COS 210-4 - Understanding the spatiotemporal dynamics of water balance in the Three-River-Source Region

Abstract: The Three-River Source Region (TRSR) located in the central part of the Qinghai-Tibetan Plateau is the headwaters of three great rivers of Asia: the Yangtze, the Yellow, and the Lancang Rivers. It is often called the “water tower of Asia” since the major rivers in China originate from the TRSR and its altitude is more than 4000 m. The TRSR is considered to be the water source region for its surrounding lowlands. However, our understanding of the spatiotemporal water balance dynamics in the TRSR remains limited. We collected weather data from 1981 to 2015 for 29 meteorological stations in and around the TRSR and used them to run SOILWAT2, a daily time step ecosystem water balance model to reveal how water balance changes in time and space in the TRSR.

We found relatively low temporal variability in water balance components (precipitation, evapotranspiration, and deep drainage) of each site across years and high spatial variability linked to altitude gradients. Precipitation, evapotranspiration and deep drainage followed a similar spatial variation pattern. All three variables first increased as the altitude increased, then decreased with additional altitude increases. Specifically, mean annual precipitation, evapotranspiration, and deep drainage at altitudes between 3,500 and 4,000 m was higher than those at altitudes below 3,500 m and above 4,000 m. The mean annual precipitation at sites below 3500 m was below 400 mm, at sites between 3500 to 4000 m it was between 500 and 700 mm, while at sites above 4000 m it was from 300 to 600 mm. Mean annual evapotranspiration at sites below 3500 m and above 4000 m was almost equal to mean annual precipitation and at sites between 3500 and 4000 m was from 400 to 500 mm. Mean annual deep drainage at sites below 3500 m and above 4000 m was near zero and at sites between 3500 to 4000 m was between 50 and 300 mm. Our results revealed that the sources of water that contributes to river flow in the TRSR are concentrated at altitudes between 3500 and 4000 meters, because sites in this altitude range had large positive deep drainage.