Hydrological drought evolution and its response to meteorological drought in the middle-lower reach of the Yangtze River triggered by Three Gorges Reservoir

Abstract

利用1960—2016年长江流域183个气象站逐月气温和降水数据以及干流3个水文站逐月径流资料, 采用标准化降水蒸散指数(SPEI)和标准化径流指数(SRI)分析三峡水库蓄水运行前后长江中下游宜昌、汉口和大通站水文干旱的多时间尺度演变以及对气象干旱的响应特征. 结果表明: (1) 三峡水库运行后下游各站冬春季旱情明显趋缓, 而秋季干旱状况略有加重; 水库蓄水后各站中旱和重旱发生频率均呈减少趋势, 其中中旱减幅明显, 而特旱发生频率则总体表现为增加趋势; (2) 三峡水库蓄水后3个站平均干旱历时的变幅相对较小, 而干旱烈度和烈度峰值的均值增幅较大; 同时, 各站短时间尺度(1和3个月) 干旱特征变量的变幅总体呈现沿程递增趋势, 而长时间尺度(6和12个月) 干旱特征变量的变幅整体表现为沿程递减趋势; (3) 水库蓄水后各站短时间尺度SRI与SPEI的相关性减小, 但相关性随时间尺度增加而迅速增强, 12个月时间尺度的相关系数达到最大并略高于蓄水前; 在年内相关性上, 蓄水后各站短时间尺度SRI与SPEI的相关系数明显减小, 冬季表现尤为突出, 而长时间尺度的相关系数则略有增加; (4) 水库影响下不同时间尺度宜昌站水文干旱滞后于气象干旱平均天数有增有减, 而汉口和大通站的滞后天数均呈显著增加趋势, 且总体表现为沿程递增趋势. 研究结果可为变化环境下水文干旱预警与水库优化调度提供参考.;Based on monthly temperature and precipitation data from 183 meteorological stations in the Yangtze River (YZR) Basin and monthly runoff data from three hydrological stations in the mainstream of the YZR during 1960—2016, this study, using the standardized precipitation evapotranspiration index (SPEI) and standardized runoff index (SRI), analyzed the multiple timescales evolution of hydrological drought and its response to meteorological drought at Yichang, Hankou, and Datong stations in the middle-lower reach of the YZR before and after the operation of the Three Gorges Reservoir (TGR). The results showed that with the operation of TGR, drought situations at the downstream hydrological stations in winter and spring were significantly reduced, while drought conditions were slightly aggravated in autumn. The occurrence frequency of moderate and severe drought at each hydrological station showed a declining trend in the post-TGR period, particularly for the moderate drought. The frequency of extreme drought demonstrated an increasing trend in general. With the TGR was impounded, the average drought duration of three hydrological stations showed relatively mild variations, whereas the average drought severity and peak exhibited a significant upward trend. Furthermore, the variation amplitude of drought characteristic variables at the short-term timescale (1 and 3 months) from three hydrological stations displayed an increasing trend along the middle-lower reach of the YZR, while decreasing trend happened at the long-term timescale (6 and 12 months). The correlation between SRI and SPEI series from three hydrological stations at short-term timescale decreased significantly, but the correlation increased rapidly with timescale increase. Correlation coefficient between the SRI and SPEI series reached the maximum at 12-month timescale and were slightly higher than that in the pre-TGR period. Meanwhile, the intra-annual correlation coefficients between the SRI and SPEI series at the short-term timescale declined evidently in the post-TGR period, particularly in winter. However, the correlation coefficients of the SRI and SPEI series at long-term timescale increased slightly. With the impacts of the TGR, average day number that hydrological drought lagged behind meteorological drought at Yichang station at different timescales increased or decreased, while the number of lagged days at Hankou and Datong stations increased significantly, and had an increasing trend along the middle-lower reach of the YZR. These results can provide reference for hydrological drought warning and optimal operation of reservoir under the changing environment.