Controls on actual evapotranspiration in wetland ecosystems across different climates

40 wetlands in temperate, cold, and polar climate regions Actual evapotranspiration (ETa) is a key driver of wetland processes, but its responses to environmental variables are poorly understood, especially regarding the roles of vegetation. Here we assessed the controls on ETa in 40 wetland ecosystems under temperate, cold, and polar climates. Mean annual ETa ( ETa ̅ ) and evaporative efficiency followed a significant climate gradient across the wetlands. While incoming shortwave radiation was the common driving force, other controls on ETa ̅ varied with climate types. Specifically, leaf area index (LAI) in cold environments also contributed strongly to ETa ̅ , and hydrological regimes, i.e., water table depth (WTD) and inundation duration positively affected ETa ̅ in temperate wetlands. In polar wetlands, LAI and vapor pressure deficit also co-controlled ETa ̅ . However, the effects of LAI in cold and WTD in temperate wetlands on daily ETa weakened. Moreover, we found four different response patterns of daily ETa to LAI in wetlands, which was associated with climate types, inundation, and vegetation coverage. These results enhance the understanding of how wetland ETa responds to environments across diverse climate types under the impacts of climate change and human activities. • Wetland ETa under temperate, cold, and polar climates showed a significant gradient. • Effects of LAI and hydrological regimes depended on climate types and timescales. • Incoming shortwave radiation and VPD were the primary drivers of daily ETa. • Daily LAI-ETa relationship was related to climate types, inundation, and vegetation.