Antigua and Barbuda Drought Hazard Assessment and Mapping
Summary Report

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 ijacks@candw.ag.


INTRODUCTION

This document, which summaries the results of a drought hazard assessment and mapping study for Antigua/Barbuda, was commissioned by the Organization of American States (OAS) as part of its Post-Georges Disaster Mitigation Project (PGDM).

One of the major objectives of the PGDM is the "development of national goals, objectives and actions to reduce the vulnerability of Antigua/Barbuda … to the effects of natural hazards."

There were two major component products of the study, namely:

Data for map preparation and for drought assessment were collected from secondary sources, reports, maps, personal communication and limited field observations. Maps were first manually prepared and then digitized, using GIS application, Arc View.

DEFINITION OF DROUGHT

Drought is a recurrent feature of Antigua/Barbuda’s climate. It occurs when there is an extended period of deficiency in precipitation (relative to what is considered normal). Drought has three critical but inter-related components:

Land use practices, such as clearing of vegetation, overgrazing by livestock and farming without trying to conserve soil and moisture make the country more vulnerable to all forms of drought. Vulnerability to drought can be reduced if such practices are changed.

PAST DROUGHTS AND THEIR EFFECTS

Between 1960 and 2000, there were eight years in which rainfall for Antigua fell below 30.74 inches. During the period 1965 to 2000, annual rainfall fell below 27.79 inches in Barbuda on 10 occasions.

The perception of what constitutes a drought year varies between persons and sectors of the economy. What can be considered the most severe drought in recent times occurred in 1983-84. The year 1983 was the worst year, when annual rainfall recorded at the Coolidge Met Office was 22.31 inches.

During the drought, damage to crops and death of livestock resulted in major income losses to farmers. Households were without piped water for months and hotels had to truck water onto properties. The country imported water to help meet local demands.

Antigua was particularly vulnerable because the Potworks Dam, at that time, provided over 50% of water used for domestic, commercial and industrial purposes. Largely as the result of the devastating effects of the 1983-84 drought, government turned to water desalination, which accounts for 62% of the island’s water consumption. In addition, a number of hotels installed reverse osmosis (RO) plants to help meet their own water needs.

Antigua is now less vulnerable to meteorological or hydrological drought because of water desalination. Barbuda remains vulnerable because it remains dependent on ground water as the primary source of water supply.

Two of the factors to be considered with respect to future vulnerability to drought are the management of existing resources and growth in water demand. Present water supply averages 4.5 million cubic meters per year. However, according to the Ministry of Planning 42% of total water supply was unaccounted for, 31% was used by domestic consumers, 17.7% by commercial and hotel users and 4.4% by agricultural users. The unusually high percentage of water not accounted for is said to result from un-metered consumption and leaks but the relative amounts have not been described.

Assumptions made by the Ministry of Planning are that the population will grow to 72,300 by 2000 and 81,000 by 2010, and that per capita domestic water consumption would remain at 0.63 cu meter/day through to 2010. It estimates that total water demand will increase to 5.8 million cu meters/yr by 2010. Before production is increased to meet the growth in anticipated demand, attempts should be made to reduce the amount of water that is lost from the system.

Water projections should however be carefully monitored because there is a degree of uncertainty associated with water demands – one reason being the difficulty in predicting growth in the tourism sector.

Water demand management therefore is major issue for drought mitigation for two reasons:

FUTURE VULNERABILITY

Crops

At the time of the 1983-84 drought, Antigua relied on surface water reservoirs to provide most of its potable water. Water supply was readily affected by meteorological drought and the country was highly vulnerable during periods of low rainfall.

Because of desalination households and hotels have become significantly less vulnerable to deficiencies in rainfall. However, vulnerability remains high for crop farming because many farmers perceive the cost of water as one of the factors working against profitability.

A heavy reliance is still placed on rainfall to provide the moisture needed by crops, even when mains water is available for irrigation.

Variable climate and precipitation remain over-riding critical natural factors contributing to the vulnerability of crop farming to drought. Practices (human factors) contributing to vulnerability include:

Livestock

Overgrazing. Overgrazing is perhaps the primary contributing factor to Antigua and Barbuda’s vulnerability to drought. Reducing vulnerability in this respect requires drastic reduction in the goat populations and rigid control over where livestock are allowed to graze.

To achieve these aims without causing unbearable economic dislocation and hardship to livestock farmers will require strategic planning, broad-based consultations with stakeholder groups and public awareness to build public support for actions to be taken.

Such actions should derive from a national program and campaign to reduce the impacts of goats on the landscape, environment and crops. The program should have two primary components:

Adequate resources would need to be applied for research, institutional building, public awareness and policy formulation in the implementation of the program.

Policy Issues

Reducing vulnerability to drought for both crop and livestock farming will require a number of critical policy initiatives, including:

Tourism

After the 1983-84 drought a number of hotels installed reverse osmosis (RO) plants and have become less vulnerable to droughts as a result. Most hotels, guesthouses, villas and other forms of visitor accommodation properties still depend on APUA for most of their potable water supply.

Although the existence of the desalination plants makes water supply more dependable, properties without the capacity to produce most of their potable water are still affected by rationing.

The extent of their vulnerability could not be determined in this assessment because a detailed survey of on-site water infrastructure, including production plants, roof catchment and storage capacity was not possible.

Based on discussions with a number of hotel managers, water conservation practices by hotels are limited to the use of water saving toilets and showerheads which have become standard for many manufacturers of bathroom fixtures.

A lot of water is believed to be still wasted on properties due to leaks, poor irrigation practices, absence of a reliable level of wastewater treatment to allow reuse for landscaping and failure to meter water for different major property uses so as to detect waste.

An inventory or audit of tourism properties, including marinas and golf courses, should be considered to determine their preparedness to deal with future droughts. The inventory or audit should be done with the involvement of the Antigua Hotels and Tourism Association (AHTA) and should cover among other things:

Settlements

Like hotels, water supply to settlements has improved with the use of desalinated water by APUA. Vulnerability has been reduced with respect to water supply but most settlements are still affected by water rationing during droughts. This is expected to continue in the future unless APUA decides to increase water production from desalination on its own or with the use of private contractors.

The relatively higher cost of producing desalinated water compared to ground and surface water is a major constraint to providing water that would not be affected by variable rainfall. High cost notwithstanding, a commitment to increasing desalinated water production may be required to reduce the vulnerability of settlements as water demands increase in the future.

In Antigua, water loss from evaporation and seepage at surface reservoirs is an issue without a cost-effective solution. In Nevis, where potable water is stored in tanks, such loss from evaporation and seepage does not occur.

Despite the need to ration water in droughts, water is frequently lost due to leaks from supply mains that APUA is often slow to repair. The occurrence of this in the future will increase the country’s vulnerability to drought.

In Barbuda, the major ground water aquifer has been affected by sand mining activity. Land and resource use will need to be managed in the future to ensure that this key water resource is not further compromised.

Finally, although most building supply stores carry water saving toilets, showerheads and faucets, there has been no national water conservation campaign that targets households.

New homes should be provided incentives to install water-saving fixtures and old households provided similar incentives to retrofit fixtures in order to conserve water. This would lessen the impact of drought on households.

DROUGHT RISK CRITERIA

Factors critical to drought were used to develop a set of criteria for ranking areas according to their level risk, namely:

Low drought risk
Moderate drought risk
High drought risk
Very high drought risk

These factors (termed drought risk criteria) fall into three categories as summarized below.

Environmental Meteorological

Hydrological/Infrastructural

Human/Landuse

Once the drought criteria were determined data maps were produced in digital format, using the GIS application Arc View. The data maps for Antigua and Barbuda are as indicated:

DROUGHT RISK RANKING

Digital data were analyzed and manipulated to determine the levels of risk by watersheds. The watershed is considered the appropriate geographic and hydrological unit for managing drought among other things. Antigua was divided into 13 watersheds and Barbuda 10 in accordance with boundaries used by OAS in a natural resources project assessment project for agriculture. In the drought hazard assessment areas were ranked by:

  1. Analyzing the spatial occurrence of vulnerability themes in the various watershed units;
  2. Overlaying (intersecting, as opposed to merging in ArcView GIS terminology) the themes to determine areas of critical risk.

The results for both Antigua and Barbuda are as shown.

Drought Risk Ranking of Antigua Watersheds

Level of Risk

Watersheds

Low

1, 2, 3

Moderate

4-11, 12-20, 21-26,

High

47-53, 54-62, 63-66, 78-84, 85-86

Very High

27-46, 67-77

Drought Risk Ranking of Barbuda Watersheds

Level of Risk

Watersheds

Low

--

Moderate

I, V, VI, VII, VIII, X

High

II, III, IV, IX

Very High

--

AREAS AND ISSUES FOR PRIORITY ATTENTION

Areas

The east, north and southeast of Antigua contain areas of high and very high risk to drought. Environmental and land use factors combine to make that region of the country the most vulnerable to drought. Within this region, the area requiring the most urgent attention falls within watershed 27-46, one of two watersheds ranked as being at very high risk to drought.

The area is at the extreme southeast of the island (between English Harbour and St. James’s Club). Environmental and human (landuse) factors combining to make this area highly vulnerable to drought include:

Denuded slopes and narrow valleys in areas forming part of the Nelson’s Dockyard National Park provide visual images of a severely degraded landscape and imminent desertification.

Similar trends are being experienced in other watersheds but perhaps not with the same degree of devastation. It is suggested that watershed 27-46 be considered for undertaking a pilot project seeking to provide strategies for reducing vulnerability and risk to drought.

The project should include:

Successful results of the pilot project would be replicated in other parts of the country.

In Barbuda, the flat lands around and south of Codrington are considered the areas of greatest risk to drought.

Major issues

While the pilot project for Antigua is being used to test approaches for mitigating the impacts of drought, actions should be considered and implemented to address other issues, including:

MAP USE AND LIMITATIONS

Use and limitations of the data maps and drought risk maps are described in the technical report. Difficulties in gathering data for mapping were key constraints in the assessment. Updating of the data maps should therefore be considered as new information becomes available.

INDICATORS FOR FUTURE IDENTIFICATION OF DROUGHTS

This section summarizes and describes indicators that suggest approaching or actual drought conditions. These indicators are discussed under the following categories:

a) Environmental Indicators

Reduction in biomass production of common grass species. Early warning is wilting, as grass roots become progressively damaged by lack of soil water; Grass cover becomes patchier as fallen leaf debris is blown away by wind in exposed areas. Home owners have no need to use lawn mowers;

Leaf fall and litter in Forests. The Forestry Division uses the increase in leaf fall and litter (detritus) on the forest floor as one indicator of drought. No measurement of volume of weight is done. Since leaf fall varies between species, measurement would need to be correlated with plant associations.

In Cactus Scrub forests, xerophytes (plants growing in dry areas) with small hard leaves can reduce water loss in extended dry periods by various methods including dropping their leaves.

Damage to "indicator" plant species. The Ficus, planted as hedge or trees; normally stays green; its small and shiny leaves limit moisture loss and its wide spreading root system allows it to seek moisture and nutrients beyond its drip line. When the Ficus looses a lot of its leaves it is an indication that the country is in a period of prolonged drought.

Some types of xerophytes, (succulents, such as cacti and agaves) utilize stored water in dry periods without noticeable damage. In fact, such plants can survive for weeks when uprooted, so that signs of damage (dried leaves or broken stems) may be an indication of negative water balance resulted from extended drought.

b) Hydrological

Reduction in Ground Water Levels. The APUA Water Division uses ground water levels at various well fields as an indicator of hydrological drought.

There is a time lapse between meteorological and agricultural drought conditions and hydrological drought as indicated by ground water levels. The latter occurs later but the time lapse cannot be accurately predicted in the absence of rainfall data that could be correlated with rates of pumping and recharge, for the watersheds in which the well fields occur.

Recovery from meteorological and agriculture droughts occurs in advance of the replenishment of ground water to average levels. Again, the data does not exist to accurately predict the gap in time between these events.

Reduction of Water Levels at Municipal Reservoirs. Receding water levels at municipal reservoirs is another drought indicator used by APUA. However, it was not determined if specific indicator levels for the various municipal reservoirs were established. Indicator levels at selected reservoirs could be determined over a period of time by widening the scope of monitoring to consistently measure meteorological and hydrological data, including, rainfall, temperature, wind speed, evaporation and seepage.

Water Rationing. APUA begins to ration water before ground water levels recede to critical points. In fact, the decision to begin rationing water appears to be influenced by perceived meteorological and agricultural drought conditions.

Reduction of Water Levels at Agricultural Reservoirs. This is another indicator observed but not measured by authorities.

Agricultural

Livestock

Goats adapt well to drought by using physiological measures to conserve water. Despite this, they and other livestock will show signs of stress during extended drought, including:

Crops

Indicators may include:

c) Socio-economic

Socio-economic indicators include changes in water use practices by households and businesses:


USAID/OAS Post-Georges Disaster Mitigation: http://www.oas.org/pgdm

Page last updated on 20 Sep 2001