Management Implications of Non-Stationary Hydrology: Decision-Scale Approaches

Climate variability and change impact the assumption of hydrologic stationarity, which has been a centerpiece of major water resources investments in the United States. Despite its obvious oversimplification of a complex system, stationarity was a necessary assumption for the planning and design of water resources projects with relatively short observed records and few sophisticated dynamic process models and computational techniques. Additional complexity is introduced because planning, design and implementation of climate-resilient water resources management measures must occur at scales from national to project level and from sub-hourly to multi-decadal to ensure that agency missions and operations are not compromised. Advances in hydrologic understanding and climate science now support hydrologic analysis and prediction more representative of the constantly changing environment. However, no clear vision has been articulated to direct the development of best practices with respect to nonstationarity or the use of hydrologic predictions. In part, this is because there is limited quantity and quality of scalable information about possible future climate effects on streamflow, extreme hydrologic events, land-surface water and energy balances, water supply, water quality, and water-related ecosystem impacts suitable for water resources decisions. Second, though numerous possible approaches to produce and apply climate change information for water resource issues have been developed, each method or analytical technique involves a set of uncertainties and potential deficiencies that are characterized and quantified to varying degrees, some of which may be sensitive to scale. The magnitude of climate change impacts and associated decisions facing water resources managers in the United States has spurred closer interagency cooperation by the two largest water resources management agencies in the US, the USACE Army Corps of Engineers and the Bureau of Reclamation. The two agencies have partnered to describe climate change challenges to federal water resources management, identify user needs for improving tools and information, assess capabilities to use weather and climate forecasts in federal water resources management, and discuss approaches to nonstationarity. Following an expert workshop in January 2010, “Nonstationarity, Hydrologic Frequency Analysis, and Water Management,” they concluded that present hydrologic analysis and design guidance for federal infrastructure must be updated to include climate variability and change resulting in non-stationary conditions. They are working with other operating and science agencies to develop principles and strategies for assessing the strengths and limits of the various approaches for producing and using hydrologic predictions at specific decision scales. This presentation addresses collaboration to date and discusses examples of decision-scale approaches to climate change-related water resources management decisions.