Assessing Global Reservoir-Based Hydrological Droughts by Fusing Storage and Evaporation

Abstract

Although reservoirs serve as a lifeline for drought mitigation and adaptation, reservoir-based droughts (RBD) have received limited attention. Especially RBD that incorporate reservoir evaporation have remained overlooked. Here, we develop an Integrated Reservoir Drought Index (IRDI) using a Frank copula by combining the effects of reservoir storage and evaporation rate for 164 global reservoirs. Results show that Africa, South America, and Australia have experienced relatively longer RBD, whereas Asia and Africa have experienced more intense RBD. Furthermore, when significant (p-value < 0.05) trends in inflow and IRDI have shown opposite signs at a given reservoir, it is implied that human influence was the dominant driver of the long-term changes in RBD. We found that RBD was driven by climate in 71% of the 38 reservoirs examined and by human activities in the remaining 29% of reservoirs. Our study provides reservoir specific drought outlook that has significant environmental and sustainability implications.