Patagonia is thought to be one of the wettest regions on Earth, although available regional precipitation estimates vary considerably. This uncertainty complicates understanding and quantifying environmental changes, such as the observed dramatic volume loss of the Patagonian Icefields, which contradicts the reported modelled positive surface mass balances. Here I use physical arguments to test the plausibility of the current precipitation estimates and their impact on the Patagonian Icefields. The results show that environmental conditions required to sustain a mean precipitation amount exceeding 7.68±0.31 m yr-1 are untenable according to the regional moisture flux. The revised precipitation values imply a 23% to 61% reduction in glacier surface mass balance compared to previously published values. These constraints reduce significantly the precipitation contribution to the glacier mass changes and provide evidence that the evolution of the glaciers is partly decoupled from the local hydroclimate and is mainly caused by dynamic adjustments of the calving glaciers in tidal and sea areas. This yields a new perspective on the response of Patagonia’s glaciers to climate change and their sea-level contribution and might also help reduce uncertainties in the change of other precipitation-driven environmental phenomena.