Change Characteristics of Daily,Monthly and Annual Solar Radiation in Ningxia Hui Autonomous Region

In this paper,the solar radiation flux and the daily,total monthly and total annual solar radiations at 20 meteorological stations during the period of 1971-2000 are simulated using the observed data of solar radiation at Yinchuan and Guyuan meteorological stations in Ningxia Hui Autonomous Region in 5 years.The results show that the simulated values of solar radiation at Yinchuan Meteorological Station were higher than the observed ones but lower than the observed ones at Guyuan Meteorological Station.The simulated results of solar radiation fluxes at Yinchuan and Guyuan stations were tested with the methods of bias error,mean absolute bias error,root mean square error and mean absolute error.It is found that the root mean square error was slightly higher,the mean absolute bias error was lower than 13% and 17% at Yinchuan and Guyuan stations respectively.Regionally,the simulated and observed values of total monthly solar radiation are in a decrease trend at Yinchuan Station in the north where it is arid.There is an increase trend in March,April,May and June,a slight increase trend in July,and a decrease trend in other months at Guyuan Station in the south where it is rainy.The total observed annual solar radiation is in a slight increase trend,and the accumulated simulated value is stable.The total annual solar radiation is significantly increased at most stations but significantly decreased at a few stations.