There are some systematic biases in prediction of solar radiation based on numerical models, the AVT method has been verified to reduce the prediction bias effectively. The AVT correction method was used to modify the forecasted solar radiation in two photovoltaic power plants in Hexi area of Gansu Province. The results state: (1) Before correction the forecast bias presented obviously diurnal variation with increase first and then decrease, while it wasn’t obvious after correction. There was a strong linear relationship between forecast deviation of solar radiation and observed values before correction, while it got weak after correction (the correlation coefficient and good fitting degree decreased). (2) There was obviously annual change characteristic of solar radiation with the highest forecast bias in spring, followed by summer, autumn and winter. After correction, its forecast bias was reduced in four seasons, especially in spring and summer.

The difference of land-atmosphere energy flux caused by the heterogeneity of underlying surface properties plays an important role in affecting the occurrence of local heavy precipitation. The transition of vegetation is fast in western part of the transition zone of China’s summer monsoon, the nature of vegetation is obviously different, and the surface heterogeneity is strong, so the extreme precipitation is prone to occurrence. In order to explore the influence of underlying surface heterogeneity on strong precipitation in this area, the characteristics of underlying surface were analyzed statistically. And on this basis the sensitivity tests with three or six kinds of landuse type and control test for a typical heavy rainfall process under the influence of the western Pacific subtropical high and cold air from 28 to 29 August 2017 were carried out by using the mesoscale model of WRF3.8 and NCAR-LSM land surface model. The influences of underlying surface change on rainstorm intensity, falling area and flux parameters were studied. The results show that the underlying surface with three to six kinds distributed in transition region of summer monsoon of China. The types of underlying surface were relatively few in eastern part of Qinghai to central Gansu, the heterogeneity was weak, while there were more than six kinds in southeastern part of Northwest China and northern Sichuan, the heterogeneity was strong. The proportion of representative vegetation in a single grid in the model was not high, and the contribution rate to land-atmosphere flux was less than 50%, which indicated that it was not suitable to consider the single underlying surface in calculating land-to-air flux during the heavy rain process. The area of precipitation with different magnitudes was closer to the actual situation with the increase of underlying surface types in the model, and the heterogeneity of land feature physical quantity strengthened in main rain zones. Compared with the control test, the simulated shallow surface temperature, surface heat flux, sensible heat flux and latent heat flux by two sensitivity tests reduced during the daytime, which shrank the bias to some extent, thus decreased convective available potential energy and restrained the occurrence of convective rainfall, further reduced the positive bias of precipitation.

Based on daily meteorological observation data at 227 weather stations of Northwest China during 1962-2017, the decadal change characteristics of drought frequency with different grades including light drought, moderate drought, heavy drought and extreme drought were analyzed by using SPEI index. The results are as follows: (1) The frequency of drought with different grades in Northwest China occurred inter-decadal transition from more to less in the 1980s. The drought mainly occurred in western part of Northwest China before the transition, while it mainly occurred in eastern part of Northwest China after the transition. (2) The frequency of light drought and moderate drought was significantly higher than that of heavy drought and extreme drought, and the frequency of light drought and moderate drought appeared opposite variation tendency after 1980. (3) The spatial difference of drought frequency with different grades was obvious. The light drought and moderate drought mainly occurred in eastern Xinjiang and southern Qinghai, while heavy drought and extreme drought mainly occurred in western part and eastern part of Northwest China, respectively.

The characteristics of surface energy fluxes at Tazhong, Naiman, Pingliang and Jinzhou stations from August to October 2015 and Dingxi station from August to October 2016 were analyzed using observed data obtained from the Drought Meteorology Scientific Research: Mechanism and Disaster Formation Processes of Drought in the North Region of China. Surface radiations over different underlying surface showed significant diurnal variations. Compared to the downward short wave radiation and the downward long wave radiation, the difference between reflected radiation and the upward long wave radiation over different underlying surface was more significant. The reflected radiation and the upward long wave radiation at Tazhong station were the largest, and they were relatively small in Jinzhou station and Pingliang station. Net radiation had significant diurnal variation characteristics. The phase of net radiation and the total radiation was consistent, and the diurnal peak value of net radiation over farmland was larger. The average surface albedo of three months was the largest at Tazhong station (0.27), and then at Dingxi station (0.19), Jinzhou station (0.16), Naiman station (0.15) and Pingliang station (0.14). The sensible heat flux and latent heat flux at 5 stations were single-peak type. The peak value (276 W·m-2) of sensible heat at Naiman station was the largest, and the peak value of latent heat flux at Pingliang station was the largest. The energy dissipation at Dingxi station and Jinzhou station was mainly sensible heat flux, and it was mainly latent heat flux at Pingliang station.