Determining land use influences on the hydrologic regime of the Chao Phraya River Basin, Thailand

Abstract

Water flows and yields in the Chao Phraya River Basin (CPRB) of Thailand were predicted using a soil and water assessment tool model. Three land use change scenarios (SC1–SC3) were simulated to investigate their influences on mean monthly water yields across the 13 sub-basins in the CPRB. The results showed that the changes in water yields in most sub-basins were 0–10%. The high increase in paddy fields but decrease in other agricultural areas in SC1 (90% paddy fields and 10% forestry areas) and SC2 (70% paddy fields, 20% other agricultural areas, and 10% forestry areas) showed a combined influence on the increase in water yields at sub-basin 7. The change was 19.2–57.3% in SC1, 13.9–32.5% in SC2, but a little (0.1–2.1%) in SC3 (40% paddy fields, 50% other agricultural areas, and 10% forestry areas). However, the changing areas of paddy fields contributed to unclear patterns of water yields in the remaining sub-basins; where paddy fields might rely mainly on irrigated water, not rainwater, which is a major source of water yields. The increase in urban and built-up areas showed varied influences on the increase (as the result of precipitation) or decrease (due to specific measures, e.g., increase of green areas or excavation of river channels) in water yields in the river basin. These findings are useful for improving the relevant management measures for the river basin.