In the flood season (from June to August) of 2020, Gansu Province experienced intensive precipitation with long duration and wide ranges. The performances of three global models (ECMWF, GRAPES_GFS and NCEP_GFS) and four regional models (GRAPES_3 km, GRAPES_LZ10 km, GRAPES_LZ3 km and regional model SMS-WARMS in East China) for 24-hour accumulated precipitation forecast were evaluated in this paper. The main results are as follows: (1) The ECMWF model surpassed the other two global models in forecast performance, while among regional models, the GRAPES_3 km and the SMS-WARMS were better, and the latter was more stable. (2) The regional models had lower accuracy of rain probability forecast and TS, ETS, POD than those of global models for light and moderate rain, but for rainstorms they outperformed global models; the POD and Bias of regional models for heavy rain and rainstorms were significantly higher than those of global models. (3) According to the differences of 500 hPa circulation pattern, the precipitation in Gansu could be divided into two types including subtropical high marginal type and low trough type. Four subtropical high marginal precipitation processes and three low trough precipitation processes in flood season of 2020 were tested and evaluated. For global models and regional models, they all had better capability in predicting precipitation with different magnitudes for the former type than the latter one. The ECMWF model and regional models were better than the NCEP_GFS model and the GRAPES_GFS model in predicting heavy rain and rainstorm. Among global models, the ECMWF model had the best forecast effect for the two precipitation types, and the East China regional model had the best forecast effect for the two precipitation types among regional models. (4) All the seven models had good forecasting capability for the spatial orientation of moderate and heavy rain for both rainfall types, while the forecast effect of rainfall location for subtropical high marginal type was better than that of low-trough type, but the predicted precipitation intensity was stronger than observations, especially for the center of precipitation.

Based on hourly precipitation data at 146 automatic weather stations of Lanzhou from 2012 to 2019, the refined characteristics of precipitation in Lanzhou were analyzed from different time scales. The results are as follows: (1) The average annual precipitation was less in the north and more in the south of Lanzhou, and that was more in the edge and less in the interior from 2012 to 2019. The inter-annual change of precipitation was obvious from 2012 to 2019, the precipitation in 2018 was abnormally more by 46%, while that in 2015 and 2017 was abnormally less, especially in 2015 it was less by 30%. (2) The precipitation mainly concentrated in July and August in Lanzhou, and it in the south was obviously more than that in the north due to the influence of atmospheric circulation situations, while the spatial difference of precipitation wasn’t obvious in other months. (3) The diurnal variation of rainfall was obvious in Lanzhou, the precipitation was less in morning and more at night, and the range of rainfall was larger at night and smaller in the daytime. The precipitation in urban areas was generally less than that in mountain areas under the influence of altitude, and it mostly concentrated from afternoon to evening due to heat island effect, the convective rainfall was more, while the diurnal distribution of rainfall was more uniform in mountain areas, the fluctuation was smaller as a whole. (4) Overall, the frequency of short-time heavy rainfall in Anning district of Lanzhou was the highest, but the short-time heavy rainfall at Liuhe station of Gaolan county and Xujiamo station of Yongdeng county was the most frequent, and that in Yongdeng county was a critical concern.

Based on the hourly precipitation data at 81 national meteorological observation stations of Gansu Province from 1981 to 2018 and NCEP reanalysis data, the climate and circulation characteristics of extreme rainstorms were emphatically analyzed in different falling areas of Gansu Province. The results are as follows: (1) The extreme rainstorm weathers occurred mainly in Longnan, Tianshui, Pingliang and Qingyang of eastern Gansu, and the heavy rainfall centers concentrated in Kangxian and Huixian of Longnan. The extreme rainstorms were classified into four types including eastern Gansu, southern Gansu, southeastern Gansu and dispersion patterns, according to the falling areas of rainstorms. (2) The extreme rainstorms were easily to occur in July and August in Gansu, especially in mid-August. The extreme rainstorms in southern Gansu were earlier than in eastern Gansu. The precipitation of extreme rainstorms at night was more than in the daytime as a whole, the night rain characteristic was remarkable in Gansu, especially in southern Gansu and southeastern Gansu. In additional, the convective characteristic was significant in Gansu. (3) There were 2.5, 5 and 10 years period of extreme rainstorms in Gansu during 1981-2018, and the 2.5-year periodic oscillation was obvious. (4) The extreme rainstorms in Gansu were correlated with the subtropical high, and the falling area of rainstorm was significantly related to the location of subtropical high. Moreover, the extreme rainstorms in eastern Gansu were also related to the easterly airflow at the bottom of northern high ridge, the extreme rainstorms with dispersion pattern were related to the tropical low pressure in South China Sea, while the extreme rainstorms in southern and southeastern Gansu depended on the intensity and location of short-wave trough in Tibet Plateau.

Based on conventional meteorological observation data, FY4A satellite data, vegetation cover data and reanalysis data, the formation mechanism, transmission characteristics and influencing factors of a largescale severe dust storm occurring from March 14 to 18, 2021 in northern China were analyzed. The results are as follows: (1) Drought, high  temperature, less rainfall and low vegetation coverage in the earlier period in most parts of northern China provided a good sand source condition for occurrence of the strong sand dust storm weather. (2) The dust weather was caused by the strong development of Mongolia cyclone and the combined action of cold high pressure behind it. (3) The dust weather process was divided into two stages. At the first stage it was caused by the strong winds passing behind the ground cold front, which mainly occurred in North China and Northeast China. At the second stage it was caused by the southward diffusion of highaltitude dust that did not dissipate at the early stage and the backflow of east wind, which mainly occurred in Northwestern China. (4) The analysis of physical quantities such as horizontal helicity, the mixing layer height and vertical velocity showed that the dust emission conditions were insufficient in most areas of China, so the sand dust weather was mainly affected by the upstream sand dust transportation. For the eastern region of China, the contribution of dust storm was mainly from the southern part of Mongolia. While in Northwest China it was mainly contributed by Mongolia and its own dust.