• Advances in seasonal forecasting for water management in Arizona: a case study of the 1997-98 El Niño

      Pagano, Thomas; Hartmann, Holly; Sorooshian, Soroosh; Bales, Roger; Department of Hydrology & Water Resources, The University of Arizona (Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1999-11)
      This 1997-98 El Niño provided a unique opportunity for climate information and forecasts to be utilized by water management agencies in the Southwestern U.S. While Arizona has experienced high streamflow associated with previous El Niño events, never before had an event of such magnitude been predicted with advance warning of several months. Likewise, the availability of information, including Internet sources and widespread media coverage, was higher than ever before. Insights about use of this information in operational water management decision processes are developed through a series of semi -structured in -depth interviews with key personnel from a broad array of agencies responsible for emergency management and water supply, with jurisdictions ranging from urban to rural and local to regional. The interviews investigate where information was acquired, how it was interpreted and how it was incorporated into specific decisions and actions. The interviews also investigate agency satisfaction with the products available to them, their operational decisions, and intentions to utilize forecast products in the future. Study findings lead to recommendations about how to more effectively provide intended users of forecasts with information required to enact mitigation measures and utilize opportunities that some climatic events present. The material presented in this report is primarily based on the Masters Thesis of Thomas Pagano.
    • Evaluation of national weather service ensemble streamflow predictions (ESP) for the Colorado river basin

      Franz, Kristie J.; Hartmann, Holly C.; Sorooshian, Soroosh; Bales, Roger; Department of Hydrology & Water Resources, The University of Arizona (Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 2003-01)
      The National Weather Service (NWS) developed the Ensemble Streamflow Prediction (ESP) system to generate probabilistic water supply forecasts that consist of an ensemble of streamflow traces (scenarios) conditioned on the initial states of the basin. Uncertainty information available from ESP may be more useful to risk-based decision makers than what is currently provided by linear regression forecasts. Because the use of ESP has been limited to date, there are few operational forecasts available for verification. Therefore, it was necessary to generate simulated operational ESP forecasts to test the forecasting procedure's potential to enhance current forecasting techniques. Simulated historical forecasts were generated for 14 forecast points in the Colorado River basin. The median and best forecast traces were analyzed as representations of ESP deterministic forecasts. General scalar statistics were used to evaluate these traces. The probability information contained in the entire ensemble was analyzed using probabilistic and conditional verification methods. It was found that the information contained in the median trace is limited and that choosing one trace is not the optimal use of ESP forecast information. ESP provides a probabilistic forecast that performs better than a probabilistic forecast based on climatology. In addition, ESP can provide accurate information about the magnitude of future streamflow discharge even at lead times of up to seven months. With shorter lead times (2-3 months), the forecasts become more informative and accurate.