水文干旱对气象干旱的响应特征与机理研究

Drought is one of the natural hazards with highest frequency and largest economic loss worldwide. The previous studies concerning droughts primarily focused on the study on the risk assessment and prediction of drought, whereas the studies related to drought response mechanism such as response time and its influencing factors among different drought types are not very common. Investigating the response mechanism of hydrological drought to meteorological drought helps to reveal the process of hydrological drought formation and propagation from the mechanism perspective. The Wei River Basin will be selected in this study, and the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) will be applied to characterize meteorological and hydrological droughts, respectively, with an aim to fully reveal the evolution characteristics of hydrological and meteorological droughts in this basin. Besides, investigation of the response time of hydrological drought to meteorological drought will be conducted. Furthermore, the Budyko hypothesis will be introduced in this study, combining with the cross wavelet analysis, to explore the impacts of the large-scale atmospheric circulation and comprehensive watershed underlying surface characteristics on the lag time of hydrological drought in response to meteorological drought. Furthermore, the relationship between Normalized Difference Vegetation Index (NDVI), elevation, slope, as well as soil moisture and the response time will be studied in this study to reveal the impacts of specific watershed characteristics on the drought response time. The findings of this study can provide a solid foundation for establishing a hydrological drought early warning system based on meteorological drought, and are helpful for reducing the economic loss caused by hydrological drought, which have important academic meaning and applied value.

干旱是全球范围内发生频率最高且造成经济损失最大的自然灾害之一。以往有关干旱的研究主要聚焦于干旱的风险评估与模拟预测，而不同干旱类型间的响应机理如响应时间及其影响因素研究并不常见。开展水文干旱对气象干旱的响应特征与机理研究，有助于从机理上揭示水文干旱的形成与传播过程。本项目以干旱半干旱的渭河流域为例，拟采用标准化的降水指数(SPI)和标准化的径流指数(SRI) 分别表征气象干旱和水文干旱，计算水文干旱对气象干旱的响应时间，揭示它们之间的响应特征；采用交叉小波技术并结合基于Budyko假设的流域水热耦合平衡公式，探究大规模的大气环流异常和流域下垫面的综合特征对其响应时间的影响。此外，拟研究NDVI、高程、坡度、以及土壤湿度与响应时间的关系，进一步揭示流域下垫面的特定特征对其响应时间的影响。研究成果可为建立基于气象干旱的水文干旱预警系统奠定坚实的基础，指导区域抗旱救灾工作。

由于流域的缓冲作用，气象干旱向水文干旱的传播往往具有明显的时滞。研究水文干旱对气象干旱的响应过程对于开发及时的干旱监测系统是必不可少的。本研究以渭河及其两大支流泾河及北洛河为研究对象，揭示了流域气象与水文干旱的时空演变规律，量化了气象干旱到水文干旱的传播时间、触发阈值以及流域对气象干旱的抵抗力，洞悉了其传播过程的动态变化及其驱动力。结果表明：（1）研究流域水文干旱对气象干旱的响应时间在春冬季长，夏秋季短，且干旱响应时间呈现春冬季加快、夏秋季变慢的趋势；（2）中等水文干旱对应的气象干旱触发阈值介于[-1.50，-1.20]，严重水文干旱对应的触发阈值介于[-2.30，-1.80]，极端水文干旱对应的触发阈值介于[-3.00，-2.40]，且冬春季节流域耐旱性明显高于其他季节；（3）基于数据归一化处理和熵权法赋权重方法构建的干旱抵抗力指标具有一定的可靠性和准确性，泾河和北洛河流域干旱抵抗力强于渭河全流域，总体上1-3月份流域干旱抵抗力最强，9-12月其次，4-8月份干旱抵抗力较弱；（4）渭河流域1月、5月、11月和12月的干旱抵抗力显著上升，3月、4月和6月干旱抵抗力显著下降，其余月份随着水文干旱程度不同而显示出不同的变化趋势，这主要受流域下垫面因素（NDVI、土地利用等）的影响。研究结果有助于深入理解水文干旱的形成机理，科学指导水文干旱的早期预警，从而完善了变化环境下干旱分析理论与技术，为我国西北旱区干旱风险管理提供科技支撑。