Paleoclimatic information for drought planning and decision making

Paleoclimatic data provide a longer temporal context for understanding the range of drought conditions that have occurred in the past and that may occur in the future under natural climate variability alone. Tree rings, because of their annual resolution and skill in documenting past drought conditions in the arid and semi-arid regions of the western U.S., have been useful tools for placing recent and current droughts in a long-term perspective. These data have been used in a variety of ways. We report two examples of projects in which water resource managers are applying information from tree rings to drought and water resources planning, in the middle Rio Grande region of New Mexico, and in California. In the Rio Grande region, through two workshops, we worked with area water managers to 1) provide a basic understanding of how tree-based reconstructions of streamflow are developed and applied to resource management, 2) understand Rio Grande water management challenges that might be addressed by streamflow reconstructions, and 3) develop data and tools useful for Rio Grande area decision making. Streamflow reconstructions and tools to assess these extended records were developed with scientific collaborators, and are now part of a web-based resource, which also includes information on the workshops: http://treeflow.info/riogr/index.html. For California, researchers partnered with the California Department of Water Resources to determine if tree-ring based reconstructions of streamflow and precipitation could inform drought planning. For this project, Urban Water Management Plans (UWMPs) for 22 water providers are being assessed to determine the robustness of water supply reliability based on instrumental record by considering worst-case droughts, which are then compared to worst-case drought in the extended reconstruction records. In many cases, much worse droughts have occurred in years prior to the 20th century. This information will be presented to water providers in the form of reports so that they may consider the use of paleohydrologic data in their updated UWMPs. These are just two examples of how paleoclimatic data are being developed in collaboration with water management agencies to help water resource managers anticipate and plan for droughts in the future.