Encore: How Temperature and Precipitation Trends Have Affected Mountain Hydrology and Ecology

Guest presenter Charles H. Luce with the US Forest Service.

While modeling the pathways to increased temperature are clear with respect to increased atmospheric CO2, precipitation changes are more uncertain. Nonetheless, precipitation changes can have tremendous influences on hydrologically mediated outcomes of climate change, including many ecological changes in forests. Interpreting hydrological and ecological trends over the last several decades requires understanding both the temperature and the precipitation contexts underlying the change. Recent work has shown that there has been a trend in precipitation in the mountains of the Northwestern U.S. associated with changes in winter westerly winds. Although it presents, on the one hand, an opportunity for a discussion about whether precipitation might decline further, a more important discussion exists in deciphering how precipitation variations and temperature variations over the past 60 years have influenced hydrological and ecological outcomes, including: snowpack, low flows, floods, and wildfire. We will discuss the historical trends in temperature and precipitation and relate them to trends and sensitivities of outcomes to explore where and how precipitation uncertainty contributes, or does not contribute, to uncertainty in hydrological and ecological outcomes.