Abstract
Abstract. Hillslopes are the dominant landscape components where incoming precipitation becomes groundwater, streamflow or atmospheric water vapor. However, directly observing flux partitioning in the soil is almost impossible. Hydrological hillslope models are therefore being used to investigate the processes involved. Here we report on a modeling experiment using the Catchment Modeling Framework (CMF) where measured stable water isotopes in vertical soil profiles along a tropical mountainous grassland hillslope transect are traced through the model to resolve potential mixing processes. CMF simulates advective transport of stable water isotopes 18O and 2H based on the Richards equation within a fully distributed 2-D representation of the hillslope. The model successfully replicates the observed temporal pattern of soil water isotope profiles (R2 0.84 and Nash–Sutcliffe efficiency (NSE) 0.42). Predicted flows are in good agreement with previous studies. We highlight the importance of groundwater recharge and shallow lateral subsurface flow, accounting for 50 and 16% of the total flow leaving the system, respectively. Surface runoff is negligible despite the steep slopes in the Ecuadorian study region.
Highlights
Delineating flow path in a hillslope is still a challenging task (Bronstert, 1999; McDonnell et al, 2007; Tetzlaff et al, 2008; Beven and Germann, 2013)
Due to the prevailing measurement techniques and the available data sets, it has become common practice to base the validation of modeled hillslope flow processes on quantitative data on storage change
System-wide storage changes are monitored by discharge and groundwater level measurements or, on more intensively instrumented hillslopes, the storage change of individual soil compartments is monitored by soil moisture sensors
Summary
Delineating flow path in a hillslope is still a challenging task (Bronstert, 1999; McDonnell et al, 2007; Tetzlaff et al, 2008; Beven and Germann, 2013). While the application of the artificial tracers is rather limited in space and time (Leibundgut et al, 2011), the latter ones can be used over a wide range of scales (Barthold et al, 2011; Genereux and Hooper, 1999; Leibundgut et al, 2011; Muñoz-Villers and McDonnell, 2012; Soulsby et al, 2003). Stable water isotopes such as oxygen-18 (18O) and hydrogen-2 (2H) are integral parts of water molecules and ideal tracers
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