Constrained CMIP6 projections indicate less warming and a slower increase in water availability across Asia

Climate projections are essential for decision-making but contain non-negligible uncertainty. To reduce projection uncertainty over Asia, where half the world’s population resides, we develop emergent constraint relationships between simulated temperature (1970–2014) and precipitation (2015–2100) growth rates using 27 CMIP6 models under four Shared Socioeconomic Pathways. Here we show that, with uncertainty successfully narrowed by 12.1–31.0%, constrained future precipitation growth rates are 0.39 ± 0.18 mm year−1 (29.36 mm °C−1, SSP126), 0.70 ± 0.22 mm year−1 (20.03 mm °C−1, SSP245), 1.10 ± 0.33 mm year−1 (17.96 mm °C−1, SSP370) and 1.42 ± 0.35 mm year−1 (17.28 mm °C−1, SSP585), indicating overestimates of 6.0–14.0% by the raw CMIP6 models. Accordingly, future temperature and total evaporation growth rates are also overestimated by 3.4–11.6% and −2.1–13.0%, respectively. The slower warming implies a lower snow cover loss rate by 10.5–40.2%. Overall, we find the projected increase in future water availability is overestimated by CMIP6 over Asia.