An automatic weather station can directly measure the rainfall of a single station or within a small range with higher precision,but it often omits severe rainfall centers or gusts because of its inadequate distribution density.Radars can probe the structure of clouds and precipitation,trace them from beginning to the end in real time,and provide the real-time precipitation of a specific region rapidly,but their measurement errors are relatively large and the precision of local rainfall measurements is not high.Combining automatic weather stations with radars,applying mathematical methods and GIS techniques,the areal rainfall that represents the mean rainfall of a specific region can be obtained.As an example of deducing the areal rainfall,the regression relationship between six-minute accumulative rain by automatic weather stations and radar echoes over Shenzhen is established by means of GIS techniques and the geographic modification of the three factors(longitude,latitude,and sea level elevation).The calculation model of the area rainfall of a specific area on radar map is developed;and then the high-precision high-resolution(spatial) grid fitting rainfall is gained;thus the areal rainfall distribution of a specific area from radar map is obtained.