Preprints
https://doi.org/10.5194/esurf-2022-65
https://doi.org/10.5194/esurf-2022-65
 
14 Dec 2022
14 Dec 2022
Status: this preprint is currently under review for the journal ESurf.

Effects of seasonal variations in vegetation and precipitation on catchment erosion rates along a climate and ecological gradient: Insights from numerical modelling

Hemanti Sharma and Todd A. Ehlers Hemanti Sharma and Todd A. Ehlers
  • Department of Geosciences, University of Tübingen, Schnarrenbergstr. 94-96, 72076, Germany

Abstract. Precipitation in wet seasons influences catchment erosion and contributes to annual erosion rates. However, wet seasons are also associated with increased vegetation cover, which helps resist erosion. This study investigates the effect of present-day seasonal variations in rainfall and vegetation cover on erosion rates for four catchments along the extreme climate and ecological gradient (from arid to temperate) of the Chilean Coastal Cordillera (~26° S – ~38° S). We do this using the Landlab-SPACE landscape evolution model modified to account for vegetation-dependent hillslope-fluvial processes and hillslope hydrology. Model inputs include present-day (90 m) topography, and a timeseries (from 2000–2019) of MODIS-derived NDVI for vegetation seasonality; weather station observations of precipitation; and evapotranspiration obtained from GLDAS NOAH. Simulations were conducted with a step-wise increase in complexity to quantify the sensitivity of catchment scale erosion rates to seasonal variations in precipitation and/or vegetation cover. Simulations were conducted for 1,000 years (20 years of vegetation and precipitation observations repeated 50 times). After detrending the results for long-term transient changes, the last 20 years were analyzed. Results indicate that when vegetation cover is varied but precipitation is held constant, the amplitude of change in erosion rates relative to mean erosion rates ranges between 6.5 % (humid-temperate) to 36 % (Mediterranean setting). In contrast, in simulations with variable precipitation change and constant vegetation cover, the amplitude of change in erosion rates is higher and ranges between 13 % (arid) to 91 % (Mediterranean setting). Finally, simulations with coupled precipitation and vegetation cover variations demonstrate variations in catchment erosion of 13 % (arid) to 97 % (Mediterranean setting). Taken together, we find that precipitation variations more strongly influence seasonal variations in erosion rates. However, the effects of seasonal variations in vegetation cover on erosion are also significant (between 5–36 %) and are most pronounced in semi-arid to Mediterranean settings and least prevalent in arid and humid-temperature settings.

Hemanti Sharma and Todd A. Ehlers

Status: open (until 05 Feb 2023)

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Hemanti Sharma and Todd A. Ehlers

Hemanti Sharma and Todd A. Ehlers

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Short summary
Seasonality in precipitation (P) and vegetation (V) jointly influence catchment erosion (E), although which factor plays the dominant role is unclear. In this study, we performed a sensitivity analysis of E to P-V seasonality through numerical modeling. Our results suggest that P variations strongly influence seasonal variations in E. While the effect of seasonal V variations is secondary but significant. This is more pronounced in moderate and least pronounced in extreme environmental settings.