Integrating multiple comparison methods for attributing hydrological drought evolution and drought propagation: The impact of climate change cannot be ignored

Abstract

Enhancing the comprehension of hydrological drought evolution and drought propagation mechanisms is crucial for effective drought risk management in a changing environment. Previous studies have either inadequately considered the effects of climate change or conflated the impacts of large reservoirs and human activities. This study presents a comprehensive framework that integrates multiple comparison methods to quantify the effects of climate change, large reservoirs, and other human activities. The framework comprises three steps: (1) preparation of four types of streamflow based on critical time, large reservoirs inflow and outflow, and hydrological model; (2) estimation of hydrological drought characteristics, including duration, severity, peak intensity, instantaneous development speed, and instantaneous recovery speed and drought propagation characteristics, such as correlation, transition rate, and three types of the propagation time (PT) based on the start point (PTS), peak point (PTP), and end point (PTE); (3) quantification of the influences of various factors on the characteristic variables. The upper Yellow River Basin, a cold basin with large cascade reservoirs, was selected as the study area to utilize the proposed framework. The results revealed that climate change and large reservoirs reduced the duration and severity of drought events with relative contribution rates ranging from 146.6% to 340.2% and 381% to 707.7%, respectively, while those were increased by human activities with relative contribution rates from 428.0% to 1147.9%. Large reservoirs played the most crucial role in the development and recovery stages, with relative contribution rates of 75% and 85%, respectively. Climate change strengthened the correlation between the two drought indices, while human activities and large reservoirs weakened the correlation. The changes in three PT indicated that climate change shortened drought development and recovery period, while those were prolonged by human activities. Many hydrological droughts occurred before meteorological droughts due to large reservoir regulations. The changes in transition rates are −30.3%, 48.0%, and −28% under the influences of climate change, human activities, and large reservoirs, respectively. The framework and results of this study provide valuable insights into the mechanisms of hydrological drought and drought propagation and serve as a scientific basis for drought mitigation in changing environments.