Holly Hartmann

CONFIDENCE BUILDERS Evaluating Seasonal Climate Forecasts from User Perspectives

Abstract Water managers, cattle ranchers, and wildland fire managers face several barriers to effectively using climate forecasts. Repeatedly, these decision makers state that they lack any quantitative basis for evaluating forecast credibility. That is because the evaluations currently available typically reflect forecaster perspectives rather thanthose of users, or are not available in forms that users can easily obtain or understand. Seasonal climateforecasts are evaluated from the perspective of distinct user groups, considering lead times, seasons, and criteria relevant to their specific situations. Examples show how results targeted for different user perspectives can providedifferent assessments of forecast performance. The forecasts evaluated are the official seasonal temperature andprecipitation outlooks issued by the NOAA Climate Prediction Center, produced in their present format since December 1994. It is considered how forecast formats can affect the ease, accuracy, and reliability of interpr...

Verification of National Weather Service Ensemble Streamflow Predictions for Water Supply Forecasting in the Colorado River Basin

The Ensemble Streamflow Prediction (ESP) system, developed by the National Weather Service (NWS), uses conceptual hydrologic models and historical data to generate a set, or ensemble, of possible streamflow scenarios conditioned on the initial states of a given basin. Using this approach, simulated historical probabilistic forecasts were generated for 14 forecast points in the Colorado River basin, and the statistical properties of the ensembles were evaluated. The median forecast traces were analyzed using ‘‘traditional’’ verification measures; these forecasts represented ‘‘deterministic ESP forecasts.’’ The minimum-error and historical traces were examined to evaluate the median forecasts and the forecast system. Distribution-oriented verification measures were used to analyze the probabilistic information contained in the entire forecast ensemble. Using a single-trace prediction, for example, the median, resulted in a loss of valuable uncertainty information about predicted seasonal volumes that is provided by the entire ensemble. The minimum-error and historical traces revealed that there are errors in the data, calibration, and models, which are part of the uncertainty provided by the probabilistic forecasts, but are not considered in the median forecast. The simulated ESP forecasts more accurately predicted future streamflow than climatology forecasts and, on average, provided useful information about the likelihood of future streamflow magnitude with a lead time of up to 7 months. Overall, the forecast provided stronger probability statements and became more reliable at shorter lead times. The distribution-oriented verification approach was shown to be applicable to ESP outlooks and appropriate for extracting detailed performance information, although interpretation of the results is complicated by inadequate sample sizes.

Understanding uncertainties in future Colorado River streamflow

The Colorado River is the primary water source for more than 30 million people in the United States and Mexico. Recent studies that project streamf low changes in the Colorado River all project annual declines, but the magnitude of the projected decreases range from less than 10% to 45% by the mid-twenty-first century. To understand these differences, we address the questions the management community has raised: Why is there such a wide range of projections of impacts of future climate change on Colorado River streamflow, and how should this uncertainty be interpreted? We identify four major sources of disparities among studies that arise from both methodological and model differences. In order of importance, these are differences in 1) the global climate models (GCMs) and emission scenarios used; 2) the ability of land surface and atmospheric models to simulate properly the high-elevation runoff source areas; 3) the sensitivities of land surface hydrology models to precipitation and temperature changes; ...

Formal Scenario Development for Environmental Impact Assessment Studies

Abstract Scenario analysis is a process of evaluating possible future events through the consideration of alternative plausible, though not equally likely, states (scenarios). The analysis is designed to enable improved decision making and assessment through a more rigorous evaluation of possible outcomes and their implications. For environmental impact and integrated assessment studies, the process of scenario development typically involves making explicit and/or implicit assumptions about potential future conditions, such as climate change, land cover and land use changes, population growth, economic development and technological changes. Realistic assessment of scenario impacts often requires complex integrated modelling frameworks that represent environmental and socioeconomic systems to the best of our knowledge, including assumptions about plausible future conditions. In addition, scenarios have to be developed in a context relevant to the stakeholders involved, and include estimation and communication of uncertainties, to establish transparency, credibility and relevance of scenario results among the stakeholders. This paper reviews the state of the art of scenario development and analysis, proposes a formal approach to scenario development in environmental studies and discusses existing issues. Major recommendations for future research in this area include proper consideration of uncertainty involved in scenario studies, construction of scenarios of a more variable nature, and sharing of information and resources among the scenario development research community.

Federal priorities and programs in the hydrological sciences

How high a priority is hydrologic research for U.S. federal agencies? Although hydrology affects human lives and economic activity significantly, federal agency research priorities ultimately reflect the ability of the research community to generate political support, both locally and nationally. Unless the research community cultivates a vocal constituency by demonstrating the practical benefits of hydrologic research products, we risk declining federal support as other scientific disciplines step forward to direct federal agency priorities. Also, several hydrology programs require immediate mobilization of support to prevent losses in research capabilities. These were the conclusions of panel members participating in a uniquely frank “Town Hall Meeting” of the Hydrology Section at the 1998 AGU Fall Meeting. Agency representatives attending included Ghassem R. Asrar, NASA Associate Administrator for Earth Science; D.James Baker, NOAA Administrator; Robert M. Hirsch, Director of the USGS Water Resources Division; and George M. Hornberger, Chair of the National Research Council (NRC) Commission on Geosciences, Environment, and Resources (CGER).