Constrained CMIP6 projections indicate higher risks of future water shortages in Australia

Australia. Observations and simulations both indicate a negative feedback between precipitation and temperature in arid environments, where low precipitation reduces the evaporative cooling effect, resulting in higher temperature. The negative sensitivity of temperature to precipitation is a key driver of the Australian land water cycle and an important source of uncertainty in climate model projections. Currently, the spread of projected future sensitivities of temperature to changes in precipitation remains substantial across models. To reduce this spread, we demonstrated the existence of a robust emergent relationship between historical wet season temperature sensitivity and future annual temperature sensitivity across all 36 CMIP6 (under emission scenarios SSP126 and SSP245) and 36 CMIP5 (under RCP26, RCP45 and RCP60) models. Combined with observations, we reduced the uncertainty of future temperature sensitivity projections. The constrained results show that the uncertainties of future sensitivities of temperature to precipitation changes are reduced by 27.0–46.8 % (CMIP6) and 11.2–31.1 % (CMIP5). We reveal that the raw CMIP5 and CMIP6 projections both largely overestimate the future negative sensitivity of temperature to precipitation in Australia. These overestimated evaporative cooling effects suggest that future decreases in soil water and increases in drought frequency are also highly underestimated. In particular, the constrained results show an increase in total evaporation across Australia, which contrasts with the decreasing trend in the raw CMIP6 outputs. • CMIP6 projections overestimate future sensitivity of temperature to precipitation by 21.9–80.0 %. • Emergent constraint reduces the uncertainties of future sensitivities of temperature to precipitation changes. • Future decreases in soil water and increases in drought frequency are underestimated in Australia.