were used together with infiltration model based on the local rainfall pattern in order to investigate the change in slope stability with time. Unsaturated flow was considered to represent the more realistic infiltration behavior. Fig. 4 gives illustrative example of this concept. The moisture content that would bring about the factor of safety to a value of 1.0 for each slope was calculated. This moisture content was called the Critical Antecedent Moisture Index or Critical Antecedent Precipitation Index (CAPE) which has the unit of mm. These critical API values together-with the initially proposed API values by the Department of Water Resources (2008) are now utilized in Thailand for the issuance of landslide and flooding early warning. The critical API value is shown in Fig. 5. If the curve goes beyond this line, landslide is likely to occur.