A framework for assessing flood frequency based on climate projection information

Abstract

Abstract. Flood safety is of the utmost concern for water resources management agencies charged with operating and maintaining reservoir systems. Risk evaluations guide design of infrastructure alterations or lead to potential changes in operations. Changes in climate may change the risk due to floods and therefore decisions to alter infrastructure with a life span of decades or longer may benefit from the use of climate projections as opposed to use of only historical observations. This manuscript presents a set of methods meant to support flood frequency evaluation based on current downscaled climate projections and the potential implications of changing flood risk on how evaluations are made. Methods are demonstrated in four case study basins: the Boise River above Lucky Peak Dam, the San Joaquin River above Friant Dam, the James River above Jamestown Dam, and the Gunnison River above Blue Mesa Dam. The analytical design includes three core elements: (1) a rationale for selecting climate projections to represent available climate projections; (2) generation of runoff projections consistent with climate projections using a process-based hydrologic model and temporal disaggregation of monthly downscaled climate projections into 6-h weather forcings required by the hydrologic model; and (3) analysis of flood frequency distributions based on runoff projection results. In addition to demonstrating the methodology, this paper also presents method choices under each analytical element, and the resulting implications to how flood frequencies are evaluated. The methods used reproduce the antecedent calibration period well. The approach results in a unidirectional shift in modeled flood magnitudes. The comparison between an expanding retrospective (current Correspondence to: D. A. Raff (draff@usbr.gov) paradigm for flood frequency estimation) and a lookahead flood frequency approach indicate potential for significant biases in flood frequency estimation.

Performance evaluation of AR4 Climate Models in simulating daily precipitation over the Indian region using skill scores

“…Daily precipitation is important at a river basin scale because it is (1) the main driver of runoff generation in river basins (Chen et al 2010;Chiew et al 2009;Kim and Pachepsky 2010;Piani et al 2010); (2) used in the evaluation of flood frequency for flood safety, which is of utmost concern for water resource management agencies for operating and maintaining reservoir systems (Raff et al 2009), and for risk evaluations to guide design of infrastructure alterations or potential changes in reservoir operations (Raff et al 2009); (3) used to study the impact produced by a precipitation pattern change in the erosion process in a river basin (Abaurrea and Asín 2005); (4) important in irrigation water management (García-Garizábal and Causapé 2010); (5) used in the estimation of water budget (Guo et al 2004), precipitation erossivity (Angulo-Martínez and Beguería 2009;Vrieling et al 2010), and groundwater recharge (Nolan et al 2007; Toews and Allen 2009); (6) used to study the effect of its changes on loads of NO 3 -N and sediment from watersheds (Chaplot 2007) and forest ecosystems (Johnson et al 2000); and (7) used to study water table fluctuations (Park and Parker 2008), atmospheric circulation, and temperature (Brandsma and Buishand 1997). Hence, the performance of daily precipitation simulated by GCMs should be evaluated at finer spatial scales.…”

Development of streamflow projections under changing climate conditions over Colorado River basin headwaters

“…Each of these headwater basins have been subject to previous study and are accompanied by significant and interesting water issues. The Gunnison River Basin has been the subject of numerous studies, particularly for the application of downscaled climate projections (e.g., Brekke and Prairie, 2009;McCabe Jr., 1994;Raff et al, 2009; US Department of the Interior, Bureau of Reclamation, Upper Colorado Region, 2009). Research on the impacts of teleconnection events on drought and streamflow conditions in the Green River Basin have provided some insight as to the role of teleconnections to climate variability over the Colorado River Basin (Tootle and Piechota, 2003).…”

“…The timing and magnitude of runoff events is of particular importance, as actual and forecasted runoff events can impact the operation of reservoirs (e.g., release schedules and magnitudes); however, climate change and anthropogenic alterations to basin characteristics increase the difficulty in accurately projecting streamflow conditions within hydrologic systems (e.g., Villarini et al, 2009). Raff et al (2009) developed a methodology to assess flood risk and runoff projections using projections of future climate. Raff et al (2009) utilized temperature and precipitation data from 112 Global Climate Models (GCMs) within the World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset (Meehl et al, 2007) subjected to statistical downscaling and bias-correction to drive the National Weather Service (NWS) River Forecasting System (RFS) hydrologic model.…”

“…Raff et al (2009) developed a methodology to assess flood risk and runoff projections using projections of future climate. Raff et al (2009) utilized temperature and precipitation data from 112 Global Climate Models (GCMs) within the World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset (Meehl et al, 2007) subjected to statistical downscaling and bias-correction to drive the National Weather Service (NWS) River Forecasting System (RFS) hydrologic model. Each of the four basins investigated in Raff et al (2009) exhibited the potential for increased flood frequency under changing climate conditions, although the authors did acknowledge the need for further study to more fully understand these results.…”

“…Christensen and Lettenmaier (2007) has previously used downscaled projections of precipitation and temperature to develop transient projections of runoff over the entire Colorado River Basin using the distributed Variable Infiltration and Capacity (VIC) model. Although this study does utilize information from the VIC model, the models and data sources presented in Raff et al (2009) are more similar to those utilized here.…”