A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management, School of Engineering and Technology

Thesis (M. Eng.) - Asian Institute of Technology, 2024

The Lower Mekong River Basin (LMRB) is a critical resource for food security, with Cambodia's Siem Reap Province heavily reliant on its hydrological ecosystem services. This study investigates the combined impacts of climate change and land use change modifications on these services, ultimately affecting food security. We analyze how these factors alter surface runoff, local recharge, sediment export, sediment retention, and nutrient export, all crucial for agricultural productivity. Focusing on Siem Reap Province, we assess vulnerabilities and explore the potential of Nature-based Solutions (NBS) to mitigate these combined impacts. NBS offers a sustainable approach to enhance the resilience of the LMRB's hydrological functions, ultimately safeguarding food security in the face of a changing environment. This research aims to identify effective NBS strategies for Siem Reap and inform a broader application across the LMRB. The study uses the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model to examine the impact of changes in land cover, land use, and climate on hydrological ecosystem services (HES). The goal is to identify trade-offs and synergies. The model is employed to analyze spatial and temporal variations in land cover and land use in the region and climate change scenarios. It also assesses their impact on the interaction of three important HESs: seasonal water yield, sediment delivery ratio, and nutrient delivery ratio. Baseline HES models for 2020 were assessed, and future scenarios from 2021 to 2100 were evaluated against SSP2-4.5 and SSP5-8.5. Siem Reap Province is a case study to assess the specific vulnerabilities and potential cascading effects on food production. This research aims to identify knowledge gaps and inform adaptation strategies to ensure long-term food security in the LMRB amidst a changing environment. The results demonstrated that converting 50% of the rice area to intercropping brings the best results. This is an important step towords a more sustainable and secure future. Implementing Nature-Based Solutions (NBS) in Siem Reap holds significant promise in enhancing food security. Both scenario, in particular, demonstrates their potential to limit water loss, local recharge, and sediment and nutrient export. This is a beacon of hope in our quest for sustainable food security.