The ebb and flow in the Lancang-Mekong River Basin (LMRB), one of the most important transboundary river basins in Asia, are subject to both climate change and reservoir operations. However, exactly what roles the two factors play was not clear until a recent study quantified their impact.
The study, which was co-authored by
Prof. Deliang CHEN, member of the
TPE executive committee and August Rohss Chair at
the University of Gothenburg (Sweden), used quantitative assessment to show that reservoir operation has reduced the increased flood risk caused by climate change in the area. CHEN said the research will “help inform water management and hydropower development in the region.”
Using a hydrological-reservoir model, the study found that reservoirs strongly altered LMRB streamflow during the 2008-2016 period, a time when many reservoirs were constructed in the area, in comparison with the baseline period of 1985-2007. YUN Xiaobo and
TANG Qiuhong, scientists from the
Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences and the first author and corresponding author of the study, described the differences between these two periods. According to YUN and TANG, the upstream reservoir operation caused a 15-37% increase in dry season streamflow at the midstream stations during the 2008-2016 period. TANG noted that the wet season streamflow was less affected by reservoir operation, however. It only declined by 2% to 24% during the study period.
The impact from upstream reservoirs was felt much less at stations downstream than at midstream stations. TANG noted that the reservoirs across the Lancang River (the upper Mekong River located in China) reduced the annual average streamflow by 5% at the Chiang Sean station in northern Thailand in 2008-2016, whereas their influence became undetectable downstream of the Vientiane station in northern Laos. TANG said that the streamflow changes downstream of the Mukdahan station in southern Laos, including the stations in Cambodia and southern Vietnam, were mainly attributed to local reservoirs and climate change.
The good news is that reservoirs are mitigating climate change in the area. The study showed that climate change increased the magnitude and frequency of floods by up to 14% and 45%, respectively. In contrast, reservoir operation reduced the magnitude and frequency of floods by 16% and 36%, respectively. This knowledge should be useful for policy makers in the region, since a boom in population and urbanization have boosted demand for hydropower development in LMRB countries in recent years.
Editor’s note: The study was supported by
Pan-TPE, a TPE-related science project.
