Hydroclimate Variability and Change over the Mekong River Basin: Modeling, Predictability, and Policy Implications

The Mekong River is the lifeblood of the national economies in Southeast Asia.

State-of-the-art in-situ and satellite-based precipitation data is analyzed to quantitatively assess the amount of water received as precipitation – Mekong Basin water – in particular, the country contributions: Laos, Thailand, and Cambodia contribute ~75% of the basin water during March-September whereas China’s contribution is 10-15% in most months except winter when it rises to 25%.

Processing of Mekong Basin water into Mekong streamflow involves accounting for the uncertain water losses, e.g., to soil moisture recharge, evapotranspiration, and infiltration. Interestingly, such accounting is not needed for processing interannual departures.

A simple hydrologic model is constructed for relating interannual variations (i.e., anomalies) in Mekong Basin water to Mekong streamflow. The model is validated using multidecadal historical monthly river discharge data from four mid-basin stations. Preliminary evidence for the impact of upstream dams on downstream flow, especially on the timing of peak summer flow, is also presented.

The influence of El Nino on Southeast (SE) Asian rainfall, characterized during both its growth and decay phases, reveals significant rainfall reductions in the fall preceding and the spring following El Nino’s peak-phase (winter); such reductions at the book-ends of the dry season in SE Asia (winter) generate drought conditions, as in 2015-16. The linear trend in 20^th-century rainfall is also computed to assess the vulnerability of SE Asia to hydroclimate change.

The analysis shows the relevance of a simple hydrologic model and the related feasibility of streamflow prediction from high-resolution precipitation observations (satellite-based) and forecasts (from weather prediction models). It raises the prospects of seasonal drought prediction based on El Nino emergence and/or its forecast. Finally, by showing the Mekong to be largely a rainfed and not snowmelt-fed river, the analysis provides a quantitative context for evaluation of the notion of Chinese control on the Mekong through construction of upriver, main stem dams.

Note: This work was undertaken during the author's Jefferson Science Fellowship at the National Academy of Sciences, and during related service as Senior Science Advisor to the US State Department’s Bureau of East Asian and Pacific Affairs, Office of Multilateral Affairs, which manages the US Lower Mekong Initiative.

Disclaimer: The views expressed are the authors’ alone and not reflective of the National Academy of Sciences or the US State Department.