Stable water isotope tracing through hydrological models for disentangling runoff generation processes at the hillslope scale

摘要

Hillslopes are the dominant landscape components where incomingprecipitation becomes groundwater, streamflow oratmospheric water vapor. However, directly observing flux partitioning inthe soil is almost impossible. Hydrological hillslope models are thereforebeing used to investigate the processes involved. Here we report on amodeling experiment using the Catchment Modeling Framework (CMF) wheremeasured stable water isotopes in vertical soil profiles along a tropicalmountainous grassland hillslope transect are traced through the model toresolve potential mixing processes. CMF simulates advective transport ofstable water isotopes 18O and 2H based on the Richards equationwithin a fully distributed 2-D representation of the hillslope. The modelsuccessfully replicates the observed temporal pattern of soil water isotopeprofiles (R2 0.84 and Nash–Sutcliffe efficiency (NSE) 0.42). Predicted flows are in goodagreement with previous studies. We highlight the importance of groundwaterrecharge and shallow lateral subsurface flow, accounting for 50 and16% of the total flow leaving the system, respectively. Surface runoff isnegligible despite the steep slopes in the Ecuadorian study region.