Dale C. S. Destin |
Amen! The Government of Antigua and Barbuda (GOAB) through the Antigua Public Utilities Authority (APUA) has finally decided to do what the masses, for decades, have been calling, if not clamouring for– the cleaning of the country’s surface water catchments.
Potworks Dam – Aug 1, 2015 | Courtesy Karen Corbin, Humane Society
Will cleaning the catchments be enough to ensure our water security, especially in light of climate variability and change? What else could be done to reduce our water insecurity? I will be sharing my thoughts on these subjects over a series of blogs. In this first one, I will focus on the potential impact of climate variability and change on freshwater resources in Antigua”. This will be followed by adaptation measures, perhaps split into parts.
Unlike most other resources, there is simply no substitute for water. Although there is a lot of it surrounding us, there are limited amounts on the island.
Limitation of freshwater has for a very long time been a major issue for Antigua; the problem dates back to, at least, the British colonial times, when there were frequent crop failures due to insufficient rainfall. In modern times, we have had the misfortune of having to import water from Dominica in 1984.
The program announced by the GOAB, through its Chief of Staff, would see the removal of overgrown vegetation and built-up silt from catchments, which have basically been left unmanaged from inception.
Bethesda Dam, July 31, 2015 | Courtesy Karen Corbin, Humane Society
Climate Variability and Change and Water Resources
Notwithstanding our relatively low rainfall, on average, I believe we currently get enough to thrive. The real challenge is collecting enough of it to sustain our socio-economic growth. However, in the long run, climate variability and change are projected to worsen our water scarcity. According to the last IPCC report, we are likely to have reduced rainfall, which will be exacerbated by increased evaporation rates caused by rising temperature.
Antigua’s surface water resources will be the most impacted by climate variability and change. Our main surface water storage, Potworks Reservoir, constitutes about 83% of total surface storage capacity. The reservoir has a maximum capacity of about 4.5 million cubic metres (m3)(1 billion imperial gallons). The structure has extensive shallow zones with an average dept of around 2.4 metres (8 feet), making it almost ideally vulnerable to high evaporation rates.
At present, Potworks alone loses around 9610 m3 (2.1 million imperial gallons – MIG) of water daily. Antigua’s daily water requirement is around 36369 m3 (8 MIG). This means, every four days we lose one day’s supply of water. One of the main drivers of evaporation is temperature. Thus, as our temperature continues to rise, we will experience greater water losses to the atmosphere.
The amount of water vapour the atmosphere can hold changes exponentially with temperature, as expressed by the Clausius-Clapeyron equation, and typically, there is a 7% change in the water holding capacity of the atmosphere per change in degree Celsius.
Although not as vulnerable to climate variability and change, ground water resources are also at risk on. There are about 56 active wells producing approximately 4546 m3 of water daily (1 MIG) and of depth ranging 1-50 metres (3-165 ft). These are clearly mostly wells which tap into unconfined aquifers that are relatively close to the surface of the ground; thus, they are exposed to the changing climate.
Confined, deeper wells would be more protected. Thus, for particularly unconfined and relative shallow aquifers, projected reduced rainfall and increased evapotranspiration due to climate variability and change will have depleting impact on groundwater sources.
Research shows that aquifer recharge is very sensitive to precipitation changes; a 15% reduction of rainfall could result in 40-50% reduction in the recharge of an aquifer. Added to that, in Antigua, the rainfall could decline by as much as 30% by 2100.
With the global climate warming and ice melting, sea level rise will exacerbate dwindling freshwater resources. As the sea rises, salt water will intrude further inland and contaminate aquifers, especially those relatively close to low-lying coastal areas.
Already, wells have been capped due to saltwater intrusion and others are likely to be capped going forward. A rise of a metre in sea level could reduce the land size of Antigua by only 1% but have a huge impact on water resources.
Based on the latest Inter-governmental Panel on Climate Change (IPCC) assessment report – AR5, it is very unclear as to how climate change will affect extreme precipitation events and droughts in Antigua, if at all. Data from the Antigua and Barbuda Meteorological Service Climate Section suggest that there is no trend with respect to extreme precipitation events and further work needs to be done on drought frequencies. However, increases in either will have negative impacts on water resources, especially with respect to quantity and quality.
There is no doubt that the government is doing the right thing by embarking on the cleaning of our surface catchments. Coping with climate variability and change will prove extremely challenging for Antigua. Tourism is the main driver of the economy and adequate water is need for its growth and sustainability.
The change of the global climate will likely have a net negative impact on all endeavours on the island, directly and indirectly. Water, the most vital resource to life, is projected to decline due to climate change. Models are projecting as much as 30% reduction of annual rainfall and contamination of coastal aquifers by saltwater intrusion due to sea level rise. Increased evaporation driven by global warming will adversely affect water storage in reservoirs and, to a lesser extent, aquifers.
Notwithstanding the challenges, the island is not without options to adapt. The next blog, on this subject, will explore some of these options.