Climate change is intensifying the hydrologic cycle and altering ecosystem function, including water flux to the atmosphere through evapotranspiration (ET). ET is made up of evaporation (E) via non-stomatal surfaces, and transpiration (T) through plant stomata which are impacted by global changes in different ways. E and T are difficult to measure independently at the ecosystem scale, especially across sites that represent different land use and land management strategies. To address this gap in understanding, we applied flux variance similarity to quantify how E and T differ across 12 different ecosystems measured using eddy covariance in a 10 × 10 km2 area from the CHEESEHEAD19 experiment in northern Wisconsin, USA. The study sites included seven deciduous broadleaf forests, three evergreen needleleaf forests, and two wetlands. Net radiation explained on average 68% of the variance of half-hourly T, which decreased from summer to autumn. Average T/ET for the study period was 55% in forested sites and 46% in wetlands. Deciduous and evergreen forests showed similar E trajectories over time despite differences in vegetation phenology. E increased dramatically after large precipitation events in loam soils but the response in sandy soils was more muted, consistent with the notion that lower infiltration rates temporarily enhance E. Results suggest that E and T partitioning methods are promising for comparing ecosystem hydrology across multiple sites to improve our process-based understanding of ecosystem water flux.
