Quantifying the Contributions of Climate Change and Human Activities to Drought Extremes, Using an Improved Evaluation Framework

An increasing amount of studies have emphasized that more frequent and extensive extreme events have occurred around the world. The effects of climate change and anthropogenic activities on the variation in runoff have been studied extensively. However, the effects of variation in hydrological extremes have rarely been studied. In this study, a modeling framework was developed to quantify the time-varying probability of extreme hydrological drought events under a changing environment, and the framework includes standardized runoff index construction, a change point test, generalized extreme value modeling, a return years analysis and an evaluation of the impact of climate change and human activities. Importantly, unlike the common change point test in the individual runoff series, the copula method was introduced to determine the change in the precipitation-runoff dependence structure. Generalized extreme value models were developed to make inferences about the return probability of the extreme standardized runoff index. The new method was applied to the Jinshajiang River Basin (JSJR). The results show that a change point in the relationship between precipitation and runoff occurred in 1995. Even though the climate became slightly drier, extreme drought was alleviated in the JSJR, and human activities were the main contributors to drought mitigation. The copula multivariate change point detection was accurate. Studying the impacts of climate change and human activities on general runoff and hydrological drought extremes is important to better understanding complex water resource variations.