Internal drivers and future evolution of the warming and wetting trend in the drylands of Northwest China

Since the 1980s, Northwest China has experienced a pronounced warming and wetting trend, sparking debate over its anthropogenic versus natural origins. Attribution is hindered by the short length of instrumental records, limiting detection of decadal-to-centennial variability in regional hydroclimate. Here, we use an extensively well-validated Paleo Hydrodynamics Data Assimilation (PHYDA) product, which blends information from a global array of proxy records constrained by a climate model, to identify a persistent ∼50-a hydrological cycle as the dominant mode of variability in Northwest China over the past millennium. This multidecadal oscillation is linked to Pacific Decadal Variability, with its positive phases contributing to wetter conditions in the region. Since the 1950s, anthropogenic warming has enhanced atmospheric moisture availability, superimposing a wetting trend onto natural cycles. Although the recent wetting remains within the envelope of natural variability, our analysis suggests that the alignment of positive-multidecadal phase with continued greenhouse gas forcing will drive an accelerated warming and wetting trajectory through at least 2040 CE.