Observed warming and moistening trend over South Asia in recent decades consistent with CMIP6 multi-model simulations

Abstract Under global warming, land surfaces have warmed substantially faster than the oceans, leading to widespread drying across most continental regions. However, across South Asia, an anomalous trend of moistening, indicated by an increase in surface relative humidity (RH), has been observed in recent decades despite continued land-surface warming. We find that this moistening pattern is consistently evident in multiple observational, reanalysis, and station-based datasets and is also present in the CMIP6 multi-model mean, indicating that the observed moistening trend is broadly consistent with the externally forced response simulated by CMIP6. These concurrent warming and moistening trends have important implications for humid-heat conditions relevant to human health, as higher RH under a warming climate can significantly reduce heat dissipation and exacerbate heat stress. We further evaluate these humid-heat implications using wet-bulb temperature and heat index. This study further discusses the possible mechanisms behind the anomalous moistening trend, focusing on the monsoon season, and highlights enhanced moisture convergence as a dynamically consistent and physically plausible contributor to the increase in surface RH under warming. The broad consistency between the observed trends and the CMIP6 multi-model mean suggests an important role for the externally forced climate response and provides a basis for future assessments of whether the South Asian moistening trend may persist or intensify under continued anthropogenic forcing. Such assessments should nevertheless account for the influences of internal variability, regional processes, and remaining model biases.