Response of the flood peak to the spatial distribution of rainfall in the Yom River basin, Thailand

The response of the flood peak to the spatial distribution of rainfall has been reported in basins with nonuniform characteristics. However, prioritization of the influences of these characteristics is still poorly understood. This study evaluated the variability in the flood peak with the spatial distribution of rainfall at Sukhothai (city) in the Yom River basin, Thailand, and investigated the influence of the basin characteristics on the flood peak. For each of the 2-, 5- and 10-y rainfalls with durations of 24, 48 and 72 h, 1000 simulated rainfall events with various spatial distributions were generated according to the observed data by using a Monte Carlo analysis and Cholesky randomization. The floods from these rainfalls were then simulated, and the peak discharges were evaluated. The flood peaks from 24-h rainfalls were usually small but highly variable and could be extremely large when the rainfalls were concentrated over the mountainous region. The flood peaks from 48 to 72-h rainfalls were consistently large and correlated with the rainfalls over the joint area between the mountainous region and plain area. The basin characteristics that influenced the response of the flood peak to the spatial distribution of the rainfall appeared to depend on the rainfall duration and magnitude. For short-duration rainfalls, the response was mainly influenced by the surface storage when the rainfall was small and by the terrain steepness when the rainfall was large. For long-duration rainfalls, the response was mainly influenced by the soil percolation rate.