Abstract
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.