The effects of reservoir storage and water use on the upstream–downstream drought propagation

Abstract

Temporal aspects (e.g., response time and propagation rate) of drought propagation have been explored extensively by many studies, yet much less is revealed about the spatial characteristics of drought propagation. In our case study region the Shaying River basin with two major reservoirs, the effects of reservoir storage and water use on drought propagation, especially the upstream–downstream drought propagation, are closely investigated. It is found that meteorological droughts propagate to reservoir droughts in the river basin with drought pooling and lengthening. How hydrological droughts propagate from upstream to downstream is closely related to drought severity. Mild and moderate upstream reservoir droughts usually did not propagate to the downstream reservoir, but severe upstream reservoir droughts could propagate to the downstream reservoirs with delayed occurrence, prolonged duration, and increased severity. Severe reservoir droughts could lead to severe streamflow droughts, even after the end of reservoir droughts as an aftermath. During the period of drought propagation from upstream to downstream, the downstreamness of stored volume (Dsv) typically keeps going down from above the downstreamness of storage capacity (Dsc) at the beginning of drought occurrence, indicating relatively more water is stored in the downstream reservoir, to below Dsc at the end of drought, indicating relatively more water stored in the upstream reservoir. Although the increase of water uses aggravated hydrological drought in the long-term, the typical exacerbating effect of water use on hydrological droughts is not observed during 2013–2018 because most human water use was industrial and domestic which was generally stable over time. In the 2013–2018 period, upstream reservoir’s drought was driven by inflow variability, while downstream reservoir's drought conditions were predominantly shaped by mainly the variation of the outflow from the upstream reservoir. These findings offer crucial implications for policymakers, aiding in the formulation of robust drought and water management strategies that consider upstream–downstream dynamics, providing essential insights for river-basin scale water resource management and drought mitigation.