The Chennai Water Crisis: Insufficient rainwater or suboptimal harnessing of runoff?

Abstract

Chennai experienced acute water shortage during 2019 summer, and four years prior, an earlywinter deluge. Analysis of 116 years (1901-2016) of rainfall in Chennai Sub-basin shows a weak climate change signal: Winter monsoon rainfall, has slightly increased, especially in December. The much larger Cauvery basin to the south also exhibits a nondescript climate change signal in winter rainfall. Late summer (September) rainfall in the Cauvery Basin has, however, precipitously declined in recent years (1987-2016). We show that this decline, as well as the mid-20th century increase, are attributable to natural multidecadal climate variability (Atlantic Multidecadal Oscillation) - cautioning against cavalier attributions of recent-period trends and the Chennai Water Crisis to climate change. Analysis of runoff - the rainwater leftover after its hydrologic and atmospheric processing - shows that harnessing even half of the winter monsoon runoff in the Chennai Sub-basin can satiate the city's water demand for about seven months; and without needing new reservoir facilities. The present analysis suggests that Chennai's water woes arise not from insufficient rainwater, but from the suboptimal harnessing of related runoff.