中国东部多类跨季节干旱的特征和机理研究

Drought is one of the most powerful and destructive hazards that affects the China’s agricultural production, economic and even ecological environment. In recent years, extreme drought events, such as prolonged seasonal drought, have remarkably increased over Eastern China, which have had a profound impact on local sustainable development. The damage caused by the multi-season drought is far more severe, contrasting to the single-season drought events. Moreover, the possible causes and mechanisms of multi-season drought formation are also more complex than that of single-season drought, which makes multi-season drought become a hot topic in the climate research. However, the characteristics and related mechanisms of multi-season drought remains largely unexplored, due to the complex nature (i.e., various time-scale and multiple types) of multi-season drought. Based on these considerations, the project attempts to take “two-season prolonged drought” events as an example, and fully investigate the types, features and possible mechanisms of such events, by using multisource (e.g., observations, reanalysis and model) data-based SPEI index. The project aims to deepen the understandings of the formation and variation of multi-season drought, provide a scientific basis for the formulation and implementation of the related policy regarding disaster prevention and mitigation and sustainable development.

干旱作为一种具有破坏性的自然灾害，严重威胁着我国的农业生产、生态环境和经济发展。近年来，我国东部极端干旱尤其是跨季节干旱事件显著增多，对当地可持续发展造成了深远的影响。相较于单一季节而言，跨季节干旱事件所带来的危害往往更为巨大、成因更加复杂，因此跨季节干旱已成为目前学者们广泛关注的热点问题。然而，跨季干旱涉及的时间尺度跨度大、类型多，针对各类跨季干旱的特征和机理还缺乏详细深入的认识。介于此，本项目拟以跨两季干旱为着眼点，基于标准化降水蒸散发指数，利用多套观测、再分析和模式资料，明确中国东部跨季干旱的具体类型，分析各类跨季干旱的演变特征及其对应的关键影响因子，进一步揭示其可能的物理机制。通过该项目的研究旨在加深对跨季干旱形成和变化的理解，为该地区防灾减灾和国民经济可持续发展的政策制定提供一定的科学依据。

跨季节的长期连旱是最具破坏性的气象灾害类型之一，干旱事件的频繁发生和长时间持续会对全球农业，生态系统和社会经济发展产生重大影响。模式预估结果显示，随着全球变暖加剧，严重的区域性干旱事件将在未来增多。因此，全面厘清各类干旱的特征和形成机理对其早期预警及灾害应对有重要意义，然而目前的研究对长时间尺度干旱事件的认识还十分不足，相应的物理过程也不清晰。基于此，本项目利用了多源观测和再分析资料，围绕我国东部多类跨季节干旱的特征和可能成因展开了全面的探索，主要进展包括：（1）明晰了我国极端干湿变化的动力成因及与多外强迫因子的联系：全面揭示我国南方冬春季极端干湿变异的机理，强调了南欧亚遥相关型和中高纬大气环流异常对我国冬季干湿变化的重要性，同时揭示了多种外强迫因子与我国极端温湿变化的可能联系；（2）厘清了我国东部四大类两季尺度极端干湿演变特征和内在联系：强调了多种类型的跨两季干旱的主要模态和季节性演变过程，明晰了其中的内在联系，并得出冬-春到夏-秋（包括冬-春、春-夏、夏-秋）和秋-冬两大类不同的跨两季干旱的重要特征；（3）揭示了影响两季尺度极端干湿变化的重要动力因子和物理途径：对于冬-春到夏-秋的连旱事件，其与前冬拉尼娜转换为后秋厄尔尼诺事件密切相关，通过ENSO激发的环流异常和多累大气遥相关型，导致我国东部地区的水汽条件和动力条件均不利于降水发生，使连旱事件形成。对于秋-冬连旱，则与中高纬度陆面异常融雪和EUP型遥相关有关，通过陆面异常加热，使得我国大范围地区，冬季风偏强，冷高压控制我国，有利于干旱发生；通过项目的研究，在跨季尺度干湿变化成因、海-陆-气相互作用机理，尤其是多类跨季节干旱类型之间的内在联系和物理机制方面获得了一些新认识，为深入理解我国长时间尺度干湿变化提供了一定的科学参考。