The Local Observed Trends and Variability in Rainfall Indices Over the Past Century of the Yom River Basin, Thailand

Abstract

A changing rainfall pattern can directly affect the frequency of occurrence of extreme event such as floods and droughts. These extreme events will cause future political conflicts, especially those dealing with water supply and flood management. The purpose of this study is to examine the variability of rainfall in the Yom River basin, Thailand, during the past 90 years . Based on rainfall data from 13 hydrological stations, long-term trends inrainfall and various rainfall-related extreme events, which consist of the annual total precipitation (PRCPTOT), consecutive dry days (CDD), consecutive wet days (CWD), number of heavy rainfall days (R10), number of very heavy rainfall days (R20), daily maximum rainfall (Rmax1), five-day maximum rainfall (Rmax5), and annual total rainy day (Rday) in the Yom River basin, were analyzed using the Mann-Kendall method with 95% confident level. The results suggest that for the PRCPTOT, Rmax1, and Rmax5 indices have experienced a significant increase trend in the western part of basin area. In addition, the decreasing trend was observed over 55% of basin considering for the CDD indices. Meanwhile, the CWD was found an increasing trend approximately 77% of the basin area except in the lower Yom River basin. Result of the annual total rainy day reveal significant decrease trend around 44% of the southern part of the basin. However, the analyses of heavy and very heavy rainfall show a significantly increasing trend at the lower part of the Yom river basin. These results suggest that the trend of flooding has significantly increased along the western part of the Yom River basin. Meanwhile, the tendency of drought events is increasing in middle portion of the basin. The impacts of changes in rainfall pattern in the Yom River basin should be considered in the future water resources planning and management of the country.