LAUSR

Stable isotope ratios of precipitation trace mechanisms of hydroclimatic change in the modern and paleoclimate record. Patterns and drivers of isotopic change at multidecadal timescales have remained unclear, however, due to limitations in the observational record. Here, we use a 65‐year global data compilation to estimate solstial season δ18Op trends. Spatially organized regions of change suggest divergent controls, and we propose that changes in atmospheric water balance dominate trends in moisture‐limited areas, whereas changes in upwind source region conditions drive trends where atmospheric water flux is large relative to precipitation. Positive trends on windward coasts suggest the latter effect, whereas we attribute the dipole patterns in trends over North America and Europe and decreasing trends in southern Australia during boreal winter to the former. Simulations from the isotope‐enabled Community Atmospheric Model match predictions for water balance, implying that the model may underrepresent the effects of changing vapor source conditions.