Effects of Climate Change on Extreme Low-Flows in Small Lowland Tributaries in the Skagit River Basin

Abstract

Abstract Management of extreme low-flows requires fundamental trade-offs between water extraction for human use (e.g. for irrigation and municipal water supply) and in-stream flows to protect aquatic ecosystems. In the context of protecting endangered salmon and other cold-water fish species in small streams, extreme low-flows are one of the most important aspects of the flow regime. We quantify projected changes in low-flow magnitude and timing for several lowland tributaries of the Skagit River basin in response to regional climate change. Ten hydrologic model simulations of mid-21st century (2030–2059) streamflows are compared against a historical period (1917–2006). Each of the hydrologic simulations are forced by atmospheric variables developed from respective CMIP3 global climate model (GCM) output downscaled to 1/16th degree resolution using the Hybrid-Delta downscaling method. Baseline historical simulations are forced by historical gridded meteorological data sets of temperature and precipitation...