Spatial and temporal rainfall distribution in Phetchaburi

The variation of rainfall distribution with respect to times and areas, if excessively large in magnitude, can cause the flood and drought to the areas. Phetchaburi province is located in the upper south region close to the Gulf of Thailand. During the past decades, the province encountered frequently the variation of rainfall distribution causing either flood or drought that occurred every 2-3 years. This study was done to collect and analyze the rainfall data to determine the statistical characteristics of spatial and temporal rainfall distribution of the 8 districts in Phetchaburi. The annual rainfall data was considered in the duration years 1970-2025 to investigate the difference of rainfall statistics between the total duration and the sub durations. For temporal rainfall distribution of annual rainfall depths, the maximum, mean, minimum, standard deviation and coefficient of variation were determined. For spatial rainfall distribution of annual rainfall depths, the mean annual rainfall depths of the districts were compared and the coefficients of correlation were determined. Comparing the mean annual rainfall depths between the districts, the difference of rainfall depths did not exceed 6%. The mountainous western region had the average annual rainfall 5.5% less than the lowland eastern region, indicating the topographic effect on the annual rainfall. The maximum annual rainfall depth occurred in the year 1972 at 43% above the mean annual rainfall depth. The minimum annual rainfall depth occurred in the year 2023 at 37% below the mean annual rainfall depth. The coefficient of variation of annual rainfall depths was 18%, indicating the large variation of rainfall and causing the risk of the flood and drought problems.