Synoptic assessment of water resource variability in reservoirs by remote sensing: General approach and application to the runoff harvesting systems of south India

This paper presents a methodological procedure based on remote sensing and image analysis techniques designed to map and quantify water stocks in small irrigation reservoirs over vast, user‐defined regions. Because the method is based on unsupervised pixel classification schemes, it is analytically transparent and entirely replicable and can therefore be used in most settings as a tool for integrated water resource management, planning, or policy making, with benefits to irrigation, land use, agriculture, and water‐related social issues. Satellite images of semiarid south India are used here to quantify fluctuating water volumes in ∼2500 reservoirs. In this pilot study, the detection of temporal trends and spatial discontinuities in land use at successive dates within reservoir beds is a proxy for assessing the performance of reservoirs and for formulating hypotheses on the environmental, socioeconomic, or anthropological reasons behind the inferred levels of infrastructural maintenance or disuse. The synoptic approach paves the way for future efforts as better ground truth data become available.