1960—2020年珠江流域跨季节尺度干旱时空变化

全球气候变化背景下，珠江流域干旱事件尤其是跨季节干旱事件频发，研究珠江流域不同时间尺度下的干旱时空特征对于流域水资源配置和农业结构调整至关重要。为了了解珠江流域跨季节干旱时间时空变化特征，研究基于1960—2020年珠江流域44个气象站逐日气象观测数据，计算不同时间尺度下的标准化降水蒸散指数（standardized precipitation evapotranspiration index，SPEI），结合线性倾向估计法、Mann-Kendall突变检验以及Morlet小波分析，分析了近60 a来珠江流域跨季节干旱时空变化特征。结果表明：1）1960—2020年间珠江流域跨季节干旱事件中，秋冬及秋冬春连旱化趋势显著，呈弱干旱化趋势，且干旱化频率有所上升，连旱强度以中旱和轻旱为主，连旱影响范围以局域性为主，其次为全域性，秋冬春季节连旱在1962年和1997年分布出现由干转湿和由湿转干的突变。2）珠江流域秋冬及秋冬春季节连旱普遍存在9～14 a变化周期，相关分析表明珠江流域干湿变化与同期厄尔尼诺现象显著相关。3）珠江流域秋冬及秋冬春季节连旱尺度下大致呈东西干而中间湿的空间分布格局，红水河至左江及郁江流域连旱化趋势减弱，但连旱化频率仍较高，东江流域秋冬季节连旱化频率高且呈弱连旱化趋势，湿润化速率自西南向东北递减，未来发生季节连旱风险高。研究结果可为珠江流域干旱监测与防灾减灾措施提供指导和建议。

Spatiotemporal variations of cross-seasonal drought in the Pearl River Basin of China from 1960 to 2020

The Pearl River Basin is one of the most important agricultural areas and water sources in the subtropical humid region of southern China. Drought events occur frequently in the Pearl River Basin under the background of global climate, especially for the continuous seasonal drought. The temporal and spatial evolution of drought at different time scales is of great significance to allocate the water resources for the agricultural planting structure in the Pearl River Basin. In this study, the daily observation data was selected from 44 meteorological stations in the Pearl River Basin from 1960 to 2020. The precipitation and potential evapotranspiration (ET0) was then calculated by the FAO Penman-Monteith, in order to obtain the standardized precipitation evapotranspiration index (SPEI) at the cross-seasonal drought time scale. Linear tendency estimation was combined with Mann-Kendall mutation test and Morlet wavelet analysis. The temporal and spatial variation of continuous seasonal drought was then analyzed over the past 60 years. The result showed that: 1) The instable precipitation was led to the complex and diverse dry and wet changes. The growth trend of the continuous drought was found in autumn-winter and autumn-winter-spring. This variation was attributed to the decrease of autumn precipitation and the concentration of winter precipitation. The frequency of drought was also higher than that before the 21st century. Specifically, the frequency of continuous drought in autumn-winter-spring increased from 0.15 times/a before 2000 to 0.25 times/a after 2000. And there were many consecutive seasonal drought events from 2000 to 2010. The intensity of drought was mostly light and moderate and the continuous drought coverage area is mainly characterized by local, followed by regional drought. Particularly, the drought from dry to wet and from wet to dry occurred in the continuous drought of autumn-winter-spring in 1962 and 1997, respectively. 2) There were the outstanding interannual and interdecadal variations of SPEI in the continuous drought of autumn-winter and autumn-winter-spring. The main periods of continuous drought were 9 and 23a, respectively, in autumn-winter and autumn-winter-spring. There was a general cycle of 9-14a. According to the short period, there was some influence of atmospheric circulation on the wet and dry variation. The correlation analysis showed that the dry and wet variations in the continuous drought in autumn-winter were affected mainly by the Southern oscillation index (SOI). And the wet and dry changes in the continuous drought of autumn-winter-spring were significantly correlated with North Atlantic oscillation index (NAO), Southern oscillation index (SOI) and Pacific Decadal oscillation index(PDO). The SOI shared the better characterization for the ENSO. As such, the ENSO events were the main influencing factors on the changes of dry and wet in autumn-winter and autumn-winter-spring. 3) 47.7 % and 54.5 % of the stations showed a downward trend under the continuous drought of autumn-winter and autumn-winter-spring, respectively. Therefore, the spatial distribution pattern of the continuous drought autumn-winter and autumn-winter-spring was roughly dry in the east and west, while wet in the middle. There were the large spatial differences in dry and wet changes in different watersheds. There was the high frequency of the continuous drought of autumn-winter and autumn-winter-spring, indicating the trend of dry early. The Youjiang, Zuojiang and Yujiang River Basin were used to share the great changes in dry and wet alternation, indicating the high frequency of drought. But there was the weakening trend of the continuous drought in autumn-winter and autumn-winter-spring in recent years. Much more attention should be paid to the extreme precipitation and flood in the future. There was some increase in the continuous drought of autumn-winter with a high frequency and a weak trend of early drought rate from northeast to southwest in the Dongjiang River Basin. The high occurrence can be found in the continuous seasonal risk.