三峡水库蓄水前后库区及周边区域降水变化及其影响因素

Precipitation change and its influencing factors in the Three Gorges Reservoir area and its surrounding areas before and after impoundment

本文利用三峡库区及周边地区共21个气象站点1955—2019年的器测气候资料,结合西南地区气候驱动因子(北极涛动指数AO、北大西洋涛动指数NAO、西南季风指数SWM、东南季风指数SEM、暖季均温WST)系统分析研究区65a来的降水特征及影响因素,对比了三峡水库2003年蓄水前后局地降水的变化并评估三峡水库修建对降水的影响。结果表明:SWM主要影响研究区夏秋季降水;SEM和WST主要影响研究区夏季降水;AO对研究区降水的影响集中在冷季;NAO对研究区降水的影响不显著。SWM、SEM、WST与降水存在较显著的1~4a短共振周期,而NAO与AO以7~11a的共振周期为主。库区西北部的年降水量在2003年存在突变现象,腹地和南部地区的年降水量无此突变,而前述气候驱动因子在蓄水当年均无突变,表明气候驱动因子不是导致近库区降水突变的原因。三峡库区蓄水可能直接或间接导致近库区西北部的年降水量明显增加,主要是2月、5—7月降水显著增加(P<0.05),3月、8—10月不显著增加(P>0.05),其原因可能是升温引起的更多的局地蒸发水汽被季风转移至西北部,导致西北部的降水量增加。水库蓄水后,腹地在8月、10月、12月降水量显著减少(P<0.05),南部在8月降水量显著减少(P<0.05),其可能的原因是水库蓄水后缓冲昼夜温差,增加水面大气下沉,抑制水面对流活动,从而抑制研究区腹地和南部形成降水。基于气候驱动因子和月降水的多元线性回归模型表明:三峡水库蓄水后,西北部的年降水比无水库的情形显著增加13.2%(P<0.05);腹地、南部的年降水比无水库的情形分别增加0.1%和减少1.5%,但均不显著(P>0.05)。总的来说,三峡水库蓄水对降水存在局地效应,其长期影响还需要进一步评估。

Based on the instrumental data of 21 meteorological stations in the Three Gorges Reservoir(TGR)area and its surrounding areas from 1955 to 2019,this paper systematically analyzes the characteristics of rainfall variation and the associated driving factors,further compares the precipitation variation before and after impounding of TGR in 2003,and evaluates the impacts of the TGR on local precipitation.The driving factors include Arctic Oscillation(AO),North Atlantic Oscillation(NAO),southwest monsoon(SWM),southeast monsoon(SEM)and warm season temperature(WST).Based on redundancy analysis,some conclusions can be drawn as follows.SWM mainly affected the precipitation in summer and autumn,SEM and WST mainly affected the precipitation in summer,AO may impose effects on precipitation in the cold season,and the effect of NAO on precipitation was not significant in the study area.1~4a frequency bands are observed in Wavelet Transform Coherence spectrum between driving factors(e.g.,SWM,SEM,WST)and precipitation,7~11a frequency bands are characterized between driving factors(e.g.,NAO,AO)and precipitation.Since the TGR impounding in 2003,an abrupt change of the AP was observed in the northwest part of the TGR area in 2003,the above climate driving factors had no such corresponding abrupt change after impoundment,implying that the TGR impounding may cause a significant increase of AP in the northwest part directly or indirectly.This may be due to the fact that more locally evaporated water vapor caused by warming was shifted to the northwest by the monsoon,resulting in increased rainfall in the northwest.The precipitation of hinterland in August,October and December decreased significantly(P<0.05)and the same as that of the southern part in August(P<0.05).The reason may be that the reservoir buffered the temperature difference between day and night after impoundment,which increased the atmospheric subsidence over the water surface and restrained the convective activity over the water surface,ultimately restraining the precipitation in the hinterland and south of the study area.The multiple linear regression model based on driving factors and monthly precipitation showed that compared with the simulated situation without the TGR,the AP in the northwest significantly increased by 13.2%(P<0.05),the AP in the hinterland and south increased by 0.1%and decreased by 1.5%,but they were not significant(P>0.05).Genarally speaking,the impoundment of the TGR has a local effect on precipitation,but its long-term impact of the impoundment of the TGR on local precipitation needs to be further evaluated.