气候变化下鄱阳湖流域旱涝急转对湖区极端水情的作用机制

Poyang Lake has a complex river-lake relationship and huge drainage area, in recent years, the extreme hydrological events, i.e. flood and drought, occurred frequently in lake area. Moreover, the lake water regime was sensitive to the inflow changes of five sub-tributaries in its catchment, and the spatio-temporal distribution of dry or wet conditions in catchment had a significant impact on the lake water regime. This study focuses on the Poyang Lake and its catchment, identifies the drought-flood abrupt alternation events in Poyang Lake catchment from the aspects of precipitation and runoff , and investigates its occurrence, spatio-temporal distribution and intensity change rules. At the same time, based on the analysis of the response relationship between the hydrological regime changes in lake and the spatial distribution of dry or wet in catchment, a hydrological and hydrodynamic coupling model was constructed for Poyang Lake-catchment system. The sensitiveness and influence mechanism of drought-flood abrupt alternation in Poyang Lake catchment on the extreme hydrological regime of lake were discussed through the scenarios simulation. Also, the study was extended to estimate the change characteristic and trend of extreme hydrological regime, i.e. flood and drought, in Poyang Lake under the different climate change scenarios in future. This study is expected to serve as useful reference and valuable information for understanding the formation mechanism of flood/drought disasters in Poyang Lake, establishing integrated management measures and ensuring water safety of Poyang Lake.

鄱阳湖河-湖关系复杂、流域面积巨大，近年来湖区洪涝、干旱等极端水情频繁出现，而湖泊水情对五河入流变化敏感，流域上旱涝急转等极端现象及其时空变化对湖区水情有重要影响。因此，本项研究以鄱阳湖湖泊-流域系统为对象，基于站点观测数据结合TRMM卫星测雨与地面校准，通过定量指标从流域降水和五河径流两个方面辨识鄱阳湖流域的旱涝急转现象，研究其发生规律、时空分布以及强度变化特征；同时，在分析典型年鄱阳湖极端水情变化与流域旱涝时空分布响应关系的基础上，通过鄱阳湖湖泊-流域系统水文水动力耦合模型，研究鄱阳湖流域旱涝急转对湖区极端水情变化的敏感性及其作用机制，并基于CMIP5多模式预估在未来气候变化情景下，鄱阳湖区洪涝、干旱等极端水情的变化特征及趋势。研究结果可为进一步认识鄱阳湖洪旱灾害的发生机理、制定流域综合管理措施、保障湖泊水安全等提供重要的科学依据。

本项目基于历史水文、气象数据，构建了旱涝急转指数，定量辨识了鄱阳湖流域上的旱涝急转事件，研究了其发生规律、时空分布以及强度、周期变化特征；分析了典型年鄱阳湖洪水形成机制及对长江与流域五河来水变化的响应；并基于CMIP5多模式和分布式水文模型，分析预测了鄱阳湖流域未来在RCP4.5和RCP8.5气候情景下旱涝急转事件的变化特征及趋势。主要结论如下：（1）鄱阳湖流域极端降水呈增加趋势，EPD和EPA分别从11天和461mm增加到27天和1313mm。但自2000后，有显著减小的趋势。鄱阳湖流域极端降水在空间分布上具有较大的空间异质性，极端降水主要集中在流域东北部。（2）鄱阳湖流域旱涝急转事件主要分布在3-10月，其中3-6月主要表现为“旱转涝”，7-10月主要表现为“涝转旱”；五河以轻度旱涝急转事件为主，且主要发生在抚河、信江和饶河流域；在年代际上，鄱阳湖流域旱涝急转事件在1990s发生的频率最高，在2000s最低。五河旱涝急转的变化存在2个特征时间尺度。（3）长江来水和流域五河入流对鄱阳湖水位的主要影响时段不同，五河水量变化对鄱阳湖4-5月水位的影响最大；而长江来水变化主要对7-8月水位的影响最大。6月份之后，长江对鄱阳湖高水位的影响远大于流域五河的影响程度。五河入湖洪峰推迟10-20天可使鄱阳湖最高水位出现时间延后4-7天；而长江洪峰提前10-20天，鄱阳湖最高水位比基准年早6-13天。（4）鄱阳湖流域在未来气候情景下月平均流量与历史时段相比呈不同程度的增加。五河洪峰出现时间有所延迟，从历史时期的6月推迟至7月。在年际上，未来气候情景下五河年径流量呈增加趋势。另外，未来五河径流的年内分布不均匀程度存在增加趋势。（5）鄱阳湖流域未来旱涝急转事件在1-7月表现为“旱转涝”，7-10月则表现为“涝转旱”；与历史时段对比，未来“旱转涝”事件年内分布范围扩大，“涝转旱”则缩小，且集中发生时段由6-8月推迟至7-9月。未来旱涝急转事件发生频次呈增加趋势，旱涝急转事件以轻度事件为主，但最强旱涝急转事件发生强度有增强趋势。