Abstract In high‐mountain Third Pole (TP), increasing transboundary fluvial floods (TFFs) threaten nearly one billion people downstream. However, the changing roles of glacier and snow melt in the future TFFs and their socio‐economic impacts remain unclear. Here, combining a high‐resolution state‐of‐the‐art cryosphere‐hydrology model with observations and the latest climate projections, we project significant increases in annual‐maximum TFFs across all TP basins from 1981 to 2100. By 2100, even under the intermediate‐emission scenario (SSP245), the frequency of peak‐over‐threshold TFFs is projected to rise by 1.2 ± 1.1 to 13.5 ± 4.1 times compared to historical levels (1981–2020) in TP, with intensity increases ranging from 23% ± 30%–106% ± 39%. Although this increase is primarily driven by more frequent rainfall extremes, meltwater will still contribute over 20% to at least one peak‐over‐threshold TFF in 7 of 10 TP basins. For the Indus basin that has the largest glacier area, the number of peak‐over‐threshold TFFs with meltwater contribution exceeding 20% will increase by 3.2 ± 2.2 times by 2100 under SSP585; particularly in the years with heavy snowfall and less rainfall, the meltwater contribution could reach 80%. Moreover, the future ranges of meltwater contributions to the TP's TFFs become much wider than historical levels. By 2100, the exposed population and GDP to TP's TFFs are projected to increase by 6.2 ± 3.2 and 18.0 ± 12.6 times under SSP245, respectively, due to rising flood risk and socio‐economic development. Further, increasing TFFs will threaten over 120,000 km 2 cropland downstream. These findings call for timely preparedness and close collaboration to cope with increasing TFFs among riparian Asian countries.
Liu et al. (2025) studied this question.