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In Tamil Nadu state at the southern tip of the Indian subcontinent, the Southwest monsoon, which can provide abundant rainfall from June to September, is blocked by the Western Ghat Mountains. As a result, only 800-1,000 mm annual rainfall falls, the lower limit necessary for paddy production. To use this limited rainfall effectively, people at least 500 years ago developed a tank irrigation system which is designed to capture surface runoff water. Frequent tank maintenance is essential for its sustainable use, but many factors, such as urban migration, have weakened the community-based tank management system and resulted in a decline in tank performance.

To cope with such problems, not only technological innovation but also the establishment of a tank management system taking into consideration socio-economical criteria may be needed. To suggest the needed intervention for sustainable water use in this area, I have been studying temporal-spatial changes in land and water use in recent decades through a combination of RS/GIS technique and fieldwork.