EARTH SCIENCES CENTRE GÖTEBORG UNIVERSITY B332 2002
THE EFFECTS OF AFFORESTATION
– a minor field study of climate, soil, land use and socio-economy in two small areas on Santiago Island, Cape Verde
Jonna Eklund Anders Kronhamn
Department of Physical Geography GÖTEBORG 2002
GÖTEBORGS UNIVERSITET Institutionen för geovetenskaper Naturgeografi Geovetarcentrum
THE EFFECTS OF AFFORESTATION
– a minor field study of climate, soil, land use and socio-economy in two small areas on Santiago Island, Cape Verde
Jonna Eklund Anders Kronhamn
ISSN 1400-3821 B332 Projketarabete Göteborg 2002
Postadress Besöksadress Telefo Telfax Earth Sciences Centre Geovetarcentrum Geovetarcentrum 031-773 19 51 031-773 19 86 Göteborg University S-405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN
Abstract The Republic of Cape Verde consists of 14 islands and is an extension of the Sahelian climatic zone. The fragile ecosystem was disrupted when the Portuguese colonised the islands in 1462. Records of droughts date back to 1719. The steep slopes on the mountainous islands give a strong orographic effect with few, but intense, precipitation events. The problems with land degradation led to large afforestation programmes which started after independence in 1975 with finanicial support from abroad. Since 53% of Cape Verdes’ approximately 408,000 inhabitants are occupied with agriculture, it is important to stop the land degrading processes through restorative measures.
The ITCZ brings rain to Cape Verde and precipitation varies radically from year to year. The statistical analysis comparing Cape Verde with Sahel show decreasing precipitation trends in all stations. The stations within Santiago show great variability in the amount of precipitations and also in the number of events.
Two small areas, Sao Goncalo in Ribeira Sao Joao on the west side of Santiago and Poilao in Ribeira Seca on the east side, were investigated during May and June in 2001. Interpretation of aerial photographs and maps and soil analysis were conducted at INIDA, Sao Jorge dos Orgaos.
The mean annual precipitation (1961-2001) in Sao Jorge dos Orgaos (350 masl) is 449 mm and in Sao Francisco (100 masl) 196 mm. The effects of ENSO (El Niño Southern Oscillation) on precipitation in Cape Verde appears to be weak. A sheltering effect of the trees on micro-climatic conditions in the afforested areas, measured through temperature and dew point temperature in transects, is not seen, but the sheltering effects are visible beneath the trees.
The soils in both areas are mainly entisols and inceptisols. These soils are arable when sufficient plant nutrients, water and erosion control are provided. The organic matter content increases with increasing vegetation cover in both areas. 54% of the land in Sao Goncalo and 12% in Poilao have been afforested since 1979. All interviewees are positive to the afforestation programmes. Previously, restorative work was an important source of income during the driest season every year, but the decrease in financial support has lead to great problems. The island faces a future of degrading processes if nothing is done.
Sumário A República de Cabo Verde é constituída por 14 ilhas e é uma extensão da zona climática do Sahel. O frágil ecossistema foi rompido pela colonização portuguesa em 1462. Registos de secas datam de 1719. As íngremes inclinações nas ilhas montanhosas produzem um forte efeito orográfico com precipitações raras mas intensas. Os problemas com a degradação das terras conduziram a grandes programas de reflorestamento que começaram logo após a independência em 1975, com apoios financeiros exteriores. Uma vez que 53% dos cabo-verdianos, cerca de 408.000 habitantes, têm como ocupação principal a agricultura, é importante acabar com o processo de degradação através de medidas construtivas.
O ITCZ traz chuvas para Cabo Verde e a precipitação é extremamente variável de ano para ano. A análise estatística que compara Cabo Verde com o Sahel mostra tendências de diminuição da precipitação em todas as estações. As estações em Santiago mostram grande variabilidade na quantidade de precipatação e igualmente no número de ocorrências. Duas pequenas áreas, São Gonçalo, na Ribeira de São João no lado oeste de Santiago, e Poilão, na Ribeira Seca no lado leste da mesma ilha, foram estudadas entre Maio e Junho de 2001. A interpretação das fotografias, mapas e análise de solos foram feitos pelo INIDA, em São Jorge dos Orgãos.
A precipitação média anual (1961-2001) em São Jorge dos Orgãos (350 masl) é de 449 mm e em São Francisco (100 masl) de 196 mm. Os efeitos do ENSO (Oscilação Setentrional do El Niño) sobre a precipitação em Cabo Verde parecem fracos. O efeito de protecção das árvores em condições micro-climáticas nas áreas reflorestadas, medido através da temperatura e da temperatura de ponto de condensação em transecto, não é assinalável, mas os efeitos de protecção são visíveis sob as árvores.
Os solos em ambas as áreas são principalmente "entisols" e "inceptisols". Estes solos são aráveis quando o fornecimento de nutrientes e de água às plantas e o controlo da erosão são suficientes. O conteúdo em matéria orgânica aumenta com aumento da cobertura de vegetação em ambas as áreas. 54% da terra em São Gonçalo e 12% em Poilão foram reflorestadas desde 1979. Todos os entrevistados estão de acordo com os programas de reflorestamento. O trabalho de reflorestamento tem sido, em cada ano, uma fonte de rendimento importante durante a estação mais seca, mas desde que o apoio financeiro diminuiu existem grandes problemas. A ilha enfrenta de novo um futuro de degradação se nada for feito. 2 Foreword This thesis is written by two authors, and has therefore been divided into separate parts. Jonna Eklund has the main responsibility for collecting data, analysing and writing the parts concerning soil and land use. Anders Kronhamn has the main responsibilty for collecting statistical information, field observations and writing the parts concerning climate. The parts concerning socio-economy have been analysed and written by both authors.
3 Abbreviations
DGASP Direccão Geral Agricultura e Pecuaria (General Administration for Agriculture Forestry and Livestock) ENSO El Niño Southern Oscillation FAIMO Frentes de Alta Intensidade de Mão Obra (High Labor Intensive Front) INGRH Instituto Nacional de Gestão de Recursos Hidricos (National Institute for Water Resources Management) INIDA Instituto Nacional de Investigacão e Desenvolvimento Agrario (National Research Institute for Agriculture and Rural Development) ITCZ Inter Tropical Convergense Zone
4 1. INTRODUCTION...... 7
PURPOSE...... 8 DEFINING LAND DEGRADATION...... 9 Land degradation - climate ...... 10 Land degradation - soil and land use...... 11 Land degradation – Cape Verde...... 11 QUESTIONS...... 12 2. THE CAPE VERDE ISLANDS ...... 13
GEOLOGY AND TOPOGRAPHY ...... 13 CLIMATE ...... 14 Agro-climatological zones on Santiago ...... 15 SOILS AND LANDUSE ...... 15 Soil and Water Conservation (SWC) structures ...... 17 3. METHODS ...... 18
INVESTIGATED AREA ...... 18 CLIMATE ...... 19 Statistical analysis...... 19 Field observations...... 19 SOIL AND LANDUSE ...... 19 Interpretation of aerial photographs and maps...... 19 Field observations...... 19 Soil samples...... 20 SOCIO-ECONOMY...... 21 Interviews...... 21 SOURCES OF ERROR...... 22 Micro-climate...... 22 Soil and land use ...... 22 Socio-economy ...... 22 4. RESULTS ...... 23
A DESCRIPTION OF THE INVESTIGATED AREAS...... 23 CLIMATE - CAPE VERDE AND MAINLAND SAHEL...... 23 REGIONAL CLIMATE ...... 29 CONNECTIONS TO EL NIÑO...... 33 LAND USE ...... 34 West area - São Gonçalo ...... 35 East area Poilão ...... 37 SOILS...... 38 West area - São Gonçalo ...... 39 East area - Poilão ...... 41 Field observations...... 42 Soil and water conservation...... 42 MICRO-CLIMATE...... 43 West area - São Gonçalo ...... 43 East area - Poilão ...... 44 FARMERS PERCEPTION...... 45 SOCIO-ECONOMY...... 46 Background questions...... 46 Crops and irrigation ...... 46 West area - São Gonçalo ...... 47 East area - Poilão ...... 47 Animals...... 47 Afforestation and SWC ...... 48 CHAPTER SUMMARY...... 49 Climate...... 49 Soil and land use ...... 49 Socio-economy ...... 49
5 5. DISCUSSION...... 50
CLIMATE ...... 50 CONNECTIONS TO ENSO...... 52 LAND USE ...... 52 Soils ...... 53 MICRO-CLIMATE...... 55 SOCIO ECONOMY...... 56 CLOSING REMARKS...... 57 6. CONCLUSIONS ...... 58
ACKNOWLEDGEMENTS ...... 59
REFERENCES...... 60
INTERNET REFERENCES...... 61 MAPS AND AERIAL PHOTOGRAPHS...... 61
6 1. Introduction The Republic of Cape Verde consists of 14 islands (9 inhabited) and this archipelago is situated in the North Atlantic Ocean approximately 500 km west of Dakar, Senegal (figure 1). The islands are an extension of the Sahelian arid and semi-arid climatic zone of Africa (de Brum Ferreira, 1996, p. 111). The archipelago is divided into Barlavento or the windward islands and Sotavento or the leeward islands, depending on whether the islands are more or less affected by the humid winds from northeast. The windward islands are Santo Antão (754 km2), São Vicente (228 km2), São Nicolau (342 km2), Sal (215 km2) and Boa Vista (622 km2) to the north, the leeward islands are Santiago (991 km2), Fogo (477 km2), Brava (65 km2) and Maio (267 km2) to the south.
Figure 1. Map showing the African continent and Cape Verde’s location
In the fifteenth century, when the Portuguese colonized the islands (leeward as early as 1462), bushes and trees covered Cape Verde (Carreira, 1982, pp 7-12, Lindskog & Delaite, 1996, pp 271-290). When the Portuguese colonised the islands, the fragile ecosystem was disrupted (Lindskog & Delaite, 1996). Historical records of droughts date back to 1719.
Cape Verde, with its strategic location, was used as an interjacent place for the growing slave- trade from West Africa to America. As long as the slave trade flourished, the country was rich and food was available. After the Restoration of the Portuguese monarchy in 1654 it became obvious that the Crown was not interested in investment for development resulting in an economic crisis (Carreira, 1982, pp 7-12). The trade with West Africa was taken over by other countries and Cape Verde lost large revenues. Independence from Portugal was attained on the 5th of July in 1975 after a prolonged period of struggle.
The population is approximately 408,999 people (UNICEF, 1999) and agriculture occupies 53% of the inhabitants.
7 The mountainous islands have steep slopes creating a strong orographic effect with few, but intense, precipitation events (Mannaerts, 2000). The disruption of the ecosystem in combination with the intense rain led to increasing land degradation (see definition below). The volcanic soils of Cape Verde need to be covered to prevent erosion, and afforestation programmes have improved the situation over a period of only 15 years (deBrum Ferreira, 1996).
Purpose The purpose of this study is to investigate the effects of the afforestation programme through climatic studies (statistics and field measurements), soil and land use studies (field studies and mapping) and interviews with people in two small areas on Santiago Island, Cape Verde. One important reason for afforestation is the worldwide problem with land degradation (definition below). The disruption of the fragile ecosystem in Cape Verde has lead to many different restorative measures after 1975 to prevent the situation from deteriorating further.
8 Defining land degradation Before defining 'land degradation' certain key issues should be clarified; Is it a physical environmental change or is it a combination where land use system and society is counted in? A land degradation wall (Stocking & Murnaghan 2001, figure 1.1) (figure 2) describes the many components which interlocks with each other. The way in which the problem is defined, and the specification of the components used, will lead to different answers.
Figure 2. Land degradation wall ( Stocking and Murnaghan, 2001)
There is a debate concerning the causes of land degradation and some attempts have been made to sort out the confusing definitions (Agnew & Warren, 1996, pp 309-320). It can be concluded that there is a need for an approach where the interaction of people and their environment is included. The need for a participatory development approach is also emphasised. Land degradation is defined (Lindskog and Tengberg, 1994, pp 365-375) as a reduction of the physical, chemical or biological status of the land, which may restrict its productive capacity. Blaikie and Brookfield (1987, p. 7) regard degradation as "a result of forces, or the product of an equation, in which both human and natural forces find place", defined as:
Net degradation = (natural degrading processes + human interference) - (natural reproduction + restorative management).
Some researchers choose to rule out the consequences of human activities, or the effects of climate, but in that case it is not possible to find the correct explanations behind what causes land degradation. If degradation is seen as a reduction of capability of the soil, the need for known or new skills in land use is clear (Blaikie & Brookfield, 1987, p. 7).
Closely linked to land degradation is desertification. The United Nations Secretariat of the Convention to Combat Desertification (UNCCD) definition is: “land degradation in arid, semi- arid and dry sub-humid areas, resulting from various factors, including climatic variations and human activities” (UNCCD, 1999). There has been an extensive debate concerning the correct definition, and UNEP now defines desertification in socio-economic terms rather than in ecological (Glenn et al., 1998, p. 73). The movement towards interfacing between social sciences and natural sciences is necessary if the problems with land degradation and desertification are to be resolved.
The definitions supplied by Blaikie and Brookfields, in combination with the land degradation wall (Stocking & Murnaghan, 2001), will be used in this paper.
9 Land degradation - climate Climatic conditions are a major factor regulating land degradation, mainly through erosion by water and wind. Investigations of the relationship between soil loss and climate show that erosion reaches a maximum in areas with an effective mean annual precipitation of 300 mm. Effective precipitation is the precipitation required to produce a specific quantity of runoff under specified temperature conditions. When precipitation totals fall below 300 mm, erosion increases as precipitation increases. However, as a consequence of increasing precipitation, the vegetation cover also increases, resulting in better protection of the soil surface. At precipitation totals above 300 mm, the protective effect of vegetation cover counteracts the erosive effect of greater precipitation, so that erosion decreases as precipitation increases (Morgan, 1995, p. 2). The consequences of soil erosion are soil loss, a breakdown of soil structure and a decline in organic matter and nutrients. But erosion also reduces available soil moisture, resulting in more drought- prone conditions (Morgan, 1995, p. 1).
Climatic change will probably cause significant shifts in climate zones and as such will affect the suitability of land for agricultural and other purposes (Glenn, et al., 1998, p. 77). The climatic changes are already present, for example, in Sahel where prolonged droughts have been predominant in the last decades (Hulme, 2001). There are quite a few links between desiccation and ocean-atmosphere interaction and/or regional feedback processes involving land cover characteristics (Hulme, 2001). These two explanations for the Sahelian desiccation are not mutually exclusive, but the discussion as to which force dominates still continues. The dominant Sea Surface Temperature (SST) anomaly configuration associated with the Sahelian desiccation has been the pattern whereby southern oceans are warmer and northern oceans are cooler than average. This pattern has tended to persist during multi-year periods of Sahelian desiccation. This relationship can account for a large part of the longer-term trend in Sahel precipitation without being able to account for any year-to-year variations. The year-to-year variability tends to be more related to SST anomaly patterns in the tropical Atlantic or associated with the El Niño Southern Oscillation (Nicholson & Kim, 1997).
The phenomena of El Niño Southern Oscillation (ENSO) has been shown to be an important factor influencing inter-annual precipitation variability in the low latitudes, but its influence over parts of Africa is still unclear. Several studies have confirmed a relationship between precipitation and ENSO in parts of eastern and southern Africa. In other parts of Africa no clear effects of ENSO on precipitation pattern exist (Nicholson & Kim, 1997). West Africa appears to be less sensitive to ENSO events, compared to other low-latitude regions . However, West Africa may experience ENSO-related climatic impacts in the form of reduced south-west monsoon precipitation amounts during exceptionally strong ENSO events. An example of this is the 1983 ENSO event (McGregor & Nieuwolt, 1998, p. 108).
Micro-climatic conditions are often dependent on the physical setting of the local environment. A vegetated surface will have a micro-climate that is different from that of a non-vegetated surface. A forest has a different micro-climate than an open, non-vegetated surface. In a forest, air motion is weak, it is cooler and more humid (Oke, 1987, p. 153). This is because the trees of a forest produce a sheltering surface and the active surface is situated in the treetops. The daytime air temperature and humidity will have their highest values at the level of maximum leaf area, where radiative absorption and transpiration provide the most heat and water vapour (Oke, 1987, p. 154). Hence the air temperature will be lower and the humidity higher in the forest than in the surrounding open areas. The sheltering surface of the trees also protects the soil surface from the erosive effects of wind and precipitation, resulting in less erosion in wooded areas.
10 Land degradation - soil and land use The concept of "more people, less erosion" was introduced by a group of researchers in Kenya in the 1980s (Tiffen, et al. 1994). The results show that even though the population rose more than five-fold, erosion was sharply reduced in the examined area. The main explanations are the rapidly increasing labour force, that the density of the trees had increased, and that most of the cultivation is performed on terraced land (Chambers, 1997, pp. 25-26). In another area of Kenya it was shown that more people give more erosion (Ovuka, 2000). These two examples show that it is difficult to make general assumptions about the relation between people and erosion.
The soil integrates a variety of important processes involving vegetation growth, the overland flow of water, infiltration, land use and land management. Soil degradation is, in itself, an indicator of land degradation (Stocking & Murnaghan 2001, ch. 2). The effects of soil degradation include, among other factors, soil fertility decline, a lowering of the water table and a loss of vegetation cover.
The main constraints on agriculture in the West African Sahel are poor soils and unfavorable climate (Breman, et al., 2001, p. 67). Worldwide comparable unfavorable soil/climate combinations are rare, and where they do exist, they have to feed only a fraction of the West African population. Few farmers in Sahel can afford to use external input, such as fertilizers, and therefore the need for locally available resources such as organic matter is important.
Improved soil management is crucial for the sustainable intensification of agriculture in the Sahel region (Breman & Kessler, 1997, p. 26). Agroforestry, which is one example of improved soil management, is defined as a land use system in which woody plants are grown in association with agricultural crops, pastures or the keeping of livestock. Production is expected to improve if the trees are capable of deep rooting, nitrogen fixation and soil conservation.
Land degradation – Cape Verde Cape Verde has, with its volcanic soils, very steep slopes and extremely irregular precipitation distribution, a very fragile ecosystem (Lindskog & Delaite, 1996, p. 285) making it sensitive to climatic and ecological changes. The ITCZ (Inter Tropical Convergence Zone) brings rain to Cape Verde on the occations it reaches the islands, but this is becoming more and more rare (Mannaerts & Gabriels, 2000, p. 207). If the rain does arrive, it often takes place as storm events, which means that almost all precipitation falls within 24 h. (Mannaerts & Gabriels, 2000, p. 211). This type of rain causes great damage because it leads to massive erosion, and the arable soil is flushed into the ocean. A tree cover protects soil from wind and water erosion. In fact, historically, there has been an awareness of appropriate response to this problem, but it was not until Cape Verdes’ independence in 1975 that the efforts of afforestation intensified with great financial help from abroad.
The most mountainous islands (Santo Antão, Santiago and Fogo) are characterised by a dramatic landscape with steep, and even practically vertical slopes. The altitude of these islands (the highest point is Mt Fogo 2829 m) gives a strong orographic effect with a wide spatial precipitation variation annually and from year to year. The climate varies from humid to arid on these three islands, and they provide more than 95% of the farmed land of Cape Verde (deBrum Ferreira, 1996, p. 112). The flat and low islands (Sal, Maio and Boa Vista) are very dry and sandy with almost no cultivation. Animal husbandry is the most important occupation for the population on these islands (Meintel, 1984, p. 19).
11 It is shown (deBrum Ferreira 1996, p. 123-124) that a minimal programme of agroecological rehabilitation, on farm level, improved the situation in Cape Verde over a period of 15 years. These projects have been financed from abroad (France, Belgium, FAO, USAID, etc) and the donors are currently giving more aid to other countries, thus facing Cape Verde with a great problem. deBrum Ferreira writes "it would be ironic if it were necessary to reduce the effort, especially when the viability of Cape Verde depends on it" (1996. p. 124). Prevention of land degradation is succeeded through cooperation with the farmers (Chambers, 1997). This strategy has shown great results in afforestation and reforestation projects, which is a viable way to prevent land degradation.
Questions Due to the facts presented in this paper about land degradation, the knowledge about the difficulties in the Cape Verde Islands, the considerable afforestation programmes and the purpose of this paper, the following questions were found to be relevant:
· Is it possible, statistically, to see any climatic changes or trends on Santiago? Can these changes be connected to global, regional, local and/or microclimatic causes?
· What does the distribution of precipitation within the island look like?
· Are there any differences in land use in the chosen investigated areas from 1979 to 2001? More or less trees, more or less agriculture?
· Will the trees in the afforested areas produce enough shadow to cause lower temperature and higher dew point temperature than in the surrounding open areas?
· Are there any differences in the soil (texture, organic matter content, surface roughness, vegetation cover etc) throughout the transect and between the investigated areas?
· How do the farmers percieve the effects of climate, afforestation programme, development (SWC, education, infrastructure and economic development), soil fertility and their future on the islands?
12 2. The Cape Verde islands
Cape Verde is only 4,033 km2 and the total population is approximately 408,000 (UNICEF, 1999) where something like 1/4 of these people live in the capital Praia on Santiago. Approximately 45% of the population is 0-14 years old, 49% is 15-64 years old. In 1999 there were 104,264 women between 15 and 64 years to compare with 92,658 men. This means that many women live alone with their children (3.6 children born/woman) (UNDP, 1999) and they often have to support themselves. During 1975-1997 the trend in population growth rate was 1.7% annually and the predicted rate for 1997-2015 is 2.1% (UNDP, 1999). In 1997 literacy was approximately 71.0% for the total population, even though there are great differences between men (82.1%) and women (62.5%) (UNDP, 1999). The population is mixed: 71% are creole, 28% are black and 1% is European. 25% of the Cape Verdeans are unemployed, and this leads to work emigration. The net migration rate is negative (-12.35/1,000).
In 1997 the Cape Verdean GDP amounted to US$ 0.4 billion. The largest revenue is services which brings in 70% of the GDP and this sector keeps 42% of the population occupied (UNDP, 1999). The industry brings in 21% and 5% works in this sector (including mining). Agriculture brings in about 9% of the GDP and occupies 53% of the population, but the islands cannot grow sufficient amounts of crops and thus need to import large quantities of food, which is expensive. Cape Verde is very dependent on foreign support, the largest part being aid from foreign countries. Cape Verdean emigrants sent home about 1/5 of the GNP 1997 (UNDP, 1999). Cape Verde is encouraging foreign investments and their goal is independence of aid. The government is trying to build a stronger human capital through investments in higher education, and a national library was opened in spring 2000.
Geology and topography The geological formations are of volcanic origin followed by sedimentary formations in the late Tertiary and Quarternary eras (Mannaerts, 1993). The origin of the archipelago could be traced to upper Jurassic- early Cretaceous (Querido 1999, p. 8). In this period the Ocean Island Volcanism started and the eruptions created lava flows and different types of pyroclastic materials with high alkaline contents. The sedimentation of the Cretaceous period was followed by volcanic hot spot activity in the Tertiary period. Extrusion and eruption of igneous rocks were followed in sequence by periods of inactivity in the late Tertiary. The younger islands of Cape Verde (Santiago, São Nicolau, Santo Antão, Fogo and Brava) are likely to have their origin from Eocene and Oligocene and the volcanic activity is still present on Fogo (erupted in 1951 and 1995).
These islands have a sharp topographic relief with high peaks (over 1000 masl). The ephemeral stream flows have created steep hillsides with sometimes nearly vertical walls. This has shaped valleys, known as ribeiras. The valleys are narrow in their upper areas and widen towards the sea. The flat areas between the mountainous parts and the coastline, known as achadas, are characterised by different levels of aridity due to their low altitude. The origin of the soils are volcanic or igneous, and they are coarse textured and shallow (Langworthy & Finan, 1997, p. 44).
13 Climate The Cape Verde archipelago is an oceanic extension of the Sahelian arid and semi-arid zone of Africa. More than 90% of the annual precipitation occurs between July and October and these rains have a high temporal and spatial variability. The annual amount results from a few days or hours of intensive rains. The precipitation is extremely variable from one year to another and it falls in a few days or hours under the influence of local convection cells of disturbances that are associated with the northernmost extension of the ITCZ and of tropical cyclones. The heavy precipitation events (more than 50 mm/ day) usually occur on the most mountainous islands (de Brum Ferreira, 1996, p. 111-112).
The climate of Cape Verde is influenced by the Azores anticyclone, the Inter Tropical Convergence Zone (ITCZ) and the macro-scale mid-Atlantic air mass movements. The seasonal changes of locations of these three factors determine the climatic conditions. The annual cyclical movements of the ITCZ and its migration to the 10-20° northern latitudes during the months of July-October bring a temporary southwest monsoonal climate to Cape Verde during these months (Mannaerts & Gabriels, 2000, p. 207). The migration of the ITCZ to the Cape Verde latitudes (15-17°N) is counteracted by the pressure fluctuations of the Azores anticyclone and other high-altitude air mass fluxes in the northern central Atlantic. This causes the extremely variable precipitation regime in Cape Verde.
The climatological conditions in Cape Verde are also influenced by the trade wind systems; the SE trade wind and the NE trade wind. The "Harmatan" is a part of the latter and it is a dry and hot wind from the African continent which occurs between January and May and carries dust (Querido, 1999, p. 10-11).
Other climatological characteristics show less variation relative to precipitation, for example humidity and insolation are mostly uniform throughout the year (Langworthy & Finan, 1997, p. 38). The average temperature is about 25°C during the year, with an average maximum of about 34°C and an average minimum of approximately 16°C. The temperature is moderated by the sea breeze (Querido, 1999, p. 11).
Annual mean precipitation has been declining since about 1952 (Langworthy & Finan, 1997, p. 37). There are records of 58 droughts (defined as “a relative term denoting a period during which rainfall is either totally absent or substantially lower than usual for the area in question” (Oxford Concise Dictionary of Earth Sciences, 1990)) from 1719 through 1947 (Langworthy & Finan, 1997, p. 37). Both rainfed and irrigated land are exposed to the droughts since aquifers dry out.
Local quantaties of precipitation also depend on the elevation above sea level, where higher elevated areas get more precipitation (figures 3a and 3b.). The prevailing winds in Cape Verde come from the north and northeast. The higher elevations that face the N and NE therefore receive more rain. This orographic effect has the added effect that coastal areas receive small amounts of precipitation and are characterised by greater levels of aridity (Langworthy & Finan, 1997, p. 37-38). The arid coastal zones get about 150 mm annually, and areas above 1,000 masl get about 800 mm.
14 180 30 180 30
160 160 25 25 140 140
120 20 120 20
100 100 15 15 80 80 Temperature (ºC) Temperature (ºC) Precipitation (mm) Precipitation (mm) 60 10 60 10
40 40 5 5 20 20
0 0 0 0 J F M A M J J A S O N D J F M A M J J A S O N D
Figure 3a. Climatic data São Francisco (100 masl), average temperature (1991-2000), precipitation (1961-2001, missing 1974-77), b. São Jorge dos Orgãos (300 masl), average temperature (1991- 2000), precipitation (1961-2001).
Agro-climatological zones on Santiago As a consequence of the orographic effect and annual precipitation, elevation and slope, four agro-climatological zones can be distinguished on Santiago: arid, semi-arid, sub-humid and humid.
The arid zone is marginal land, often highly eroded and has a flat to undulated topography. The precipitation is normally less than 150 mm/year. The arid zone is always associated with the coastal zone and it is usually selected for afforestation. The semi-arid zone is situated inland of the arid zone and has an average annual precipitation of 150-300 mm/year. The semi-arid zone is normally used for rainfed agriculture. The sub-humid zone is associated with the higher altitudes and steep slopes further inland. In the sub-humid zone the average annual precipitation is 300- 600 mm/year (Querido, 1999 p. 13). Farming in the sub-humid zone is mostly rainfed and irrigation is used in some parts of some ribeiras.
The humid zone is very small and restricted to the top areas of the two mountain ranges on Santiago: Pico da Antonia and Serra da Malagueta (Diniz & de Matos, 1986).
Soils and landuse The soils on Santiago are classified according to US soil taxonomy. In the arid zone aridisols, vertisols, entisols and inceptisols are common. The aridisols have very little organic matter in their surface but many may contain calcium carbonate and/or soluble-salt accumulations. The vertisols contain more than 30% clay and are associated with seasonally wet and dry environments. The entisols have no distinct pedogenic horizons. This type of soil is common on recent floodplains and steep eroding slopes. The incepitisols have one or more soil horizons in which mineral materials have been weathered. This soil is in the early stages of forming visible horizons and it is often called brown earth. In the semi-arid and sub-humid zones the most predominant soil types are the same as in the arid zone, but with less aridisols and with the addition of mollisols. The mollisols have a well-decomposed and finely-distributed organic content. The humid zone has incepitisols and entisols and lack aridisols.
15 The mountain complexes are very fragile and need to be protected from erosion. One way to prevent soil erosion is to protect the heights with trees. The government of Cape Verde started a large afforestation programme, with support from USAID, in 1975 and about 60,000 ha had been afforested in 1991. The plantation was performed by work fronts - Frentes da Alta Intensidade de Mão-de-Obra (FAIMO), where the rural population, mostly women, did the work. The annual rate of afforestation (mainly Santiago and Santo Antao) between 1986-1990 was 5,700 ha (Santiago received about 80 % or 4,560 ha). This was a big step towards land restoration. Afforestation still continues, but not to the same extent as previously. Two regions benefit from the afforestation, both the mountainous parts of the islands in the valley heads and the arid and semi-arid zones. The flat islands are generally very dry and not suitable for agriculture.
The early settlers cultivated African grains and root crops to support the subsistence economy. Around the end of the fifteenth century or the beginning of the sixteenth century, maize was introduced from America (Carreira, 1982, pp 6-7). Today maize and beans are the most grown subsistence crops. Agriculture occupies an important position in the Cape Verdean economy even though these crops only cover 20 to 40% of the national consumption (Baptista, 1996, p. 4). The Portuguese land-owning system has lead to a concentrated ownership structure on Santiago and Fogo. This means that a small number of farmers own most of the arable land (Langworthy & Finan, 1997, pp 57-58). About 40,000 ha is cultivated and 5% of this area is irrigated, the rest is nonirrigated or rainfed land. Santiago is the largest producer of food crops.
The agricultural cycle begins in June or July. Since Cape Verde has a constant lack of water it is important for the farmers to use the available moisture as much as possible and therefore they eliminate any vegetation covers during the critical stages. They also use maize and bean straw as fodder, which means that little organic material is mixed into the soil. The combination of the removal of vegetation cover, and the fact that goats graze any shrubs available has largely contributed to soil erosion and degradation (Baptista, 1996, ch. 2, p. 4).
Farmers prepare the soils by removing most vegetation from their fields and some burn it just before the rains come. The seeding practices vary from area to area; in some areas seeding occurs before the initial precipitation and in others seeding is done after the first precipitation. Most of the agriculture is low-input farming of subsistence crops (Baptista, 1996), and even though the harvest continuously fails, farmers intercrop 4 seeds of maize with 2-3 seeds of beans every year on their stony fields (Querido, 1999, p.15)
The largest cause of soil erosion is the high-velocity flooding which moves not only topsoil but also coarser material (even boulders) downstream (Langworthy & Finan, 1997, pp 47). When the sheet wash declines it changes from continuous layer flow into subdivided rill wash (Cook, et al., 1993, pp 198). Along with sheet wash another important factor is wind erosion.
16 Soil and Water Conservation (SWC) structures The upper parts of the slopes, along the ribeiras, are dominated by contour rock walls (arretos) (figures 4 and 5), contour furrows (banquettas) and microcatchmets (caldeiras). These are built up to collect and retain water and sediment and different kinds of drought-tolerant trees (like Acacia spp.) are planted inside them. Checkdams (diques de correcão torrencial) (figure 6) are built in gullies to slow down surface flow and to get new agricultural land when sediments accumulate behind the dams. Even bigger checkdams (catacões) are built crossing the ribeira bottoms to catch the subsurface flows through the alluvium (Langworthy & Finan, 1997, p 48). Aloe spp. (locally known as Babosa) is planted along the contour lines and in rills and gullies. Aloe spp. is resistant to droughts and the plants act like barriers forcing water to infiltrate the soil diminishing runoff and erosion (Querido, 1999, p. 23).
Figure 5. Acacia spp. in an arretos, São Gonçalo.
Figure 4. Arretos in the vicinity of São Gonçalo. Figure 6. Checkdam in Ribeira Seca.
17 3. Methods
Investigated area Santiago (990.9 km2) is the largest island of Cape Verde (figure 1). Two mountain ranges, the complex of Pico da Antonia in the south and Serra da Malagueta complex in the north dominate the central parts of Santiago (figure 7). The highest point is in Pico da Antonia (1,394 masl) and the average altitude is 278.5 masl. There are two types of flat regions on Santiago; in the interiors of both mountain complexes (pillow lavas) and the coastal regions called achadas (Querido 1999 pp 9-10).
Many of the villages on Santiago are situated close to a ribeira. Two of the largest ribeiras, São João (on the west side of the island) and Seca (on the east side of the island) were chosen (figure 4). Two areas were chosen (one in each ribeira) after a recognition tour, with our field supervisor, in combination with the interpretation of topographic maps (nos. 55 and 57, from 1975), an agroecological map (Diniz & de Matos, 1986), a hypsographic map (Marques, 1991) and aerial photographs (taken in 1979). The target areas should also cross a ribeira (valley bottom, with intermittent stream), be afforested, be in the same (or close to the same) agro-climatic zone and reach at least one hillcrest.
The two villages (figure 3) São Gonçalo (west area) and Poilão (east area) were chosen because of their similar size and closeness to the roads. A transect was created in each area by crossing the contours on the topographic map from the top towards the village and down to the valley floor at the bottom of the ribeira (and up on the other side in Poilão).
Tarafal # # Santaigo Chão Bom
#Pedro Badejo
Assomada # # Poilao
Rivers # S. Jorge dos Orgao Cities Pico Leao # # Other villages # Sao Domingos Capital city ÚÊ Sao Fransisco # Roads Sao Goncalo N Big #
Sm all # Santiago Sao Joao Baptista W E # Mountain_area ÚÊ Cidade Velha Praia S
Figure 7. Map of Santiago Island, darker areas show the higher internal areas of the island and the major roads between the villages and cities are marked out.
18 Climate
Statistical analysis The precipitation data for the stations in mainland Sahel, Praia and São Vicente were collected from the Global Historical Climatology Network (GHCN) (www.cdiac.esd.ornl.gov /ghcn /ghcn.html) where the time series stretched as far back as around the 1860s at the most, up to 2000. The data for São Jorge dos Orgãos and São Francisco (1961-2001) and the daily data (1991- 2000) were obtained from Instituto Nacional de Investigacão e Desenvolvimento Agrario (National Research Institute for Agriculture and Rural Development - INIDA) in Cape Verde.
The precipitation data was analysed in Winstat with time series analysis using simple regression. The precipitation data was detrended, and the given residuals were then displayed in a periodogramme. The peaks in the periodogramme were used for calculating the returning periods in precipitation events.
Field observations Two climatic transect walks were made using a Testo 615 measuring instrument giving temperature, relative air humidity and dew point temperature at a height of approximately 1 m. This measuring instrument does not have a logger function. The Testo 615 has a fixed measuring antenna in which the measuring unit is situated. The top of the antenna is not entirely closed, but protects the measuring unit from direct solar radiation and allows the surrounding air to circulate through the top of the antenna.
During the transect walks the values from the Testo 615 were read and noted after standing still for about one minute. The walks took about one to three hours, and were conducted during the middle of the day. Two complete walks were performed, one in the east area, and one in the west area. The walks were made on the 1st and the 5th of June.
Soil and landuse
Interpretation of aerial photographs and maps Aerial photographs (1979, 79-ICV.1/150 Uag 1068 152.16) and topographic maps were analysed and mapped. The aerial photographs were interpreted in stereoscope at INIDA. The photographs (nos. 280 and 281 cover the east area, nos. 36 and 37 the west area) were used as reference material when mapping the areas visually.
Field observations The two areas were covered on foot. Two transect walks were performed from afforested mountain crests to cultivated valley floors. Each plot was chosen to provide a representative view within the transect. Soil samples were collected from each plot, into one joint sample, and the choice of sample sites depended on whether it was possible to dig up soil or not. Investigated factors:
1. Slope angle, with inclinometer (Suunto). 2. Visual observation of what crops the farmers grow on different parts of the slope.
19 3. Visual observations (according to Herweg, 1996) of erosion, rills, gullies (length, width and depth), slope shape (convex, concave, linear, depression or irregular), surface roughness (very, rough, rough, medium, fine, smooth) (figure 8), vegetation cover (in %) (figure 9), depth of topsoil, vegetation types (trees, cultivated or other) and SWC constructions (contour furrows/vegetation, microcatchments, aloe spp., other) were measured and mapped.
Figure 8. Determination of surface roughness in the field (Herweg, 1996)
Surface roughness is, in this text, used to describe the whole surface of the soil, not only the aggregates. This assessment illustrates the harsh environment comprised of bedrock at various weathering stages and containing stones of different sizes. Surface roughness ties in with the infiltration capacity of the soil.
Figure 9. Determination of vegetation cover in the field (Herweg, 1996).
Vegetation cover is an important factor in keeping soil in place, and in reducing the effects of erosion and surface runoff.
Soil samples Soil samples were collected in 10X10 m plots along the transect. Soil texture, P and K content, organic matter content, conductivity and pH from each spot were to be analysed at INIDA and in Sweden. The soil samples were taken (3 samples from each spot, combined integrated to 1 sample) at the surface and at a depth of 10cm.
20 The analyses of soil texture were made through the Pipette method and the particle size grade was classified according to USDA standards (Landon, 1991). The Olsen method was used for determining the P2O5 and K2O content. These results were then converted to P and K content (Landon, 1991, p. 333).
The salinity of the soil electrical conductivity (EC) was done by suspending the soil sample in water (1:2) to get ECW followed by measurements with a conductivimeter. pH was measured using a pH meter in a suspension of soil in water (1:2.5). Organic matter content samples were analysed through the combustion of approximately 20 g. soil at 700º C for 12 hours in Sweden. The weight loss yields the organic matter content.
No soil classification was performed in the field, because no classification schemes were available. Litterature studies form the base of this classification, following US soil taxonomy.
Socio-economy
Interviews The transect walks were combined with a questionnaire (see appendix) which provided the farmers’ views and attitudes on the effects of afforestation, farming, climate and other factors. Since the farmers’ point of view of agriculture and about afforestation programmes are very important, a questionnaire was made but not handed out. The interviews were a combination of closed quantitative, semi-structured interviews, and wealth ranking (Mikkelsen 1995, 75 ff.). The questionnaire was originally written in English, translated to Portuguese and occasionally the interviewer translated the material into Crioulo during the course of the interview.
Almost all households (one or more people living together who may or may not be related) in the two investigated areas were interviewed. The interviews opened with questions regarding background information about the household: size, education, history of the land use and its ownership.
The next group of questions concerned their perception of the climate, the soil, agriculture, the different types of cropping, and the production rates. The effects (positive and negative) of afforestation programs in the farming area were outlined by next group of questions, and the questions were concluded with an overall view of the interviewees’ situation by way of a wealth ranking where 13 different issues were ranked (see appendix).
21 Sources of error
Micro-climate The constantly blowing winds caused by the sea breeze mixed the air effectively, causing temperatures to fluctuate widely. The investigation was made during the driest season and the circumstances were not favourable with respect to noticeable beneficial effects. The trees in the west area were quite leafless and did not provide much shadow. The time needed to finish the transect walks may have been too long. During the course of the walk the temperature had risen in the investigated areas due to the increased insolation.
Soil and land use The P and K values are difficult to obtain and occasional power failures made it even more so. General conclusions drawn from soil analytic results give rise to at least four difficulties (Landon, 1991, p. 106 ff):
1) The soil samples may not be representative, inadequate field-sampling techniques, effects of pre-treatments, cropping history, management practices and the time of year influences the samples. 2) Standard methods are used, but they do not necessarily reflect the availability of a nutrient to the plant. 3) Interpretations of laboratory results are seldom universally applicable. 4) The variability of soil analytic results tends to be high.
The erosion in this type of soil and area is often characterised by sheet wash, small rills and cracks and is therefore visible only during and directly following precipitation.
Socio-economy The interviews were made with an interpreter and the language difficulties have to be taken into account as they may be a possible source of error. Many of the questions were difficult to follow up due to language problems. Since nearly every household was interviewed, the answers should be representative, but this is difficult to assess.
The wealth rankings were intended to give a picture of how the interviewees perceive their situation. As it turned out, they gave a more general view of what the interviewees felt was more or less good/important in their lives, and did not reflect their reality.
22 4. Results
A description of the investigated areas The west area, with the village São Gonçalo, is situated in one of the driest parts of the island (figure 7) and large parts of this region are using afforestation as a form of SWC. One large ribeira, São João, runs from the top of Pico da Antonio down the canyon-shaped valley towards the ocean. The records kept by the climatic station of Pico Leão (500 masl) situated in the upper part of Ribeira Belèm which runs into Ribeira São João are used to get a picture of the produced runoff. There are two roads leading to São Gonçalo, one that follows the ribeira during the dry season and one that runs along the edge of the hillside. The closest towns are São João Baptista (approx. 2 km away) and Cidade Velha (approx. 6 km away). São Gonçalo is situated on a plateau between the upper road and the ribeira. The surface of the reddish soil is medium to rough with a great deal of visible bedrock in different weathering stages. This area is characterised by sparse vegetation, small and thin trees (some more like shrubs than trees) with stems that split close to the ground. The village has a nice big tree that shades the square surrounded by houses. The square has a built-up area with some very small trees. These trees are tendered by the elderly men of the village, who protect the trees from goats and give them all the wastewater they can.
The east area, with the village Poilão, is situated in one of the food-basket areas in Ribeira Seca on Santiago. The station of São Jorge dos Orgãos (350 masl) is situated in the upper part of Ribeira Seca, and the records provide a picture of the runoff reaching Poilão. This area has a lot of SWC but not so much in the form of afforestation. The SWC efforts are concentrated to the farming land in the ribeira and are targeted as restoring it after the rains. Large checkdams (four within the investigated area) cross Ribeira Seca. One quite large road passes Poilão and leads to the coastal town Pedro Badejo (approx. 6 km away), and it is quite easy to travel there by the local cars called "yaz". Poilão is a sprawling type of village with no specific centre. The village is separated both by the ribeira and the small road crossing the ribeira. The vegetation is rich, by Cape Verde standards, even during the driest times of the years. The trees have well-defined stems, and they are about 3-4 m high. There is a great deal of shrubs and grasses, and the surface of the brown to reddish soil is medium to fine. An area with greyish sand in the bottom of the ribeira is used as a small football field.
Climate - Cape Verde and mainland Sahel Since the Cape Verde islands are an oceanic extension of the Sahelian arid and semi-arid zone, the precipitation data for Cape Verde (Mindelo on São Vicente, Praia on Santiago) is compared with data from seven stations in mainland Sahel, to investigate to what degree Cape Verde conforms to the Sahelian precipitation events and characteristics. Of the seven selected Sahelian stations three have been chosen: Dakar in Senegal, Ouagadougou in Burkina Faso and N’djamena in Chad. These stations are situated at approximately 12-15ºN.
The graphs (figures 10-14) show the precipitation data for the five different stations. In all the graphs a linear regression trend has been added to show whether the trend is decreasing, increasing or if no trend is apparent. All five stations show decreasing trends.
Some yearly data is missing in the statistic material, and some years, especially in the 1990s, have been excluded since the lack of monthly data in the wet season is too severe to permit accurate
23 yearly summaries. For Praia the year 1906 has been excluded because of its extremely high and unrealistic value, 1,051.3 mm.
In Mindelo on the island of São Vicente (figures 10a+b) precipitation shows a decreasing trend (years 1884-1975, missing years;1886, 1888, 1896 and 1901) and the mean annual precipitation is 104 mm. The graph shows that precipitation is very variable from year to year.
1200 1100 1000 900 800 700 600 500
Precipitation (mm) 400 300 200 100 0 1884 1890 1894 1899 1904 1908 1912 1916 1920 1924 1928 1932 1936 1940 1944 1948 1952 1956 1960 1964 1968 1972 Years
Figure 10a. Precipitation in Mindelo, São Vicente, Cape Verde (1884-1975).
600
500
400
300
200
100
0
-100
-200
Deviation from mean in mm precipitation -300
-400
-500 1884 1891 1897 1903 1908 1913 1918 1923 1928 1933 1938 1943 1948 1953 1958 1963 1968 1973 Years
Figure 10b. Deviation from mean precipitation in Mindelo, São Vicente, Cape Verde (1884-1975).
24 The station in Praia, Santiago (figures 11a+b) has a mean annual precipitation of 219 mm (years 1865-1973, missing years; 1886-1874, 1882-1884, 1906, 1928, 1931, 1934 and 1936). There is a decreasing trend in precipitation. Just like on São Vicente the precipitation has a high inter-annual variability.
Mindelo on São Vicente is situated in rain-shadow, which explains why the mean annual precipitation is lower than in Praia, Santiago.
1200 1100 1000 900 800 700 600 500
Precipitation (mm) 400 300 200 100 0 1865 1878 1885 1889 1893 1897 1901 1905 1910 1914 1918 1922 1926 1932 1938 1942 1946 1950 1954 1958 1962 1966 1970 Years
Figure 11a. Precipitation in Praia, Santiago, Cape Verde (1865-1973).
600
500
400
300
200
100
0
-100
-200
-300 Deviation from mean in mm precipitation
-400
-500 1865 1879 1887 1892 1897 1902 1908 1913 1918 1923 1929 1937 1942 1947 1952 1957 1962 1967 1972 Years
Figure 11b. Deviation from mean precipitation in Praia, Santiago, Cape Verde (1865-1973).
25 The African mainland station closest to Cape Verde is Dakar, Senegal (figures 12a+b). The mean annual precipitation in Dakar (years 1898-2000, missing years; 1991, 1994 and 1998) is 493 mm. The trend in precipitation in Dakar is also decreasing.
1200 1100 1000 900 800 700 600 500
Precipitation (mm) 400 300 200 100 0 1898 1903 1908 1913 1918 1923 1928 1933 1938 1943 1948 1953 1958 1963 1968 1973 1978 1983 1988 1995 Years
Figure 12a. Precipitation in Dakar, Senegal (1898-2000).
600
500
400
300
200
100
0
-100
-200
-300 Deviation from mean in mm precipitation -400
-500 1898 1903 1908 1913 1918 1923 1928 1933 1938 1943 1948 1953 1958 1963 1968 1973 1978 1983 1988 1995 Years
Figure 12b. Deviation from mean precipitation in Dakar, Senegal (1898-2000).
26 Further inland in the Sahel, in Ouagadougou, Burkina Faso (figures 13a+b) the mean annual precipitation is 797 mm (years 1902-2000, missing years; 1992, 1994 and 1997-1998) and the precipitation shows a slightly decreasing trend.
1200
1100
1000
900
800
700
600
500
Precipitation (mm) 400
300
200
100
0 1902 1906 1910 1914 1918 1922 1926 1930 1934 1938 1942 1946 1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1996 Years
Figure 13a. Precipitation in Ouagadougou, Burkina Faso (1902-2000).
600
500
400
300
200
100
0
-100
-200
Deviation from mean in mm precipitation -300
-400
-500 1902 1907 1912 1917 1922 1927 1932 1937 1942 1947 1952 1957 1962 1967 1972 1977 1982 1987 1993 Years
Figure 13b. Deviation from mean precipitation in Ouagadougou, Burkina Faso (1902-2000).
27 In N´djamena, Chad (figures 14a+b) the mean annual precipitation is 580 mm (years 1905-1999, missing years; 1909, 1914-1931 and 1991-1997) and the trend in precipitation is decreasing.
1200 1100 1000 900 800 700 600 500 400 Precipitation (mm) 300 200 100 0 1905 1910 1932 1936 1940 1944 1948 1952 1956 1960 1964 1968 1972 1976 1980 1984 1988 1999 Years
Figure 14a. Precipitation in N'Djamena, Chad (1905-1999).
600
500
400
300
200
100
0
-100
-200
-300 Deviation from mean in mm precipitation
-400
-500 1905 1911 1934 1939 1944 1949 1954 1959 1964 1969 1974 1979 1984 1989 Years
Figure 14b. Deviation from mean precipitation in N'Djamena, Chad (1905-1999).
28 Regional climate The stations of São Francisco (figures 15a+b) and São Jorge dos Orgãos (figures 16a+b), both on Santiago, clearly show the orographic effect of elevation on precipitation. São Francisco is situated in the low-lying arid coastal zone on the eastern side of Santiago, and has a mean annual precipitation of 196 mm (years 1961-2001, missing years; 1974-1977). São Jorge dos Orgãos is situated in the sub-humid zone in the more highly elevated central parts of the island, and has a mean annual precipitation of 449 mm (years 1961-2001). The precipitation in São Francisco shows a slightly increasing trend while São Jorge dos Orgãos displays a decreasing trend.
1200 1100 1000 900 800 700 600 500
Precipitation (mm) 400 300 200 100 0 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 Years Figure 15a. Precipitation in São Fransisco, Santiago, Cape Verde (1961-2001).
600 500 400 300 200 100 0 -100 -200 -300 Deviation from mean in mm precip. -400 -500 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 Years Figure 15b. Deviation from mean precipitation in São Fransisco, Santiago, Cape Verde (1961-2001). The unfilled bars show ENSO years.
29 1200 1100 1000 900 800 700 600 500
Precipitation (mm) 400 300 200 100 0 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 Years
Figure 16a. Precipitation in São Jorge dos Orgãos, Santiago, Cape Verde (1961-2001).
600 500 400 300 200 100 0 -100 -200 -300
Deviation from mean in mm precipitation -400 -500 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 Years
Figure 16b. Deviation from mean precipitation in São Jorge dos Orgãos, Santiago, Cape Verde (1961-2001). The unfilled bars show ENSO years.
Even though the stations of São Fransisco and São Jorge dos Orgãos are situated only 11 km apart, annual precipitation does not always follow the same pattern. However, most of the years when one of the two stations has precipitation above or below mean, the other station experience the same fluctuation, but this is by no means always the case.
The daily data (1991-2000) for São Francisco, São Jorge dos Orgãos and Chão Bom (figure 7) in precipitation intervals are displayed in tables 1, 2 and 3. The number of days with rain in São Francisco range from 6 to 26, in São Jorge dos Orgãos from 44 to 103 and in Chão Bom from 5 to 16. Most of the events yield only small amounts of rain, 0.1-5 mm. The substantial events are more rare and the most intense rains occur only once or just a few times a year. However, these events contribute significantly to the total precipitation amount.
30 Table 1. Daily precipitation events in São Francisco (1991-2000), Santiago, Cape Verde
Years Total Total No. of No. of No. of No. of No of 3 largest events precipitation no. of events events events events events in % of yearly (mm) events 0.1- 5.0 5.1-15.0 15.1-25.0 25.1-40.0 >40.1- precipitation mm mm mm mm mm 1991 51.8 9 6 2 1 0 0 82.4 1992 239.1 12 7 1 0 2 2 76.1 1993 178.5 12 4 5 1 1 1 66.9 1994 40.5 9 6 3 0 0 0 63.0 1995 373.0 20 6 9 1 1 3 58.4 1996 116.0 6 0 4 0 1 1 80.2 1997 251.0 17 7 3 3 3 1 48.2 1998 90.6 11 3 7 1 0 0 51.9 1999 298.5 26 10 9 4 3 0 32.7 2000 337.0 25 13 7 2 1 2 57.9 Mean 14.7 61.8
Table 2. Daily precipitation events in São Jorge dos Orgãos (1991-2000), Santiago, Cape Verde
Years Total Total No. of No. of No. of No of No. of 3 largest events precipitation no. of events events 5.1- events events 25.1- events in % of yearly (mm) events 0.1- 5.0 15.0 mm 15.1-25.0 40.0 mm >40.1- precipitation. mm mm mm 1991 229.2 42 36 3 1 0 2 70.3 1992 433.5 63 48 7 4 1 3 50.9 1993 386.4 74 57 8 5 2 2 40.2 1994 173.7 43 33 8 0 2 0 47.0 1995 448.4 53 32 13 2 2 4 35.5 1996 282.2 59 48 7 0 2 2 44.9 1997 341.2 44 29 9 1 2 3 44.4 1998 297.5 61 46 8 3 3 1 36.8 1999 663.0 103 75 9 9 9 1 19.4 2000 545.0 90 75 4 2 5 4 38.5 Mean 63.2 42.8
Table 3. Daily precipitation events in Chão Bom (1991-2000), Santiago, Cape Verde
Years Total Total No. of No. of No. of No. of No. of 3 largest events precipitation no. of events events events 15.1- events 25.1- events in % of yearly (mm) events 0.1- 5.0 5.1-15.0 25.0 mm 40.0 mm >40.1- precipitation. mm mm mm 1991 180.7 14 7 4 1 1 1 69.4 1992 204.8 16 8 4 2 1 1 60.5 1993 352.8 12 4 2 1 0 5 62.0 1994 65.6 5 2 2 0 1 0 86.6 1995 74.6 10 6 2 2 0 0 65.1 1996 51,3 5 1 3 1 0 0 81.7 1997 83.9 7 3 1 3 0 0 77.7 1998 69.7 7 2 3 2 0 0 79.8 1999 664.3 15 0 6 1 1 7 52.4 2000 172.1 12 3 4 3 1 1 53.3 Mean 10.3 68.9
31 In São Francisco the three largest yearly precipitation events (1991-2000) produce 32.7-82.4% of the annual rainfall. The mean event gives 61.8% of the annual amount. In São Jorge dos Orgãos the three largest yearly events (1991-2000) give 19.4-70.3% of the annual amounts. The mean event gives 42.8% of the annual amount. In Chão Bom the three largest yearly events (1991- 2000) give 52.4-86.6% of the annual amounts. The mean event gives 68.9% of the annual amount.
In São Francisco and Chão Bom the three largest events every year therefore have a greater impact on the total annual precipitation than in São Jorge dos Orgãos. In São Jorge dos Orgãos the number of events with small amounts of precipitation is greater than in São Francisco and Chão Bom, and therefore also have a greater impact on the total annual amounts.
The precipitation for Chão Bom, Pico Leão, São Francisco and São Jorge dos Orgãos during the period 1991-2000 (for Pico Leão only the years 1997-2000) is displayed below (figure 17). The precipitation in Pico Leão resembles that of São Jorge dos Orgãos.
700
600 Chao Bom Pico Leao Sao Franscisco Sao Jorge dos Orgaos 500
400
300 precipitation (mm)
200
100
0 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 years
Figure 17. Yearly precipitation in Chão Bom, Pico Leão, São Francisco and São Jorge dos Orgãos.
In order to investigate simultaneous precipitation events, daily data from the stations of Belèm (1999-2000), Chão Bom (1991-2000), Pico Leão (1997-2000), São Francisco (1991-2000), São João Baptista (1991-1993, 1997, 1999) and Trindade (1991-2000) was compared with the daily precipitation events in São Jorge dos Orgãos (1991-2000). This shows that São Jorge dos Orgãos over the 10 year period has 632 days with precipitation and the total amount of precipitation days for all the other stations together is 446 days. 51 days of the stations total number (446 days) have precipitation when São Jorge dos Orgãos does not.
32 Connections to ENSO In eight of the eleven (Mindelo, Praia, São Francisco and São Jorge dos Orgãos in Cape Verde, Dakar in Senegal, Kayes and Tombouctou in Mali, Ouagadougou in Burkina Faso, Niamey and Zinder in Niger, N’Djamena in Chad) analysed stations a 4-year cycle is seen (values range from 3.8 to 4.6 years). In five of the eleven stations a 6-year cycle can be seen (values range from 5.8 to 6.5 years). In all eleven stations 2-year cycles are seen (figure 18). These 2-, 4- and 6-year cycles can be related to ENSO since ENSO events occur every two to seven years (Climate System Monitoring, 1985). Since 1970 ENSO events have become more frequent than earlier during the century, with an average time between events of around four years, and a range of two to ten years (McGregor & Nieuwolt, 1998).
In the graphs for São Francisco (figure 15) and São Jorge dos Orgãos (figure 16) ENSO years (www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.html) are marked (bright bars represent ENSO years). The ENSO years are 1963, 1965-1966, 1969, 1972-1973, 1982-1983, 1986-1987, 1991-1995 and 1997-1998. In São Francisco 8 of the 17 El Niño years have above-average precipitation (1965-1966, 1969, 1986, 1987, 1992, 1995 and 1997) and 9 years have below-average precipitation (1963, 1972-1973, 1982-1983, 1991, 1993, 1994 and 1998).
For São Jorge dos Orgãos 5 of the 17 ENSO years have precipitation above average (1963, 1965- 1966 and 1986-1987). Of the remaining twelve years, eleven have precipitation below average (1969, 1972-1973, 1982-1983, 1991-1994 and 1997-1998), and 1 year have approximately average precipitation (1995).
When taking only strong ENSO events into account such as those taking place during 1965, 1972, 1982-1983, 1987, 1992 and 1997, the precipitation in São Francisco is above average 4 of these 7 years (1965, 1987, 1992 and 1997), and below average the remaining 3 years (1972, 1982 and 1983). For São Jorge dos Orgãos the precipitation is above average 2 of the 7 years (1965 and 1987) and below average the remaining 5 years (1972, 1982, 1983, 1992 and 1997).
2000
Power
1000
0 0,0 0,1 0,2 0,3 0,4 0,5 Spectral frequency
Figure 18. A periodogramme, with linear regression of the detrended yearly precipitation in Praia, Santiago, Cape Verde.
33 Land use The farmed land is very hard to detect in the aerial photographs from 1979, since the fields are small and do not have straight lines to define them. The areas without afforestation look the same in 2001 and the farmed land is therefore interpreted as farmed land from the pictures. Four large checkdams have been built in the area close to Poilão and by allowing sediment to accumulate more arable land has been created for the farmers.
Table 4. Land use 1979/2001 in Poilão and in São Gonçalo.
Poilão Poilão São Gonçalo São Gonçalo 1979 2001 1979 2001 Agriculture - 29% - 3% Afforested 0% 12% 0% 54%
Land use differs a great deal between the areas (table 4) and statistics clearly show which areas lie in the food basket and which do not (figure 19). Of the 29% agriculture land in Poilão, 9% is terraced and this feature is not even measurable in the 3% of agriculture land in São Gonçalo. In Poilão most of the efforts are focused on agriculture and in São Gonçalo the goal is afforestation.
Figure 19. Investigated areas a. São Gonçalo, b. Poilão.
34 West area - São Gonçalo The west area is approximately 3.5 km2 (figure 20), and interpretation of aerial photographs shows that 54% has been afforested after 1979 (figures 21a+b). The investigated area inclines to west/southwest. It stretches from a hillcrest, close to the road, down to a valley floor, in Ribeira Belèm, and includes a small village called São Gonçalo. The area consists of 3% farmed land that is terraced to a very limited extent. The people in São Gonçalo are dependent on water from pumphouses (owned by INGRH), to be able to cultivate. Those who own land along the valley floors are able to grow crops (both subsistence and cash crops) both there and on the valley sides. The rest of the population in São Gonçalo could also possibly grow crops on the slopes of the valley, but water is too expensive and the lack of precipitation on this side of Santiago is severe. This means that the risk of loosing their input (having to buy maize and bean seeds) by failing growth is too great. Many people in São Gonçalo lack the opportunity to grow even the slightest bean or maize crops.
São Gon
Transect Old gully Roads Ribeira São Joã São Goncalo Reforested area Farmed land Grassland and n
Figure 20. Field mapping of São Gonçalo area 2001.
Most of the trees (Prosopis juliflora, Acacia spp. and Ziziphus mauritianus) are low (< 2m.) and the main stem of the trees split close to the surface. Prosopis juliflora, locally known as Acacia americana, dominates. Many of these trees look almost dead, but scratch the surface of the tree, and a green layer will come to light, thus proving that the tree is in fact alive. The trees conserve water and only a few have sparse leaves that are protected from grazing by long thorns. The trees closer to the ribeira have more developed main stems and are generally taller (approx. 4 m.). in addition to the trees there is some, but not much, dry grass of different species.
35 Sao Goncalo 1979 Sao Goncalo 2001
3 1 2 0% 5% 1% 1 2 5% 1% 4 3 0% 3%
5 37%
4 54% 5 94%
Poilao 2001 Poilao 1979
1 1 2 2 3 3%1% 3%1% 0%
4 0% 3 29% 1
2 5 3 55%
4
5 4 12%
5 96%
Figure 21. Land use types in São Gonçalo, a: 1979 and b 2001, and in Poilão c. 1979, d. 2001. 1.Valley floor 2.Village area 3.Agriculture land 4.Afforestation 5.Grassland and non-vegetated areas
36 East area - Poilão The east area is approximately 3.2 km2 (figure 22), and 12% of the land has been afforested after 1979 (figures 21c+d). This area in Ribeira Seca stretches from one hillcrest to another and includes a ribeira and a small village called Poilão. The farmed land occupies 29%, and 9% of this is terraced. The people in the east area use a great part of the ribeira to grow crops and the fields are generally larger on this side. Some of the farmed area is reclaimed land, resulting from the accumulation of sediment behind the large checkdams. In Poilão people take water free of charge from wells. The interviewees grow crops both close to their houses on the slopes of the valley and down on the valley floor. Access to water gives all of the interviewees an opportunity to grow crops at least for subsistence. The best land for cash crops is found on the valley floor.
T C R R P R F G
Figure 22. Field mapping of the Poilão area, 2001.
This area has three tree species: Acacia farnesiana, Acacia albida and Ziziphus mauritianus. The trees have a main stem that splits at a height of 1 m, and the crowns are dense. The trees vary in height but most of them are about 3 m high. The trees in this area have enough water to carry many green leaves even during the driest season. There is a lot of undervegetation, mostly different grass species.
37 Soils The investigated areas are dominated by entisols and inseptisols (Diniz, & deMatos, 1986). The area close to the village is dominated by entisols. The entisols are commonly arable when sufficient amounts of plant nutrients and water are added. The incepitisols are usually arable when erosion control and drainage are done appropriately. The mollisols are fertile soils.
The soils are immature and bedrock is visible in many places. The weathering phenomena were not mapped but the processes in these two areas appear similar even though the soil layer is a bit thicker in the east area.
The organic matter content is relatively high (3.0-10.5%) in both areas (figures 23 and 24). There is a greater span in the values of the west area (3.0-10.5%) than in the east area (3.6-6.9%). The median value in the west area is 7.4% , while in the east area it is 5.5%. The three lowest values in the west area are in the plots along the valley floor where soil is coarser in texture and there is almost no vegetation cover. The vegetation cover is denser in the east area with a mean value of 60%, in comparison to the west areas’ mean value of 24%.
350 12
300 10
250 8
200 6
Elevation 150
4 100
2 50
0 0 0 200 400 600 800 1000 1200 Distance (m) Figure 23. São Gonçalo. Broad line shows organic matter content (%), with a trend line. Dotted line shows elevation.
38 350 12
300 10
250 8
200 6
Elevation 150
4 100
2 50
0 0 0 100 200 300 400 500 600 Distance (m) Figure 24. Poilão. Broad line shows organic matter content (%), with two trend lines. Dotted line shows elevation.
West area - São Gonçalo The organic matter content in the west area varies between 3.0 and 10.5%, with a mean value of approximately 6.8 % with two samples below 3.5 % (figure 23). Two samples have values below 3.5%. The trend is decreasing down the transect, but the values are very shifting.
The vegetation cover varies from 0 to 70% with a strong domination below 40%. The organic matter content and vegetation cover is displayed in figure 25 and shows that more vegetation cover gives higher organic matter content.
12
10
8
6 Organic matter (%) 4
2
0 0 10 20 30 40 50 60 70 80 90 100 Vegetation cover (%)
Figure 25. The relation between organic matter content and vegetation cover in São Gonçalo.
39 The soil texture is dominated by silty loam and sandy loam. The conductivity (ECW) varies between 0.16-0.41 mScm-1 with a mean of 0.24 mScm-1. The correlation between soil texture and conductivity shows a slightly increasing trend of salinity with coarser texture (figure 26).
0,45
0,4
0,35
0,3
0,25
0,2 Conductivity mS/cm 0,15
0,1
0,05
0 1 2 3 4 5 Texture Figure 26. São Gonçalo, conductivity and texture. 1. Loam 2. Silty loam 3. Sandy loam 4. Loamy sand 5. Sand
The correlation between conductivity and vegetation cover shows a decreasing trend with increasing vegetation cover (figure 27).
0,45
0,4
0,35
0,3
0,25
0,2 Conductivity mS/cm 0,15
0,1
0,05
0 0 10 20 30 40 50 60 70 80 90 100 Vegetation cover (%) Figure 27. São Gonçalo, the relation between conductivity and vegetation cover.
The pH values range from 6.9 to 8.2 and the pH trend decreases as the vegetation cover increases, and increases with coarser soil texture. The slope angles are less than 20º in all plots, but two that have values of 20º and 22º. This area is characterised by a very thin soil layer (approx. 5-15 cm) on the hillsides and a rough to medium rough surface.
40 East area - Poilão The organic matter content in the east area varies between 3.6 and 6.9% with a mean value of 5.6% (figure 24). The transect was split into two separate parts to be able to apply a linear trend. The trend shows a decreasing organic matter content down both slopes in the transect. The vegetation cover varies between 20 and 90% with a mean at approximately 60%. The relation between organic matter content and vegetation cover is displayed in figure 28 and shows that more vegetation cover gives a higher organic matter content.
12
10
8
6 Organic matter (%) 4
2
0 0 10 20 30 40 50 60 70 80 90 100 Vegetation cover (%) Figure 28. Poilão, the relation between organic matter and vegetation cover.
Sandy loam is most apparent in the soil texture. The conductivity (ECW) varies between 0.19 and 0.39 mScm-1 with a mean value at 0.25 mScm-1. The linear trend shows an increase in salinity in coarser material (figure 29).
0,45
0,4
0,35
0,3
0,25
0,2
Conductivity mS/cm 0,15
0,1
0,05
0 1 2 3 4 5 Texture Figure 29. Poilão, conductivity and texture. 1. Loam 2. Silty loam 3. Sandy loam 4. Loamy sand 5. Sand
The correlation between conductivity and vegetation cover shows a decrease in salinity with increased vegetation cover (figure 30).
41 0,45
0,4
0,35
0,3
0,25
0,2 Conductivity mS/cm 0,15
0,1
0,05
0 0 10 20 30 40 50 60 70 80 90 100 Vegetation cover (%) Figure 30. Poilão, conductivity and vegetation cover.
The pH values vary from 6.9 to 7.8 and show a decreasing trend where vegetation cover increases and an increasing trend with coarser soil texture. The slope angle varies from 0° to 32°, where 11- 30° is the predominant angle. This is an area with a shallow soil layer (approx. 10-25 cm) on the hillsides and the surface is medium rough.
Field observations Since the top soils are mostly quite thin, the formation of larger rills and gullies in the investigated areas is rare. The erosion caused by flowing water is difficult to detect except during and directly after the rains.
Soil and water conservation The afforestation is led by work fronts (FAIMO) consisting of people from rural areas. Each tree in the west area is planted in a halfmoon of stones (arretos) that collects and retains a substantial amount of fine textured soils. The soil retained is a result of both wind and water erosion from higher areas. These micro-catchments also collect water from precipitation, and the tree roots help keep the soil in place. In one cultivated area on a slope in the west area, a farmer had built terraces. This was irrigated land where crops like manioc and sweet potatoes were grown in intercropping. In the west area, one old large gully exists in the higher situated part of the area. The continued incision in the gully has been almost eliminated through the construction of several small checkdams, stone lines and tree plantations at the bottom of the gully. In one plot, along the transect in the east area, an Aloe barbadensis was planted in a rill (>10m length, 1.5m width and 0.5m depth) to prevent further erosion. Much sediment had accumulated behind the aloe and the rill was starting to "heal". In 1979 two large checkdams were built in the east area and by 2001 there were four.
São Gonçalo: Seven of the households use SWC, four of them have contour walls, two have stone lines and one has terraced the farming land.
Poilão: Eleven of the households use SWC, all contour walls. The large checkdams (four) traversing the valley floor are not included.
42 Micro-climate
West area - São Gonçalo In the west area the highest temperatures (figure 31a), 29.7ºC and 29.6ºC, were recorded along the steep slope of the afforested area and in the farmed area below the afforested area. The lowest temperatures were recorded in the afforested area situated on the top of the hill. However, this is where the measurement started at 10.25 a.m. and the temperature rose steadily during this time of the day. At the end of the measurement the recorded temperatures were generally higher which probably is the effect of the increased insolation.
Distance (m) 0 72,7 127 181 265 356 615 715 808 910 941 1000 1075 1175 31 350
30 300
29 250
28 200
27 150 Elevation (masl) Temperature ( ºC)
26 100
25 50
24 0
aff slope aff slope aff slope afforested afforested afforested afforested afforested afforested valley floor valley floor valley floor farmed area farmed area Terrain Figure 31a. Temperature in transect at São Gonçalo, June 1st 2001, 10.25 a.m.- 13.00 p.m..
Distance (m) 0 23,3 81,6 154 207 289 391 448 504 551 31 350
30 300
29 250
28 200
27 150 Elevation (masl) Temperature (º C) 26 100
25 50
24 0
aff slope aff slope aff slope afforested valley floor afforested farmed area
hillcrest, afforested slope, no vegetation hillcrest, no vegetation Terrain Figure 31b. Temperature in transect at Poilão, June 5th 2001, 11.10 a.m.- 12.20 p.m..
43 The dew point temperature values (figure 32a) show an irregular pattern, ranging from 16.5ºC to 18.3ºC. The highest values were found on the afforested slope and along the valley floor. The lowest values were found in the farming area below the slope and in the afforested area at the top of the hill. The dew point temperature is higher for moist air than dry air.
Distance (m) 0 72,7 127 181 265 356 615 715 808 910 941 1000 1075 1175 20 350
19,5 300
19 250
18,5 200 18 150
17,5 Elevation (masl) Dew point temp. (º C) 100 17
16,5 50
16 0
aff slope aff slope aff slope afforested afforested afforested afforested afforested afforested valley floor valley floor valley floor farmed area farmed area Terrain Figure 32a. Dew point temperature in transect at São Gonçalo, Santiago, Cape Verde
Distance (m) 0 23,3 81,6 154 207 289 391 448 504 551 20 350
19,5 300 19 250 18,5 200 18 150 17,5
100 Elevation (masl)
Dew point temp (º C) 17 16,5 50 16 0
aff slope aff slope aff slope afforested valley floor afforested farmed area
slope, no vegetationhillcrest, afforested hillcrest, no vegetation Terrain
Figure 32b. Dew point temperature in transect at Poilão, Santiago, Cape Verde.
East area - Poilão In the east area the highest temperatures (figure 31b), 30.6ºC and 29.9ºC, were recorded in the afforested slopes and on the non-vegetated slope on the other side of the valley floor. The lowest temperatures were found on the afforested slope and at the afforested hillcrest. The dew point temperature (figure 32b) ranges from 17.4ºC to 19.4ºC, the highest values were found in the non- vegetated farming area on the other side of the valley floor and on the non-vegetated slope.
44 Farmers perception All but one of the farmers interviewed in Poilão believe that precipitation has increased (table 7). In São Gonçalo the figures are different. Three of the interviewed women do not see any change in precipitation and three of them see a decrease. The change in precipitation lacks a follow-up question about the time perspective and it is therefore possible that the answers refer to different time spans since the interviewees vary in age.
Table 7. Change in precipitation according to informants in Poilão and São Gonçalo.
Poilão São Gonçalo Total All interviewed Noticeable Female Male Female São Gonçalo Female Male n=30 change n=9 n=6 n=9 male n=6 n=18 n=12 Increased 8 6 5 4 13 10 23 Decreased 1 1 2 2 2 4 No change 3 3 3
The question about soil depth (table 8) shows that ten individuals in Poilão think that there has been a change. Two do not see any change, three did not answer. In São Gonçalo six of the interviewees see a change and one does not. Eight of the interviewees in São Gonçalo did not answer this question. The question about soil depth should have been followed up better as it is possible that the different answers show a pattern. The soil depth can differ (be deeper) along the valley floor and not on the slopes. This could show that the transportation of sediment by water and wind comes from an up-stream area, and that the slopes close by are not effected by the erosive factors. It could also show that the soil depth on the slopes has decreased and that the transportation carries the sediment downstream.
Table 8. Change in soil depth according to informants in Poilão and São Gonçalo.
Poilão São Gonçalo Total All interviewed Noticeable Female Male Female Male Female Male n=30 change n=9 n=6 n=9 n=6 n=18 n=12 Yes 6 4 1 5 7 9 16 No 2 0 1 0 3 0 3 No answer 1 2 7 1 8 3 11
An attempt to make a wealth ranking was performed after each interview. This was to get a better view of how the farmers perceived the situation in the household, and to see what they value the most. The farmers ranked 13 different issues from 1 to 5, where 1 is very bad/not important at all, 2 is bad/not important, 3 is acceptable, 4 is good/important and 5 is very good/very important.
It was clear that some issues have more importance, in both areas, than other. The type of house, access to transport, closeness to a market place, number of animals, field size, field access, crop yield and income from other sectors were by most people ranked as good/important.
The access to water was ranked as good/important and very good/very important in both areas.
45 The type of house and its location in the village were ranked as acceptable and good/important.
People in São Gonçalo rate the importance of having relatives abroad as falling between good/important to very good/very important. While most of the inhabitants of Poilão feel it is good/important.
Socio-economy Fifteen people were interviewed in each area, nine women and six men. The group did not answer all the questions. One category of questions that none of the interviewees answered pertained to crop yield and if they sell crops. Concerning the questions about crops and irrigation and the questions about animals, the focus will be on the answers given by the heads of the households. This is to get a fair picture of the economic situation in these two types of households. The answers of the wives are interpreted, in certain cases, as representing the head of the household, because of the individual’s position in the household. The sons (one in each area) and daughters (two in Poilão) are difficult to interpret and are therefore ruled out in these two groups of questions. Few of the interviewees have attended school (primary), but one boy (in São Gonçalo ) is attending the Liceu (gymnasium). Many of the children help out a lot at home, they fetch water, they take care of their younger siblings and they tend the animals.
Background questions Nine females and six males were interviewed in each area. There are four female and nine male household heads in the group of São Gonçalo. The group in Poilão consists of three female and nine male household heads. The household size varies from 3 to 15 persons in São Gonçalo (a total of 93 persons) and in Poilão the households consist of between 3 to 11 persons (a total of 96 persons). The household income varies a great deal and different incomes can occur in one household (table 9).
Table 9. Income to the households in Poilão and São Gonçalo.
Income-bringing Poilão São sector n=15 Gonçalo n=15 Agriculture 15 9 FAIMO 7 4 Relatives abroad 7 6 Other 5 9
Crops and irrigation Maize and beans are generally grown on rainfed slopes. Manioc, sweet potatoes, sugarcane, bananas and vegetables are generally grown on terraces or on valley floors, and these crops need irrigation. Some people grow vegetables and sweet potatoes for subsistence close to their houses and irrigate with wastewater.
Those who grow crops on the valley floor use irrigation for their crops in both areas (table 10). Many of the farmers complain about a decreasing yield partly because of the lack of soil nutritients and because of the growing problems with insects ruining the crops. One of the male heads in São Gonçalo uses fertilizer (manure) and pesticides (biological). Six of the male heads in
46 Poilão use fertilizers (both chemical and manure) and five uses pesticides (biological). One female head in Poilão uses fertilizer (manure).
Table 10. Factors concerning crops in São Gonçalo and Poilão.
São Gonçalo Poilão Female Male Female Male n=4 n=9 n=3 n=9 Crops in valley 1 4 1 5 Crops on slopes 1 3 3 8 Irrigation 1 4 1 5 Use of fertilizer 0 1 1 6 Use of pesticides 0 1 0 5
São Gonçalo: Four of the male heads and one female head grow crops in the valley. Three of the male heads and one female grow crops on the slopes. Poilão: Five of the male heads and one female head grow crops in the valley. Eight of the male heads and three of the female heads grow crops on the slopes.
West area - São Gonçalo In São Gonçalo many of the individuals depend on food aid. Six of the nine interviewed women do not grow any crops, and two of them do not have any animals. All of the interviewed men grow crops like maize, beans, manioc and sweet potato. Sugarcane is also grown in this area. They grow their maize and beans on slopes and the rest of the crops are grown along the valley floor.
All households buy water from INGRH. The interviewees all believe that the biggest constraint to farming in the area is the lack of rain.
East area - Poilão A majority of the interviewees grow maize and beans, and many grow sweet potatoes, manioc and Bongalon (a type of bean). They grow their maize and beans on slopes and the rest of the crops are grown along the valley floors in the ribeira. Two of the households grow a portion of their crops close to their houses. The six interviewed men believe that the water shortage is the biggest constraint to farming in the area.
Animals The animals can be divided into small (goats, pigs and chicken) and large (cattle and donkeys).
São Gonçalo: The households with a female head have few and small animals. Most of the households with a male head have more animals, both small and large ones. One female and one male head do not have any animals.
Poilão: All households have animals. Two of the three female heads have either cattle or donkeys and both have goats, pigs and chicken. The third female head has pigs only. Eight of the male heads have large animals and all have goats, pigs and chicken.
47 Afforestation and SWC All of the informants (n=30) see the effect of afforestation as positive and all of them use the woods (table 11) either for collecting firewood or as fodder for their animals. They are allowed to collect branches from the ground and just before the rains they can apply for permission to cut down branches from some trees. None of the informants have chosen this kind of afforestation. Four households in São Gonçalo have members who work for FAIMO with different kinds of SWC and in the afforestation programmes. Seven households in Poilão are involved in work with FAIMOs programmes, mostly concerning the farming land. Discontent is widespread among the interviewed concerning the payment from FAIMO.
Table 11. The usage of afforestation in São Gonçalo and Poilão according to the informants.
São Gonçalo n=15 Poilão n=15
Usage of forest Female n=9 Male n=6 Female n=9 Male n=6 Firewood 9 6 9 6 Fodder 4 5 7 6
48 Chapter summary
Climate · The two Cape Verdean and three Sahelian stations all show decreasing precipitation trends. · The regional variation in mean precipitation is great on Santiago, where São Francisco (approx. 100 masl) has 196 mm, and São Jorge dos Orgãos (approx. 350 masl) has 449 mm. The regional variation is even more apparent with regard to the daily data, where São Francisco has 16-26 days with precipitation, São Jorge dos Orgãos 44-103, and Chão Bom 5- 16 days (1991-2000). · The three largest precipitation events represent as much as 87% of the total yearly precipitation, but also as little as 19%. · The connection to ENSO events is weak, with El Niño events occurring both in years with precipitation above average and in years with precipitation below average. · It is difficult to see effects of the afforested areas on temperature and dew point temperature. Most probably due to increased insolation, small trees and turbulence caused by the sea breeze. · 9 households in São Gonçalo and 14 in Poilão see an increase in precipitation. 3 in São Gonçalo and 1 in Poilão see a decrease in precipitation. 3 in São Gonçalo do not see any change.
Soil and land use · 54% of the land in the São Gonçalo area is afforested, compared to 12% in the Poilão area, in 2001. Many trees in São Gonçalo are low (<2m) and the stems split close to the surface. In Poilão the trees are approximately 3m with well-developed stems that split at 1m and that have dense crowns. · All individuals interviewed (n=30) believe that afforestation is positive, and they all use the forest as firewood and some use it for animal fodder. · Both areas are dominated by entisols and inceptisols, both are arable when enough water, nutrients and erosion control are available. · 3% is agricultural land in São Gonçalo, compared to 29% in Poilão (9% is terraced), in 2001. · The organic matter content is relatively high in both areas (>3%). The organic matter content increases with increasing vegetation cover in both areas. 7 people in Poilão use fertilizers and only 1 in São Gonçalo. · In both areas the conductivity (mScm-1) shows an increasing trend as soil texture gets coarser. An increasing pH trend is also apparent in both areas. The conductivity shows a decreasing trend with increasing vegetation cover in both areas. The pH trend is also decreasing with increasing vegetation cover in both areas. · 6 households in São Gonçalo, and 10 in Poilão, see a change in soil depth. 1 household in São Gonçalo and 2 in Poilão do not see any change. 8 households in São Gonçalo and 3 in Poilão did not answer this question.
Socio-economy · Many of the households keep goats. All households in Poilão have animals, and many have large animals like donkeys and cattle. · Many people have income from more than one sector. · 9 interviewees in São Gonçalo, and 15 in Poilão, have agriculture as a household income. · In São Gonçalo people buy water, in Poilão they take it from wells where it is free of charge.
49 5. Discussion
Climate In stations where data reaches the 1990s, a clear reduction in precipitation can be seen from the 1970s. This desiccation has been examined in several studies, and recent research attributes it to natural causes (that is, not suggesting it is caused by the degradation of regional land cover caused by land use changes, or the general warming of the planet). The most probable cause of the these drier circumstances is the coupled ocean-atmosphere system, and the dominant Sea Surface Temperature (SST) anomaly configuration associated with the Sahelian desiccation has been the pattern where southern oceans are warmer and northern oceans are cooler than average. This pattern has tended to persist during the multi-year dry periods in Sahel (Hulme, 2001). This relationship can account for a large part of the longer-term trend in Sahel precipitation without being able to account for the year-to-year variations around this trend. The year-to-year variability tends to be more related to SST anomaly patterns in the tropical Atlantic or associated with the El Niño Southern Oscillation (Nicholson & Kim, 1997).
The long-term precipitation records for the stations of Praia and Mindelo in Cape Verde do not reach past 1975 and nothing can therefore be said about their current situation. The data for São Jorge dos Orgãos and São Francisco does however show that dry years keep returning even though the last three years have given substantial precipitation amounts.
The precipitation is caused by local convection cells associated with the northernmost extension of the ITCZ and the tropical cyclones (de Brum Ferreira, 1996, p 112). But orographic lifting gives the mountainous areas more precipitation than the flat, lower situated areas. Since most precipitation falls in the mountains, the south-western part of the island of Santiago tends to get only small amounts of precipitation. The precipitation data for the west side of Santiago is however insufficient, and for the 1990s two years have enough data to allow accurate annual summaries. However the differences in precipitation amounts between the areas around Poilão and São Gonçalo are clearly apparent when looking at the vegetation. On the west side, where São Gonçalo is situated, the trees are generally in less good shape than those in Poilão, and some trees, particularly in the higher-elevated areas, are more like shrubs than trees. The differences in undergrowth are even more obvious. In São Gonçalo (west area) the undergrowth is very sparse and in higher elevated ground, almost non-existent. In Poilão, on the contrary, the undergrowth (mainly grass) is abundant and more dense than in São Gonçalo .
The precipitation falling in the mountains reaches the lower sites as runoff in the ribeiras. Since the mountains in the eastern parts of Santiago receives most precipitation, the lower-situated parts of eastern Santiago benefit more from the runoff than the western parts of Santiago. Rain shadow makes the western parts of Santiago less suitable for farming, and rainfed farming is almost impossible.
The number of days with precipitation for the stations of São Francisco, São Jorge dos Orgãos and Chão Bom reveal the impact of the large precipitation events on the yearly totals. In the tables (3, 4, 5) for the daily events, the three largest precipitation events every year (1991-2000) are shown as percentage of the yearly precipitation. The values range from as low as 19.4% (São Jorge dos Orgãos, 1994) to as high as 86.6% (Chão Bom, 1994). On the average, the three largest events give 61.8% of the total precipitation in São Francisco, 42.8% in São Jorge dos Orgãos and 68.9% in Chão Bom (years 1991-2000, all three stations). The marked difference between São
50 Jorge dos Orgãos and the stations of São Francisco and Chão Bom can be explained by the locations of the stations. While São Jorge dos Orgãos is situated in the mountains in the central parts of the islands, the stations of Chão Bom and São Francisco are situated in the low-lying arid/semi-arid parts of the island, in the north-west and in the south-east respectively. São Jorge dos Orgãos therefore benefits from the orographic effects on precipitation, receiving a higher total precipitation and having more days with precipitation. The higher number of days with precipitation in São Jorge dos Orgãos is an effect of orographic lifting, which results in more days with low amounts of precipitation than what occurs in the low-lying parts of the island. The higher number of days with low precipitation amounts is, to a large extent, responsible for the higher yearly totals in São Jorge dos Orgãos, and the three largest events therefore affect the yearly total to a lesser extent at this station than they do in the stations of Chão Bom and São Francisco. From the tables (3, 4, 5) it is also clear that the number of precipitation events varies considerably from year to year. This variability is one of the characteristics of the Sahelian climate (Hulme, 2001, p. 19).
The daily data for the stations of Belèm (1999-2000), Chão Bom (1991-2000), Pico Leão (1997- 2000), São Francisco (1991-2000), São João Baptista (1991-1993, 1997, 1999), São Jorge dos Orgãos (1991-2000) and Trindade (1991-2000) reveals that, when using São Jorge dos Orgãos as a reference, almost all precipitation events coincide. That is, when precipitation occurs at one of the stations mentioned above, São Jorge dos Orgãos most certainly also experiences precipitation. However, precipitation may occur at one station and not in São Jorge dos Orgãos, but normally this happens only a few times a year, and some years not at all. Precipitation may however occur at one station and not at any of the other stations, disregarding São Jorge dos Orgãos. The distribution of precipitation could therefore be considered to vary widely spatially.
The eastern parts of Santiago clearly benefits from the orographic induced precipitation brought by the NE trade winds. This has made the eastern side of Santiago the food basket of the island, and most areas here are used for agriculture, except for some parts of the heights and the most low-lying parts facing the sea, which are used for afforestation. When comparing the land use in Poilão and São Gonçalo, the differences in afforestation and agriculture are striking. In Poilão, situated on the east side of Santiago, 29% of the land is used for agriculture, while in São Gonçalo only 3% of the land is used for agriculture. When comparing the figures for afforestation, Poilão 12%, and São Gonçalo 54%, it is quite clear that the two areas have vastly different conditions regarding land use. Since the area of Poilão benefits from its eastward facing position, getting more precipitation and water runoff, it is much more suitable for farming than the westward area of São Gonçalo, which is situated in rain shadow. The area of São Gonçalo is practically impossible to farm without irrigation and is instead mostly used for afforestation.
The aquifers in the valley floors are annually recharged through precipitation. Even though precipitation falls in Pico Leão, the amounts are less and the events are fewer than in São Jorge dos Orgãos, and the produced runoff reaching São Gonçalo is less than in Poilão.
Both investigated areas are situated in approximately the same climatic zone, the semi-arid, but the area of Poilão benefits greatly from its eastward facing position getting more runoff from the higher areas, and therefore having water more readily available than the area of São Gonçalo .
The orographic effects of elevation on precipitation are clearly shown by the differences between São Francisco and São Jorge dos Orgãos. The regional climate in São Francisco is much drier than in São Jorge dos Orgãos as a result of the differences in altitude.
51 It is surprising that São Francisco shows a slightly increasing precipitation trend while São Jorge dos Orgãos and the other stations all show decreasing trends. The slightly increasing trend might be caused by the fact that the years 1974-1977 are lacking certain data in São Francisco, but not in São Jorge dos Orgãos. The year of 1977 was the driest year recorded in São Jorge dos Orgãos 1961-2001.
During the last three years (1999-2001), the precipitation has been good on Santiago, and that is the most probable explanation to why some of the interviewed farmers believe that precipitation has increased.
Connections to ENSO The influence of ENSO on the precipitation in Cape Verde is displayed in the graphs of São Francisco and São Jorge dos Orgãos (figures 15b and 16b). Although the time series analysis indicates that there may be connections to ENSO, with cycles of 2, 4 and 6 years, the graphs with ENSO years marked show that ENSO can not entirely be linked to years which are drier than normal. ENSO events occur both during years with more precipitation than normal and years with less precipitation than normal. This indicates that the Cape Verde islands are not as sensitive to ENSO events as other parts of Africa. This supports the theory that West Africa appears to be less sensitive to ENSO events compared to other low-latitude regions (McGregor & Nieuwolt, 1998).
Nicholson & Kim (1997) found that no clear ENSO effect of rainfall is evident in the Sahel, although some anomalies could be attributed to ENSO. The strongest effects of ENSO found were the reduction of rainfall in eastern equatorial and south-eastern Africa during the second half of the ENSO-cycle.
Land use The farming of Cape Verde does not meet the needs of its population. The lack of water, no or little access to fertilizers, and the poor soil are major constraints (Breman, et al, 2001, p 68) that probably makes it difficult for Cape Verde to ever be completely self-supporting in food crops. There are large differences in land use from 1979 to 2001.
Different restorative management plans, financed by FAIMO, have helped “build up” both areas since 1979. Since work fronts traditionally offer jobs to the rural population during times of crops failure or droughts, they have provided a possible source of income. This extra income has made it possible for many of the interviewees to stay in their villages thus eliminated the need to seek work elsewhere. In São Gonçalo many trees have been planted and many arretos have been built. More than 50% of the region was afforested during that period in the drier west area. This area is not suited for cash crops, and barely for subsistence crops like maize and beans either. Efforts have been concentrated on afforestation rather than on farming. Trees take care of themselves and can be used as firewood and animal fodder during the driest periods of the year. Those who grow cash crops in São Gonçalo have access to the flat areas, on the valley floor, and water. Only 3% of São Gonçalo is farmed. This area is isolated and the frequency of transportation opportunities is low.
In Poilão a lot of the farmed land has been terraced, two large checkdams have been built and plantation of trees on the steep slopes and on the heights have been made since 1979. In the east area, a part of the island where a lot of cash crops are grown, only 12% is afforested. Since the
52 hillcrests and the steepest slopes are the only places where farming is more difficult this is where trees are planted. 29% of the land is used for agriculture. In Poilão the efforts are focused on restorative work around and in the farming land. They build large checkdams and try to heal the wounds caused by erosion by planting aloe babosa in rills. The east area is situated in the “food basket region” close to Pedro Badejo and close to a road that gives farmers good opportunities for transport to and from market places.
Prosopis juliflora and Acacia spp are trees that are well suited to Cape Verde's type of harsh environment. They are quite easy to establish and they are very drought resistant. Contour walls function as a micro-catchment, trapping soil and moisture. The tree-plants have better chances of survival with these types of conservation methods than if they were planted in bare soil. Efforts such as building arretos and planting trees slow down the speed of wind and water erosion. These types of trees have been widely used around the world and since they provide the animals with fodder and the people with firewood they are benificial, but the use of Prosopis juliflora and Acacia spp may also lead to problems when they spread spontaneously along valley floors. These trees have highly effective taproots. The farmers are prohibited to remove these trees, even though they think they disturb the growth of their crops in the valleys. A conflict between the afforestation programmes and the farmers is not desirable. Afforestation is generally believed to protect the heights so it would be fine to cut down the trees in the valleys. Perhaps it would be good to move the already established trees up the hills?
The restorative measures in both areas of farmed land are needed, and they improve the situation (deBrum Ferreira, 1996) otherwise erosion most probably will increase. Efforts are financed by FAIMO, and since there have been problems with the payments, the farmers have lost an important source of income and the signs of erosion are starting to show. This shows that more people may give more erosion (Ovuka, 2000) if the restorative measures do not reach the needed level. This level can only be reached if people get paid for their work and if they are included in the decisions concerning their land (Blaikie &Brookfield, 1987).
The damage caused in arable land is often restored directly after the rains with financial aid from FAIMO. This makes visual observations of erosion difficult.
There are great risks involved in growing crops in the ribeiras. Even though the rains are very infrequent the effects of flooding are devastating when they do occur. Maize is sensitive to drought and the soil is more suited to for sorghum and millet, since they are more drought- tolerant and yield better than maize (Langworthy and Finan, 1997, p. 9).
Soils The entisols and the inceptisols both need the addition of fertilizer, water and erosion control and this is expensive for the farmers. The lack of water and fertilizer in São Gonçalo is therefore a major constraint to farming and this situation will probably not be remedied in the future.
The soils in both areas are alkaline. This is due to the volcanic origin of the mountains, and because of the upward movement of calcium carbonates and other salt accumulations in dry areas (Beaumont, 1989, p 36). The organic matter content is generally high, over 3.5%. This leads the soil to have quite high waterholding capacity thereby preventing some erosion. The high values for organic matter can be derived from the afforestation programmes that started about 20 years ago. It is possible that the use of the land through farming exceeds the rebuilding capacities of organic matter from the tree plantation.
53 Both areas show an increasing trend in organic matter content with increasing vegetation cover. The organic matter content decreases downslopes towards the valley floor and the agriculture land in both areas. It is possible that the organic matter is used by the crops and that the lack of fertilization causes this negative trend on the valley floors. The trees grow slowly and use only a small amount of the organic matter content. When the animals graze from the trees and from the undervegetation their manure remains on the ground.
The reason why conductivity and pH values increase with coarser soil texture is because salts accumulate in the spaces between the particles in the soil. Increasing vegetation cover, on the contrary, gives a decreasing trend both with regard to conductivity and pH values in the soils in the transects in both areas. This can mean that the vegetation collects fine grained soils and the trees use the available soil water.
The soil surface is rough in many of the rainfed fields, a condition regarded by the farmers to be favourable. The stones in the fields retain dew longer in the morning, giving the plants more available water. This is not an issue we tried to verify, but it is a prevalent belief among the farmers.
54 Micro-climate A major problem when performing the microclimatic transects was the constantly changing values given by the measuring instrument (Testo 615). Upon arriving at a measuring plot, the temperature often changed 3-4ºC within one minute, and the given values were only stable for a few seconds. The dew point temperature was also constantly fluctuating, often up to 1ºC. This presented a major problem in assessing the values and reading the values after approximately one minute became a way to deal with it. Whether the constantly changing values were an effect of air pockets in the surrounding environment set in motion by the sea breeze and/or an effect of the measuring instrument being less suited to outdoor use, is hard to say. Because of the difficulties in getting reliable readings, microclimatic transects were only made once in each investigated area.
In São Gonçalo the highest temperatures were found on the afforested steep slope and in the farmed area below the slope. The lowest temperatures were found in the afforested area situated above the slope, the site where the measurement commenced at 10.25 a.m., and the lower temperatures are most certainly an affect of increased insolation. The trees in the afforested area above the slope are in many cases no bigger than shrubs, and do not provide much shade. In São Gonçalo the most moist air (highest dew point values) was found on the afforested slope and along the valley floor. The most dense parts of the afforestation are found on the slope and if the trees had any sheltering effect this could explain the more moist air there. But almost the same dew point temperature is found along the valley floor where no vegetation at all is present, and that is hard to explain other than by the constantly changing values. The relative difference between the highest value (18.3ºC) and the lowest value (16.5ºC) is only 1.8ºC and, taking into account that the values often changed as much as 1ºC, that is not much to use as an indicator.
In Poilão the highest temperatures were found on the afforested slope and on the non-vegetated slope. The lowest temperatures were also found on the afforested slope and on the afforested hillcrest. The temperature was also low on the non-vegetated hillcrest where measurement commenced. The highest dew point temperatures were found in the farmed area, in the afforested area next to the farmed area and on the non-vegetated slope. The lowest values were found on the non-vegetated hillcrest, along the valley floor and on the afforested hillcrest. This does not give a clear picture of what factors control dew point temperature. The relative difference between the highest (19.5ºC) and the lowest (17.4ºC) value is only 2.1ºC.
According to Oke (1987, p. 141), the amplitude of the temperature wave is depressed due to the radiation shading afforded by the forest canopy. In a forest, air motion is weak, it is cooler and more humid (Oke, 1987, p. 153). This may be true in temperate areas, but it is not as marked in the investigated afforested areas, where the tree density is poor, the canopy in most cases is not particulary developed and the trees are more like shrubs, producing a very limited sheltering effect. Neither the lowest temperatures nor the highest dew point temperatures were found in the afforested areas.
The most probable reasons why no sheltering effect of the trees in the afforested areas could be found were 1) the effect of the sea breeze, causing the temperatures and dew point temperatures to fluctuate 2) the poor tree density and size of the trees in the afforested areas.
The effects of the afforested areas may not be enough to effectively lower temperature and increase dew point temperature, at least not during the drier season, but the trees are most certainly important due to their reduction of wind speed and subsequent reduction of wind erosion.
55 Socio economy Population survival strategies are often short-sighted, due to a constant shortage of water, land to farm and money. The inhabitants do their best and spread their risks on many different sectors but the most important sector, despite all the problems entailed, is farming.
The differences in welfare within the investigated villages are large, and much depends on whether the farmers have good land to cultivate or not. The best soils for farming lie within the ribeiras on flat land. These areas are often what is known as reclaimed land, which builds up behind large checkdams in Ribeira Seca on the east side of Santiago. Farmers seldom have the possibility to store food, fodder or to save money, but if they could they would have the opportunity to act more for the future. They do not see the longterm benefits in planting (fruit or other) trees on terraces or in growing more drought-resistant crops, because they generally need to deal with their day-to-day survival.
The farmers in Poilão have more large animals, like cattle and donkeys, than the farmers in São Gonçalo. All animals serve as a money reserve, and large ones are very expensive. These differences in combination with the fact that the people in Poilão get their water from wells free of charge, while those in São Gonçalo have to pay for their water (taken from pumphouses) makes life easier for the villagers of Poilão. The household sizes vary from 3 to 15 persons in São Gonçalo and from 4 to 11 persons in Poilão. The richer families generally consist of more members than those with lesser earnings. Households with relatives abroad generally have a better situation but things may be difficult anyway. If an adult from a household moves abroad, the available work power is reduced and this leads to even harder work for those who stay. They might not even be able to take care of their crops.
In São Gonçalo the dry environment, costly water and shallow soils yield some subsistence crops and only a small amount of cash crops. FAIMO used to be a source of income for many households. In Poilão, people need to repair the damages caused by water erosion after the rains. They generally wait to do this until FAIMO arrives with a project and financial aid. The amount of damage is generally lesser in São Gonçalo, and people do not grow seeds on the slopes as much as in Poilão. Many people in São Gonçalo leave their village and work in cities like Praia or Cidade Velha, and some have their husbands or wives abroad.
There is a long history of work fronts in Cape Verde. The idea is to give the farmers the opportunity to gain an income during droughts. FAIMO is one of these fronts and they used to have people (often women) build different kinds of erosion-prevention measures on the slopes nearby the farming areas. Because of the lack of participatory approach when the afforestation programmes began, the people do not feel responsible for keeping up the restorative management if they are not paid to do so. Work fronts like FAIMO do not have the full support of the population. There are perhaps several reasons for this and one problem is that FAIMO almost never had a plan for the projects, and as a consequence of this, the farmers were unable to participate in the planning of the projects. "They just did some kind of work and got paid without knowing for what and without seeing the benefits of the projects, and recently they have not even received any money" (oral information from anonymous).
56 Closing remarks Natural degrading processes like erosion (originating from wind and water) decrease if a vegetation cover protects the soil. The vegetation cover is more easily established with help from restorative management like afforestation and SWC measures. Human interference (in the form of farming, lowering of the water table and letting animals graze) breaks down the environment if restorative measures are not appropriate and fast. To make the future of the Cape Verde Islands look brighter, it is crucial to keep improving the restorative management and to let natural reproduction (the accumulation of sediment around vegetation to build up better nutritions in the soil) take its time.
If the foreign aid programmes are discontinued, it will be devastating for Cape Verde. The country does not have the money needed to perform large afforestation programmes on its own. Many of the positive effects from the programmes over the years will be lost in a few years and the erosion effects on farming will probably give a decline in the yield of most crops.
57 6. Conclusions
· Precipitation has decreased both in Sahel and in Cape Verde during the 20th century. This trend is connected to world climatic changes. However, during the last three years precipitation has been good on Santiago. · The great variability in precipitation in addition to the recurring droughts should be considered as normal features of Cape Verde’s climate. Extra-dry years do not seem to be connected to ENSO events, since these events occur both during wet and dry years. · The trees in the afforested areas do not seem to provide enough sheltering effect to give lower temperatures and higher dew point temperatures due to their small size and sparse spatial distribution. The sea breeze effectively mixes the lower air layers causing temperatures to fluctuate significantly close to the sea. · The afforestation programmes have established forests that cover a great part of the island. This helps prevent both wind and water erosion in many parts of the island. · The organic matter content has increased in the afforested areas. This gives better crop- growing capabilities. · The farmers believe that the afforestation programmes have positive impact on their lives. They use the woods for firewood in their households and for animal fodder. · The people of Poilão are more fortunate than the people of São Gonçalo. This is a direct effect of the regional climate.
58 Acknowledgements
We are grateful to KTH and Sida for the Minor Field Study grant which financed this study. We are also grateful to PhD student Lisa Åkesson for providing important and valuable information about Cape Verde before our departure, and to University Lecturer Per Lindskog for help with the initial contacts, literature and information.
The authors would like to thank the supervisors at Göteborg University, Department of Earth Sciences, Assoc. Prof. Lars Franzén, Assoc. Prof. Torbjörn Gustavsson, Assoc. Prof. Björn Holmer and University Lecturer Margit Werner for all their help and support. The help, support and good advise from Hans Alter, PhD Mira Ovuka, PhD Madelene Ostwald, PhD student Staffan Rosell, and PhD student Sofia Thorsson was also invaluable and highly appreciated.
Last, but certainly not least, we would like to thank the entire personnel at INIDA, São Jorge dos Orgãos, and especially Dr José Levy who provided us with a contact at INIDA (since he left as president of the institute just before our arrival in Cape Verde); Mrs Zuleika Levy for “mothering” all the students from both near and far; our field supervisor Antonio Querido who helped us tremendously with our field work and with practical issues; our interviewer ”Zelito” for being so patient during the interviews; Isaurinda Baptista for being there all the time and beyond; Manuela Santos for performing the soil analysis; Abel Monteiro, the very friendly and helpful librarian; and all the dedicated and helpful drivers. We would also like to thank the people of São Jorge dos Orgãos, São Gonçalo and Poilão for their friendliness and helpfulness. The opportunity to meet all these wonderful people is one of the greatest things with a Minor Field Study.
And for those not mentioned, you are not forgotten - THANK YOU ALL!
59 References
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60 Mikkelsen, B., (1995): Methods for Development Work and Research - a guide for practitioners, Sage Publications, 296 pp. Morgan, R., P., C., (1995): Soil erosion & Conservation, 198pp. 2nd ed. Longman, 198 pp. Nicholson, S.,E., Kim, J., (1997): The relationship of El Niño-Southern Oscillation to African rainfall, International Journal of Climatology, Vol 17, 117-135. Oke, T., R., (1987): Boundary Layer Climates, 435pp. 2nd ed.Routledge Ovuka, M., (2000): More people, less erosion? - Land use, soil erosion and soil productivity in Murang'a district, Kenya, Land degradation and development, 11:111-124 Oxford Concise dictionary of Earth sciences, Allaby, A., Allaby, M., 1990, Oxford University Press Querido, A., (1999): Watershed system analysis for evaluating the efficiency of soil and water conservation works - a case study in Ribeira Seca, Santiago Island, Cape Verde, ITC, Enschede Stocking,M., A., Murnaghan, N., (2001): Handbook for the field assessment of land degradation, Earthscan 169pp. Tiffen, M., Mortimore, M., Gichuki, F., (1994): More people, less erosion - environmental recovery in Kenya, John Wiley & Sons, 311pp. UNEP, (1997): World Atlas of Desertification 2nd edition UNDP, (1999): Human development report, 262pp. Oxford University Press
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Maps and aerial photographs Diniz, A., C., de Matos, G., C., (1986): Carta de Zongem Agro-Ecológica e da Vegetação de Cabo Verde, I- Ilha de Santiago, Separata de Garcia de Orta, Sér. Bot.,Lisboa, 8 (1-2) 1986 Marques, M., M., (1991): Notíca explicativa da carta hipsométrica Da ilha de Santiago (República da Cabo Verde), Centro de Documentação e Informação do IICT, Lisboa, Portugal
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