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.