Thailand has a dry season during December to April and a rainy season starting from May to September. The study domain for analyses rainfall over Thailand, firstly focused over latitude 10°N during 10°N to 21°N during June, July and August (JJA), because JJA is rainy season over this domain and secondly focused on below latitude 10°N during 5°N to 10°N during September, October and November (SON), because this season is rainy season over this domain. For the winter is the December, January and February (DJF) and the summer is the March, April and May (MAM) (Roongroj Chokngamwong and Long S.Chiu, 2004). The climatology is the long-term average of data over Thailand from APHRODITE’s data during 1951 to 2007. It is studied the mean of rainfall seasonal data over Thailand with resolution as shown in Figure 3.5.