Thursday, January 17, 2008
2:00-3:00 (Philip Mote presentation from 1:30-2:00)
Effects of changing 20th century precipitation variability on annual streamflow resources and hydropower production in the western U.S.
Cool season precipitation variability explains upwards of 80% of the variance in annual streamflow in the Columbia River basin (PNW), more than 90% of the variability in the Sacramento San Joaquin (SSJ) basins, and roughly 60% of the variability in Colorado River basin (CRB). Persistent and fundamental changes in cool season precipitation variability have been observed since the mid-1970s, and include increased coefficient of variation, persistence, and inter-regional covariation. Using long term temperature and precipitation data sets from 1916-2003 to drive the Variable Infiltration Capacity hydrologic simulation model, we simulate monthly streamflow from 1916-2003 at a number of river locations which in turn is used to drive three reservoir simulation models for the PNW, SSJ, and CRB. Despite differences in climate and water resources infrastructure and management in the three regions examined, changes in streamflow and hydropower production since the 1970s have largely mirrored changes in cool season precipitation variability outlined above. These changes in the variability of hydropower resources have increased vulnerability to energy shortages in the western U.S. because droughts in the late 20th century are both longer and more intense, and tend to be more coincident from region to region. Similar changes are apparent for high flow conditions when abundant hydropower resources have been available west-wide. The paleorecord from 1858-1977 suggests that the observed pattern of variability from 1977-2003 is very unusual in the context of natural variability. The changes in cool season precipitation variability, streamflow and hydropower resources have also been coincident with strong anthropogenically forced warming at the global scale (and are broadly consistent with the effects predicted by global climate model simulations), it remains to be seen if these changes are systematic and physically related to global warming in some way, or if they are simply a temporary feature of natural variations in precipitation that have been unusual in the earlier parts of the record. If these changes are in fact systematic in nature, ongoing changes in energy and water management to cope with the altered variability will be needed.
Alan Hamlet is a Research Scientist with the CIG and a Research Assistant Professor the UW Department of Civil & Environmental Engineering.