利用交叉小波技术分析三峡水库蓄排水过程对库区降雨量的影响

Cross Wavelet Analysis on the Influence of the Three Gorges Dam Impounding on the Reservoir Precipitation

三峡大坝蓄水过程对邻近区域气候的影响一直是国内外学术界广泛关注的热点问题。三峡大坝从2003年投入使用至今,水位从66 m上升至175 m,经历了3个蓄水阶段,为观测水库水位与库区降雨量相关性提供了极佳的窗口期。为了精准分辨两者在多周期多尺度的相互影响,基于三峡库区的4个国家气象观测站的历史逐日降雨数据和三峡蓄排水过程水位变化数据,进行交叉小波分析,提取能量谱、凝聚谱和相位谱,展现两类数据时频域多尺度的相关细节。结果表明,三峡大坝蓄排水过程对库区降雨有影响,第一期蓄水期最明显,表现为库区降雨年周期性相对减弱,高频模式增强;历史数据表明库区降雨主要表现为1.0 a主周期和2.0 a、4.0 a等多个次长周期;三期蓄水之后,库区降雨量的1.0 a主周期没有改变,而多个次长周期特征变化明显。交叉小波相位谱揭示水库蓄排水过程对库区降雨的人工调节和自然调节影响,前者表现为水位变化与降雨1.0 a主周期的完全反相,明显不同于蓄水之前的同相特征;后者表现为高频分量(1/128~1/32 a)的反相特征,其规模效应随大坝建成而增强。值得关注的现象是巴东站与荆州站的降雨存在3.5 a次长周期的反相特征,可能是大坝蓄水后改变了水循环的范围。

How the Three Gorges Dam impounding impact on local climate environment is a hot issue in science and engineering communities. Since the dam worked in 2003, the reservoir water level changes from 66 m up to 175 m in three stages, providing a perfect period observing the coherence of water level and rainfall. In order to diagnose their interaction in multiple periodic windows, historical water level changes of the Three Gorges Reservoir and the daily precipitation data recorded at four national weathering stations are analyzed with temporal full-scales spectra by Morlet cross wavelet analysis with power spectra, coherence spectra, and phase spectra. The results show that the obvious impact of water impounding on the reservoir rainfalls, of which the strongest impacting period occurred at the first impounding stage, causing reservoir rainfall reduction of one year period and increment of high frequencies. Historical reservoir precipitations have premier period 1.0 a,and multiple secondary longer periods, such as 2.0 a and 4.0 a. The premier period keeps after three stages, but the secondary period, 2 a, at dam area change obviously. There are two influences of reservoir impounding on reservoir rainfall in phase spectra: Artificial control and natural regulation. The former is completely antiphase at the premier period 1.0 a, which is obviously different from the inphase before the dam construction. The latter is reflected in the anti-phase of water level and rainfall in hi-frequency components at zone(1/128-1/32 a), the scale effect increases with the increasing reservoir water level. The noted fact is that the coherence 3.5 a period at Badong and Jingzhou stations antiphase, possiblyindicating the water cycle changed spatially. Besides, water-level change corresponds to rainfall in antiphase annual variations of dam’s function of water control, different from their variations in-phase before the dam construction.