Woody plant encroachment has a larger impact than climate change on dryland water budgets

Authors: SCHREINER-MCGRAW, ADAM - University Of California; VIVONI, ENRIQUE - Arizona State University; AJAMI, HOORI - University Of New South Wales; SALA, OSVALDO - Arizona State University; THROOP, HEATHER - Arizona State University; Peters, Debra

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2020
Publication Date: 5/15/2020
Citation: Schreiner-McGraw, A., Vivoni, E., Ajami, H., Sala, O., Throop, H., Peters, D.C. 2020. Woody plant encroachment has a larger impact than climate change on dryland water budgets. Scientific Reports. 10:8112. https://doi.org/10.1038/s41598-020-65094-x.
DOI: https://doi.org/10.1038/s41598-020-65094-x

Interpretive Summary: Woody plant enroachment into dryland occurs globally with consequences on ecosystem structure and function. Quantifying effects on hydrological processes at the watershed scales has been challenging. We used a process-based ecohydrologic model to simulate impacts of woody plant encroachment on recharge through streambeds. We show that when grasslands convert to shrublands streambed infiltrtaion increases by 29% when bare soil increases. When bare soil cover does not change, transmission losses are reduced by 18%. Our results show that feedbacks between shrub encroachment and plant available water can lead to further shrub encroachment.

Technical Abstract: Woody plant encroachment (WPE) into grasslands is a global phenomenon that is associated with land degradation via xerifcation, which replaces grasses with shrubs and bare soil patches. It remains uncertain how the global processes of WPE and climate change may combine to impact water availability for ecosystems. Using a process-based model constrained by watershed observations, our results suggest that both xerifcation and climate change augment groundwater recharge by increasing channel transmission losses at the expense of plant available water. Conversion from grasslands to shrublands without creating additional bare soil, however, reduces transmission losses. Model simulations considering both WPE and climate change are used to assess their relative roles in a late 21st century condition. Results indicate that changes in focused channel recharge are determined primarily by the WPE pathway. As a result, WPE should be given consideration when assessing the vulnerability of groundwater aquifers to climate change.