Solar radiation as a global driver of hillslope asymmetry: Insights from an ecogeomorphic landscape evolution model

Omer Yetemen*, Erkan Istanbulluoglu, Alison R. Duvall

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Citations (Scopus)


Observations at the field, catchment, and continental scales across a range of arid and semiarid climates and latitudes reveal aspect-controlled patterns in soil properties, vegetation types, ecohydrologic fluxes, and hillslope morphology. Although the global distribution of solar radiation on earth's surface and its implications on vegetation dynamics are well documented, we know little about how variation of solar radiation across latitudes influence landscape evolution and resulting geomorphic difference. Here, we used a landscape evolution model that couples the continuity equations for water, sediment, and aboveground vegetation biomass at each model element in order to explore the controls of latitude and mean annual precipitation (MAP) on the development of hillslope asymmetry (HA). In our model, asymmetric hillslopes emerged from the competition between soil creep and vegetation-modulated fluvial transport, driven by spatial distribution of solar radiation. Latitude was a primary driver of HA because of its effects on the global distribution of solar radiation. In the Northern Hemisphere, north-facing slopes (NFS), which support more vegetation cover and have lower transport efficiency, get steeper toward the North Pole while south-facing slopes (SFS) get gentler. In the Southern Hemisphere, the patterns are reversed and SFS get steeper toward the South Pole. For any given latitude, MAP is found to have minor control on HA. Our results underscore the potential influence of solar radiation as a global control on the development of asymmetric hillslopes in fluvial landscapes.

Original languageEnglish
Pages (from-to)9843-9861
Number of pages19
JournalWater Resources Research
Issue number12
Publication statusPublished - Dec 2015
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2015. American Geophysical Union. All Rights Reserved.


Simulation results can be obtained from the first author on request. The DEM data cited in this manuscript are publicly available and can be accessed from the following repositories: 1-arc DEM data (~30 m) for Upper Rio Salado and Cerro Robles and 10 m DEM data for Cache La Poudre are available at online repository of USGS National Elevation Data set ( and SRTM 1 arc-second Global Data set, respectively. 1 m LiDAR data for Gordon Gulch are available at Boulder Creek CZO online data repository ( 10 m DEM data for Dry Creek are available at Dry Creek Experimental Watershed online data repository ( 10 m DEM data for Walnut Gulch are available at Southwest Watershed Research Center''s online data repository ( 10 m DEM data for Sevilleta are available at Sevilleta LTER online repository ( We thank Patricia Saco (AE), Daniel B. Collins, and two anonymous reviewers for their comments, which contributed to improving this paper. We thank Alan G. Barr (Environment Canada) for his helpful comments on the manuscript, Zilefac Asong and Willemijn Appels (both from the University of Saskatchewan) for their help for figure preparations. Simulations are run at different clusters. We acknowledge support from the Research Computing Group of the University of Saskatchewan for using the cluster Plato; the GIWS at the University of Saskatchewan for using cluster Water, and the University of Colorado - CSDMS for using the cluster Beach. We thank NSF for financial support provided through grants: NSF-EAR 0963858, NSF-ACI 1148305. Yetemen acknowledges support from the GSA Farouk El-Baz student research award.

FundersFunder number
GSA Farouk El-Baz
Research Computing Group
U.S. Geological Survey
University of Saskatchewan
University of ColoradoNSF-EAR 0963858
Environment Canada


    • hillslope asymmetry
    • hillslope asymmetry index
    • landscape evolution
    • latitude
    • solar radiation
    • vegetation dynamics


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