Aerosol-induced surface cooling elevates relative humidity on the Indo-Gangetic Plain

Abstract

The Indo-Gangetic Plain has experienced a substantial rise in relative humidity in recent decades, with implications for human health and well-being. Here we use atmospheric reanalysis and large-ensemble climate model simulations to assess changes since the 1960s. Relative humidity increased by 10.3 +/- 0.3 percent, mainly due to a 2.9 +/- 0.1 grams per kilogram rise in specific humidity and a slight decrease in air temperature (-0.2 +/- 0.1 degrees Celsius). Aerosol-induced surface cooling played a crucial role in enabling this moistening. Decomposition analysis reveals that specific humidity accounts for 95% of the increase, with cooling explaining the rest. Future projections show contrasting trends. High-emission scenarios peak and then decline after the 2040s, as greenhouse gas warming overtakes weakening aerosol effects. In contrast, low-emission scenarios maintain stable or slightly increasing humidity. These findings reveal how aerosols and greenhouse gases exert opposing influences on humidity and underscore the need for coordinated climate strategies in this vulnerable region.