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].
INTRODUCTION
This document, which summaries the results of a drought hazard assessment and mapping study for Nevis, 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 Nevis … 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 Nevis’ 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 island more vulnerable to all forms of drought. Vulnerability can be reduced by changes to such practices.
PAST DROUGHTS AND THEIR EFFECTS
Historic Drought
Based on rainfall records obtained from the Department of Agriculture, three (3) periods of drought have been identified for the last decade, namely:
1990 – 1991
1993
1997
The year 2000 may also turn out to be one of below average rainfall – the average rainfall from January to November being 32.51 inches.
In 1990, average rainfall was 46.77 inches but 15.11 inches was recorded for the month of October. For the rest of the year rainfall was 31.66 inches and for the months of January to September only 24.37. Even with the 15.11 inches of rain recorded for October 1990, the average rainfall for the two-year period was 37.07.
In 1993, average rainfall was 37.10 inches and in 1997, 34.06 inches.
Actual yearly rainfall figures before 1990 were not obtained but 1974 was said to be perhaps the worst period of drought in recent times (Richard Lupinacci, Hermitage Hotel, pers. comm.) Lupinacci said that the dryness and wilting of vegetation in 1974 was the most severe experienced in recent times even in higher elevations such as Hermitage, where average rainfall is about 55 inches/year.
DROUGHT IMPACTS
Environmental Impacts
a) Vegetation and Landscape
Drought impacts were particularly severe in watersheds where plants with shallow root systems on shallow soils were among the first to be affected by deficiencies in soil water.
No studies were made of soil conditions during the 1990-91 drought. However, it is assumed that moisture deficiencies during this and other droughts gradually lead to the reduction in soil fertility. Plant growth and crop yield is affected as a result.
Leaf and stem loss in herbaceous and woody plants were followed by plant mortality in certain species in the 1974 drought (R. Lupinacci, pers. comm.). As plants wilted and died, canopy cover decreased in wooded areas and the landscape generally became visibly brown, dusty and harsh looking.
Soil exposure due to overgrazing makes more land vulnerable to accelerated erosion with each drought. Soil loss is therefore a major environmental impact from drought particularly on the east, northeast and southeast coastal areas that are very exposed to wind.
b) Habitat
In Nevis, wildlife habitats are sometimes also used for grazing by livestock. Such areas may have a combination of scrub, grass and woody plants with sufficient canopy cover to attract species of birds. Irrespective of plant characteristics, ecosystems require adequate moisture to function reliably as habitats for wildlife. Inadequate moisture during the droughts created conditions that were stressful to bird, reptile (lizards) and amphibian (frogs) species.
Stressful conditions are exacerbated by competition for resources and space from goats and other livestock. Livestock population densities in some areas are in excess of what is considered sustainable for such ecosystems.
One constraint in assessing habitat impacts is the absence of detailed listings of plant species preferred by goats. Unlike cattle and sheep, goats browse (rather than graze) normally on various herbaceous plants and woody shrubs, along with ornamental plants if they get access to household gardens.
Since biomass production of grass used by livestock in Nevis declines faster relative to many species used by goats, grazing livestock are likely to reach the critical threshold of nutritional stress earlier than goats.
Economic Impacts
a) Agriculture
In 1975 31% of the land in Nevis was under agriculture (IRF, Nevis Country Environmental Profile). The preliminary findings of the 2000 agricultural and fisheries census indicates that there were 3,278.5 acres of land in agricultural holdings representing 14% of total land area in Nevis. It is instructive however that only 5% of the land is devoted to what the census terms "agricultural purposes". What is termed "common grazing lands" is not included in the acreage of agricultural holdings given by the census. The figures nevertheless suggest a significant decline in lands used for cultivation.
The relationships of holdings to water resources (aquifers, wells) and infrastructure (storage reservoirs) could not be determined. Such relationships are helpful in making assumptions about past impacts on droughts geographically or spatially, where data is lacking and more importantly in trying to determine agricultural areas vulnerable to future droughts.
For example, the parish of St. George has five (5) reservoirs with total capacity of 1,155,500 imperial gallons located at various areas within its borders that could allow for gravity flow to farm areas. It also has six (6) wells with total yield of 442,080 IGPD.
However, farming in the parish remains mainly rain-fed because of the cost of domestic water. Here vulnerability to drought could be reduced if a way could be found to subsidize the purchase of water.
Farmers in the Cades area of St. Thomas on the other hand benefit from free (subsidized) water supplied by government dams located in the spring Hill/Westbury area. These farmers remain vulnerable to drought since they use irrigated water from dams totally dependent on rainfall.
In response to request for information, a written summary was received from the Department of Agriculture on the impact of drought on the agricultural sector. This summary is provided below as given, namely:
Dams
Agricultural dams in Nevis are located in:
Cades Bay
New River
Potworks
Matters
Farms in the Cades Bay area are gravity fed from the dams at higher elevations with a total capacity of 3.5 million gallons. Potworks farms benefit from a dam with the storage capacity of 600,000 gallons, while dams supplying farms at New River have a total capacity of only 16,000 gallons.
According to the Department of Agriculture, drip irrigation is the most common method of irrigation in these areas but sprinkler systems are also used.
The initial impact on farmers during times of drought is monetary. When dam sources dwindle or dry up farmers are forced to use domestic water bought at the cost of EC$25 per 1000 gallons. Water cost becomes then a major factor in the ability of farmers to keep crops supplied with the level of moisture required to achieve normal yields, particularly where drought conditions result in higher temperatures and evaporation rates.
The quantification of effects from drought relative to the availability of water and the understanding of future vulnerability are hindered by:
Reduction in Farm Operations
The Department of Agriculture’s conclusion that farmers reduce the scale of their operations when water in dams becomes limited is understandable. There is however no data readily available to determine quantitatively:
Use of Domestic Water
A monetary impact on the use of domestic water by farmers as a substitute for dam water could easily be determined if supply from dams was metered. Metered dam water supply would also allow authorities to estimate additional demands for water from farms during drought periods.
Increased Importation of Vegetables and Fruits
Based on number of holdings and acreage under cultivation, sweet peppers, sweet potatoes, tomatoes, cabbages, pumpkins, carrots, chive, tannia, yams and cucumbers are major annual crops on Nevis.
Among permanent crops, bananas, mangoes and coconuts have relatively large holdings (between 355 and 461 acres), while breadfruit, sugar apples, soursop, avocado pears, limes, golden apples, guavas and guinep have holdings ranging between 150 and 200 acres.
Bananas are moisture-loving plants, whose growth and yield is readily affected adversely by extended periods of dry weather. Coconuts on the other hand use a lot of water but are less vulnerable to drought particularly where located in areas with high water table.
Thus, rarely would there be a need to import coconuts, while the tendency is to import bananas at the first indication that local production is down.
The same is true for vegetables in relatively high demand such as carrots, tomatoes and sweet peppers.
Quality of Vegetables
Water-loving vegetables such as lettuce, cucumber and watermelon and fruits such as bananas, decline in quality when they experience moisture stress. The impact is most severe for farms without access to dam or domestic water.
Impact is also relative to space requirements of crops. For example, lettuce can be intensely grown in small parcels thus moisture requirements are more easily managed than for plants requiring more space per plant.
Quality of Livestock Feed
When there is a deficit of rainfall biomass productivity among species of grass used by grazing livestock drops relatively quickly. This is true for managed livestock ranges (labeled grazing on the land use data map) and unmanaged livestock ranges (labeled rough grazing).
Animal Health
The droughts affected the health, weight (hence marketability) and productivity of livestock. Hot weather caused heat stress, which is said to reduce fertility through sperm damage. Hot weather also affects libido in male animals, decreases milk production in cows and kills chickens (Dr. Paul Cadogan, 2000).
Animals also suffered from dehydration caused by shortages of water.
Livestock Mortality
Death of livestock caused by drought was confirmed by the Department of Agriculture after consultation with the Veterinary Division. However, drought related mortality figures were not available.
Economic Impacts
The economic impacts could be summarized as:
Absence of Drought Insurance
The economic impacts on agriculture from drought were compounded by the absence of drought insurance for crops and livestock. Insurance is lacking for three key reasons:
In the absence of being able to file claims for crop damages and/or loss, farmers had to absorb their own financial losses. The experience was difficult and stressful for many farmers and in some cases it dampened the enthusiasm for future investment in agriculture.
b) Tourism
Nevis has 478 rooms divided between hotels/resorts, condominiums/villas, plantation inns and guesthouses.
A number of the plantation inns and guest houses are located south of Nevis Peak within the rainfall "shadow", where temperatures are relatively more comfortable and conditions for plant growth better.
Most of the hotel rooms are on the west coast. A few of the plantation inns and guesthouses are located on the relatively exposed north coast. Fortunately, none are sited on the lower elevations of the east coast where exposure and dryness in periods of drought make vacations less comfortable.
Landscape, Product and Climate
Nevis’ tourism is promoted on the strength of its climate, sea and beaches. Several ground tours are designed around its ecology and scenic landscape.
Drought adversely affects the quality of the biological landscape (that is the living landscape of plants and animals) and the physical (non-living) landscape; the latter due mainly to the heat and dust associated with extended periods of low precipitation.
During the droughts the general quality of the visitors’ experience was affected by relatively hotter and drier conditions and a landscape stressed from heat and moisture deficiencies.
Property Landscape
One impact from droughts was the loss of plants on hotel property. Hotels did not have to purchase water from other than normal sources but indications were that some rationing of water occurred on properties.
At an average cost of EC$25 per 1000 gallons, some hoteliers view water as expensive. Consequently, although water was available from the local water authority, water was sparingly used on plants. As a result, a property such as Hermitage reported a loss of plants.
Local Produce
During previous droughts, hotels had difficulties securing local fresh fruits and vegetables. Hermitage reported difficulties in purchasing local bananas, melons and other fruits, lettuce and various other vegetables.
Effects on Workers
Unlike Antigua, where a number of properties laid off workers due to a decline in tourism sector, hotels in Nevis did not lay off workers as a direct consequence of the droughts.
Impact on Natural Attractions
Natural attractions of vegetation and scenic interests lose their visual appeal due to moisture deficiency.
The Nevis Island Development Plan 1996-2005, Volume 1, Island Profile Survey lists the following natural attractions:
It is not known if the volume of visitor trips to any of these attractions was affected by drought conditions. Even if there were a reduction in visitor volumes, it would have been difficult to obtain supporting data because the infrastructure to record visitor trips to most, if not all, of these attractions does not exist.
Settlements
The effect of past droughts on settlements has not been documented. However, it is assumed that settlements on the east, northeast and southeast coasts because of the relative exposure to prevailing winds and location within the lower rainfall belt would have been more severely affected. Settlement elevation in relation to booster pumps and water storage reservoirs was evaluated during the assessment. The findings indicate that relatively few residences are located higher than their supply reservoirs and the Water Department confirmed that for the most part settlements were adequately served by its water distribution network. Data on the number of households connected to mains supply was not secured. Households without connection would normally be vulnerable and would perhaps become more so during droughts.
FUTURE VUILNERABILITY
Agriculture
The agricultural sector remains highly vulnerable to future droughts for several reasons, namely:
Location of crops. Crops located in areas where rainfall is below the national yearly average will remain vulnerable to drought if rain continues to be the main source of water for plants. Vulnerability can be reduced if water for irrigation is made available at reduced or subsidized rates.
Vegetable crops grown in shallow soils on relatively steep slopes will also remain vulnerable unless water and soil conservation measures are applied. Depending on the level of constraints posed by shallow soils and steep slopes, soil and water conservation measures could be very costly and may prove to be uneconomical in some applications. Cultivation practices that cannot be sustained can be considered economically vulnerable.
Cost of water. Although the number of farms with access to water for irrigation is increasing, irrigation remains uneconomical for most small farmers because of the cost of water. As a result, even if farms have access to potable water, cost could prove a deterrent to its use in meeting irrigation requirements.
Overgrazing. High livestock population density will continue to adversely affect the landscape, soil, habitat and plant growth unless radical policy interventions are made to mitigate these impacts. If mitigation does not occur, large sections of the island’s landscape will remain vulnerable to drought.
Better control of livestock populations will be necessary to reduce and eventually eliminate crop damage from goats and sheep, which increases during periods of drought.
Tourism
Recent increases in water supply will reduce the impacts of meteorological drought on the hotel sector. Where dry weather conditions persist long enough to drastically reduce ground water yield, water rationing would be required and this would affect hotels.
Growth in the hotel sector, along with the construction of any additional golf courses, would significantly increase demand to the point where supply could become inadequate. For this reason, growth in water demand should be anticipated and investment made to increase supply to reduce vulnerability to drought.
Settlements
Settlements have become less vulnerable to droughts because water supply and distribution has improved in recent years. A few settlements are affected by low water pressure because of water transmission and supply problems.
The majority of settlements are not expected to suffer major water shortages for household use unless rainfall deficiencies remain long enough to affect ground water yields. However, households headed by farmers that are dependent on agriculture for all or part of their incomes will remain vulnerable to meteorological droughts, where costs prohibit irrigation of crops.
Certain characteristics that may suggest the need for mitigating the vulnerability of settlements to drought can be identified, namely:
Understanding and Applying the Concept of Risk
Drought risk for the purposes of this analysis is considered as having two (2) contributing factors, namely:
In addition, existing policy may also contribute to the island’s vulnerability to drought. Vulnerability could be reduce if policy interventions are made in the following areas:
Areas at Risk to Drought
Drought Risk Criteria for Mapping
Mapping of areas on the basis of their risk to drought, namely, low, moderate, high, very high was based on a set of criteria. Each criterion is given a value of one (1) and the total value of an area determines its rank:
Low drought risk 3-4
Moderate drought risk 5-6
High drought risk 6-7
Low drought risk 8-10
The listing of drought risk criteria is shown below:
Environmental Meteorological
Hydrological/Infrastructural
Human/Landuse
Areas
The assessment confirms, what perhaps is already known, that the central mountain area of moist forest has the lowest risk to drought. Moderate risk areas include the northwest and north of the island.
High-risk areas include the Charlestown water zone and the Butlers/Mannings water zone on the east of the island. The south and southeast section of the island is considered to be of very high risk to drought.
It is suggested that additional work be undertaken to confirm these drought risk designations. The work should include field observations to update the data maps where necessary.
Emphasis should also be placed on identifying more appropriate boundaries for water resources and drought management. A thorough analysis of drainage basins on the island could provide the basis for the delineation of the management boundaries.
Follow-up should also involve the refinement of the methodology used for drought risk ranking. Selective merging of drainage basins into units for managing drought would require re-evaluation and adjustment to the drought risk zones.
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:
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 find no need to use lawn mowers on lawns;
Leaf fall and litter in Forests. The increase in leaf fall and litter (detritus) on the forest floor can be used as one indicator of drought. Since leaf fall varies between species, measurement would need to be correlated with plant associations.
Damage to "indicator" plant species. 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. Ground water levels at various well fields are 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 drainage basins 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 Agricultural Reservoirs. Receding water levels at agricultural reservoirs is another drought indicator. Indicator levels at selected reservoirs could be determined over a period of time by monitoring to consistently measure meteorological and hydrological data, including, rainfall, temperature, wind speed, evaporation and seepage.
Water Rationing. The Water Department rations 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.
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:
Socio-economic indicators include changes in water use practices by households and businesses:
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