Droughts dominate ecosystem recovery from fires in the Western U.S.

A steady rise in fires in the Western United States, coincident with intensifying droughts, imparts significant modifications to the underlying vegetation, hydrology, and overall ecosystem. Relationships between droughts and fire properties have been explored; however, it remains uncertain the extent to which compounding disturbances from droughts influence post-fire hydrologic and ecosystem recovery. Here, we use remote sensing-derived high-resolution evapotranspiration estimates to show that ecoregions dominated by grasslands and savannas are more susceptible to drought stresses, which amplify fire-induced ET decline and, subsequently, shift water flux partitioning. In contrast, severely burned forests respond with slow or incomplete recovery, but with a lower sensitivity to dry extremes. We conclude that the dynamics of water balance recovery in post-fire regimes is dominated by moisture-limited conditions. This explains why moderate to extreme droughts aggravate impacts to the water balance in grasslands and savannas, while moisture accessed by deeper roots in forests helps meet evaporative demands unless severe burns disrupt internal tree structure and deplete fuel load availability. Our results highlight the dominant control of drought on altering the resilience of vegetation to fires, with critical implications for terrestrial ecosystem stability in the face of anthropogenic climate change in the western U.S.