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

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 at the basin scale, and none at the regional scale. In this work, we evaluate the impacts of forest disturbances and climate change for a headwater basin to the Colorado River, the San Juan River watershed, using a robustly-calibrated (Nash Sutcliff 0.80) 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 ET and increase streamflow. In this study, annual average regional streamflow under the coupled climate-disturbances scenarios is at least 6–11 % lower than those scenarios accounting for climate change alone, and 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 lower water availability for forested headwater systems to the Colorado River basin. These findings also indicate that explicit representation of land cover disturbances is required in modelling efforts that consider the impact of climate change on water resources.

Mechanisms of woody-plant mortality under rising drought, CO2 and vapour pressure deficit

“…Given that tree mortality leads to substantial changes in the structure and function of ecosystems, understanding drought-related mortality is fundamental to basic biology, ecosystem management and climate feedback predictions 57,58 . Changes in ecosystem structure and function due to mortality lead to large ecohydrologic shifts, with abrupt and potentially sustained changes in streamflow 59 as well as downstream water quality, quantity and timing 60,61 . Long-term shifts in forest demographics might also result from shifts in tree mortality rates 62 with corresponding limitations to net terrestrial carbon storage 63 ; a doubling of mortality halves forest carbon storage over 50 years if net primary production doesn't equally increase.…”