Creating a culture of rainfall monitoring to combat the negative impacts of climate extremes and any future climate change

Rainfall extremes and their impacts have always been a part of the climate and physical landscapes of Barbados. They are a part of and not apart from the climate. Rainfall in the Caribbean islands is characterised by a wet and a dry season in each year. It is not unusual to experience significant dry spells during the wet season or very wet spells in the dry season. With the suggestion by the IPCC of reduced total rainfall of up to 15 to 20 % by 2100, the frequency and severity of dry spells and droughts are expected to increase. There is also the prediction, and patterns are already noticed, of an increasing number of high intensity rainfall events. 

Drought is viewed as abnormally low water availability, often due to abnormally low precipitation. It is a slow, creeping disaster that may only be recognised when it is already upon you – then it might be too late. Droughts range in intensity, duration (weeks to years) and spatial extent (which is normally greater than for other climate hazards). Drought impacts are normally cumulative and the effects are magnified when occurring from one season to the next. It is for these reasons that the Caribbean Drought and Precipitation Network (CDPMN) was established; to be a system that will closely monitor precipitation for such occurrences. It is important to note that even though the concept of rainfall monitoring was developed mainly for the negative extreme of rainfall, the indices and indicators being developed and used also provide useful information on excessively high precipitation, which will form part of the information provided to the Caribbean community. 

The CDPMN: The concept in action 

The Caribbean Drought and Precipitation Monitoring Network was launched in January 2009 under the project the Caribbean Water Initiative (CARIWIN, www.mcgill.ca/cariwin). The goal of CARIWIN is to increase the capacity of Caribbean countries to deliver equitable and sustainable Integrated Water resources Management (IWRM). CARIWIN, launched in February of 2007, is jointly implemented by the Brace Centre for Water Resources Management of McGill University, CIMH, and the partner countries of Grenada, Guyana and Jamaica. The CDPMN is expected to be fully operational by the end of 2010. 

Drought and the general precipitation status will be monitored on two scales: (i) regional, encompassing the entire Caribbean basin (this activity was operational from the time of launching) and (ii) national; using a number of indices and indicators. Indices such as the Standardized Precipitation Index and Deciles would be indicators of normal or abnormal rainfall. Other indices can provide information on normal or abnormal soil moisture (Palmer Drought Severity index, PDSI, Crop Moisture Index, CMI) or status of vegetation (Normalised Difference Vegetation Index, NDVI). Other indicators can provide information on stream and river flow, lake and reservoir levels and ground water quantities. 

At the regional scale, because of the dominance of water surface, only rainfall indices are being used. So far, national scale activity has begun in Barbados, Trinidad and Tobago and Guyana and are all in the development phase and are therefore not yet operational. 

Once fully operational, the final rainfall status of the region/country will be determined, by consensus, by a network of persons from different sectors, institutions, communities and backgrounds embracing the diversity in definitions and impacts of drought and by utilising the spectrum of indices and indicators. 

CIMH currently produces a precipitation outlook for the Caribbean from Guyana in the south, across the island chain to Belize in the West. The information is in the form of probabilities of normal, above normal and below normal rainfall with a lead time of three months. The forecasts will be used in combination with the monitoring output to provide projections of precipitation index values with lead times of up to three months. 

Outcomes and benefits expected from CDPMN 

In addition to monitoring trends, implementing early warning systems, and networking, the CDPMN will define knowledge gaps and uncover the needs to address extreme events and coping mechanisms. The network will be valuable for decision makers to be able to target their efforts on the most vulnerable regions and communities. Researchers and decision makers will gain access to a community of professionals working on drought and flood issues. 

The 2009 – 10 Drought 

The eastern Caribbean is gripped by a severe to extreme drought. The drought first expressed itself during the wet season of 2009 (in particular from the month of October) in the south eastern Caribbean, and spread northward. The 5 to 6 month drought was particularly harsh on the region’s farmers. The severity of impacts were also felt in the water resources sectors, forcing many Caribbean countries to take measures to control the rate of water use. During February 2010, rainfall totals were amongst the lowest (and in some cases the lowest) on record across the eastern Caribbean. 

During the March to May 2010 period, there should be a gradual return to near-normal conditions. However, one must be reminded that this period is the climatological dry season and therefore the cumulative impacts from the drought should continue during this period. 

Adrian Trotman

Chief of Applied Meteorology and Climatology

Caribbean Institute for Meteorology and Hydrology

http://www.cimh.edu.bb/Staff%20profiles/Staff%20profiles/Atrotman.htm