In order to make a further understand of the difference and representativeness between gridded merging real-time product and observed data, the paper evaluated and corrected the CLDAS 2 m temperature merging product based on the observational data of automatic stations in Lanzhou and Wuwei region. The results are as follows: (1) The hourly temperature and daily minimum temperature products are lower than observations, and these errors decrease with the altitude going up below 2 500 m. The mean error of the daily maximum temperature product is negative around the altitude of 1 500 m, and changes to positive values above 1 500 m, then the positive mean error increases with the increase of altitude. The errors of daily maximum and minimum temperature are larger than those of hourly temperature, but their mean errors are all within 2 ℃. (2) The near gridding validation further shows that the diurnal change of CLDAS hourly temperature is generally similar to observations in the daytime, while it is relatively 0.2 ℃ lower than observations at night. The daily average temperature of CLDAS merging product is generally lower about 1 ℃, and the negative deviation in Lanzhou urban area is relatively small. Spatial distribution of high temperature days above 30 ℃ of merging products is basically consistent with observations, but there are more actual high temperature days in Lanzhou urban area. (3) Both the linear regression and the decaying averaging method have a certain correction effect on CLDAS temperature merging products, and the latter has a better correction effect. The correction effect becomes better with the altitude increasing. To sum up, the CDLAS temperature merging products can better reflect the characteristics of actual temperature change in Lanzhou and Wuwei region, but its ability to reflect the daily maximum and minimum temperature is not as good as the hourly temperature, and the error is relatively large in complex terrain.

An extremely heavy rainstorm occurred on 14-15 July 2022 in Longdong, Gansu Province, which is located in semi-arid region, the daily rainfall and hourly rainfall intensity at several stations broke the historical extreme values. Based on the minutely and hourly precipitation observation data from 20:00 BST 14 to 20:00 BST 15 July 2022, the daily and hourly precipitation data from 192 regional meteorological stations since the establishment of them in Qingyang of Gansu Province, and the CMPAS (CMA Multi-source Merged Precipitation Analysis System) 10-minute and hourly precipitation data, the precipitation characteristics and extremity of the torrential rain event are analyzed. The results show that the extremely torrential rain event is characterized by large cumulative precipitation, concentrated rainfall area of rainstorm and above, strong convective precipitation, stable and less movement of the rainfall centers, and long duration of short-term strong precipitation, among which the extremities of cumulative precipitation, hourly precipitation intensity and short-term heavy precipitation duration are obvious. The heavy rainstorm center, Zhaijiahe station, is located in the middle and north part of Qingcheng County, the maximum accumulated rainfall is 373.2 mm, which is the maximum since the station establishment, and is nearly twice of daily precipitation extreme values at all national stations in Gansu Province. The maximum hourly rainfall is 84.9 mm, ranking the third in historical records at all stations in Qingyang, and the longest duration of short-term strong rainfall is as long as 6 hours, which is the maximum in historical records at all stations in Qingyang since establishment of them. The evolution of minutely precipitation shows that the precipitation intensity in the heavy precipitation center has pulsating change, and the precipitation location has swing in the east, west, south and north, but the swing amplitude is small.