OOS 28-4 - Vulnerability of coastal watersheds to climate change

In rain-dominated Pacific Northwest (PNW) systems, changes in precipitation regime are projected to cause coincident changes in streamflow regimes, including extended summer low flows and shorter, more intense winter storm runoff events. Natural watershed storage greatly influences seasonal streamflow regimes as well as hydrological responses to projected changes in the climate. Relative to other systems in the PNW, the rain-dominated, coastal watersheds of western Oregon are storage-limited. In general, little to no water is stored as snow, the aquifers are relatively shallow, and the topography is largely characterized by steep, narrow, and short mountain valleys. As a result, precipitation is routed quickly through the hydrological system, causing runoff to closely follow rainfall. Summer low flows are supported entirely by water stored in the subsurface. Given the seasonality of streamflow and storage limitations in coastal, rain-dominated watersheds, changes in the temporal patterns of precipitation have the potential to magnify the risk of extreme streamflow conditions during both high- and low-flow periods. This presentation addresses hydrogeomorphic factors that influence streamflow generation processes in rain-dominated watershed in coastal Oregon, and how a “bottom up” approach to climate change vulnerability assessments in rain-dominated freshwater environments improves our ability to predict potential hydrological responses at high resolutions.