Divergent mountain runoff dynamics but declining per capita freshwater availability across the Third Pole by mid-21st century

The mountainous Third Pole is a critical source of freshwater for water resource management across Asia, yet the historical and future dynamics of per-capita freshwater supply in this region remain poorly constrained by observations from a coherent, pan-regional perspective. Here, we show that by the end of the 21st century, mountain runoff in the Third Pole’s monsoon domain will increase substantially, whereas runoff in the westerlies domain will experience a non-significant decline. This finding challenges the prevailing paradigm that future runoff across the entire Third Pole will follow a unidirectional increasing trend as future precipitation. Regarding long-term freshwater availability till the end-of-21-century (1960‒2100), although mountain runoff shows a contrasting pattern with increase (decrease) at first and then decrease (increase) in the westerlies (monsoon) domain, the per-capita freshwater supply (for mountain basins and their downstream dependent regions) drops a lot in both westerlies and monsoon domains from the past (1960‒1970) to the near future (2030‒2050) due to rapid population increase. These findings provide vital information to cope with fast-growing water demands and achieve Sustainable Development Goals.