Regionalization Of Rainfall In Northeastern Thailand

Abstract

Rainfall is one of the most valuable natural resources for northeastern Thailand, a region whose livelihood of more than 80% of the population depend predominantly on rainfed agriculture. Rainfall events can also cause severe natural hazard, therefore proper water resources and flood management is crucial to this region. Regionalization of rainfall can facilitate the management of water resources and floods by delineating a region with rainfall patterns that vary in both time and space into areas with more homogeneous rainfall characteristics. This study applied both hierarchical and K-means clustering methods to separate the entire Northeast into three precipitation zones using monthly rainfall data from 38 stations over 30 years from 1987 to 2016. The temporal variation of zoning was also investigated by dividing the data into three 10-year periods, 1987-1996, 1997-2006, and 2007-2016. The regionalization by both methods gave similar results that are comparable to the mean annual rainfall of the entire region. Mean annual rainfall values were highest in the northeastern part of the region with a gradual decreasing trend to the southwest. The clustering methods, on the other hand resulted in the highest rainfall zone in the northern part, the moderate rainfall on the southeastern, and the lowest on the southwestern part. As it relates to temporal variation, the results from 1987-1996 for both methods are mostly the same but those from 1997-2006 and 2007-2016 are not quite the same especially results from the last decade. Homogeneous rainfall regionalization by clustering methods is preferable to merely geographical and mean annual rainfall values because they take into account several factors such as monthly rainfall distribution.