Drought Hazard Assessment and Mapping for Antigua and Barbuda
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Drought Hazard Assessment and Mapping for Antigua and Barbuda Post-Georges Disaster Mitigation Project in Antigua & Barbuda and St. Kitts & Nevis April 2001 This report was prepared under contract with the OAS by Ivor Jackson, Ivor Jackson & Associates, Environmental & Landuse Planning and Landscape Architecture, P.O. Box 1327, St. John’s, Antigua. Tel/fax: 268 460 1469. E-mail [email protected]. CONTENTS 2.3.1.3 Farming Practices 20 2.3.2 Livestock Farming 20 1.0 BACKGROUND 4 2.3.2.1 Livestock Population 20 2.3.2.2 Livestock Distribution 21 1.1 Introduction 5 2.3.2.3 Livestock Management 1.2 Terms of Reference 5 Practices 22 1.3 Methodology 5 2.3.2.4 Market and Prices 22 1.3.1 Data Collection 5 1.3.2 Mapping 5 2.3.3 Settlements and 1.4 Definitions 5 Communities 22 1.4.1 Drought 5 2.3.4 Hotels and Tourist Zones 24 1.4.2 Drought Hazard 7 1.4.3 Drought Vulnerability 7 2.4 Infrastructure 25 1.4.4 Drought Risk 7 1.4.5 Use of the Term Drought 7 2.4.1 Dams and other Storage Reservoirs 25 2.0 ASSESSMENT 8 2.4.2 Wells 26 2.4.3 Desalt and other Water 2.1 Meteorological Conditions 9 Treatment Plants 27 2.4.4 Wastewater Treatment 2.1.1 Precipitation 9 Plants 28 2.1.2 Temperature 10 2.4.5 Irrigation Systems 28 2.1.3 Winds 10 2.4.6 Water Distribution 29 2.1.4 Relative Exposure of Slopes 11 2.4.7 Roof Catchments and Storage 2.1.5 Relative Humidity 12 Cisterns 29 2.1.6 Sunshine and Cloud Cover 12 2.5 Water Supply and Demand 29 2.1.7 Evaporation and Transpiration 12 3.0 IMPACT AND VULNERABILITY 31 2.2 General Environmental Conditions 13 3.1 Historic Drought 32 3.1.1 Description of Drought 2.2.1 Geology 13 Events 32 2.2.2 Slopes 13 3.1.2 Drought Impacts 32 2.2.3 Soils 13 3.1.2.1 Environmental Impacts 32 2.2.4 Vegetation 15 3.1.2.2 Economic Impacts 34 2.2.5 Soil Water Deficiencies 16 2.2.6 Water Resources 17 a) Agriculture 34 2.3 Land Use and Land Management b) Tourism 36 Practices 18 c) Settlements 37 2.3.1 Crop and Vegetable Farming 18 2.3.1.1 Major Farming Areas 18 2.3.1.2 Type of Crops 18 Drought Hazard Assessment & Mapping for Antigua and Barbuda CONTENTS (Continued) 3.2 Future Vulnerability 38 Appendices 59 3.2.1 Agriculture 38 3.2.2 Tourism 39 1 Terms of Reference 60 3.2.3 Settlements 40 2 Average Yearly Rainfall, Recorded at the Meteorological 3.3 Institutional Arrangements 41 Office, V.C. Bird International Airport, 1960 – 2000 62 3.3.1 Key Agencies 41 3 Antigua Annual Rainfall, 1950- 3.3.2 Procedures and Information 41 1984 62 4 1991 Population Density, 4.0 ANALYSIS OF AREAS AT Antigua and Barbuda 63 RISK 42 5 Structure (Content) of Mapped Data Sets, Antigua and 4.1 Understanding and Applying the Barbuda 64 Concept of Risk 43 4.2 Areas at Risk to Drought 43 6(a) Drought Risk Totals by 4.2.1 Drought Risk Criteria for Watersheds, Antigua 65 Mapping 43 6(b) Drought Risk Totals by 4.2.2 Area and Issues for Priority Watersheds, Barbuda 66 Attention 47 7 Map References from Antigua and Barbuda Country environ- 5.0 DROUGHT MAPPING 50 mental Profile, IRF, 1991 67 8 List of Contacts 68 5.1 Data Collection Sources 51 5.2 Structure and Content of Maps 51 5.3 Analysis of Data 51 5.4 Map Use and Limitations 52 6.0 INDICATORS FOR FUTURE IDENTIFICATION OF DROUGHTS 54 References 58 1 Drought Hazard Assessment & Mapping for Antigua and Barbuda List Of Tables Table 1: Categories of Drought as Table 9: Location and Capacity of Defined by % of Average Yearly Agricultural Reservoirs, Antigua 25 Rainfall of 40.98 Inches (Antigua) 6 Table 10: Municipal Reservoirs, Table 2: Rainfall, Windspeed and Antigua 26 Relative Humidity, Driest and Wettest Months of the Year 10 Table 11: Major Well Fields of Antigua 26 Table 3: Water Balance at Potworks Reservoir November Table 12: Water Storage and Well Yield 1995 – May 1996 12 by Watersheds, Antigua 27 Table 4: Slope Classes, Barbuda 13 Table 13: Water Supply, Antigua and Barbuda 30 Table 5: Livestock Population in Antigua/Barbuda, 1984 20 Table 14: Drought Years in Antigua/ Barbuda 1960-2000 32 Table 6: Cattle, Sheep and Goat Populations Antigua, 2001 20 Table 15: Drought Risk Criteria 44 Table 7: Tourism Accommodation, Table 16: Drought Risk Ranking of Antigua and Barbuda, 2001 24 Antigua Watersheds 51 Table 8: Distribution of Hotel Properties Table 17: Drought Risk Ranking of by Watersheds 24 Barbuda Watersheds 52 Table 18: Drought Levels at Well Fields, Antigua 56 2 Drought Hazard Assessment & Mapping for Antigua and Barbuda _________________________________ 1.0 BACKGROUND 3 Drought Hazard Assessment & Mapping for Antigua and Barbuda 1.1 Introduction 1.4 Definitions The Organization of American States For the purposes of the study and in (OAS) as part of its Post-Georges agreement with relevant authorities, a Disaster Mitigation Project (PGDM) definition of drought has been drafted, as commissioned this drought hazard indicated below. Other relevant assessment and mapping study for definitions are also provided to facilitate Antigua/Barbuda. both the drought hazard assessment and mapping work. One of the major objectives of the PGDM is the “development of national 1.4.1 Drought goals, objectives and actions to reduce the vulnerability of Antigua/Barbuda … Drought is a recurrent feature of to the effects of natural hazards.” Antigua/Barbuda’s climate. It occurs when there is an extended period of 1.2 Terms of Reference deficiency in precipitation (relative to what is considered normal), which is The Terms of Reference (TOR) for the then insufficient to meet economic, study is attached as Appendix 1. There social and environmental demands. are two major component products of Given their relatively small size, drought this assignment, (i) a drought hazard effects in Antigua and Barbuda are felt assessment report and (ii) island wide island-wide. GIS data layers depicting drought hazard risk areas and drought hazard maps for For reasons of analysis and in view of Antigua/Barbuda. the need to determine appropriate responses to drought impacts and 1.3 Methodology vulnerability, drought is defined as having three critical but inter-related 1.3.1 Data Collection components (as taken from the US National Drought Mitigation Center’s Data for map preparation and for definition) namely: drought assessment were collected using secondary sources, reports, maps, · Meteorological drought personal communication and limited · Agricultural drought field observations. · Hydrological drought 1.3.2 Mapping a) Meteorological drought Maps were first manually prepared and Meteorological drought is defined then digitized using GIS application, Arc mainly by deficiencies in precipitation. View. Along with deficient rainfall, conditions during drought may be accompanied or aggravated by high temperatures, strong winds, low relative humidity, greater sunshine and less cloud cover. 4 Drought Hazard Assessment & Mapping for Antigua and Barbuda These conditions can be expected to Meteorological drought for bring increased evaporation and Antigua/Barbuda is defined using a transpiration, reduced water infiltration precipitation level of 80% or less of into soils and a reduction in deep yearly average rainfall (or < 30.74 percolation and ground water recharge. inches, Antigua and < 27.79 inches, Barbuda) for a drought year. A The Antigua/Barbuda Meteorological limitation in using this definition is that Office (Met Office) has categorized drought designation is mostly done on drought from slight to extreme, as the basis of a calendar year and usually shown in Table 1. after the event occurs. Table 1 Categories of Drought, as For the purpose of drought Defined by % of Average Yearly preparedness, it is suggested that Rainfall of 40.98 inches (Antigua) precipitation deficiencies over a six (6) month period could be used to predict Category Rainfall % of Ave. an imminent drought. Drought (inches) Annual Rainfall For example, if the average monthly _______________________________ rainfall for the dry period of the year, January to April, (2.06 inches for Slight 38.93 95 Antigua) is experienced over a six (6) Mild 36.88 90 month period, it would in public Moderate 32.78 85 perception signal that a drought was Moderate/ imminent. At the end of a six (6) month Severe 30.74 80 period in which total rainfall is < 12.36 Severe 28.69 75 inches, effects associated with Extreme 24.50 70 meteorological drought would begin to _______________________________ emerge. (Source: Meteorological Office, 2001) b) Agricultural drought Based on annual rainfall assigned to each category by the MET Office, some Agricultural drought occurs when plant form of drought occurred in Antigua in water demands cannot be met due to 20 of the 40 years between 1960 and soil water deficiency resulting from 2000. Rainfall records for the period dryness brought on by meteorological or were collected by the Met Office (see hydrological drought. Appendix 2). In such cases plant water stress may be This does not match public recollection evidenced from reduced biomass and and perception of drought. A more plant yield. One common indicator simplified definition of meteorological species is the “evergreen” ficus, which drought using the Met Office’s responds by first dropping most or all its Moderately Severe category, as the cut- leaves followed by the death of its off point would provide a definition stems.