Impact of reservoir network on propagation from meteorological to hydrological drought in a semi-arid basin of India

Reservoirs play an important role in mitigating ill effects of drought. There could however be both desirable and undesirable effects of reservoirs on the water cycle. Many studies have explored the temporal aspects such as propagation rate and response time of drought propagation, yet not much has been revealed about the spatial characteristics of drought propagation. The present study aims to quantify the effects of reservoir networks on drought propagation from meteorological to hydrological drought via agricultural and reservoir drought, considering 7 major reservoirs in the semi-arid Krishna River Basin of India using 19 years of data from 2000 to 2019. The Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Soil Moisture Index (SSMI), Standardized Reservoir Storage Index (SRSI) and Standardized Streamflow Index (SSI) representing meteorological, agricultural, reservoir and hydrological drought, respectively, were estimated at 1 and 3-months and at a threshold value of 0. The spatial water distribution is described using the ‘downstreamness concept’, and the upstream-downstream drought propagation were closely investigated. The results indicate that the meteorological drought propagates to agricultural and reservoir drought with drought lengthening. Whereas the hydrological drought propagation from upstream to downstream is attributed mainly to drought severity. Usually, the mild and moderate upstream reservoir droughts do not propagate to the downstream reservoirs, but severe drought propagates to downstream reservoirs with prolongation of duration and increase in severity. During drought propagation from upstream to downstream, the downstreamness of stored volume (Dsv) decreases from above the downstreamness of storage capacity (Dsc) at the start, indicating more water in the downstream reservoir, to below Dsc at the end, indicating more water in the upstream reservoir. Importantly, the findings from the study provides essential insights for implications for policymakers for river-basin scale water resource management and drought mitigation considering upstream–downstream drought propagation dynamics.

Keywords: Drought Propagation, Meteorological to Hydrological Drought, Downstreamness, Upstream-Downstream.