Subhumid 2535 Humid 157 46.1 Semiarid 28.3 Semiarid 26.7 Semihumid 0.47 Semiarid 1914 Humid 159 75.3 Subhumid 42.7 Subhumid 40.6 Very Humid 0.66 Subhumid 3820 Humid 160 53.9 Semiarid 37.0 Subhumid 35.4 Very Humid 0.72 Subhumid 2992 Humid

61 Climate types and aridity indices

Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 161 61.2 Subhumid 37.2 Subhumid 35.3 Very Humid 0.62 Dry subhumid 2356 Humid 162 85.2 Subhumid 61.4 Subhumid 58.9 Extremely 1.25 Humid 3275 Humid 164 96.0 Subhumid 66.1 Humid 63.4 Humid 1.29 Humid 3229 Humid 163 47.6 Semiarid 32.7 Subhumid 31.2 Humid 0.63 Dry subhumid 2639 Humid 165 74.2 Subhumid 56.0 Subhumid 54.1 Very Humid 1.19 Humid 1377 Humid 166 85.3 Subhumid 61.4 Subhumid 58.9 1.25 Humid 2676 Humid 167 98.3 Subhumid 70.9 Humid 67.8 Extremely 1.44 Humid 3083 Humid 170 81.7 Subhumid 58.2 Subhumid 55.7 Humid 1.17 Humid 4532 Humid 182 81.3 Subhumid 61.6 Subhumid 58.7 1.29 Humid 1034 Humid 168 24.0 Arid 18.0 Semiarid 17.5 Semiarid 0.39 Semiarid 1204 Humid 169 32.6 Arid 24.8 Semiarid 23.8 Mediterran 0.53 Dry subhumid 606 Humid 171 33.2 Arid 24.9 Semiarid 24.0 Mediterran 0.53 Dry subhumid 422 Humid 172 70.0 Subhumid 47.8 Subhumid 46.0 Very Humid 0.93 Subhumid 2515 Humid 173 69.2 Subhumid 47.5 Subhumid 45.4 Very Humid 0.92 Subhumid 3838 Humid 174 75.4 Subhumid 51.8 Subhumid 49.5 Very Humid 1.00 Humid 4184 Humid 175 37.8 Arid 28.8 Semiarid 27.3 Semihumid 0.60 Dry subhumid 481 Humid 176 51.7 Semiarid 39.1 Subhumid 37.7 Very Humid 0.83 Subhumid 959 Humid 177 67.6 Subhumid 51.4 Subhumid 48.8 Very Humid 1.07 Humid 860 Humid 178 66.0 Subhumid 50.4 Subhumid 48.8 Very Humid 1.08 Humid 1849 Humid 179 53.4 Semiarid 37.1 Subhumid 35.5 Very Humid 0.73 Subhumid 2972 Humid 180 56.5 Semiarid 42.4 Subhumid 41.2 Very Humid 0.91 Subhumid 1050 Humid 181 54.9 Semiarid 41.2 Subhumid 40.1 Very Humid 0.88 Subhumid 1020 Humid 183 51.3 Semiarid 38.3 Subhumid 37.0 Very Humid 0.81 Subhumid 2360 Humid 184 34.3 Arid 25.6 Semiarid 24.7 Semihumid 0.54 Dry subhumid 1577 Humid

Figure 24 demonstrates that dry lands are spread over the area and are not continuous. For the Lang classification, the northern part is completely dry, with some inclusions in the South. For the other indices, only a small part in the North is dry and other small areas appear in the South. The non continuous distribution can be explained due to this region is a complex of mountains and hills with different altitudes and intra- mountainous valleys and canyons which gives a very heterogeneous and complex distribution of wind and precipitation in this zone.

62 Climate types and aridity indices

170 00 00 170 00 00 0 Lang Climatic 0 Thornthwaite Climatic 0 0 0 factor type 0 Index type 00 00 6 6 1 20-40 Arid 1 16-32 Semiarid 40-60 Semiarid 32-64 Subhumid Humid 0 0 60-100 Subhumid 64-128 00 00 0 100-160 Humid 0 0 0 15 15

00 00

014000 014000 0 0 30 00 30 00 1 1 0 0 0 0

12000 12000 050100 Km 0 50 100 Km

1100000 120 0000 1300000 1100000 1200000 1300000

Martonne Climatic Index type UNEP Climatic 00 170 00 00 170 0000 0 0 Index type 00 00

10-20 Semiarid 6 6 0.2-0.5 Semi arid 1 20-24 Mediterranean 1 24-28 Semihumid 0.5-0.65 Dry subhumid 28-35 Humid 0.65 - 1 SubHumid 0 35-55 Very humid 0 Humid 00 00 > 1 0 0

> 55 Extremely 0 50 1 humid 15

00 140 00 00 30 00 30 0000 140 00 00 1 1

0 0

12000 00 050100 Km12000 0 50 100 Km

Figure 24. Climate classifications of the Santanderes and Cesar zone

63 Climate types and aridity indices

The Bagnouls - Gaussen Index gives a dominant “Moist” class with BGI values lower than 16. Dry periods differ in this zone from 0 to 8 dry months per year. The BGI index values vary from North to South with the highest values in the North and irregular distribution in the central part. Figure 25 shows the BGI values and the distribution of dry periods.

Table 20. Climate classification using Bagnouls - Gaussen Dry months Number of Area BGI values per year stations (ha) 0 24 0 Humid 629654 1-2 20 1-4 3 - 5 19 5 - 12 Moist 3361407 6 - 8 4 12-16

Figure 25. Bagnouls - Gaussen Index distribution in the Santanderes and Cesar zone

64 Climate types and aridity indices

The BGI values are quite different for each station because they are located at altitudes from 90 to more than 3000 m.a.s.l., with mean temperatures from 28ºC in the lowest altitudes to 11ºC in the highest altitudes. Figure 26 shows the curves of precipitation, ½ETo and 2T for some stations at different altitudes.

Station 120, 1100 masl Station 157, 2645 masl BGI BGI 120 60 100 DP P 50 DP 100 P 50 80 40 0.5 ETo 80 40 60 30 60 0.5 ETo 30 2T

40 20 Temp °C Temp °C 40 20 2T

20 10 Precipitation (mm) 20 10 Precipitation (mm) 0 0 0 0 Jan Feb Mar Apr y Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ma Months Months

Station 163, 1850 masl BGI DP Station 168, 170 masl 180 90 120 60 160 DP P 80 BGI P 100 50 140 70 120 60 80 0.5 ETo 40 100 50 60 30 80 40 2T Temp °C 0.5 ETo Temp °C 60 30 40 20 40 2T 20 Precipitation (mm) Precipitation (mm) 20 10 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months

Figure 26. Omberothermic curves different stations in the Santanderes and Cesar

Some of the stations have two moist seasons with two short dry periods, and others one moist long humid period with a very short dry period. The dry months are from December to February and in some cases till March.

The same figure shows ½ ETo calculated Thornthwaite formula (1948). The curve of ½ETo indicates that the dry period is higher than using the BGI. For the stations 163 and 168, there appears another dry period from June to July. The station 120 shows also a second dry period from June to August.

65 Climate types and aridity indices

6.4. CUNDIBOYACENSE HIGH PLATEAU

For this zone, the Lang and UNEP classifications are quite similar in surface area, but not all the same stations are considered by both indices as Dry. The UNEP index indicates that 45% of the zone is “Dry” given by 23 stations and the Lang index indicates almost 44% with 20 stations. Table 21 shows the different stations and those classified as “Dry” are highlighted. The Thornthwaite classification gives almost 13% of the zone as “Dry”. With the de Martonne classification less than 1% and with the Emberger index all the stations are classified as “Humid”.

Table 21. Climate indices of the Cundiboyacense high plateau Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 185 39.3 Arid 24.3 Semiarid 23.1 Mediterran 0.42 Semiarid 3269 Humid 186 50.7 Semiarid 30.8 Semiarid 29.3 Humid 0.52 Dry subhumid 2104 Humid 187 56.7 Semiarid 33.9 Subhumid 32.3 Humid 0.56 Dry subhumid 3524 Humid 188 56.0 Semiarid 38.2 Subhumid 36.4 Very Humid 0.73 Subhumid 2147 Humid 189 62.1 Subhumid 37.2 Subhumid 35.4 Very Humid 0.61 Dry subhumid 3858 Humid 190 54.1 Semiarid 33.2 Subhumid 31.7 Humid 0.57 Dry subhumid 2671 Humid 191 51.7 Semiarid 32.2 Subhumid 30.7 Humid 0.56 Dry subhumid 1586 Humid 192 58.8 Semiarid 35.0 Subhumid 33.4 Humid 0.58 Dry subhumid 2928 Humid 193 60.8 Subhumid 37.1 Subhumid 35.4 Very Humid 0.63 Dry subhumid 2161 Humid 194 82.5 Subhumid 49.4 Subhumid 46.9 Very Humid 0.81 Subhumid 5122 Humid 195 99.7 Subhumid 57.4 Subhumid 54.5 Very Humid 0.90 Subhumid 7066 Humid 196 43.0 Semiarid 26.8 Semiarid 25.5 Semihumid 0.46 Semiarid 1319 Humid 197 77.2 Subhumid 44.5 Subhumid 42.2 Very Humid 0.70 Subhumid 5473 Humid 198 66.3 Subhumid 40.5 Subhumid 38.6 Very Humid 0.68 Subhumid 4116 Humid 199 63.1 Subhumid 38.3 Subhumid 36.5 Very Humid 0.64 Dry subhumid 2618 Humid 200 72.4 Subhumid 43.3 Subhumid 41.2 Very Humid 0.71 Subhumid 4497 Humid 201 76.6 Subhumid 46.5 Subhumid 44.3 Very Humid 0.78 Subhumid 3178 Humid 202 69.2 Subhumid 41.4 Subhumid 39.4 Very Humid 0.68 Subhumid 4300 Humid 203 67.6 Subhumid 42.1 Subhumid 40.2 Very Humid 0.73 Subhumid 2074 Humid 204 52.8 Semiarid 32.4 Subhumid 30.9 Humid 0.55 Dry subhumid 2607 Humid 205 46.5 Semiarid 44.8 Subhumid 27.3 Semihumid 0.76 Subhumid 2300 Humid 206 46.1 Semiarid 28.5 Semiarid 27.1 Semihumid 0.49 Semiarid 3833 Humid 207 57.3 Semiarid 34.8 Subhumid 33.1 Humid 0.58 Dry subhumid 2382 Humid 208 48.2 Semiarid 30.0 Semiarid 28.6 Humid 0.52 Dry subhumid 1479 Humid 209 61.1 Subhumid 37.1 Subhumid 35.4 Very Humid 0.62 Dry subhumid 2536 Humid 210 50.0 Semiarid 34.1 Subhumid 32.5 Humid 0.65 Subhumid 2472 Humid 211 48.0 Semiarid 28.7 Semiarid 27.3 Semihumid 0.47 Semiarid 2980 Humid 212 50.6 Semiarid 30.7 Semiarid 29.3 Humid 0.52 Dry subhumid 2100 Humid 213 73.0 Subhumid 45.7 Subhumid 43.4 Very Humid 0.79 Subhumid 2240 Humid

66 Climate types and aridity indices

Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 214 79.8 Subhumid 48.7 Subhumid 46.2 Very Humid 0.82 Subhumid 3309 Humid 215 60.2 Subhumid 37.0 Subhumid 35.3 Very Humid 0.63 Dry subhumid 2976 Humid 216 57.2 Semiarid 34.2 Subhumid 32.6 Humid 0.56 Dry subhumid 3553 Humid 217 76.6 Subhumid 46.4 Subhumid 44.3 Very Humid 0.78 Subhumid 3176 Humid 218 48.3 Semiarid 30.0 Semiarid 28.7 Humid 0.52 Dry subhumid 1481 Humid 219 70.3 Subhumid 42.0 Subhumid 40.0 Very Humid 0.69 Subhumid 4366 Humid 220 50.7 Semiarid 30.8 Semiarid 29.4 Humid 0.52 Dry subhumid 2104 Humid 221 59.8 Semiarid 36.7 Subhumid 35.0 Very Humid 0.63 Dry subhumid 2955 Humid 222 67.2 Subhumid 38.6 Subhumid 36.7 Very Humid 0.61 Dry subhumid 4762 Humid 223 69.7 Subhumid 42.4 Subhumid 40.4 Very Humid 0.71 Subhumid 2893 Humid 224 101.5 Humid 58.4 Subhumid 55.5 Extr Humid 0.92 Subhumid 7196 Humid

Using the Lang classification, the drylands in the Cundiboyacense zone are located in three areas, one in the South and the two others in the centre of the zone. Using the UNED index, the north-eastern part of the zone appears also as dry land. Both classification systems accord with the main problems of erosion reported in this zone. They include in the northern part, Villa de Leyva, La Candelaria desert, and in the South, Soacha, Sabrinsky and Mondoñedo badlands. Using Thornthwaite classification, the northern and central part have less surface area of drylands, which is classified as dry with the Lang and UNEP indices, does not appear (figure 27).

67 Climate types and aridity indices

050100 Km 050100 Km

100000 1150000

Lang Climatic Thornthwaite Climatic factor type Index type 20-40 Arid 16-32 Semiarid 40-60 Semiarid 32-64 Subhumid 60-100 Subhumid

1000000 1050000 1 64-128 Humid 100-160 Humid

1000000 1050000 1100000 1150000 1000000 1050000 1100000 1150000 050100 Km 050100 Km

100000 1150000

Martonne Climatic Index type UNEP Climatic 20-24 Mediterranean Index type 24-28 Semihumid 28-35 Humid 0.2-0.5 Semi arid 35-55 Very humid Dry subhumid > 55 Extremely 0.5 – 0.65 1000000 1050000 1 1000000 1050000 1 humid 0.65 - 1 Subhumid

Figure 27. Climate classifications of the Cundiboyacense high plateau

The Bagnouls - Gaussen Index gives a dominant “Moist” class with BGI values lower than 16 (able 22). Dry periods differ from 0 to 8 dry months per year. Although there is a clear variation of BGI values from north to south (with the highest values in the North). The distribution in the central part is irregular. Figure 28 shows the values of BGI and the

68 Climate types and aridity indices distribution of dry periods. 17 stations of the 40 stations evaluated show a period of “Dry” months from December till February, using BGI.

Table 22. Climate classification using Bagnouls - Gaussen

Number of Dry months Area BGI values stations per year (ha) 23 0 0 Humid 576860 13 1 0 - 10 Moist 478797 4 2 - 3

Figure 28. Bagnouls - Gaussen Index distribution in the Cundiboyacense High plateau

Areas classified as moist correspond partly to “drylands” classified using the Lang index. The southern moist part is the only one that is drylands according to the Lang, Thornthwaite and UNEP indices.

69 Climate types and aridity indices

Figure 29 shows the curves of precipitation (P), Temperature (2T) and ½ ETo of some stations evaluated in the Cundiboyacense high plateau. Using the BGI classification, dry periods are less than three months but if ½ ETo is used, the dry period increases and some stations (i.e. 185 and 186) show a second dry period from June to September of almost the same magnitude. BGI also seems to underestimate in this case the dry periods.

Station 185 (Mosquera), 2550 masl Station 186 (Duitama), 2532 masl DP 120 P 60 120 DP 60 BGI 100 50 100 BGI 50 P 80 40 80 40 ½ETo 60 30 60 30 ½ ETo Temp °C 40 20 Temp °C 40 20 2T 2T Precipitation (mm) Precipitation (mm) 20 10 20 10

0 0 0 0 r Jul Nov Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Ap May Jun Aug Sep Oct Dec

Months Months

Station 187 (El Hato), 3100 masl Station 188 (Macheta), 2100 masl DP DP 120 BGI 60 180 90 160 BGI P 80 100 50 P 140 70 80 40 120 60 100 50 60 30 ½ETo 80 40 Temp °C 40 20 Temp °C 60 ½ ETo 30 2T 40 2T 20 Precipitation (mm) Precipitation (mm) 20 10 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months

Figure 29. Omberothermic curves for the Cundiboyacense high plateau

70 Climate types and aridity indices

6.5. HIGH MAGDALENA BASIN

In this zone, 33% of the area is considered “dry” according to the Lang Index. The Thornthwaite and UNEP classifications result in only 1% and the de Martonne, and the Emberger index considers all the area as humid. In this case there is a high difference between Lang index and the remaining four indices.

Table 23. Climate classifications of the Low Magdalena basin Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 225 45.7 Semiarid 34.6 Subhumid 33.5 Humid 0.74 Subhumid 2080 Humid 226 41.3 Semiarid 31.7 Subhumid 30.5 Humid 0.68 Subhumid 934 Humid 227 45.7 Semiarid 34.5 Subhumid 33.3 Humid 0.74 Subhumid 2518 Humid 228 47.2 Semiarid 35.9 Subhumid 34.6 Humid 0.77 Subhumid 1683 Humid 229 55.4 Semiarid 41.6 Subhumid 40.1 Very Humid 0.88 Subhumid 2775 Humid 231 75.5 Subhumid 54.9 Subhumid 52.7 Very Humid 1.13 Humid 1627 Humid 234 83.0 Subhumid 57.2 Subhumid 54.7 Very Humid 1.11 Humid 4626 Humid 232 67.9 Subhumid 49.7 Subhumid 47.7 Very Humid 1.03 Humid 1245 Humid 230 127.1 Humid 92.0 Humid 88.3 1.88 Humid 7086 Humid 233 80.6 Subhumid 58.0 Subhumid 55.6 1.18 Humid 2515 Humid 235 104.1 Humid 73.6 Humid 70.5 1.47 Humid 8712 Humid 236 92.0 Subhumid 65.4 Humid 62.2 Extremely 1.30 Humid 2878 Humid 237 94.6 Subhumid 66.8 Humid 63.9 Humid 1.33 Humid 3365 Humid 240 99.2 Subhumid 69.2 Humid 66.1 1.36 Humid 4498 Humid 243 89.2 Subhumid 62.9 Subhumid 60.2 1.25 Humid 2217 Humid 247 101.7 Humid 69.7 Humid 66.6 1.34 Humid 8501 Humid 238 70.6 Subhumid 49.2 Subhumid 47.0 Very Humid 0.96 Subhumid 5049 Humid 239 59.1 Semiarid 40.6 Subhumid 38.7 Very Humid 0.78 Subhumid 3278 Humid 241 64.0 Subhumid 44.7 Subhumid 42.7 Very Humid 0.88 Subhumid 4589 Humid 242 68.3 Subhumid 49.3 Subhumid 47.3 Very Humid 1.01 Humid 1207 Humid 244 68.1 Subhumid 47.4 Subhumid 45.2 Very Humid 0.93 Subhumid 3792 Humid 245 52.7 Semiarid 36.0 Subhumid 34.4 Humid 0.69 Subhumid 3768 Humid 246 67.3 Subhumid 46.5 Subhumid 44.4 Very Humid 0.91 Subhumid 3391 Humid 248 57.4 Semiarid 39.5 Subhumid 37.7 Very Humid 0.76 Subhumid 3185 Humid 249 94.5 Subhumid 64.9 Humid 61.9 1.25 Humid 5246 Humid 250 141.8 Humid 99.6 Humid 95.1 Extremely 1.97 Humid 7915 Humid 251 100.6 Humid 68.6 Humid 65.4 Humid 1.31 Humid 3379 Humid 252 85.4 Subhumid 59.2 Subhumid 56.6 1.16 Humid 3050 Humid 253 88.6 Subhumid 62.3 Subhumid 59.4 1.23 Humid 3164 Humid Extremely 254 94.9 Subhumid 65.5 Humid 62.5 1.27 Humid 4362 Humid Humid 256 111.1 Humid 76.1 Humid 72.4 1.46 Humid 6199 Humid

71 Climate types and aridity indices

255 65.3 Subhumid 45.9 Subhumid 43.8 Very Humid 0.91 Subhumid 4095 Humid 257 87.0 Subhumid 54.5 Subhumid 51.9 Very Humid 0.95 Subhumid 5435 Humid 258 66.8 Subhumid 50.7 Subhumid 48.9 Very Humid 1.08 Humid 3040 Humid 259 50.0 Semiarid 37.9 Subhumid 36.6 Very Humid 0.81 Subhumid 2273 Humid 260 75.3 Subhumid 50.9 Subhumid 48.6 Very Humid 0.97 Subhumid 3443 Humid 261 42.8 Semiarid 32.5 Subhumid 31.4 Humid 0.69 Subhumid 1947 Humid 262 59.7 Semiarid 45.2 Subhumid 43.5 Very Humid 0.96 Subhumid 2714 Humid 263 63.6 Subhumid 48.1 Subhumid 46.4 Very Humid 1.02 Humid 2889 Humid 264 33.7 Arid 25.5 Semiarid 24.6 Semihumid 0.54 Dry subhumid 1530 Humid 265 50.1 Semiarid 38.3 Subhumid 36.9 Very Humid 0.82 Subhumid 1788 Humid 266 57.4 Semiarid 43.3 Subhumid 41.9 Very Humid 0.93 Subhumid 3163 Humid 267 70.5 Subhumid 53.3 Subhumid 51.5 Very Humid 1.14 Humid 3886 Humid 269 50.1 Semiarid 37.8 Subhumid 36.5 Very Humid 0.81 Subhumid 2759 Humid 270 61.3 Subhumid 46.0 Subhumid 44.3 Very Humid 0.97 Subhumid 3791 Humid 271 43.1 Semiarid 32.4 Subhumid 31.2 Humid 0.69 Subhumid 2666 Humid 272 52.3 Semiarid 39.3 Subhumid 37.9 Very Humid 0.83 Subhumid 3238 Humid 273 56.0 Semiarid 42.1 Subhumid 40.5 Very Humid 0.89 Subhumid 3461 Humid 274 54.5 Semiarid 41.0 Subhumid 39.4 Very Humid 0.87 Subhumid 2692 Humid 275 43.3 Semiarid 32.5 Subhumid 31.3 Humid 0.69 Subhumid 2395 Humid 276 52.2 Semiarid 39.1 Subhumid 37.7 Very Humid 0.83 Subhumid 2888 Humid 277 48.0 Semiarid 36.6 Subhumid 35.2 Very Humid 0.78 Subhumid 1721 Humid 278 39.0 Arid 29.8 Semiarid 28.7 Humid 0.63 Dry subhumid 1401 Humid 279 47.4 Semiarid 35.5 Subhumid 34.2 Humid 0.75 Subhumid 2371 Humid 268 81.3 Subhumid 61.4 Subhumid 59.3 1.31 Humid 4479 Humid Extremely 280 78.1 Subhumid 58.6 Subhumid 56.4 1.24 Humid 3910 Humid Humid 286 79.5 Subhumid 59.6 Subhumid 57.4 1.26 Humid 3979 Humid 281 50.1 Semiarid 37.5 Subhumid 36.2 Very Humid 0.79 Subhumid 2506 Humid 282 40.2 Semiarid 30.2 Semiarid 29.0 Humid 0.64 Dry subhumid 2012 Humid 283 53.2 Semiarid 39.8 Subhumid 38.4 Very Humid 0.84 Subhumid 2660 Humid 284 62.5 Subhumid 46.8 Subhumid 45.1 Very Humid 0.99 Subhumid 3127 Humid 285 57.1 Semiarid 42.8 Subhumid 41.3 Very Humid 0.91 Subhumid 2858 Humid 287 46.4 Semiarid 34.8 Subhumid 33.5 Humid 0.74 Subhumid 2321 Humid 288 51.8 Semiarid 35.0 Subhumid 33.4 Humid 0.66 Subhumid 2901 Humid 289 42.2 Semiarid 30.6 Semiarid 29.5 Humid 0.64 Dry subhumid 2099 Humid 290 45.1 Semiarid 32.8 Subhumid 31.6 Humid 0.68 Subhumid 2246 Humid 291 54.1 Semiarid 39.3 Subhumid 37.9 Very Humid 0.81 Subhumid 1807 Humid 292 68.0 Subhumid 49.0 Subhumid 47.4 Very Humid 1.02 Humid 1703 Humid 293 43.2 Semiarid 31.3 Subhumid 30.1 Humid 0.65 Dry subhumid 1082 Humid 294 82.2 Subhumid 59.5 Subhumid 57.3 1.23 Humid 2060 Humid Extremely 296 99.6 Subhumid 72.0 Humid 69.4 1.49 Humid 2486 Humid Humid 299 113.3 Humid 81.5 Humid 78.3 1.67 Humid 2242 Humid 295 60.5 Subhumid 43.9 Subhumid 42.2 Very Humid 0.90 Subhumid 1515 Humid 297 45.1 Semiarid 32.7 Subhumid 31.4 Humid 0.67 Subhumid 1126 Humid 298 47.8 Semiarid 34.6 Subhumid 33.3 Humid 0.71 Subhumid 1194 Humid 300 68.7 Subhumid 50.2 Subhumid 48.4 Very Humid 1.04 Humid 2462 Humid 301 52.0 Semiarid 37.9 Subhumid 36.4 Very Humid 0.78 Subhumid 3260 Humid 302 50.6 Semiarid 37.0 Subhumid 35.4 Very Humid 0.76 Subhumid 3172 Humid 303 75.0 Subhumid 54.7 Subhumid 52.5 Very Humid 1.13 Humid 4698 Humid

72 Climate types and aridity indices

304 63.0 Subhumid 46.0 Subhumid 44.1 Very Humid 0.95 Subhumid 3946 Humid 305 59.0 Semiarid 42.7 Subhumid 41.0 Very Humid 0.88 Subhumid 3291 Humid 307 65.2 Subhumid 47.4 Subhumid 45.6 Very Humid 0.98 Subhumid 1406 Humid 308 75.4 Subhumid 54.9 Subhumid 52.7 Very Humid 1.13 Humid 1626 Humid 306 115.5 Humid 83.6 Humid 80.2 Extremely 1.71 Humid 6440 Humid 309 79.5 Subhumid 58.2 Subhumid 55.8 Humid 1.20 Humid 1458 Humid 310 44.9 Semiarid 32.9 Subhumid 31.6 Humid 0.68 Subhumid 824 Humid 311 76.9 Subhumid 54.4 Subhumid 52.0 Very Humid 1.09 Humid 2406 Humid 312 66.9 Subhumid 46.6 Subhumid 44.6 Very Humid 0.92 Subhumid 3033 Humid 313 67.9 Subhumid 47.5 Subhumid 45.3 Very Humid 0.93 Subhumid 3080 Humid 314 64.5 Subhumid 45.0 Subhumid 43.0 Very Humid 0.88 Subhumid 2925 Humid 315 59.6 Semiarid 41.5 Subhumid 39.7 Very Humid 0.82 Subhumid 2702 Humid 316 69.5 Subhumid 48.2 Subhumid 46.1 Very Humid 0.94 Subhumid 5801 Humid 317 53.8 Semiarid 37.6 Subhumid 35.9 Very Humid 0.74 Subhumid 3857 Humid 318 106.0 Humid 73.7 Humid 70.4 1.44 Humid 5903 Humid Extremely 319 82.2 Subhumid 57.6 Subhumid 55.1 1.14 Humid 5144 Humid Humid 320 93.1 Subhumid 65.2 Humid 62.4 1.29 Humid 5827 Humid 321 63.0 Subhumid 43.0 Subhumid 41.1 Very Humid 0.83 Subhumid 3514 Humid

The dry part in this zone is located along the Magdalena River in the centre of the zone from North to South and includes the named Tatacoa desert. This part is delineated using only the Lang index. The Tatacoa Desert (figure 31) and other areas with severe erosion and xerophytes are not shown using the Thornthwaite or UNEP indices. In this case the Lang index is the only one that is representing the dry lands for this zone. The Tatacoa named “desert” (figure 30) is a dry ecosystem of badlands and xerophitic vegetation of more than 300000 hectares delineated clearly using aerial photographs. The fact that this region is not considered as dry land using the UNEP or Thornthwaite climate classification, may be due to the lack of available stations.

Figure 30. Tatacoa named “desert”

73 Climate types and aridity indices

Lang Climatic Thornthwaite Climatic factor type Index type 20-40 Arid 16-32 Semiarid 40-60 Semiarid 32-64 Subhumid 1100000 60-100 Subhumid 1100000 64-128 Humid 100-160 Humid

00 1000000 10000

900000 900000

0 0 800000 8000

700000 700000 0 50 100 Km 0 50 100 Km

700000 800000 900000 1000000 700000 800000 900000 1000000 Martonne Climatic UNEP Climatic Index type Index type 24-28 Semihumid 0 0 Dry subhumid 0 28-35 Humid 0.5-0.65 00

1100000 11 35-55 Very humid 0.65 - 1 SubHumid Humid > 55 Extremely > 1 humid

000000 1000000 1

0 00 0 00000

90 9

00 0 800 800000

00 0 700000

700 0 50 100 Km 0 50 100 Km

Figure 31. Climate zones of the High Magdalena River basin

74 Climate types and aridity indices

Using the Bagnouls - Gaussen classification, the Magdalena zone is considered between humid and moist. From the 97 stations, 54 are considered humid and 43 moist with BGI values lower than 8. 23 stations show a dry period between 2 to 3 months and only 4 have 4 months of dry period (table 24).

Table 24. Bagnouls - Gaussen classification of the High Magdalena River basin

Number of Dry months Area BGI values stations per year (ha) 54 0 0 Humid 2069781 16 1 1 - 6 23 2 - 3 Moist 1894561 4 4 7 - 8

Figure 32. Bagnouls - Gaussen Index distribution in the High Magdalena River basin

75 Climate types and aridity indices

Comparing the BGI and the ETo by Thornthwaite, values for determining dry months are also lower if two times the temperature is used than if half of the ETo is used. Figure 33 shows the precipitation values (P), half ETo, and temperature (2T) for some stations of the Magdalena zone. From this figure dry periods using BGI occur only in station 270 and it last only two months, between August and September, but using ½ ETo the dry period appears in all stations and lasts for almost three months.

Station 248, (1550 masl) DP Station 270 (370 masl) BGI 200 DP 100 240 100 180 90 220 90 200 160 80 80 180 140 70 70 P 160 P 120 60 140 60 100 50 120 50 80 40 100 40 Temp °C 0.5 ETo Temp °C 80 0.5 ETo 60 30 30 60 40 20 20 Precipitation (mm) Precipitation (mm) 2T 40 2T 20 10 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months Station 302 (1950 masl) Station 310 (1155 masl) 160 100 140 100 140 90 P 90 P 80 120 120 80 70 100 70 100 60 80 60 80 50 0.5 ETo 50 DP 0.5 ETo 40 60 40 Temp °C 60 DP Temp °C 30 2T 30 40 2T 40 20 20 Precipitation (mm)

Precipitation (mm) 20 20 10 10 0 0 0 0 J an Apr Jun Jul ug Nov Feb Mar May A Sep Oct Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months

Figure 33. Omberothermic curves for the Magdalena river basin

Dry period in the Magdalena zone does not occur from December to February as is common for the previous study zones, but here from June or July to September, which is the second shortest dry period compared to the other zones.

76 Climate types and aridity indices

6.6. CAUCA VALLEY

The Cauca valley zone has 51% of drylands when the Lang factor classification is applied. Using the Thornthwaite index 10% is considered dry and with the UNEP index only 8.6%. With de Martonne and the Emberger indices the entire zone is humid.

Table 25. Climate classifications of the Cauca valley Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 322 38.8 Arid 28.6 Semiarid 27.5 Semihumid 0.59 Dry subhumid 2158 Humid 323 53.2 Semiarid 36.9 Subhumid 35.3 Very Humid 0.72 Subhumid 2225 Humid 324 54.9 Semiarid 38.1 Subhumid 36.4 Very Humid 0.74 Subhumid 3438 Humid 325 41.8 Semiarid 30.6 Semiarid 29.3 Humid 0.63 Dry subhumid 2329 Humid 326 43.1 Semiarid 31.8 Subhumid 30.5 Humid 0.66 Subhumid 1551 Humid 327 74.8 Subhumid 52.2 Subhumid 49.9 Very Humid 1.03 Humid 2205 Humid 328 48.0 Semiarid 34.8 Subhumid 33.4 Humid 0.71 Subhumid 1332 Humid 329 40.9 Semiarid 29.8 Semiarid 28.5 Humid 0.61 Dry subhumid 1868 Humid 330 73.4 Subhumid 53.9 Subhumid 51.8 Very Humid 1.12 Humid 3665 Humid 331 60.6 Subhumid 44.7 Subhumid 42.9 Very Humid 0.93 Subhumid 2180 Humid 332 42.7 Semiarid 31.5 Subhumid 30.2 Humid 0.65 Subhumid 1537 Humid 333 59.9 Semiarid 43.6 Subhumid 41.7 Very Humid 0.89 Subhumid 1857 Humid 334 58.7 Semiarid 42.7 Subhumid 40.9 Very Humid 0.87 Subhumid 1821 Humid 335 56.4 Semiarid 41.0 Subhumid 39.3 Very Humid 0.84 Subhumid 1750 Humid 336 62.7 Subhumid 45.6 Subhumid 43.6 Very Humid 0.93 Subhumid 1945 Humid 337 63.9 Subhumid 46.5 Subhumid 44.5 Very Humid 0.95 Subhumid 1982 Humid 338 42.5 Semiarid 31.2 Subhumid 30.0 Humid 0.65 Dry subhumid 2354 Humid 339 36.7 Arid 26.6 Semiarid 25.6 Semihumid 0.55 Dry subhumid 1231 Humid 340 48.9 Semiarid 35.7 Subhumid 34.3 Humid 0.74 Subhumid 2715 Humid 341 41.3 Semiarid 30.0 Semiarid 28.8 Humid 0.62 Dry subhumid 1282 Humid 342 55.5 Semiarid 40.4 Subhumid 38.7 Very Humid 0.83 Subhumid 1723 Humid 343 65.7 Subhumid 48.3 Subhumid 46.4 Very Humid 1.01 Humid 3649 Humid 344 45.2 Semiarid 33.3 Subhumid 31.9 Humid 0.69 Subhumid 1624 Humid 345 79.0 Subhumid 55.7 Subhumid 53.2 Very Humid 1.10 Humid 3586 Humid 347 46.9 Semiarid 34.6 Subhumid 33.2 Humid 0.72 Subhumid 1688 Humid 348 45.8 Semiarid 33.7 Subhumid 32.4 Humid 0.70 Subhumid 1648 Humid 349 70.3 Subhumid 48.2 Subhumid 46.0 Very Humid 0.93 Subhumid 2720 Humid 350 57.2 Semiarid 42.1 Subhumid 40.5 Very Humid 0.88 Subhumid 3181 Humid 351 66.5 Subhumid 48.3 Subhumid 46.4 Very Humid 0.99 Subhumid 3034 Humid 352 78.9 Subhumid 57.2 Subhumid 54.9 Very Humid 1.17 Humid 2190 Humid 346 93.0 Subhumid 67.4 Humid 64.7Extremely 1.38 Humid 2581 Humid 353 115.8 Humid 80.3 Humid 76.7 Humid 1.57 Humid 7249 Humid

77 Climate types and aridity indices

From the 33 stations, 20 are classified as dry with the Lang index, 5 with the Thornthwaite and 6 with the UNEP indices. Stations 322 and 339 are classified as arid using Lang factor, which is after Desert the lower dry class, but using UNEP the same stations are classified as dry subhumid or the higher dry class, closer to humid.

050100 Km 050100 Km

Lang Climatic Martonne Climatic factor type Index type 20-40 Arid 28-35 Humid 40-60 Semiarid 35-55 Very humid 60-100 Subhumid 1000000 > 55 Extremely 100-160 Humid humid

900000

700000 800000 700000 800000 050100 Km 050100 Km

Thornthwaite Climatic UNEP Climatic Index type Index type Dry subhumid 16-32 Semiarid 0.5-0.65 0.65 - 1 SubHumid 32-64 Subhumid > 1 Humid Humid 1000000 64-128

900000

Figure 34. Climate classifications of the Cauca valley

78 Climate types and aridity indices

Using the BGI classification, this zone is considered from humid to moist. From the 32 stations, 15 show dry period of less than three months. Figure 35 shows the stations with dry periods and the climate classes delineated using the BGI. The humid class corresponds to the North of the zone and the Moist to the South.

Table 26. Climate classification using Bagnouls - Gaussen

Number of Dry months Area BGI values stations per year (ha) 17 0 0 Humid 709844 15 1 - 3 1 - 3 Moist 359494

Figure 35. Bagnouls - Gaussen Index distribution in the Cauca valley

The dry period determined by BGI occurs mainly during July to August, although some stations show another dry period, shorter in January (station 322). If ½ETo is used to

79 Climate types and aridity indices delineate dry periods, the first dry period occurs from June to September and the second is evident in all the stations, occurring from December to January. Figure 36 demonstrates the curves of monthly precipitation (P), mean temperature (2T) and monthly half ETo for some stations of this zone. DP is the dry period using Thornthwaite ETo and BGI the monthly arid index.

Station 322, 965 masl DP Station 332, 975 masl DP BGI 160 BGI 140 70 160 P 120 60 140 P 70 100 50 120 60 80 0.5 ETo 40 100 50

60 30 Temp °C 80 40 2T 0.5 ETo

40 20 60 30 Temp °C

Precipitation (mm) 2T 20 10 40 20 0 0 Precipitation (mm) 20 10 n l 0 0 u ec Ja eb Apr ay Jun J l F Mar M Aug Sep Oct Nov D Jan Feb Mar Apr May Jun Ju Aug Sep Oct Nov Dec Months Months Station 338, 1041 masl Station 339, 989 masl DP 140 DP BGI 160 P 120 BGI P 140 100 50 120 60 80 40 100 50 0.5ETo 80 40 60 30 Temp °C 0.5ETo DP 2T 60 30 Temp °C 40 20 40 BGI 2T 20 Precipitation (mm) 20 10 Precipitation (mm) 20 10 0 0 0 0 Jan eb ar Apr ay Jun Jul AugSep Oct NovDec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec F M M Months Months

Figure 36. Omberothermic curve for the Cauca valley

80 Climate types and aridity indices

6.7. NARIÑO AND POPAYAN HIGH PLATEAUS

This is the zone with less area of drylands according to all classification systems used. Lang factor gives an area of 8% of the zone, meanwhile De Martonne, UNEP and Thornthwaite less than 1%.

Using the Lang factor, only 8 stations are classified as dry, 6 of them as semiarid and 2 as arid that is the lower aridity class. The same two stations are classified as dry when applying the Thornthwaite, de Martonne and UNEP indices. Both stations are located in the Patía valley, one in Mercaderes and the other one in Policarpa (department of Nariño). It is clear then that there is a small dry area in this zone but another area is also classified as dry in Taminango. Other places of this zone do not appear as dry using those classification systems. In this case, Lang is the only one that classifies those areas as dry.

Table 27 shows the values of the different indices for the stations of the Nariño and Popayan high plateaus. Emberger index shows all the stations as humid. There is not any difference because the mean monthly temperatures along the year are almost constant. The difference between the mean maximum and mean minimum temperatures is less than three degrees (3°C) for all the stations.

Figure 37 shows the climate classes according to the Lang, Thornthwaite, de Martonne and UNEP indices.

81 Climate types and aridity indices

Table 27. Climate classifications of the Nariño and Popayan High plateaus Lang Thornthwaite De Martonne Emberger Num UNEP FL IT IM IE 354 115.5 Humid 79.1 Humid 75.5 1.52 Humid 8272 Humid 356 111.3 Humid 74.2 Humid 70.9 1.39 Humid 3221 Humid 357 109.7 Humid 73.5 Humid 69.8 1.37 Humid 4991 Humid 358 86.1 Subhumid 59.4 Subhumid 57.1 1.17 Humid 2885 Humid 359 100.2 Humid 67.9 Humid 64.6 1.28 Humid 4578 Humid 360 103.9 Humid 70.2 Humid 66.7 Extremely 1.32 Humid 4723 Humid 361 122.8 Humid 82.6 Humid 78.5 Humid 1.55 Humid 5601 Humid 362 138.5 Humid 91.5 Humid 87.6 1.71 Humid 4665 Humid 363 98.5 Subhumid 68.0 Humid 64.9 1.32 Humid 4501 Humid 364 182.9 Very humid 131.2 Wet 125.9 2.67 Humid 5310 Humid 367 109.7 Humid 73.6 Humid 69.8 1.37 Humid 5007 Humid 369 121.2 Humid 80.9 Humid 77.2 1.51 Humid 7541 Humid 370 186.4 Very humid 102.1 Humid 96.6 1.51 Humid 5963 Humid 355 79.7 Subhumid 57.0 Subhumid 54.7 Very Humid 1.16 Humid 3096 Humid 365 73.3 Subhumid 48.6 Subhumid 46.2 Very Humid 0.90 Subhumid 1897 Humid 366 77.4 Subhumid 52.2 Subhumid 49.7 Very Humid 0.98 Subhumid 2968 Humid 368 32.6 Arid 23.7 Semiarid 22.7 Mediterran 0.64 Dry subhumid 1600 Humid 371 86.5 Subhumid 46.9 Subhumid 44.8 Very Humid 0.70 Subhumid 2768 Humid 372 96.2 Subhumid 51.2 Subhumid 48.6 Very Humid 0.74 Subhumid 2105 Humid 373 67.1 Subhumid 41.7 Subhumid 40.0 Very Humid 0.73 Subhumid 3411 Humid 374 71.5 Subhumid 43.3 Subhumid 41.3 Very Humid 0.73 Subhumid 3620 Humid 375 57.4 Semiarid 39.7 Subhumid 37.9 Very Humid 0.77 Subhumid 2625 Humid 376 59.6 Semiarid 35.7 Subhumid 33.9 Humid 0.59 Dry subhumid 3700 Humid 377 58.0 Semiarid 39.8 Subhumid 37.9 Very Humid 0.76 Subhumid 2640 Humid 378 68.3 Subhumid 46.7 Subhumid 44.4 Very Humid 0.89 Subhumid 4287 Humid 379 72.8 Subhumid 48.7 Subhumid 46.3 Very Humid 0.91 Subhumid 3322 Humid 380 59.2 Semiarid 40.9 Subhumid 39.0 Very Humid 0.79 Subhumid 2707 Humid 381 78.9 Subhumid 49.1 Subhumid 46.9 Very Humid 0.85 Subhumid 3993 Humid 382 99.2 Subhumid 52.7 Subhumid 49.7 Very Humid 0.75 Subhumid 2135 Humid 383 30.7 Arid 22.4 Semiarid 21.4 Mediterran 0.46 Semiarid 1517 Humid 384 65.3 Subhumid 46.6 Subhumid 44.6 Very Humid 0.94 Subhumid 2749 Humid 385 58.6 Semiarid 42.8 Subhumid 41.0 Very Humid 0.88 Subhumid 2899 Humid 386 57.8 Semiarid 41.3 Subhumid 39.6 Very Humid 0.84 Subhumid 5793 Humid 387 77.7 Subhumid 55.4 Subhumid 53.0 Very Humid 1.12 Humid 3270 Humid 388 130.2 Humid 88.2 Humid 83.9 1.67 Humid 7254 Humid Extremely 389 113.7 Humid 77.0 Humid 73.3 1.45 Humid 6336 Humid Humid 390 109.5 Humid 74.2 Humid 70.5 1.40 Humid 6097 Humid

391 101.7 Humid 72.5 Humid 69.5 1.46 Humid 4284 Humid

82 Climate types and aridity indices

Lang Climatic Thornthwaite Climatic factor type Index type 20-40 Arid 16 - 32 40-60 Semiarid Semiarid 32-64 Subhumid 60-100 Subhumid 100-160 Humid 64-128 Humid >160 Very humid 750000 800000 > 128 Very Humid

600000 650000 700000 600000 650000 700000 050100 Km 0 50 100 Km

500000 550000 600000 650000 700000 500000 550000 600000 650000 700000

Martonne Climatic UNEP Climatic Index type Index type 20-24 Mediterranean 0.5-0.65 Semiarid 24-28 Semihumid 28-35 Humid 0.5-0.65 Dry subhumid 35-55 Very humid 0.65 - 1 SubHumid > 55 Extremely Humid

750000 800000 > 1 humid

600000 650000 700000 600000 650000 700000 050100 Km 0 50 100 Km

Figure 37. Climate classifications of the Nariño and Popayan high plateaus

83 Climate types and aridity indices

Using the BGI this zone is also considered as humid to moist with BGI values very low, lower than 7. From the 40 stations, 18 do not have dry months, 15 have from 1 to 2 and 5 stations from 3 to 4 dry months (table 28). Figure 38 shows the stations with dry periods and the climate classes delineated using the BGI. There are two main humid areas, one is located to the North and the other at the Southeast of the zone.

Table 28. Bagnouls – Gaussen climate classification

Number of Dry months Area BGI values stations per year (ha) 18 0 0 Humid 615973 15 1-2 1 - 3 Moist 1399375 5 3- 4 4-7

Figure 38. Bagnouls - Gaussen Index of Nariño and Popayan

84 Climate types and aridity indices

The dry period determined using BGI occurs in the middle of the year (July to August). When using ½ETo to delineate dry periods, the dry period increases from June to September and the stations of the driest places show another second dry period in January and February (station 368, Mercaderes). This is the case only for the five stations with 4 dry months. Figure 39 shows the curves of monthly precipitation (P), mean temperature (2T) and monthly half ETo for some stations of this zone. DP is the dry period using Thornthwaite ETo and BGI the monthly arid index.

Station 357 (Florida), 1850 masl 240 Station 366 (San Pablo), 1780 masl 120 320 160 220 110 200 100 280 140 180 90 240 120 160 P 80 140 70 200 100 P 120 60 160 80 100 50 80 40 Temp °C 120 60 ½ETo

Temp °C 60 30 DP 80 ½ETo 40 Precipitation (mm) 40 2T 20 Precipitation (mm) DP 20 BGI 10 40 2T 20 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar AprMay Jun JulAugSep Oct NovDec Months Months Station 368 (Mercaderes), 580 masl Station 373 (Nariño), 2440 masl 140 70 160 80 140 70 120 P 60 120 60 100 50 100 P 50 80 40 80 40 60 ½ETo 30 DP 60 ½ETo 30 Temp °C Temp °C 40 2T 20 40 DP 20 BGI 2T Precipitation (mm) Precipitation (mm) 20 10 20 10 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Months

Figure 39. Omberothermic curves for the Nariño and Popayan high plateaus

85 Rainfall aggressivity indices

7. RAINFALL AGGRESSIVITY INDICES

7.1. PRECIPITATION CONCENTRATION INDEX (PCI)

Seasonal and Temporal precipitation Concentration Index are calculated for every station. PCI1, (Seasonal) estimated with the mean monthly precipitation over a number of years and PCI2 (Temporal) the average of annual PCI calculated with monthly data, annually. For every region a linear and a quadratic regression is applied in order to establish the best relationship between those two indices. Table 29 shows for each zone the results of the linear and quadratic regressions together with the correlation coefficient (R 2) which explains if linear or quadratic regressions fits better for the relationship PCI1-PCI2.

Table 29. Relationship between PCI1 and PCI2

STUDY Linear Regression Quadratic Regression Stations ZONE PCI 2 = a PCI 1 + b R 2 PCI 2 = a PCI 1 b R 2 Guajira peninsula 24 y = 1.5384x + 6.8366 0.2195 y = 3.9545x0.7474 0.1924 Caribbean plateaus 93 y = 2.1518x - 10.118 0.7781 y = 0.3378x1.541 0.7794 Santanderes and Cesar 67 y = 1.7018x - 4.1765 0.6638 y = 0.6859x1.271 0.6847 Cundiboyacence 40 y = 1.9475x - 6.6883 0.1158 y = 0.494x1.4104 0.123 High Magdalena 97 y = 1.6414x - 3.7871 0.8105 y = 0.6189x1.3089 0.8089 Cauca valley 32 y = 1.8343x - 5.8133 0.7105 y = 0.3852x1.5126 0.704 Nariño and Popayan 38 y = 1.1035x + 1.3083 0.4168 y = 1.5242x0.9077 0.4279

There are not great differences between the linear and quadratic regression. Values of R2 between the two methods are similar for every region but there are great differences between the study zones. The best correlation is showed for the High Magdalena river basin and for the Caribbean plateaus. Santanderes and Cesar zone and Cauca valley show some correlation. For the Nariño and Popayan high plateaus the correlation is low and for the Guajira and Cundiboyacense high plateau very low.

86 Rainfall aggressivity indices

The same relationship between PCI1 and PCI2 for all the stations of the country is shown in figures 40a and 40b. The study zones from higher latitudes such as the Caribbean plateaus and the Guajira Peninsula show values far and higher from the rest of the study zones. The Guajira peninsula, the zone with more dry lands, lower precipitation values and more dry months per year, is the zone with a very low correlation and the highest and the more disperse values. Figure 40a shows the zones with extreme values, in which Cauca valley and Magdalena Basin show a high concentration of the data.

Figure 40 a. 43

38 y = 2,4378x - 12,071 R2 = 0,9175 33

28 Zones PCI2 23 Guajira Caribbean plateaus 18 Cundiboyaca HP

Cauca Valley 13 Linear relationship for all the country 8 8 10121416182022 PCI1

Figure 40b 38 y = 2,4378x - 12,071 R 2 = 0,9175 33

PCI2 23 Zones Santanderes 18 Magdalena R Basin Nariño & Popayan 13 Linear relationship for all the country 8 8 10121416182022 PCI1 Figure 40a -40b. Linear relationship between PCI1 and PCI2 in the study zones

87 Rainfall aggressivity indices

Figures 41 to 47 show the distribution of PCI1 and PCI2 for each study zone. In general, there is a pattern in the PCI distribution related with dry lands. The most driest areas show high seasonality. The areas with higher climate indices or most humid are those with low seasonality.

For the Guajira peninsula, using PCI1, almost the entire region is considered seasonal with PCI values between 50 and 20. When PCI2 is used, absolutely all the region turns into highly concentrated.

1150000 1200000 1250000 1300000 1100000 1150000 1200000 1250000 1300000 Temporal PCI1 Seasonal PCI2 Distribution

Distribution 1900000 10-15 Moderately 20-50 Highly seasonal Concentrated 15-20 Seasonal 20-50 Highly Seasonal 1850000

1800000

0 50 100 Km 1750000 0 50 100 Km

Figure 41. Seasonal and Temporal Rainfall Distribution of the Guajira peninsula

The southern part of the Caribbean plateaus, which is the most humid, with the highest precipitation values has uniform seasonality (PCI1). The driest part in the North is seasonal. The rest of the area is moderately seasonal. When PCI2 is applied, concentration increases from South to North. The northern driest places are concentrated to highly concentrated.

88 Rainfall aggressivity indices

In the Santanderes and Cesar region, when using PCI1, the zone is considered uniform in the South, which is the most humid part. The rest of the area is moderately seasonal. Using PCI2 the driest places in the North and in the centre have a concentrated temporal rainfall distribution. The rest of the region has moderately concentrated rainfall distribution.

The Cundiboyacense high plateau has seasonal rainfall distribution (PCI1) from uniform to moderate seasonality and the temporal rainfall distribution (PCI2) if moderately concentrated in almost all the area, except in the driest part which is concentrated.

The High Magdalena River Basin and the Nariño and Popayan high plateaus show some uniformity seasonality in the most humid areas when PCI1 is applied but then they turn into concentrated when PCI2 is used.

The Cauca valley has in almost all the stations uniform seasonality and concentrated rainfall temporal distribution.

700000 800000 9000000 100000 1100000 700000 800000 9000000 100000 1100000

1700000

1600000

1500000 Seasonal Temporal PCI1 PCI2 Distribution Distribution

< 10 Uniform 10-15 Moderately concentrated

10-15 Moderately 1400000 15-20 Concentrated seasonal Highly < 20 15-20 Seasonal Concentrated 0 50 100 Km 050100 Km 1300000

Figure 42. Seasonal and Temporal Rainfall Distribution in the Caribbean plateaus

89 Rainfall aggressivity indices

110 0000 1200000 1300000 1100000 120 0000 1300000

Seasonal 00 170 00 00 PCI1 00 170 00 00 Temporal 0 0 PCI2 Distribution Distribution 00 00 6 Uniform 6 1 1 < 10 10-15 Moderately concentrated 10-15 Moderately seasonal 15-20 Concentrated 0 0 0 0 0 0 0 0 50 50 1 1

30 0000 140 00 00 30 0000 140 00 00 1 1

2000 0 0 50 100 Km 050100 Km 12000 00 1 Figure 43. PCI Distribution in the Santanderes and Cesar zone 1000000 1050000 1100000 1150000 1000000 1050000 1100000 1150000

1150000 1150000

100000 100000 1 1 100000 1150000 100000 1150000

PCI1 Seasonal 1050000 1 1050000 1 Temporal Distribution PCI2 Distribution < 10 Uniform 10-15 Moderately 10-15 Moderately concentrated seasonal 10000001000000 1050000 1050000 000000 000000 15-20 Concentrated 1 1 0 50 100 Km 050100 Km

Figure 44. PCI Distribution in the Cundiboyacense high plateau

90 Rainfall aggressivity indices

700000 800000 900000 1000000 700000 800000 900000 1000000

Seasonal Temporal PCI1 PCI2 Distribution Distribution Uniform Uniform 0 < 10 < 10 0

00 Moderately 0 1100000 11 Moderately 10-15 10-15 concentrated seasonal

000000 1000000 1

00000 900000 9

00000 00000 8 8

0 0 00 00 0 0 70 70 0 50 100 Km 050100 Km

Figure 45. PCI Distribution in the High Magdalena River Basin

700000 800000 700000 800000 Seasonal PCI1 Temporal Distribution PCI2 Distribution < 10 Uniform Moderately 10-15 Moderately 10-15 seasonal concentrated

050100 Km 050100 Km

1000000

900000

Figure 46. Distribution of the PCI in the Cauca valley

91 Rainfall aggressivity indices

500000 550000 600000 650000 700000 500000 550000 600000 650000 700000

Seasonal Temporal PCI1 PCI2 Distribution Distribution < 10 Uniform 10-15 Moderately concentrated 10-15 Moderately seasonal

750000 800000

600000 650000 700000 0 50 100 Km 0 50 100 Km

Figure 47. Distribution of the PCI in the Nariño and Popayan high plateaus

7.2. MODIFIED FOURNIER INDEX (MFI)

MFI1 is estimated with the mean monthly precipitation data over a number of years and MFI2 with the average of annual MFI, annually. For every region, a linear regression and quadratic regression is applied in order to establish the best relationship between those two indices. Table 30 shows for each study zone the results of linear and quadratic regressions.

Table 30. Climate classification using Bagnouls - Gaussen

STUDY Linear regression Quadratic regression Stations ZONE MFI 2 = a MFI 1 + b R 2 MFI 2 = a MFI 1 b R 2 Guajira peninsula 24 y = 1.4163x + 22.548 0.8462 y = 3.6995x0.8232 0.8804 Caribbean plateaus 93 y = 0.977x + 41.271 0.7761 y = 6.049x0.6849 0.7698 Santanderes & Cesar 67 y = 1.231x + 6.424 0.9365 y = 1.781x0.9324 0.9406 Cundiboyacence 40 y = 0.9925x + 22.438 0.8304 y = 3.0884x0.7976 0.816 High Magdalena 97 y = 1.1272x + 18.333 0.9557 y = 1.8055x0.927 0.9441 Cauca valley 32 y = 1.1092x + 12.488 0.9807 y = 1.6254x0.9388 0.9826 Nariño and Popayan 38 y = 1.1897x + 4.9437 0.9871 y = 1.2985x0.9886 0.9879

92 Rainfall aggressivity indices

Differences between the linear and quadratic regression are very low but they vary per zone. For the Caribbean, Cundiboyacense and Magdalena zones, the best relation is the linear regression. For the Guajira, Santanderes, Cauca and Nariño, the best relationship is expressed by a quadratic regression.

With both methods, differences of R2 between every study zones are lower. All the regions show a high correlation between MFI1 and MFI2. The best correlation is for the Santanderes, Magdalena, Cauca and Nariño zones with more than 0.93 value of R2. The Caribbean plateau is the zone with lower correlation (0.77).

The relationship between MFI1 and MFI2 for all the stations of the country is shown in figure 48. Values for the Guajira and Cundiboyacense zones are concentrated in the lower part. The other study zones show a wide distribution. Caribbean and Santanderes zones also show dispersed values.

300 MFI2 = 1,084*MFI1 + 24,403 2 R = 0,9218 250

200 MFI Guajira MFI2 Caribbean plateaus 150 Santanderes Cundiboyaca HP Magdalena R Basin 100 Cauca Valley Nariño & Popayan HP Linear (MFI)

50 20 40 60 80 100 120 140 160 180 200 220 240 260 MFI1

Figure 48. Linear relationship between MFI1 and MFI2 for all the regions

93 Rainfall aggressivity indices

Figures 49 to 55 show the distribution of the Modified Fournier Index (MFI1 and MFI2) for every study zone.

The Guajira peninsula has “very low” to “low” values of MFI1. Those values increase and this zone is dominant “moderate” to “high” class with MFI2. The Caribbean, Santanderes and Magdalena are the zones with higher values of MFI. Those zones are dominant “very high” class using MFI2. The Cundiboyacense zone has “low” to “moderate” class of MFI1 and those values increase from “moderate” to “high” with MFI2. Cauca and Nariño zones from “moderate” to “high” using MFI1 and from “High” to “very high” with MFI2.

1150000 1200000 1250000 1300000 1150000 1200000 1250000 1300000 MFI2 DESCRIPTION MFI1 DESCRIPTION 1900000 60-90 Low < 60 Very low 60-90 Low 90-120 Moderate High 90-120 Moderate 120-160

1850000 < 160 Very High

1800000

0 50 100 Km 1750000 0 50 100 Km

Figure 49. Distribution of the MFI in the Guajira peninsula

94 Rainfall aggressivity indices

700000 800000 9000000 100000 1100000 700000 800000 9000000 100000 1100000

1700000

1600000

MFI1 DESCRIPTION 1500000 60-90 Low MFI2 DESCRIPTION 90-120 Moderate 90-120 Moderate High 120-160 High 120-160 1400000 < 160 Very high < 160 Very high

0 50 100 Km 0 50 100 Km

1300000 Figure 50. Distribution of the MFI in the Caribbean plateaus

1100000 1200000 1300000 1100000 1200000 1300000

70 00 00

00 170 00 00 00 MFI1 DESCRIPTION MFI2 DESCRIPTION 0 0 0 00 0 Low Low 6 6 60-90 60-90 1 1 90-120 Moderate 90-120 Moderate 120-160 High 120-160 High 0 0 00 00 < 160 Very high < 160 Very high 0 0 50 150 1 0 0

40 00 0 1

30 0000 140 00 0 30 0000 1 1

0 0 00 00 0

0 0 0 0 50 100 Km 0 50 100 Km 12 12 Figure 51. Distribution of the MFI in the Santanderes and Cesar zone

95 Rainfall aggressivity indices

1000000 1050000 1100000 1150000 1000000 1050000 1100000 1150000

100000 1150000 100000 1150000 100000 1150000 1 1

MFI2 DESCRIPTION

MFI1 DESCRIPTION 60-90 Low 60-90 Low 90-120 Moderate 90-120 Moderate 120-160 High 1000000 1050000 1 1000000 1050000 1000000 1050000

0 50 100 Km 050100 Km

Figure 52. Distribution of the MFI in the Cundiboyacense high plateau

700000 800000 900000 1000000 700000 800000 900000 1000000 MFI1 DESCRIPTION MFI2 DESCRIPTION 90-120 Moderate 90-120 Moderate

120-160 High 120-160 High 00 00 0 0 < 160 Very high < 160 Very high 1100 1100

1000000 1000000

900000 900000

800000 800000

0 0 0 0

7000 7000 0 50 100 Km 0 50 100 Km

Figure 53. Distribution of the MFI in the High Magdalena River Basin

96 Rainfall aggressivity indices

700000 800000 700000 800000 MFI1 DESCRIPTION MFI2 DESCRIPTION

60 - 90 Low 90-120 Moderate 90-120 Moderate 120-160 High 120-160 High < 160 Very high < 160 Very high 0 50 100 Km

1000000

050100 Km

900000

Figure 54. Distribution of the MFI in the Cauca valley

500000 550000 600000 650000 700000 500000 550000 600000 650000 700000

MFI2 DESCRIPTION MFI1 DESCRIPTION 90-120 Moderate 60-90 Low High 90-120 Moderate 120-160 Very high 120-160 High < 160 < 160 Very high

750000 800000

600000 650000 700000 600000 650000 700000 050100 Km 0 50 100 Km

Figure 55. Distribution of the MFI in the Nariño and Popayan high plateaus

97 Rainfall aggressivity indices

7.3. EROSIVITY INDEX OF CORINE (1995)

The erosivity index (ErIn) estimated using the CORINE methodology is represented for each study zone using the same interpolation method (IDW) in the figures 56 to 59.

The Guajira peninsula shows 82.7% of the area with moderate erosivity and 17.3% with high values. Areas with higher values are spread out in the North and South.

The Caribbean plateaus zone has dominant high ErIn values. 93.1% of this zone has high erosivity and only 6.9% moderate values. The zone with moderate values is located in the driest North, and in the most humid southern zone. In this case the extreme values of precipitation (the lowest and the highest) give lower values of erosivity.

The Santanderes and Cesar zone show values of erosivity from 4 to 10. 52% of the zone consists of moderate values and 48% are high erosivity values. The areas with high erosivity values are the northern part (except the extreme top) and the extreme Southwest.

The Magdalena river basin shows ErIn values from “low” to “high” class. The areas with higher erosivity index (31%) are located in the middle of the region, from North to South following the pattern of the lowest place of the valley. The rest of the area, which is more mountainous and with higher altitudes, has moderate values of ErIn (67%).

The Cundiboyacense high plateau is the zone with lower erosivity values. Those vary from 2 to 7. 26% of the zone presents low erosivity and 74% moderate. The areas with lower erosivity ranges are the driest places.

The Cauca valley shows a dominant moderate ErIn values in 95% of the zone and only 5% of its area, located to the Southeast, shows high erosivity values.

The Nariño and Popayan high plateaus have erosivity ranges from “low” to “high”. In this case, there is no relationship between the ErIn values and the moisture regime.

98 Rainfall aggressivity indices

1150000 1200000 1250000 1300000 700000 800000 9000000 100000 1100000 ErIn DESCRIPTION

4-5 1700000 1900000 5-6 Moderate 6-7 7-8 8-9 High

9-10 1600000

1850000

1500000

1800000 ErIn DESCRIPTION 5-6 Moderate 6-7 7-8 1400000 8-9 High

1750000 0 50 100 Km 9-10

0 50 100 Km 1300000

Figure 56. Distribution of “ErIn” for the Guajira and Caribbean zones

700000 800000 900000 1000000 1100000 1200000 1300000

ErIn DESCRIPTION 3-4 Low 4-5 00000

1 5-6 ErIn DESCRIPTION Moderate 00 170 00 00 6-7 0 4-5 00 7-8 6 5-6 1 Moderate 6-7 8-9 High 7-8 9-10

1000000 0 8-9 High 00 0 9-10 150

900000 0

800000

30 0000 140 000 1

0000 0 7 0 00

0 050100 Km 0 0 50 100 Km 12 Figure 57. Distribution of “ErIn” for the Santanderes and Magdalena zones

99 Rainfall aggressivity indices

1000000 1050000 1100000 1150000 700000 800000 ErIn DESCRIPTION 0 50 100 Km 4-5 5-6 Moderate 6-7 7-8 8-9 High 9-10 1000000 100000 1150000

ErIn DESCRIPTION 2-3 Low 3-4 4-5 900000 5-6 Moderate 6-7 1000000 1050000 1 1000000 1050000 1 7-8 0 50 100 Km

Figure 58. Distribution of “ErIn” for the Cundiboyacense and Cauca zones

500000 550000 600000 650000 700000

ErIn DESCRIPTION 3-4 Low 4-5 5-6 Moderate 6-7 7-8 8-9 High 750000 800000 9-10

600000 650000 700000 600000 650000 700000 0 50 100 Km

Figure 59. Distribution of “ErIn” for the Nariño and Popayan high plateaus

100 Conclusions

8. CONCLUSIONS

CLIMATE INDICES

The five climate indices evaluated to delineate dry lands in Colombia, show different results for every study zone. The Lang and the UNEP indices define a low class of aridity named “desert” for Lang and “hyperarid” for UNEP. The next class is “arid”, which is the first class for the other indices (de Martonne, Thornthwaite and Emberger). The Bagnouls–Gaussen index does not use the term desert or arid but “dry”.

The Lang climate index tends to classify more areas as dry than the other indices. Applying Lang, Colombia has the lowest class of climate types which is “desert”. This desert climate is found in the whole Guajira zone (1,136.381 ha) and in the north of the Caribbean plateaus (11.802 ha). If the Lang index is used, in each of the study zones appear dry lands and this is related to the erosion and degradation processes reported by secondary studies, in which other characteristics such as vegetation, erosion and soils are used to delineate areas with desertification problems.

The Emberger index classifies absolutely all the stations of Colombia as “humid”, which is the higher climate class. This index is not suitable in Colombia because it is based on the differences between the mean temperatures of the hottest and the coldest months. In the case of Colombia, those differences are very low due to the tropical and equatorial location of the country. The mean temperatures over the year do not vary more than four degrees. This index can be applied in seasonal latitudes where the difference of temperatures in between summer and winter is very high.

The de Martonne index tends to classify every study zone as more humid in comparison to the other indices, although the entire Guajira zone appears to be between

101 Conclusions arid and semiarid. This index seems to classify only as dry lands the areas with extreme low precipitation values.

The UNEP and Thornthwaite indices agree for the Guajira zone, with Lang and de Martonne, when the whole Guajira zone is classified as dry. With the Thornthwaite index the whole zone is classified as arid which is the lower class, with the UNEP index half of the Guajira zone is arid and half is semiarid. In this case, Thornthwaite agrees with Lang, but UNEP and Lang differ. The Thornthwaite and UNEP indices are also similar for the Santanderes, Magdalena, Cauca and Nariño zones but they differ in the Caribbean and in the Cundiboyacense zones. With the Thornthwaite index the Caribbean plateaus has 24.5% of the area as dry and with the UNEP index only 16.6%. In the Cundiboyacense zone the result is opposite. The UNEP index considers 44.5% of the area as dry, in contrast with the Thornthwaite index where the result is only 13.2% dry.

Using the Bagnouls-Gaussen classification, based on 2 times temperature and precipitation, there is a clear differentiation of dry monthly periods. But when the BGI is calculated annually, all the zones are classified between humid and moist. The fact that Bagnouls-Gaussen proposes only four categories, then the classification of drylands are zones with extreme low or no rainfall values and with extremely high temperature. This is not the case for the latitudes in which Colombia is located. Maximum temperatures in Colombia are not more than 33ºC, while Mediterranean or subtropical zones report more than 38ºC in the summer. Four classes are not enough to evaluate the climate differences at regional level in equatorial latitudes.

Determination of dry months using BGI gives less dry periods than when half ETo calculated with the Thornthwaite formula is used. As ETo by Thornthwaite underestimates dry periods, then the estimated dry periods in this study should be even longer. In this case, BGI is not very approximate to assess dry periods based on the temperature for these latitudes.

102 Conclusions

DRY LANDS

Using the same interpolation method to delineate dry lands for different climate indices, it is possible to estimate the dryland areas in each zone. Nevertheless it is necessary to consider the effect of other factors such as relief and wind.

Table 31 shows the area in hectares and the percentage for each study zone according to the Lang, UNEP, Thornthwaite and de Martonne climatic indices. The Guajira peninsula is the only zone completely classified as dry by all indices. The other regions show contrasts between the different indices.

Some areas known as very dry with badlands, like the “Tatacoa desert” (in the Magdalena zone), with more than 300000 ha and the Taminango xerophitic ecosystem (in Nariño) appear in those zone as dry lands only with the Lang climate classification. This is not the case when other indices are used.

Table 31. Areas (ha) and percentage of drylands per study zone according to different climate indices

LANG UNEP THORNTWAITE MARTONNE STUDY ZONE (ha) % (ha) % (ha) % (ha) % GUAJIRA 1136381 100.01136381 100.0 1136381 100.0 1136381100.0 CARIBE 5365201 90.5 98434116.6 145529224.5 2235143.8 SANTANDERES 2121912 53.2 345175 8.6 270883 6.8 91073 2.3 CUNDBOY 463137 43.9 46959844.5 13970513.2 12870.1 MAGDALENA 1333399 33.6 18931 0.5 50617 1.3 00.0 CAUCA 544312 50.9 922248.6 1036489.7 00.0 NARIÑO 157733 7.8 171170.8 163350.8 49540.2

103 Conclusions

The Lang climate classification gives more area as drylands than the other indices and this may be due that it is considering mean annual temperature, which in the case of Colombia is almost constant all the year.

The UNEP and Thornthwaite indices give less drylands than the Lang index. The UNEP index is giving less dry lands area may be because the ETo was calculated by Thornthwaite method, which according to the literature is underestimating ETo for dry periods or overestimating for humid periods.

Another cause of the differences between the Lang, UNEP and Thornthwaite indices is the fact that the boundaries for dry class are not the same.

RAINFALL AGRESSIVITY

Relationship between PCI1 and PCI2 varies for each study zone. The Magdalena and the Caribbean zone show the best correlation (R2 values of 0.81 and 0.77 respectively), while the Cundiboyacense and Guajira zones show the lower values (0.12 and 0.21). In the case of Colombia, relation of PCI1 and PCI2 varies highly between zones.

For almost each study zones, PCI shows higher seasonality in the driest areas than in the moist areas. Using PCI2, the entire Guajira zone is classified with high seasonality. The class “seasonal” appears only in the driest places of the Caribbean, Santanderes and Cundiboyacense zones. The rest of the areas are considered as moderated seasonal.

Differences between the MFI1 and MFI2 relationship in the different study is relatively low. The Santanderes, Magdalena, Cauca and Nariño zones show coefficient values of 0.94, 0.96, 0.98 and 0.99 respectively, which is very high. The lower value is found in the Caribbean plateaus (0.77), still relatively acceptable.

Using the MFI2, in general for all the zones, more than 90% of the area is considered between high to very high classes of aggressivity index. The zones with

104 Conclusions relatively more area of very high aggressivity are the Caribbean (with 87% of the area), Magdalena (83%), Santanderes (70%) and Nariño (64%). The Guajira peninsula is the zone with less aggressivity index, with 57% of the area between low and very low and 43% as moderate.

EROSIVITY

Using the CORINE methodology, the Caribbean plateaus are the zones with highest erosivity index. 93% of the area shows values higher than 8. Santanderes, Nariño and Magdalena zones show moderate to high values. The Guajira and Cauca zones have dominant moderate values in almost all the area and the Cundiboyacense zone is between low to moderate.

105 References

9. REFERENCES

Arnoldus, H. 1980. An approximation of the rainfall factor in the Universal Soil Loss Equation. In: De Boodt, M. and Gabriels, D. (Eds) Assessment of Erosion. John Wiley and sons.

Bailey, R. G. 1996. Climate Classification of the Mid-Columbia Region Ecosystem Geography. Springer-Verlag, New York.

Brady, C. N. 2002. The Nature and properties of soils. Pearson Education Asia. India.

Bagnouls, F., Gaussen, H. 1952. L´indice xérothermique. Bulletin de l´association de Géographes français. Nº 222-223, jan.-févr., Paris.

Bagnouls, F., Gaussen, H. 1952. Les climats biologiques et leur classification. Ann de Geogr. Nº 258. Paris.

CORINE. 1995. Soil erosion risk and important land resources in the southern regions of the European Community. EUR 13233 EN.

Cortes, L. A. 1981. Los Suelos del Anden Pacífico y su Aptitud de Uso. Subdirección Agrológica. Instituto Geográfico Agustín Codazzi. Bogotá.

Cortes, L. A., Malagón D. C., 1984. Geografía de Suelos de Colombia. Universidad de Bogota Jorge Tadeo Lozano. Bogotá.

Cortes, L. A. 1994. Suelos de Colombia: reguladores de recursos. Universidad de Bogota Jorge Tadeo Lozano. Bogotá.

DANE. 2001. Estadísticas Nacionales. http://www.dane.gov.co/inf_est/series_proyecciones.htm

De Martonne, E. 1923. Aridité et indices d´aridité. Académie des Sciences. Comptes Rendus, 182 (23) : 1935-1938.

106 References

Dengüz, O. 2005. Soil Erosion Risk Assessment of the Gölbaşi Environmental Protection Area and Its Vicinity Using the CORINE Model In: Turk Agriculture Journal. 29 439-448 T.BÜTAK

Dregne, H., Hassan H. 1997. Natural Habitats And Ecosystems Management In Drylands: An Overview. Natural Habitats And Ecosystems Management Series. The World Bank. Paper No 51.

Emberger, E. 1932. Su rune formule climatique et ses applications en botanique. La Météorologie.

El-Swaify, S. A., Dangler, E. W., Armstrong, C. L. 1982. Soil erosion by water in the tropics. Research Extension Series 024. College of tropical Agriculture and Human Resources, Univ. of Hawaii. Environmental Systems Research Institute, IC. 2002. Arc/view version 3.2 User’s Guide.

El-Swaify, S. A. 1977. Susceptibilities of certain tropical soils to erosion by water. In Greenland, D. and Lal, R. (Eds). Soil Conservation and Management in the Humid Tropics.

FAO. 1983. Guidelines: Land Evaluation for Rainfed Agriculture. FAO Soils Bulletin, 52; FAO, Rome.

Fajardo, R. Z, Guzmán, Ma del R. 2002. Segundo Informe Nacional de Implementación de la Convención de las Naciones Unidas de Lucha Contra la Desertificación y la Sequía – CCD. Ministerio Del Medio Ambiente. Bogotá, Colombia.

Fournier, F. 1960. Climat et érosion: la relation entre l’érosion des sols par l’eau et les précipitations atmosphériques, Presses universitaires de France, Paris.

Gabriels, D. 2000. Rain Erosivity in Europe In: ESSC III Int. Congress. Key Notes. Man and Soil at the Third Millenium. (Rubio, J. L., Asins, S, Andreu, V., de Paz, J. M., and Gimeno, E. eds.) Valencia. Pp 31.43.

Gabriels, D. 2006. Water Erosion (lecture notes) Department of Soil and Management and Soil Care. Faculty of Bioengineering. Universiteit Gent. België.

García, M., Carvajal, Y. 2006. Mapa regional de Zonas áridas, semiáridas y subhúmedas secas de de América Latina y El Caribe caso de estudio Colombia. Universidad del valle, Colombia.

Gomez, A. 1987. La zona Andina Colombiana. Erosión y Conservación de Suelos. In: Congreso Colombiano de la Ciencia del Suelo, 4. Coloquio de la degradación de los suelos en Colombia. Neiva, Colombia

107 References

Gomez, A., Ramirez H., Cruz K., Rivera, P. 1992. Manejo y control integrado de malezas en cafetales y potreros de la Zona Cafetera. Chinchiná- Colombia), FEDERACAFE. Cenicafé.254 p.

Gonzalez, W., Neira, F., Montañez, I. 1999. Levantamiento edafológico semidetallado de suelos en los ecosistemas estratégicos de la zona rural de Bogotá. DAMA - CORPOICA.

IDEAM. 1996. Dinámica de los factores de la erosión y sedimentación en el país. Subdirección de Geomorfología y Suelos. Santa Fe de Bogotá.

IDEAM. 1998. Estudio Nacional de Procesos Morfodinámicos. La erosión, la sedimentación y la estabilidad de la formación superficial en Colombia. Santa Fe de Bogotá, 1998. 1-32 p.

IDEAM. 1999. Indicadores ambientales y sostenibilidad. Subdirección de Geomorfología y Suelos. Población y Asentamientos Humanos. Ecosistemas. Documento Interno. Santa Fe de Bogotá. 1-18 p.

IDEAM - Ministerio Del Medio Ambiente. 2001. Degradación de suelos y tierras en Colombia y estado de la Desertificación. Bogotá, Colombia.

IGAC. 2000. Mapa de suelos de Colombia. Instituto Geográfico Agustín Codazzi. Bogotá.

Lal, R. 1988. Erodibility and Erosivity. In: Soil Erosion Research Methods. Edited by Lal R. Soil and Water Conservation Service. Wageningen, The Netherlands. Pp 141 – 160.

Laflen, J., Moldenhauer, W. 2003. Pioneering Soil Erosion Prediction. The USLE Story. World Association of Soil & Water Conservation – WASWC. Special Publication No. 1.

Leon, S. T. 2003. Relaciones Agricultura – Ambiente En La Degradación De Tierras En Colombia. IDEAN. Bogotá, Colombia.

Malagón, D. C. 2003. Los Suelos de Colombia. SOCOLGEO. Bogotá. Colombia.

Masahiro, M. 1995. Managing Water for Peace in the Middle East: Alternative Strategies. United Nations. University Press Tokyo.

Zare, M. E. Gabriels, D. 2006. Estimation and Classification of Climatic Indices for Yazd Region (Iran). Department of Soil Management and Soil Care, International Centre for Eremology, Ghent University, Belgium

Michiels, P., Gabriels, D., Hartmann, R. 1992. Using the Seasonal and Temporal precipitation concentration index for characterising the monthly rainfall distribution in Spain. Catena , Vol 19 43 - 58.

108 References

Neira, F. 2001. Caracterización de los procesos de degradación física de suelos en la región del Alto Patía. CORPOICA - INAT. Tibaitatá.

Ojeda, O., Arias, R. 2000. Informe Nacional Sobre La Gestión Del Agua En Colombia

Oliver, J.E. 1980. Monthly precipitation distribution: a comparative index. Professional Geographer, 32, 300 – 309.

PHI-LAC. 2006. Guía metodológica para la elaboración del mapa de zonas áridas, semiáridas y subhúmedas secas de América Latina y el Caribe. Programa Hidrológico Internacional de la UNESCO para América Latina y el Caribe. PHI-VI / Documento técnico Nº 3.

Poessen, J. 1992. Mechanisms of overland flow generation and sediment production on loamy and sandy soils with and without rock fragments. In Over-flow hydraulics and erosion mechanics, A.J. Parsons and A. D. Abrahams (Eds).

Pérez, S. 2001. Modelo para evaluar la erosión hídrica en Colombia utilizando Sistemas de Información Geográfica. Universidad Industrial de Santander – IDEAM.

Renard, K. 1995. Soil loss and runoff estimation. In: Soil Erosion, Conservation, and Rehabilitation. Edited by Door Menachem Agassi

Rivera, P. J. 1999. Causas y consecuencias de la erosión de suelos de ladera colombiana. CENICAFE, Bogotá.

Rivera, P. J. 2001. Susceptibilidad y predicción de la erosión en suelos de ladera de la zona Cafetera Colombiana. Universidad Nacional de Colombia. Medellín.

Renard, K. G., Freimund, J. R. 1994. Using monthly precipitation data to estimate the R-factor in the revised USLE. Journal of Hydrology 157, 287-306.

Suárez De Castro, F. 1951 Desyerbas con machete en los cafetales. Chinchiná (Colombia), Cenicafé, Campaña de Defensa y Restauración de Suelos.

Suárez De Castro, F., Rodríguez, G. 1962. Investigaciones sobre la erosión y la conservación de los suelos en Colombia. Bogotá (Colombia), Federación Nacional de Cafeteros de Colombia.

SYS, C., Van Ranst, E., Debaveye. J. 1991. Land Evaluation. Principles in Land Evaluation and Crop Production Calculations. Agricultural Publications Nº 7. General Administration for Development Cooperation. Brussels. Belgium.

109 References

Trisorio, L., Ladina, G., Todorovic, M. 2005. Identification of Areas Sensitive to Desertification in Semi-Arid Mediterranean Environments: The Case Study of the Abulia Region (Southern Italy). In: International Conference on: Water, Land and Food Security in Arid and Semi-Arid Regions. (Compiled by Atef Hamdy) Mediterranean Agronomic Institute. Valenzano, Bari-Italy.

UNEP. 1997. United Nations Environment Programme. World Atlas of Desertification, 2nd edition. Edited by N. Middleton and D. Thomas. London: UNEP. 182pp.

Uribe, H. 1971. Erosión y Conservación de suelos en café y otros cultivos. Cenicafé (Colombia).

USDA. 1993. Soil Survey Manual. Soil conservation Service. United States Department of Agriculture. Washington, USA.

Van Ranst, E., Verdoodt, A. 2005. Land Evaluation. Part III: Quantitative Methods in Land Evaluation. International Centre for Physical land Resources. Gent Universiteit. Belgium

White, R., Nackoney, J. 2002. Drylands, People, And Ecosystem Goods And Services: A Web-Based Geospatial Analysis. World Resources Institute. Washington, DC.

Wischmeier, W.H. 1976. 'Use and misuse of the universal soil loss equation', Joumal of Soil and Water Conservation 31, pp. 5-9.

Wischmeier, W.H., Smith, D.D. 1965. 'Predicting rainfall-erosion losses from cropland east of the Rocky mountains', USDA Agricultural Handbook 282, Washington DC.

Wischmeier, W.H., Johnson, C.B., Cross, B.V. 1971. 'A soil erodibility nomograph for farmland and construction sites', Joumal of Soil and Water Conservation 26.

110