A topographic mechanism for arcing of dryland vegetation bands

TL;DR

This paper introduces a modified water-transport model to explain how terrain curvature influences the arcing direction of dryland vegetation bands, aligning with remote sensing observations across different aridity levels.

Contribution

It presents a new model incorporating terrain curvature effects to explain vegetation band arcing, supported by simulations and remote sensing data.

Findings

Vegetation bands switch arcing direction depending on terrain curvature.

Model predictions align with remote sensing observations.

Aridity influences whether bands grow on ridges, valleys, or both.

Abstract

Banded patterns consisting of alternating bare soil and dense vegetation have been observed in water-limited ecosystems across the globe, often appearing along gently sloped terrain with the stripes aligned transverse to the elevation gradient. In many cases these vegetation bands are arced, with field observations suggesting a link between the orientation of arcing relative to the grade and the curvature of the underlying terrain. We modify the water transport in the Klausmeier model of water-biomass interactions, originally posed on a uniform hillslope, to qualitatively capture the influence of terrain curvature on the vegetation patterns. Numerical simulations of this modified model indicate that the vegetation bands change arcing-direction from convex-downslope when growing on top of a ridge to convex-upslope when growing in a valley. This behavior is consistent with observations from remote sensing data that we present here. Model simulations show further that whether bands grow on ridges, valleys, or both depends on the precipitation level. A survey of three banded vegetation sites, each with a different aridity level, indicates qualitatively similar behavior.