Hydrological response to climate and land use change in the forested watersheds of Thailand | |
| Author | Jessada Techamahasaranont |
| Call Number | AIT Diss no.WM-19-01 |
| Subject(s) | Land use--Thailand Watersheds--Thailandll Forest hydrology Climatic changes |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Water Engineering and Management, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WM-19-01 |
| Abstract | Thailand has undergone significant forest cover changes in recent decades, and this is likely to have altered the hydrological functioning of many watersheds; however, such potential impacts are not fully understood. In addition, hypotheses involving long term forest cover in mountainous areas could change according to the hydrological properties and when mountainous watersheds degrade forestation, it has a significant effect. To contribute towards a better understanding of the potential hydrological impacts of forest cover changes, this study examines the temporal trends in long-term data (25–34 years) from eight watersheds in Thailand over the period from 1982–2015. Seven hydrological indices (runoff coefficient, dryness index, baseflow index, high flow, medium flow, low flow, and streamflow elasticity) were analyzed using a combined Mann-Kendall trend-testing approach, to assess the magnitude and significance of patterns in the observed data. The results indicate that two watersheds, particularly those undergoing reforestation and rubber plantation, show different trends in hydrological response compared to other watersheds covered with evergreen and deciduous forest. This trend can be attributed to the disturbances in physical properties of the watershed due to plantation activities. Watersheds covered with evergreen and deciduous forest show an increasing trend in baseflow compared to those with reforestation and para rubber plantations. This can be attributed to the increase in forest cover and good water storage capacity in undisturbed watersheds. Watersheds covered with evergreen and deciduous forest show an insignificant increasing trend of high flow (Q5) and low flow (Q95), whereas these flows show a significant decreasing trend in watersheds which have undergone rubber plantation. Since watersheds covered with evergreen and deciduous forest increase water storage capacity, particularly baseflow, watershed managers could plant these tree species in deforested watersheds to increase water availability. An analysis of climate change and land use change impacts on the seven hydrological indices in the selected watershed (Huai Linthin) found three future climate change scenarios (2010–2050), namely RCP4.5, RCP8.5 and a historical trend of rainfall for results generated from the SWAT model. The land use change scenarios were determined into five cases: fixed land use in 2015 (LUFix); continual land use change according to historical trend (LUCon); maintaining 40% of forest area and increasing orchard by 2050 (LUF-O); maintaining 40% of forest area and increasing agriculture by 2050 (LUF-A); and converting areas with less than a 35% slope to agriculture (LUS35). The results indicate that the rainfall factor, especially for the CC4.5 scenario, show that a decreasing trend in the future is influenced by the runoff coefficient and high flow (Q5). The future rainfall in CCH and CC8.5 scenarios show increasing trends, affecting the baseflow index (BFI) and low flow (Q95). Land use change scenarios are shown to have an insignificant effect on all hydrological indices since this watershed is mostly covered by natural forest with several canopy layers, deep soil and high soil infiltration. Therefore, the hydrological properties of the HLTn watershed are shown to be more affected by climate conditions than land use/land cover change. Watershed management for highland requires in-depth study since the climate factor is uncontrollable for highland management. |
| Year | 2019 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-19-01 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Shrestha, Sangam; |
| Examination Committee(s) | Babel, Mukand S. ;Shrestha, Rajendra Prasad ;Duc Hoang Nguyen;So Kazama; |
| Scholarship Donor(s) | Kasetsart University Chalermphrakiat Sakon Nakhon Province Campus (KUCSC) ;National Research Council of Thailand (NRCT); |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2019 |