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Articles |
National Geophysical Research Institute, Hyderabad-500 007, India (e-mail: bssngri{at}rediffmail.com)
Extreme climate conditions are expected in the twenty-first century in the form of higher maximum temperature (with more hot days) resulting in frequent droughts. The continents of Africa and Asia are anticipated to be extremely vulnerable to droughts. In the impending extreme climate conditions, humanity's sustenance hinges on groundwater as it forms the world's largest freshwater resource. Adaptive and mitigation measures entail well planned strategies for sustained groundwater through extreme climate conditions including droughts. In this paper two such strategies are discussed to overcome the problem of droughts: (i) artificial groundwater recharge using percolation ponds; and (ii) identifying and characterizing deep aquifers resilient to droughts through detailed geophysical, hydrogeological and isotopic studies.
Percolation ponds act as artificial recharge structures which are constructed across monsoon streams with the purpose of harvesting surface runoff caused by monsoon streams. Conventional and tracer methods were developed in India to determine how effective these artificial recharge structures could be. From studies carried out on percolation ponds located in diverse geological formations such as granites, basalts and sandstones, it was concluded that these structures are quite useful for overcoming droughts in semi-arid and arid regions, and it was demonstrated that the role of geology outweighs the effect of climate on such structures. It has been shown that in a similar climatic environment, the percolation ponds in sandstones were far more efficient (efficiency 60%) than those in basalts (efficiency 20–30%).
Recently it has been realized that certain deep aquifers can yield a good quantity and quality of water even during extreme climate events. The Neyveli aquifer in southern India has been demonstrated to be such a representative aquifer for mitigation of droughts. Very extensive and intensive hydrogeological and isotopic studies on the aquifer revealed that the aquifer has distinct characteristics, namely: (i) distinct recharge area; (ii) extensive groundwater regime with high degree of recharge rate; (iii) wide span of radiocarbon ages from Modern to >30 000 years BP indicating modern as well as palaeorecharge; and (iv) minimal changes in groundwater quality despite very heavy and continuous withdrawal during the last four decades. All these criteria provide the necessary ingredients for drought resilient aquifers which can be used to identify similar aquifers elsewhere in the world.
