How multiple factors control evapotranspiration in North America evergreen needleleaf forests

Identifying the factors dominating ecosystem water flux is a critical step for predicting evapotranspiration (ET). Here, the fuzzy rough set with binary shuffled frog leaping (BSFL-FRSA) was used to identify both individual factors and multi-factor combinations that dominate the half-hourly ET variation at evergreen needleleaf forests (ENFs) sites across three different climatic zones in the North America. Among 21factors, air temperature (TA), atmospheric CO₂ concentration (CCO₂), soil temperature (TS), soil water content (SWC) and net radiation (NETRAD) were evaluated as dominant single factors, contributed to the ET variation averaged for all ENF sites by 48%, 36%, 32%, 18% and 13%, respectively. While the importance order would vary with climatic zones, and TA was assessed as the most influential factor at a single climatic zone level, counting a contribution rate of 54.7%, 49.9%, and 38.6% in the subarctic, warm summer continental, and Mediterranean climatic zones, respectively. In view of impacts of each multi-factors combination on ET, both TA and CCO₂ made a contribution of 71% across three climate zones; the combination of TA, CCO₂ and NETRAD was evaluated the most dominant at Mediterranean and subarctic ENF sites, and the combination of TA, CCO₂ and TS at warm summer continental sites. Our results suggest that temperature was most critical for ET variation at the warm summer continental ENF.