Assessing the Evolution of Climate Change Impacts Studies on California Hydrology: A Background For The IPCC Fourth Assessment's Studies

The Third IPCC Assessment recognized that climate change has the potential to impact hydrology and water resources throughout the world, especially in mountainous regions like California's Sierra Nevada Mountains. These mountainous regions are especially vulnerable due to their dependence on mountain snow accumulation and the snowmelt process, two processes which are especially susceptible to changes in temperature. This research investigates the evolution of climate change impact studies on California hydrology, and serves as a background for current studies that will be included in the IPCC Fourth Assessment. Over 40 studies in the last 20 years have attempted to assess the impacts of climate change on the California hydrology. We have classified these studies in two major groups: the first group involves the question: what evidence of climate change do we see in historical streamflows to date? The second category covers studies that are focused on prediction of the potential effect of climate change on streamflow. We recognize that there have been improvements in the methodological approaches used over 20 years. Despite some disagreements among the studies, there is a consistent message that California will receive more water when we don't need it and less when we need it.