Regional drought process and its variation characteristics in the middle-lower reaches of the Yangtze River from 1961 to 2019

Objectively identifying regional drought processes and assessing their intensity is the operational basis for conducting accurate and detailed monitoring and assessment of drought impacts. Based on daily temperature and precipitation data collected at 502 national meteorological stations from 1961 to 2019 and the historical drought disaster information from 1971 to 2019 in the middle-lower reaches of the Yangtze River, 126 regional drought processes in the middle-lower reaches of the Yangtze River were identified using the meteorological drought composite index (MCI) and regional drought process identification method. The number of drought processes decreases obviously with the increase of duration days, and the determination coefficient reaches 0.89. From 1961 to 2019, there were 6 extremely strong regional drought processes, 19 strong regional drought processes and 38 sub strong regional drought processes in the middle-lower reaches of the Yangtze River, and the remaining 63 were general regional drought processes. The variation trend of duration days, average intensity, average affected area and comprehensive intensity index of regional drought processes present different forms. The distribution of annual drought days in the middle-lower reaches of the Yangtze River is generally "more in the north than in the south, more in the plain than in the mountainous area", and the trend shows a pattern of "increasing in the northwest and decreasing in the southeast". The variation trend of drought days is consistent with that of drought affected area, and the correlation coefficient reaches 0.66. According to the monitoring and assessment of typical regional drought processes, there is an obvious positive correlation between the comprehensive drought intensity index and the number of stations that experienced drought. The stronger the comprehensive drought intensity index, the larger the number of stations experiencing various levels of drought. The number of drought days in different regions is consistent with the size of drought disaster area. The more drought days, the greater the drought disaster area. In general, results of identification and assessment of regional drought processes are consistent with drought disaster information. The method of identification and assessment of regional drought processes can well identify the regional drought process, and monitor and assessment the drought process from the perspectives of duration days, average intensity, average affected area and comprehensive drought intensity.