Climate change and land use change impacts on hydro meteorological extremes in the Mun River Basin, Thailand | |
| Author | Khadka, Dibesh |
| Call Number | AIT Diss. no.WM-21-02 |
| Subject(s) | Climatic changes--Thailand--Mun River Basin Land use--Thailand--Mun River Basin Hydrometeorology--Thailand--Mun River Basin |
| 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-21-02 |
| Abstract | Climate change (CC) is expected to exacerbate the hydro-meteorological extremes in the future. Improving the climate projections and quantifying the plausible future extremes are paramount in understanding climate-related risks and formulating suitable policies. In addition to CC, land-use changes (LUC) may also amplify future extreme events, particularly the droughts. Although the CC impacts on the hydro-meteorological extremes are extensively studied, there are no such studies which have assessed LUC's impacts on the hydro-meteorological extremes. This study aims to provide a comprehensive assessment of climate change and land-use change on the hydro meteorological extremes in the Mun River Basin in Northeast of Thailand. Extreme climate indices, drought indices, and the probability distributions are used for the assessment. Process-based evaluation of 60 climate models (from CMIP5 and CMIP6) is carried out to identify models that better replicate southeast Asia's regional climate (SEA) and produce robust future projections in the region. Fourteen most apt models from CMIP5 and eight models from CMIP6 are selected to provide near future (2021-2050) climate assessments with reference to baseline (1981-2010). The future river flows under CC and LUC are simulated using the Soil and Water Assessment Tool (SWAT). The meteorological, hydrological, and agricultural droughts are characterized for the observed period using three standardized drought indices (SPEI, SRI, and SSMI) at four timescales (1-, 3-, 6-, and 12-month). The projected changes in the drought characteristics are assessed under CC and LUC scenarios (Business as usual-BAU and Combination of forest conservation and urban growth-CCU). Evaluation of climate models shows the superiority of CMIP6 models to CMIP5 models in simulating annual rainfall cycle and large-scale atmospheric circulation patterns. The subsets of most skilled models from both phases of CMIPs are identified for their applicability in the SEA domain. In the near future, the trends of temperature rise will get stronger. The CMIP6 ensemble suggests an increase in maximum and minimum temperatures by 1.45°C (0.8-1.9°C) and 1.54°C (1.1-1.9°C) under the high emission scenario, which is well above the projections of CMIP5: 1.10°C (0.5-1.7°C) and 1.13°C (0.7-1.6°C) respectively. Although the annual average rainfall will not change significantly, it will be temporally more uneven with projected decreases (6-11%) during the pre-rainy season (March-May) and increases (2-8%) during the rainy season (June-October). An increase in the magnitude of temperature extremes will be higher than the mean temperature as the 20-year return values of maximum and minimum temperature will increase by 2.3-3.3°C and 1.7-2.0°C, respectively. Annual warm spells will also increase by 26-32 days. The rainfall intensity is expected to increase by 10%, and the 20-year return values of 1-day and consecutive 5-day maximum rainfall will also increase by 26-49%. These, along with the projected decrease of the annual number of rainy days as much as 15, indicate temporal re-distribution of the rainfall consequently increase in both rainfall extremities (wet/dry) in the near future. CC and LUC will have the opposite effect on future water yield in the basin as the flows will increase by 11% under CC while decrease by 6% under LUC. Under the combined drivers of CC and LUC, the annual flows will increase by 8%, which shows CC has a dominating impact on future flows than LUC. Observed drought analyses suggest the meteorological droughts in the basin propagate to agricultural droughts with a lag of 1 month and to hydrological droughts with a lag of 2 months. Drought hazards are high in the central region of Nakhon Ratchasima and Buriram provinces and the southern part of Si Sa Ket province. Under CC, the average durations and severities of the meteorological droughts will increase by 9-22% and 45-63%, respectively. Increases are mainly due to higher evapotranspiration demands under increased temperature and increased temporal variabilities of the rainfall. As water yield is expected to rise under CC, hydrological droughts at intermediate timescales (3- and 6-month) will be shorter in the near future while they will increase at a longer timescale of 12-month. LUCs will have negligible impacts on the hydrological droughts as compared to CC. However, the study's important findings are that LUCs have comparable impacts on agricultural droughts as of CC, and the impacts of both drivers will amplify drought durations and severities. Under the combined stressors, the average drought durations and severities are expected to increase by 60% and 165%, respectively. The finding of this study will be helpful in updating disaster mitigation plans and policies based on projected changes in future extremes. It will also have relevance in risk assessments, disaster risk reduction, disaster preparedness, infrastructure planning, and developing adaptation measures for the basin to cope with expected future changes. |
| Year | 2021 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-21-02 |
| 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) | Babel, Mukand S.; |
| Examination Committee(s) | Shrestha, Sangam;Virdis, Salvatore G.P.; |
| Scholarship Donor(s) | WEM Projects;Asian Institute of Technology Fellowship; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2021 |