HYDROLOGIC RESPONSE OF YOUNG VOLCANIC TERRANES TO CLIMATE WARMING: PERSPECTIVES AND PARADOXES

An expanding area of research is forecasting likely impacts of climate warming on specific geographic regions. With respect to effects on water resources, much of the focus up to now has been on streamflow response to changing snow accumulation and melt regimes under conditions of warming winters and earlier springs. Geological factors governing streamflow response have generally been less emphasized. However, both long-term streamflow data and hydrologic modeling reveal that geology, as reflected primarily in the landscape-level storage properties and transmissivity, is a first-order control on streamflow response to climate change. In particular, the extremely high permeabilities of young volcanic terranes, such as the Cascade Mountains, make these among the most sensitive to climate warming, as revealed by changing patterns of late-summer streamflow. Application of a process-based hydrologic model to four watersheds in the Western Cordillera reveals that, contingent on timing of snowmelt, young volcanic watersheds are likely to have more water in summer but paradoxically are subject to the greatest summer water losses under a 1.5C warming scenario. These results highlight the importance of geological factors in interpreting hydrologic response to climate change, and argue for a geoclimatic framework that incorporates geology as well as snowmelt timing in predicting future changes to streamflow and designing monitoring networks that will become the basis for assessing climate change impacts in mountain regions globally.