In order to deeply understand the water vapor characteristics and sources of persistent rainstorms in the Sichuan Basin and improve the rainstorm forecast capability in this region, the meteorological observation data from 4 955 national and regional automatic meteorological stations in Sichuan Province, the global data assimilation system (GDAS) data, the fifth-generation atmospheric reanalysis (ERA5) from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used to analyze the water vapor transport characteristics of a continuous rainstorm process in August 2020 in the Sichuan Basin by using the Lagrangian method. The results show that the characteristics of water vapor transport at different initial height layers are different before and during the heavy precipitation process. In the middle and high level (from 5 500 to 10 000 m), the low latitude ocean is main source of air mass trajectory before the heavy precipitation occurring, while the southern coast of the Mediterranean is main source of air mass trajectory during the heavy precipitation process and dry and cold air in the middle and high latitude westerlies is brought to the basin. In the middle and lower level (from 1 500 to 5 500 m), during the heavy precipitation process, the source of water vapor trajectory adjusts from the southern coast of the Mediterranean to the low latitude ocean surface and warm and humid air on the low latitude ocean surface is brought to the basin. In the lower level (from ground to 1 500 m), the source of water vapor trajectory first adjusts to the low latitude ocean surface before the heavy precipitation occurring, and warmer and wetter air flow is delivered to the basin compared with the middle and lower level. Quantitative analysis of the water vapor contribution rates of different sources shows that the water vapor from the Bay of Bengal to the Gulf of Thailand is the dominant (66.6%), followed by the Arabian Sea (23.9%), and the South China Sea is the lowest (9.5%).

Based on cloud macro and micro characteristic parameters (hereinafter referred to as cloud parameters) retrieved by the FY-2G geostationary satellite data, the temporal and spatial distribution of cloud characteristic parameters in Qinghai Province and 3 sub-regions from 2018 to 2020 were analyzed.The result show that the annual average cloud top height (CTH), cloud top temperature (CTT), overcooled layer depth (OLD), cloud optical depth (COD), effective radius (ER) and liquid water path (LWP) in Qinghai Province are 3.8 km, -9.7 ℃, 2.0 km, 7.1, 7.1 μm and 63.7 g∙m^-2, respectively. Except for CTT, the monthly variation of cloud parameters in the Qaidam Basin and Northeastern Qinghai Province with the same latitude showed roughly two peaks and two valleys and its peaks basically appeared in May and November, and the valleys basically appeared in August, September, December and January. Each cloud parameter was roughly unimodal in Three River Source Region, with a peak in November. The spatial distribution of annual average of each cloud parameter was roughly distributed along the topography and mountain range. Except for CTT, high-value areas corresponded to high mountains, low-value areas corresponded to desert basins and low-altitude areas, there was a low-value area in four seasons in the Qaidam Basin, and its range was largest in summer. There were obvious high-value areas in the Three River Source Region and the Qilian Mountains in Qinghai in spring and winter. The OLD, COD and LWP in Three River Source region were larger in spring and autumn, OLD and LWP in the northeastern Qinghai region were largest in spring. Spring and autumn were good time for artificial rainfall enhancement for the purpose of water conservation, drought resistance and disaster reduction.

 Based on eddy correlation instrument observation data at 5 observation stations with different underlying surfaces (The underlying surfaces of A’li station, Zhufeng station and Mushitage station are gravel and sparse short grass, and the underlying surfaces of Naqu station and A’rou station are alpine meadow and alpine grassland, respectively.) in the Tibetan plateau in 2013, the actual evaporations were caculated and the correlation between the daily actual evapotranspiration and meteorological factors (net radiation flux,  soil humidity, soil surface temperature, air temperature, wind speed and saturated water vapor pressure difference) were analyzed. The results are as follows: (1) The variation trend of daily actual evapotranspiration on different underlying surfaces was roughly the same, but the variation range was different. The daily actual evapotranspiration and monthly actual evapotranspiration on the underlying surface of the alpine grassland were the most, followed by the underlying surface of the alpine meadow, and on the underlying surface of the gravel sparse short grass it was the least. (2) The variation trends of ground temperature, air temperature and net radiation of different underlying surfaces in the Tibetan plateau were roughly the same, and the daily actual evapotranspirations of the different underlying surfaces were significantly correlated with ground temperature, air temperature and net radiation, while the correlation between wind speed and daily actual evapotranspiration was relatively small. (3) Thermal factors and water supply conditions had a greater impact on the daily actual evapotranspiration of the Tibetan plateau, while dynamic factor had little influence on the actual daily evapotranspiration.

 The SAL quantitative verification method was used to evaluate precipitation forecast  results of the Grapes-Meso model on the rainfall event occurring on 5 September 2018 in Sichuan Province firstly, in this process, the optimal precipitation threshold scheme was selected through combination of three threshold schemes to identify the precipitation body. On this basis, SAL verification was applied to precipitation forecast of three heavy rainfall events in 2018 and rainfall processes from July to September in 2018 in Sichuan Province, and the verification results were compared with test score (TS) to understand prediction effect of the Grapes-Meso model in flood season in Sichuan Province. The conclusions are as follows: (1) The selected threshold determining method could identify the precipitation body well and the “connected neighborhood method” provided a good support for automatic identification of precipitation individuals. (2) The value of L reflected prediction effect of the model on precipitation forecast to a certain extent. If the value of L and the absolute value of A were both small, the probability of better prediction effect was bigger. (3)The overall prediction effect of the Grapes-Meso model on rainfall processes in Sichuan Province showed that the forecasted rainfall intensity was stronger and rainfall range was larger than actual rainfall, or forecasted precipitation center was smaller than the actual, or both cases were existed at the same time.

Based on the data of sea temperature of North Pacific，500 hPa geopotential height over the North Hemisphere and air tern-perature of Ruoqiang，Qiemo and Hetian stations during 1951—2005，the climatic variation of summer high temperature years in South-err Xinjiang and its climatic background were analyzed．Results show that the emergence of summer high temperature in this region is closely connected with the abnormal variations of atmospheric circulation over the North Hemisphere and sea tempe rature of North Pacif-ic．It is also showed that the character indices of the subtropical high over the Northern Hemisphere in the preceding October and Feb-mary have indication for summer temperature in the region．Namely，since January of each high —summer—temperature year of South-ern Xinjiang，the departure distribution of sea temperature which is high in the southwest sea area and low in the northeast has appeared in North Pacific．and often lasted until May．However，sea temperature variations of the two sea areas were diferent，in January and February，the variation is smaller in southwest sea area while bigger in the northeast，on the contrary，it’S biger in the southwest and smaller in the northeast from March to May．

Based on the data of sea temperature of North Pacific，500 hPa geopotential height over the North Hemisphere and air ternperature of Ruoqiang，Qiemo and Hetian stations during 1951—2005，the climatic variation of summer high temperature years in Southerr Xinjiang and its climatic background were analyzed．Results show that the emergence of summer high temperature in this region is closely connected with the abnormal variations of atmospheric circulation over the North Hemisphere and sea tempe rature of North Pacific．It is also showed that the character indices of the subtropical high over the Northern Hemisphere in the preceding October and Febmary have indication for summer temperature in the region．Namely，since January of each high —summer—temperature year of Southern Xinjiang，the departure distribution of sea temperature which is high in the southwest sea area and low in the northeast has appeared in North Pacific．and often lasted until May．However，sea temperature variations of the two sea areas were diferent，in January and February，the variation is smaller in southwest sea area while bigger in the northeast，on the contrary，it’S biger in the southwest and smaller in the northeast from March to May．