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There has been substantial overestimation of the terrestrial water storage loss (TWS) in major headwater basins on the Tibetan Plateau. The overestimation is extremely high in the Indus river and Yarkant river basins, reaching up to 50.8 per cent and 77.6 per cent respectively.
For the first time, researchers quantified the contribution of sediment transport to gravity satellite-based estimation of TWS change on the Tibetan Plateau. Neglecting the contribution of sediment transport leads to an overestimation of the TWS loss by 10.1 per cent on average. “The overestimated TWS loss is equivalent to the annual water demand of an additional 0.62 million people in surrounding nations,” said the study published in the journal Geophysical Research Letters August 8, 2024.
TWS is the total amount of water in all continental storage compartments (ice caps, glaciers, snow cover, soil moisture, groundwater, surface water bodies and biomass).
TWS changes are commonly estimated using gravity satellites through observations of the total terrestrial mass storage (TMS) change, with an implicit assumption of a negligible contribution from sediment transport. Through long-term (2002-17) sediment flux observations in seven headwater basins on the Tibetan Plateau, the study found that the gravity satellite-derived TMS has decreased at a rate of 3.85 gigatonnes per year (Gt yr−1) in the seven basins, of which 0.35 Gt yr−1 is contributed by sediment transport.
Headwater basins of seven rivers that originate on the Tibetan Plateau were selected for the study — Yarlung Tsangpo (called Brahmaputra in India), Nujiang, Yangtze, Indus, Yellow, Lancang and Yarkant.
Accurate quantification of the change in the terrestrial water storage on the Tibetan Plateau is important to improve the assessment of water availability that are critical for 2 billion people downstream. Through long-term sediment flux observations, the researchers found that sediment transport makes a substantial contribution to gravity satellite-derived TWS change in regions with a high erosion rate such as the TP, which has never been taken into consideration in previous studies.
Neglecting this contribution leads to an overestimation of TWS loss by about 10 per cent on average for the seven headwater basins on the Tibetan Plateau. The contribution is especially high in Indus and Yarkant basins.
“Soil erosion is considerably high on the western, northern and southern regions of the Tibetan Plateau. The largest average soil erosion rates can reach up to 39.1 and 34.7 Mg ha−1 yr−1 for Indus river, and Yarkant river basins in 2015, respectively, equivalent to 0.76 and 0.16 Gt yr−1, respectively. In the basins on the southeast TP, which experience moderate soil erosion, the rates ranged from 0.007 Gt yr−1 to 0.177 Gt yr−1,” the study said.
The Tibetan Plateau, or the ‘water tower of Asia’, encompasses the headwaters of more than 10 large rivers in Asia that supply a quarter of the world’s population. Recent rapid climate change has considerably altered the regional hydrological cycle and the water tower is experiencing serious imbalance.
The findings improve the regional estimation of water availability and thus support climate adaptation and sustainable water resource management.
Rivers originating from high mountain Asia have experienced large increases in runoff and sediment fluxes over the past six decades. A 2021 study in the journal Science indicated that sediment flux from those rivers could more than double by 2050 in the case of extreme climate change, with potentially serious impacts on the region's hydropower capacity, food security and environment.