Elucidating the effects of mega reservoir on watershed drought tolerance based on a drought propagation analytical method

Abstract

As a large control project in a river basin, mega reservoir has obvious influences on hydrological process, and is also very important to drought risk management. However, how much mega reservoir has improved the drought tolerance of the watershed is still an unsolved question. To end this, we explored the effects of mega reservoir on watershed drought tolerance from the perspective of drought propagation in this study. Firstly, the drought propagation characteristics before and after reservoir construction were calculated to reveal the influences of mega reservoir on propagation process from meteorological to hydrological drought. Then, based on drought propagation characteristics and the Bayesian network, a novel drought propagation threshold model was proposed and calculated the cumulative precipitation deficit thresholds that triggered different levels of hydrological drought before and after the reservoir was built, respectively, and the sensitivity of the response of hydrological drought to meteorological drought was also explored based on the Bayesian network model. Finally, we further comparatively analyzed the effects of environment change and mega reservoir on watershed drought tolerance to verify the reliability of the results. The upper Yellow river basin (UYRB) was selected as a case study. Results indicated that (1) mega reservoir could delay the propagation from meteorological to hydrological drought in the UYRB, and this effect was weakening with the increase of the distance from hydrological station to the reservoir; (2) the construction and operation of mega reservoir enhanced the drought tolerance of the UYRB, and the probability of severe hydrological drought in the downstream of the reservoir was significantly reduced; (3) environment change accelerated the propagation from meteorological to hydrological drought and had a negative effect on drought tolerance in the UYRB, while mega reservoir could effectively resist the influence of environment change.