Predicting Hydrologic Response to Climate Change in Upper Nan Sub-watershed Using IFAS Model

Abstract

This research aims to predict the hydrological response using Integrated Flood Analysis  (IFAS) model in upper Nan sub-watershed. The rainfall amount data for the past 30 years (1986 - 2015) which are classified as normal and La Nina year. Moreover, predicted runoff from climate change scenario (2050 and 2070 yr.) which based on the global climate change forecast model (GCM) under RCP 8.5 of The UN Intergovernmental Panel on Climate Change (IPCC) issue 5. Then some hydrological characteristics include a percentage of rainfall runoff ratio, specific yield, total flow and peak flow were analyzed. The results found that the annual average runoff during 1986 - 2015 was 3,446.19 m³/s which is highest in the year of La Nina (2011) as 4,893.24 m³/s. It was found that the IFAS model performs well in predicting runoff compared with measurement data with the NSE ranged 0.81 to 0.83 and the percentage error ranged 1.45 – 24.11%. While, runoff estimation during the climate change scenario was predicted in 2050 and 2070 years. The average annual runoff were 1,736.88 and 1,795.85 m³/s, respectively and lower than normal years as 13.1% and 10.2%, respectively. Beside, some hydrological characteristics in the upper Nan sub-watershed found that percentage of rainfall runoff was 17.29%, specific yield was 10.78 m³/s/km²/year, total flow was 23,989.62 m³/s and peak flow was 367.44 m³/s. It can be implied that IFAS model can perform well to predict streamflow in the upper Nan sub-watershed and less effect a climate change on streamflow.