Improving Evapotranspiration Mechanisms in the U.S. Environmental Protection Agency’s Storm Water Management Model

Abstract

AbstractMost stormwater models oversimplify evapotranspiration (ET) processes, which restricts their applications in water budget analyses, ecosystem services assessments, and coupled modeling studies such as with urban climate models to investigate benefits of green infrastructure (GI) implementation. To address this need, the Penman–Monteith scheme was incorporated into the United States Environmental Protection Agency’s storm water management model (SWMM) to improve the latter’s ET routine. The modified SWMM allows heterogeneous and subdaily potential ET (PET) inputs, and includes the effects of water stress on actual ET (AET). The updated ET routine was validated for GI, including bioretention (R2=0.57) and green roof (R2=0.78), by comparing with direct measurements. A case study showed the upgraded SWMM model generates improved daily ET estimates and more accurate temporal patterns than previous SWMM versions. The results also suggest that water cycle fluxes could be miscalculated if a homogeneous po...