Quantifying the extent of drought and flood magnitude and frequency under the climate change impacts is essential for an effective water resource management. In this study, we utilize the Soil and Water Assessment Tool (SWAT) hydrological model, drought indices as well as the Interquartile Range (IQR) method for a comprehensive analysis of the river flow response to projected climate change scenarios. Four General Circulation Models (GCMs) under two Shared Socioeconomic Pathways (SSP2-4.5 and 5-8.5) have been used for our analysis (2023-2090). Our objective is to reveal the future projected drought and flood events in terms of intensity, frequency, and potential consequences for local livelihoods in the Srepok River basin (SRB), a tributary of the Mekong River basin (MRB), Southeast Asia. Our findings serve as the scientific basis for stakeholders and decisionmakers to develop adaptative strategies and sustainable plans to promote the region's resilience.

Sustainably managing resources in a transboundary freshwater basin is a complex problem, particularly when considering the compounding impacts of climate change, hydropower development, and evolving water governance paradigms. In this study, we used a mixed methods approach to analyze potential impacts of climate change on regional hydrology, the ability of dam operation rules to keep downstream flow within acceptable limits, and the present state of water governance in Laos, Vietnam, and Cambodia. Our results suggest that future river flows in the 3S river system could move closer to natural (i.e., pre-development) conditions during the dry season and experience increased floods during the wet season. This anticipated new flow regime in the 3S region would require a shift in the current dam operations, from maintaining minimum flows to reducing flood hazards. Moreover, our Governance and Stakeholders survey assessment results revealed that existing water governance systems in Laos, Vietnam, and Cambodia are ill-prepared to address such anticipated future water resource management problems. Our results indicate that the solution space for addressing these complex issues in the 3S river basins will be highly constrained unless major deficiencies in transboundary water governance, strategic planning, financial capacity, information sharing, and law enforcement are remedied in the next decade. This work is part of an ongoing research partnership between the National Aeronautical and Space Agency (NASA) and the Conservation International (CI) dedicated to improving natural resources assessment for conservation and sustainable management.

Index Terms: 1622: Earth system modeling; 1630: Land/atmosphere interactions; 1800: Hydrology; 1836 Hydrological cycles and budgets; 1840 Hydrometeorology; 1855: Remote sensing; 1996 Web Services; 4305: Space weather; 6334: Regional Planning This work addresses a key objective of SERVIR-Mekong Project related to integrating geospatial information in government decision-making, planning, and communication for societal good. The SERVIR-Mekong is a partnership between the U.S. Agency for International Development (USAID) and the U.S. National Aeronautics and Space Agency (NASA) formed to help regional organizations in the Lower Mekong Region to use information provided by Earth observing satellites and geospatial technologies in managing climate risks. Our work integrated multiple satellite-based earth observation systems, in-situ station data and spatial data with the Soil & Water Assessment Tool (SWAT) hydrologic model employed in the Mekong River Basin region to develop a Lower Mekong River Basin region’s hydrological decision support system. Simulated hydrological fluxes of streamflow, soil moisture, and evapotranspiration at the Lower Mekong River Basin were presented utilizing our developed hydrological decision support system. Our work results have been presented via multiple Tethys platforms, Tethys is an easily customizable platform that hosts web applications, that facilitate accessing NASA satellite-based earth observation systems as well as the Lower Mekong River Basin region’s hydrological decision support system. Earth observations data has provided solutions to assist people in the Lower Mekong River Basin to overcome various obstacles experienced in enhancing hydrological decisions that are related to difficult access and incompleteness, inconsistency, scarcity, as well as poor spatial representation of in situ data products.

This presentation will show an ongoing freshwater health assessment stemming from a partnership between the National Aeronautical and Space Agency (NASA) and Conservation International (CI) that is dedicated to improving natural resources assessment for conservation and sustainable management. The goal of this work is to develop a calibrated satellite- and hydrologic modeling-based tool to support the assessment of hydrologic environmental health and value natural capital in the Lower Mekong River Basin. Vollmer et al., (2018) have presented the social-ecological framework named the Freshwater Health Index (FHI), which takes account of the interplay between governance, stakeholders, freshwater ecosystems and the ecosystem services they provide. The FHI framework and its accompanying indicators are oriented toward management and stakeholder engagement, and they make a significant contribution by providing a systematic, evidence-based quantitative tool that supports the integration between social and ecological nature of fresh waters at the basin level. Since the FHI is intended to be used iteratively, we leverage multiple data products and hydrological modelling capabilities specifically created to improve decision support in the Lower Mekong basin (Mohammed et al., 2018). Mohammed et al. modelling capabilities enable the integration of satellite-based daily gridded precipitation, air temperature, digital elevation model, soil characteristics, and land cover and land use information to drive watershed model water simulations over the Lower Mekong River Basin. Multiple dam reservoirs scenarios have been envisioned and tested based on stakeholder engagement to enhance the results of the integrative social and ecological nature of fresh waters at the Srepok, Sesan, and Sekong (3S) River Basins of the Lower Mekong. This assessment provides a comprehensive picture of freshwater ecosystem health, the services it provides and the status of its governance at the Lower Mekong.

This contribution highlights part of training events designed to collect, analyze, and manage water and water-related data (e.g., climate, weather, land, soils) and information products for the purposes of reducing water-related risks, and improving regional responses to environmental emergencies in the Mekong region. In this work, we discuss multiple tools and applications developed by National Aeronautics and Space Administration (NASA) scientists to lower technical barriers through current web technologies and leveraging data sharing capabilities among existing programs and institutions within different parts of the Mekong region. The aim of this training contribution is to leverage a well-established suite of tools that include but are not limited to remote sensing precipitation data adjustment techniques, i.e., the SWATOnline visualization and modeling system, and the NASAaccess data toolkit. The collaborative training events, which this contribution is part of, are administered by the United States Department of State (DOS) and the Ministry of Foreign Affairs - Republic of Korea under the Mekong-US Partnership and its Mekong Water Data Initiative facilitated by Sustainable Infrastructure Partnership (SIP) program. The Mekong Water Data is a DOS Initiative consists of multiple efforts and programs with an overarching objective of building the capacity of Mekong riparian countries and the Mekong River Commission Secretariat (MRCS), National Mekong Committees and line agencies in the Lower Mekong countries to improve the management of the Mekong River.

Better understanding of the hydrological cycle of the Lower Mekong River Basin (LMRB) and addressing the value-added information of using remote sensing data on the spatial variability of soil moisture over the Mekong Basin is the objective of this work. In this work, we present the development and assessment of the LMRB (drainage area of 495,000 km2) Soil and Water Assessment Tool (SWAT). The coupled model framework presented is part of SERVIR, a joint capacity building venture between NASA and the U.S. Agency for International Development, providing state-of-the-art, satellite-based earth monitoring, imaging and mapping data, geospatial information, predictive models, and science applications to improve environmental decision-making among multiple developing nations. The developed LMRB SWAT model enables the integration of satellite-based daily gridded precipitation, air temperature, digital elevation model, soil texture, and land cover and land use data to drive SWAT model simulations over the Lower Mekong River Basin. The LMRB SWAT model driven by remote sensing climate data was calibrated and verified with observed runoff data at the watershed outlet as well as at multiple sites along the main river course. Another LMRB SWAT model set driven by in-situ climate observations was also calibrated and verified to streamflow data. Simulated soil moisture estimates from the two models were then examined and compared to a downscaled Soil Moisture Active Passive Sensor (SMAP) 36 km radiometer products. Results from this work present a framework for improving SWAT performance by utilizing a downscaled SMAP soil moisture products used for model calibration and validation.