Climate-driven disturbances in the San Juan River sub-basin of the Colorado River

Katrina E Bennett,Theodore J Bohn,Richard S Middleton,Kurt Solander,Enrique Vivoni,Chonggang Xu,Nathan G Mcdowell

doi:10.5194/hess-22-709-2018

Katrina E Bennett, Theodore J Bohn + Show 5 more

Open Access

https://doi.org/10.5194/hess-22-709-2018

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Abstract

Abstract. Accelerated climate change and associated forest disturbances in the southwestern USA are anticipated to have substantial impacts on regional water resources. Few studies have quantified the impact of both climate change and land cover disturbances on water balances on the basin scale, and none on the regional scale. In this work, we evaluate the impacts of forest disturbances and climate change on a headwater basin to the Colorado River, the San Juan River watershed, using a robustly calibrated (Nash–Sutcliffe efficiency 0.76) hydrologic model run with updated formulations that improve estimates of evapotranspiration for semi-arid regions. Our results show that future disturbances will have a substantial impact on streamflow with implications for water resource management. Our findings are in contradiction with conventional thinking that forest disturbances reduce evapotranspiration and increase streamflow. In this study, annual average regional streamflow under the coupled climate–disturbance scenarios is at least 6–11 % lower than those scenarios accounting for climate change alone; for forested zones of the San Juan River basin, streamflow is 15–21 % lower. The monthly signals of altered streamflow point to an emergent streamflow pattern related to changes in forests of the disturbed systems. Exacerbated reductions of mean and low flows under disturbance scenarios indicate a high risk of low water availability for forested headwater systems of the Colorado River basin. These findings also indicate that explicit representation of land cover disturbances is required in modeling efforts that consider the impact of climate change on water resources.

Highlights

Widespread forest disturbances are projected to increase with climate change (McDowell et al, 2016; Allen et al, 2010; Van Mantgem et al, 2009) and this will have major implications for ecosystem services (Anderegg et al, 2013)
This is salient for regions of the USA such as the Colorado River basin (CRB), where forest cover is anticipated to be significantly impacted by a higher incidence of wildfire, drought, and pest infestations (Williams et al, 2013)
We found that failing to consider climate change coupled with vegetation disturbances could result in a ∼ 10 % over-estimation of the annual water availability for this basin

Summary

Introduction

Widespread forest disturbances are projected to increase with climate change (McDowell et al, 2016; Allen et al, 2010; Van Mantgem et al, 2009) and this will have major implications for ecosystem services (Anderegg et al, 2013). Climate-induced changes in forests will feedback to the climate system by altering the albedo and reducing the carbon sink, which is anticipated to further transform ecosystems in either positive or negative ways (Dale et al, 2001). This is salient for regions of the USA such as the Colorado River basin (CRB), where forest cover is anticipated to be significantly impacted by a higher incidence of wildfire, drought, and pest infestations (Williams et al, 2013)

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