Application of non-parametric approaches to identify trends in streamflow for the Mae Klong River Basin, Thailand

Abstract

Mean monthly streamflow records of ten gauging stations in the Mae Klong River Basin, Thailand, were analyzed for trends using non-parametric approaches for the period 2000–2015. The statistical significance of trends was tested on monthly, seasonal, and annual scales using three non-parametric tests; Mann–Kendall (MK), Spearman’s rho (SR), and innovative trend analysis (ITA) on a 5% significance level. The streamflow stations were grouped into two categories: naturalized streamflow (four stations) and regulated streamflow (six stations). In both the dry and wet seasons, decreasing trends were observed in the naturalized inflows to the Srinagarind and Vajiralongkorn Dams. On an annual basis, all the naturalized streamflow stations showed decreasing trends. For the regulated streamflow stations, in the dry season, four out of six stations showed increasing trends, while in the wet season, five out of six stations indicated decreasing trends. On an annual basis, five stations showed decreasing trends by both the MK and SR tests, while the ITA method indicated decreasing trends for four regulated streamflow stations. The results of this study can help water resources managers for better assessment and planning of water resources in the basin.