Response of typical large-scale persistent drought events to atmospheric circulation in China

Frequent drought has posed widespread, large-scale and extremely severe impact on the ecological environment under global climate and human activities. This study aims to analyze the spatiotemporal dynamic evolution of drought in China. A threshold of -0.5 was chosen to identify drought conditions. A raster was set as the drought state at standardized precipitation evapotranspiration index (SPEI) less than -0.5. The start and end times of drought were varied for each raster within a single event, indicating the dynamic and evolving drought. At the same time, some rasters exited the drought states, while others entering. The contribution rates of drought to rasters were calculated at a given time, in order to capture the dynamic changes in drought. Three perspectives were considered: the extent of drought impact, duration, and severity. The SPEI was then used to assess the drought, in order to introduce the concept of persistent drought rasters. Large-scale and persistent drought events were identified to investigate the spatiotemporal dynamic evolution from 1961 to 2020, together with their response mechanisms to the atmospheric circulation. The research findings can be summarized as follows: 1) A total of 47 events occurred between 1961 and 2020. The 1970s witnessed the highest frequency of large-scale persistent drought events, with 10 occurrences, while the 2000s and 2010s each experienced 9 such events. The average duration of these drought events was 7.14 months, with the longest average duration in the 1960s at 11.83 months. The average extent was 28.66%, with the highest average extent index reaching 33.75% in the 2000s.The average severity was -2.86 for the 47 large-scale persistent drought events. Between 1980 and 2010, the average area affected by persistent drought events each decade showed a continuous expanding trend. Between 1970 and 2020, the average duration of persistent drought events each decade was concentrated between 4 to 8 months. 2) Before the 1990s, the lag time of Oceanic Niño Index's impact on spring precipitation was 3 and 9 months. From then on, the ONI's influence on summer and autumn precipitation extended to 6, 9, and 12 months. Once La Niña events occurred, there was the decrease in the spring precipitation, thereby increasing the frequency of spring droughts in China. 3) There was a resonance period of 16-48 months between ONI and SPEI3 during the years 1961-1976, 1980-1988, 1994-2001, and 2006-2020. The ONI index also demonstrated the strongest correlation with SPEI3 in this timeframe. While the WP index exhibited the weakest correlation with SPEI3 during the same periods.The research results help further understand the causes and patterns of drought in China, thereby enhancing the scientific basis and precision of drought prevention and mitigation policies.