Figure 5 shows the time series of the daily area average rainfall of gauge and TRMM 3B42. The bias is -0.88 mm/day and the RMSD is 9.7096 mm/day. It is interesting to note that the bias of the area average is smaller than the monthly for 3B42. We also calculate the daily bias for different seasons for all different regions, the results of which are shown in Table 2. TRMM 3B42 is higher than gauges except in the JJA season in the east region of Thailand, which is near the Gulf of Thailand.