CNH-EX: Monsoon Harvests: Assessing the Impact of Distributed Storage Tanks on the Vulnerability of Subsistence-Level Agriculture in Tamil Nadu, India

The overall objective of this project is to better our understanding of the ways in which rainwater harvesting tanks (ponds) are able to enhance water storage and increase groundwater recharge in water-scarce agricultural areas of Tamil Nadu in southern India. The intent is also to enhance our knowledge of the role that these tank irrigation systems play within the village communities that depend on them, especially with respect to minimizing social, economic and environmental vulnerability. To achieve these goals the project team will access a variety of data sources, obtaining information about climate, land-use, the number of tanks and their locations, water governance systems, groundwater depletion, the amount of water contributed by the tanks, and labor markets. Areas in Tamil Nadu in which tank irrigation systems have declined over the years will be identified and compared with areas where use of the tanks has persisted. To understand the water-storage dynamics associated with the tanks, the project team will place water level sensors in an identified series of tanks that will provide continuous data regarding water storage throughout the monsoon and dry seasons. It is hypothesized that the ecological and economic benefits provided by these tanks, when adequately maintained and with effective community governance structures, can make these subsistence-level farming communities less vulnerable to variations in the region's yearly monsoons, especially in the face of climate change and rapid groundwater depletion.

The Madurai region of southern Tamil Nadu, India, faces issues of acute water scarcity, making extensive irrigation systems necessary. As the areas under cultivation in Tamil Nadu have grown in recent decades, so has the demand for irrigation water. With this growth, groundwater supplies have become increasingly depleted. As such, the need for a more sustainable means of providing irrigation water is now being acknowledged. A promising trend in water management has been to reassess and revive the use of older, local-scale irrigation practices that utilize tank systems. These tanks, which are, essentially, small reservoirs used for local rainwater harvesting, collect water for both surface water irrigation and groundwater recharge, and have been a source of irrigation and drinking water in India for thousands of years. The current project will focus on improving our understanding of the dynamics of water storage and groundwater recharge associated with these small irrigation systems, and the importance of the systems to the associated villages. This project will lead to a better understanding of the ways in which traditional rainwater harvesting practices can increase access to both drinking and irrigation water in regions of acute water scarcity. As 800 million people worldwide live in regions where water scarcity issues are an ongoing problem, the greater understanding that is gained in India with regard to rainwater harvesting and groundwater recharge will inevitably have cross-cultural value and potential application to a range of regions, from sub-Saharan Africa to the southwestern United States. The research carried out in this project will lay the groundwork for additional explorations of local-level water management systems and institutions in a variety of cultural contexts.

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