Assessing climate change impacts on surface water flow in Srepok River Basin, Việt Nam

VIET NAM NATIONAL UNIVERSITY, HANOI VIET NAM JAPAN UNIVERSITY VU THI HAI HA ASSESSING CLIMATE CHANGE IMPACTS ON SURFACE WATER FLOW FOR SUSTAINABLE EXPLOITATION AND UTILIZATION OF WATER RESOURCES IN THE SREPOK RIVER BASIN IN VIET NAM MASTER’S THESIS VIET NAM NATIONAL UNIVERSITY, HANOI VIET NAM JAPAN UNIVERSITY VU THI HAI HA ASSESSING CLIMATE CHANGE IMPACTS ON SURFACE WATER FLOW TOWARD SUSTAINABLE EXPLOITATION AND UTILIZATION OF WATER RESOURCES IN THE SREPOK RIVER BASIN IN VIET NAM MAJOR: CLIMATE CHANGE AND DEVELOPMENT CODE: 8900201.02QTD RESEARCH SUPERVISOR: Dr. Akihiko Kotera Prof. Koshi Yoshida Ha Noi, 2021 DECLARATION I hereby declare that this thesis is the result of my research and has not been published. The use of other research results and other documents must comply with the regulation.

The citations and references to documents, books, research, and websites must be listed as the thesis references. Author of the thesis Vu Thi Hai Ha ACKNOWLEDGEMENT First and foremost, my appreciation and gratitude go to excellent supervisors for their guidance during the thesis research, namely Prof. Dr Koshi Yoshida and Dr Akihiko Kotera. They have been great mentors and always being available and responding to my emails and questions.

I would like to thank the National Center for Water Resources Planning and Investigation and the Vietnam Meteorological and Hydrological Administration for their enthusiastic support in providing materials and guiding me in writing my thesis. I am also very grateful to the Danish Hydraulic Institute (DHI) offices in Ha Noi for the incredible internship assisting me in the modelling tutorial and MIKE license supply. My special thanks go to Mr Nguyen Ngoc Bach, who gave me so much meaningful advice in study MIKE models. I am very grateful for all the support, continuously encouragement, teaching and guidance from all the teachers of the MCCD program have extended to me during my time study here at Viet Nam Japan University, Hanoi National University.

Last but not least, I would like to express my indebtedness to my families and friends who have given me constant encouragement, great patience and utmost love to overcome all difficulties in the thesis completion. Thank you very much! TABLE OF CONTENTS DECLARATION ACKNOWLEDGEMENT TABLE OF CONTENTS LIST OF TABLES .i LIST OF FIGURES. ii LIST OF ABBREVIATIONS .2 The research question and hypothesis .3 Research objectives and tasks .4 Objects and scope of the research .5 Matrix of learning outcomes for the master's thesis .6 Contribution of the thesis .7 Framework of the Master’s thesis .9 Overview of the study area. Description of study area.

Socio-economic features .10 Overview climate change in Viet Nam and the Srepok river basin. MATERIALS AND METHODS. Hydro-meteorological data. Water demand data.

Reservoirs and hydropower plants data .2 Rainfall-runoff and water balance models. MIKE NAM model .2 The MIKE HYDRO BASIN model. RESULTS AND DISCUSSIONS .1 Calibration and validation of MIKE NAM model .2 Calibration and validation of MIKE HYDRO BASIN model .3 Impacts of climate change on flow. The average annual flow.

The average flow in the rainy season. The average flow in the dry season .4 Assessing the capacity of sustainable exploitation and using water resources under the context of climate change. Water demand assessment. Assessing the capacity of sustainable exploitation and using water resources under the context of climate change.

SOLUTION AND RECOMMENDATION. Solution and recommendation. Innovation of policy and management: IWRM (Solutions for water resource management). Agriculture and solutions.

Structural measures in the Srepok river basin. Recommendations to the government. CONCLUSIONS AND RECOMMENDATIONS. Recommendations for further study.

82 Appendix A: The MIKE NAM model results. 82 Appendix B: The water demand in the Srepok river basin. 86 Appendix C: The reservoirs and hydropower plants information. 86 Appendix D: The rainfall projection.

101 LIST OF TABLES Table 1.1: Research question and hypothesis .2: Objective and tasks.3: Relations between results of the Master's thesis and MCCD's Program Learning Outcomes (PLOs) .4: Characteristics of the main tributaries in the Srepok river basin in Viet Nam .5: Average monthly flow in 1980-2015 in the Srepok Basin (m³/s) .1: List of rainfall stations used in MIKE NAM .2: The variation of annual average rainfall compared to the baseline period in four provinces in the Srepok river basin.3: Changes in seasonal rainfall (%) compared with the baseline period in four provinces in the Srepok river basin .4: Water demand in the Srepok river basin (million m3) .5: Reservoirs and hydropower plans .6: MIKE NAM model parameter .7: The sub-basins in the Srepok river basin .8: The evaporation and rainfall stations in the area of Duc Xuyen station .9: The evaporation and rainfall stations in the area of Cau14 station .10: The evaporation and rainfall stations in the area of Giang Son station .11: The calibration and validation period of MIKE NAM.12: The average monthly flow for the 1986-2015 period (m3/s) in the Srepok river basin .13: Hydropower plants information in Srepok river basin .14: The calibration and validation period of MIKE HYDRO BASIN .1: The parameter of calibration and validation model .2: Results of calibration and validation of MIKE– NAM model at three hydrological stations Giang Son, Duc Xuyen and Cau 14 in the study basin .3: Criteria evaluation result of calibration and validation of MIKE HYDRO BASIN model at 2 hydrological stations Giang Son and Cau 14 .4: Water demand deficit in 2017 (million m3) .5: Water demand deficit in 2017 by sector (million m3) .6: Water demand deficit in 2030 with P=85% (million m3) .7: Water demand deficit in 2030 with P=85% by sector (million m3) .8: Water demand deficit in 2030 with P=50% (million m3) .9: Water demand deficit in 2030 with P=50% by sector (million m3) .10: The percentage reduces to meet the 85% water supply in agriculture. 65 i LIST OF FIGURES Figure 1.1: Framework of the thesis .2: The Srepok river basin .3: The Srepok River system .4: Average monthly water level at Cau 14 station in 1980–2018 .5: Average monthly water level at Duc Xuyen station in 1980–2018 .6: Average monthly water level at Giang Son station in 1980–2018 .7: The percentage of annual average surface water resources of sub-basins in the Srepok river basin in 1980-2015 .8: Temperature in some stations in the Srepok river basin (oC) .9: Rainfall in some stations in the Srepok river basin (mm) .1: The hydro-meteorological stations, reservoirs and hydropower plants network.2: The process and concept for the MIKE NAM and MIKE HYDRO BASIN models. Structure of NAM model .4: Sub-basin in MIKE NAM model .5: Thiessen polygon calculates the average rainfall of the basin to the Duc Xuyen hydrological station.6: Thiessen polygon calculates the average rainfall of the basin to the Cau 14 hydrological station.7: Thiessen polygon calculates the average rainfall of the basin to the Cau 14 hydrological station.8: Thesis’s MIKE HYDRO BASIN model setting .9: Water users connected to the river network in thesis .10: Reservoir information in the thesis .11: The position of Reservoir and Hydropower plant in thesis’s model .1: Calibration and validation in Giang Son station .2: Calibration and validation in Duc Xuyen station.3: Calibration and validation in Cau 14 station .5: Frequency curve and respective flow values calculation by computer program FFC 2008 .6: Observed and simulated flow at Giang Son station and Cau 14 station .7: Average annual flow in 1986–2005 and 2016–2035 periods .8: The average annual flow change in 1986–2005 and 2017–2035 periods .9: The average flow years in the rainy season .10: The average flow years change in the rainy season .11: The average annual flow in the dry season .12: The average annual flow years in the dry season .13: The water demand in 2017 .14: The water demand in 2030 .15: The water demand by sector in 2017 .16: The water demand by sector in 2030. 61 iii LIST OF ABBREVIATIONS CC Climate change CMIP5 Coupled Model Inter comparison Project Phase 5 DHI Danish Hydraulic Institute DWRPIS Division for Water Resources Planning and Investigation for the South of Viet Nam IPCC Intergovernmental Panel on Climate Change GCM General Circulation Model HPP Hydropower plant NAWAPI National Center for Water Resources Planning and Investigation MONRE Ministry of Natural Resources and Environment MARD Ministry of Agriculture and Rural Development RCPs Representative Concentration Pathways R-R Rainfall-Runoff SWAT Soil and Water Assessment Tool UNICEF United Nations International Children's Emergency Fund VMHA Vietnam Meteorological and Hydrological Administration WMO World Meteorological Organization iv CHAPTER 1.1 Background Given the impacts of global warming and sea-level rise, climate change is one of the biggest challenges to humanity in the 21st century, especially for the island and coastal states.

Climate change has been making the impacts of natural disasters more severe, exacerbated the harmful effects of floods and droughts in many places, exacerbating water scarcity and contaminating water supplies (UNICEF, 2021). According to the Inter-governmental Panel on Climate Change (IPCC) report on climate change, Viet Nam is one of the most affected countries by those impacts (IPCC, 2007). Furthermore, Viet Nam also faces many challenges, especially in water resource management and use - one of the fields directly and severely affected by climate change. Climate change increases temperature and changes the seasonal distribution of rainfall, causing changes in inflows, floods frequency and drought characteristics.

Meanwhile, due to socio-economic development and population growth, water demand increases, leading to the imbalance of supply and demand, which consequently leads to competition and crisis in water use. These factors directly affect not only economic development but also social security. Therefore, it is necessary to have synchronous and specific solutions with a long-term strategic vision to solve sustainable water use in the context of climate change. For this purpose, the thesis "Assessing Climate Change Impacts on Surface Water Flow toward Sustainable Exploitation and Utilization of Water Resources in the Srepok river basin in Viet Nam" is developed to provide a partial overview of climate change impacts on water resources.

Besides, the problems of using water resources will be thoroughly analyzed. Finally, the thesis will provide specific solutions to solve the problem. However, within the framework of a master's thesis, it will be challenging to consider the above problem on a national scale due to time constraints and other factors. Hence, the author has selected the Srepok basin to study and solve the above issues.

1 The Srepok river basin, a sub-basin in the Lower Mekong, was selected as the study area. Located within Viet Nam, the river basin area spans an area of 18.264km2 and covers the administrative boundaries of four provinces: Gia Lai, DakLak, DakNong, and Lam Dong (MONRE, 2017). Recent studies have shown that climate change in the Srepok basin is indicated in the increasing trend of rainfall reduction and temperature (Dao, 2013). The results of projecting climate change scenarios based on the Statistical downscaling model (SDSM) determined that annual rainfall and annual temperature will increase in the future, but rainfall will decrease in the dry season (Dao et al.

The study based on three-climate change scenarios has been detailed from the IPCC’s CMIP5 program indicates that in the Srepok river basin, the flow tends to decrease sharply in several months. The transfer between the two seasons and the dry season, especially at Duc Xuyen station, reduces by nearly 80% in June. This has increased the risk of a prolonged drought in the basin (Nguyen et al. Therefore, it can be seen that climate change is implicit in extreme weather events with increasing intensity and unpredictability.

In addition, significant problems exist in the management of water resources in the Srepok river basin, including floods, droughts leading to environmental degradation (such as water pollution), erosion, and sedimentation of reservoirs, over-exploitation of groundwater, conflict of water use for different purposes, conflict of river boundaries (between provinces and districts). In 2016, over 70% of dams and over 80% of dug wells went dry due to prolonged drought.