Xin’an River Basin is a typical water-abundant area. Characteristics exploration of the drought events and study on the response of hydrological drought to meteorological drought in Xin’an River Basin largely benefits the scientific reference for basin water management. This study calculated the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) with the monthly data of inflow runoff and precipitation from 1960 to 2022 in Xin’an River Basin. Based on SPI and SRI, the evolution of meteorological and hydrological droughts under different time scales and the seasonal response of hydrological drought to meteorological drought were analyzed. The results are as follows: (1) From 1960 to 2022, meteorological and hydrological droughts in the Xin’an River Basin mainly occurred in the 1960s, late 1970s to mid-1980s and early 2000s. Meteorological and hydrological droughts have rarely occurred since the 21st century; dry and wet alternated frequently over the remaining periods of time. (2) Mann-Kendall trend test results show a wetting trend during the past 63 years, and the effects of drought have mitigated. While in winter and summer, it showed drought decreasing trend in the basin. The hydrological trend of becoming wet was more obvious than that of meteorological. (3) The correlation between hydrological drought and meteorological drought in Xin’an River is high. Also, the hydrological drought lags behind the meteorological drought for 1-3 months. The seasonal response of hydrological drought to meteorological drought in flood season shows higher correlation and faster speed than that in dry season. Because of the quick response of hydrological drought to meteorological drought in flood season, more focus and targeted steps should be taken on the drought state of the basin in the flood season.

Based on meteorological observation data, Doppler radar (CINRAD/CA) observation data, global topography data (1°×1°) and NCEP FNL 6-hour reanalysis data (1°×1°), the blizzard weather in spring in southeastern Inner Mongolia on 20 March 2019 was analyzed. The results show that the process was a typical backflow heavy snowstorm weather, the southwesterly warm and humid air at 700 hPa climbed along the low-level cold pad to produce frontogenesis, which was the main cause of this backflow blizzard. Obvious vertical wind shear and temperature differences generated because of the northeasterly jet at 925 hPa and southwesterly jet at 700 hPa, resulting in strong dynamic frontogenesis, and the dynamic frontogenesis mechanism played a significant role. The convergence of divergence at low-level was conducive to development of vertical upward movement. The southerly and easterly at 850 hPa transported water vapor to the southeast of Inner Mongolia. There was a strong inversion stratification between 850 hPa and 700 hPa, where the cold and warm air met violently. The north-south topography of the Greater Khingan Mountains had a blocking effect on the northeasterly ultra-low-level jet stream on the windward slope of the eastern foothills, which was conducive to accumulation of dry and cold air for a long time and increasing thickness of the cold pad in lower layer. Then the warm and humid air flow was forced to lift to higher layer, which was conducive to condensation of water vapor and increase of snowfall. At the strongest period of snowfall, there was a northerly in lower layer, and an obvious “S” shape in middle layer for warm advection on the radial velocity chart of radar. At the upper level, there was a southwesterly jet maintaining for a long time, and the shear lines of northwest-southwesterly wind and southwest-southeasterly wind maintained at the same time. There was a good correspondence between the strong snowfall and the warm and humid jet from southwest climbing on the cold pad on the radar radial velocity chart, which was instructive for short-term forecast and early warning.