Current Science

Sumant Nigam ¹, Alfredo Ruiz-Barradas ², Agniv Sengupta ³

Affiliations
1 Fulbright-Nehru Fellow at the Indian Institute of Technology, Mandi 175 001,, IN
2 Department of Atmospheric and Oceanic Science, University of Maryland College Park, US
3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, US

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.

Keywords

Climate Change, Monsoon Rainfall, Multidecadal Variability, River Basin, Runoff.

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