Objective evaluation of the relationships among different types of droughts remains a challenging task due to the combined impacts of climate change and land surface modification caused by human activities. Based on the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) at the 3- and 6-month timescales, this study presents a systematic analysis of the relationships between the severity (S) and duration (D) of meteorological (MD) and hydrological droughts (HD) in the three catchments of the upper Huai River Basin in China. The relation between SPI and SRI is explored by the maximal information coefficient and the mutual entropy. The spatial propagation mechanism of MD is identified by the centroid trajectory, and the response of HD to MD is quantified by the model averaging method. The results indicate a drying (wetting) trend in the upstream (downstream) area, while the centroid trajectory of MD is found in the midstream area, but not associated with the large (or small) S and D simultaneously. There is a strong correlation (determination coefficient > 0.55) between SPI and SRI in all three subareas, particularly at the 6-month timescale. The increasing influences of human activities (e.g., regulation of water conservancy facilities) from upstream to downstream lead to a weaker correlation between SPI and SRI as well as a decreasing threshold of D for MD to trigger HD in downstream. By contrast, the drier climatic conditions are the main reason for the increasing threshold of S for MD to trigger HD from upstream to downstream.

由于人类活动引起的气候变化和土地表面变化的综合影响，客观评估不同类型干旱之间的关系仍然是一项艰巨的任务。基于3个月和6个月时间尺度上的标准降水指数（SPI）和标准径流指数（SRI），本研究对严重程度（S）和持续时间（D）和淮河上游三个集水区的气象干旱和水文干旱（HD）。通过最大信息系数和互熵来探索SPI和SRI之间的关系。MD的空间传播机制通过质心轨迹确定，HD对MD的响应通过模型平均法进行量化。结果表明上游（下游）区域有干燥（润湿）趋势，而MD的质心轨迹位于中游区域，但与大（或小）S和D不相关同时。在所有三个子区域中，特别是在6个月的时间范围内，SPI和SRI之间都有很强的相关性（确定系数> 0.55）。人类活动（例如，对水利设施的调节）从上游到下游的影响不断增加，导致SPI和SRI之间的相关性减弱，并且MD触发下游HD的D阈值降低。相比之下，较干燥的气候条件是S阈值增加的主要原因，以使MD从上游向下游触发HD。