Study on Effect of Climate Change on Hydrological Response in the Xe Bang Fai River Basin

Abstract

The Xe Bang Fai river basin is a sub-basin of the Mekong River Basin. The significant activity of agricultural land management in this basin area is cropping such as rice and vegetables plantation. All of these have been being grown well. The sector of agriculture is the significant part of irrigated region, additionally over the decades quick outgrowth of population, industrialization and urbanization, especially transforms in activities of social and economic sector, have affected to enlarged, but the amount of streams flow in watershed are declining continuously. The Xe Bang Fai river basin is provisionally flooded due to Typhoon, which is affected from climate change nowadays, during wet season. Severe heavy rainfall has continuously been found in this basin area, in which it has been become a cause of floods at downstream of the Xe Bang Fai river basin. Besides that, the precipitation is main variant in each year, but the precipitation intenseness is great, which this is pretty normal in the region of central Lao PDR. Consequently, the major objective of this thesis is to assess the climate variation on hydrology of the Xe Bang Fai river basin in Laos applying data driven and modeling methods. In Chapter 2 represents the trends of annual and seasonal precipitation and additionally the trends of annual temperature in the Xe Bang Fai river basin, Lao PDR was evaluated using the Mann-Kendall test and Sens Slope estimates method (MAKESENS). The purpose of this study is to look for the effect of climate variation by discussing a relationship with the current enlargement of hazardous natural disasters. The increased trend of precipitation, for instance annual monthly maximum etc., was observed at Signo and Mahaxay stations in the northern part of the Xe Bang Fai river basin. The annual decreased trend of precipitation related to drought risk was additionally observed at Donghen and Xepon stations in the southern part of the Xe Bang Fai river basin. The results of this study offer significant formation to manage the water resources in the basin area. In Chapter 3 represents the river discharge simulation of the Xe Bang Fai river basin by using SWAT model. The hydrological model was successfully calibrated and validated in this basin by applying SUFI-2 algorithm. In the SWAT model, the sensitivity analysis of the hydrological model, the discharge parameter is not sensitive, but also the parameter of HRUs delineation thresholds followed by sub-watershed continuous affectation. The result of study indicated that 716 HRUs are suitable in this basin, in which the represented SUFI-2 algorithm is be modified while simulating flow in the Xe Bang Fai river basin. The calibration and validation model are implemented in the two periods: calibration periods (2001-2005) and validation period (2006-2010). In this study, the results of the monthly river discharge simulation R2 and ENS are 0.970 and 0.967 during the calibration periods and also 0.966 and 0.960 during the validation period. The SWAT model can generate good simulation results of monthly time processes which they are valuable for water resources management in the Xe Bang Fai river basin as well as the whole sub-watershed in the Mekong river basin. The model was already calibrated successfully. It can be applied for more analysis of climate variation and land use changes as well as other distinct management models on the hydrology. In Chapter 4 represents the comparing calibrated model was run with the three climate change scenarios offered by the Mekong River Commission (MRC). In this study, these climate change scenarios were reconsidered to run the model during the period: 2001-2010 with the change factors of climate (IPSL CM5A-MR, GISS E2-R-CC and GFDL CM3) to design the surface runoff for the year 2030. Various research institutes studied the climate change factors, as the result IPSL CM5A-MR 2030, GISS E2-R-CC 2030 and GFDL CM3 2030, which represented the discharge in both dry season and wet season. In the study, the results of IPSL 2030, the discharge in the dry season (Feb-May) are lower than the baseline, while the end of the wet season is above the baseline. In the river discharge, the scenarios of climate change produced more 800 m3/s for the months including July, August and September on the baseline of the Xebangfai@bridge station. The cause of the peak discharge in these months is the effect of southwest monsoon, which affects commonly the watersheds from middle of May to early October (wet season). This is predominant phenomena when air pressure is low more than Laos and result in heavy rainfall. The severe variation was found with three scenarios (IPSL CM5A-MR 2030, GISS E2-R-CC 2030 and GFDL CM3 2030), which causes the high volume monthly runoff, raises the large monthly runoff duration by expanding the large runoff season until the first week on September. The results of model simulation with the scenarios of climate change can be applied for preferable information in future researches. Overall of this study concentrated on the effects of climate change on hydrological response in the Xe Bang Fai river basin, Lao PDR. After analyzing precipitation and temperature trends in this basin, the procedure conducted the model calibration and validation of stream flow. The following chapters, then, the study concentrated on the scenarios of climate change to design surface runoff for the period of year 2030s in this basin. The results gained in this study increase the knowledge of climate change effects on hydrological response in Laos. In addition, the results of the study can be provided beneficial information to plan water resources management, especially Nam Theun 2 Dam for water management and also it will be useful information for planning flood disaster risk management in the Xe Bang Fai river basin. Moreover, the study offers valuable information to plan for developing hydropower project and flood disaster risk reduction by following Laos government strategy on 8th National Social-Economic Development Plan (2016-2020) about adaptation on climate change which are essential for the sustainable development of Lao PDR in the future. Keyword: Climate Change, Hydrological Model, SWAT Model, Xe Bang Fai river basin, Mann-Kendall and Sens Slope Method. Student Number: 2013-31271