An experimental forecast system based on modern hydrologic models facilitates the evaluation of data assimilation methods, ensemble climate forecasts, and dissemination of visual nowcast and forecast products in ways not possible with current operational methods. H ydrologic extremes are costly to the nation. Annual U.S. drought and flood damages over the last decade have averaged between $6–$8 and $2 billion, respectively (FEMA 1995). Losses associated with the four-year 2000s drought in the western United States are likely to be in the tens of billions of dollars. To the extent that floods and droughts can be mitigated by management of water stored in reservoirs, improved streamflow prediction

This article applies formal detection and attribution techniques to investigate the nature of observed shifts in the timing of streamflow in the western United States (US). Previous studies have shown that the snow hydrology of the western US has changed in the second half of the 20 th century. Such changes manifest themselves in the form of more rain and less snow, in reductions in the snow water contents and in earlier snowmelt and associated advances in streamflow “center ” timing (the day in the “water-year ” on average when half the water-year flow at a point has passed). However, with one exception over a more limited domain, no other study has attempted to formally attribute these changes to anthropogenic increases of greenhouse gases in the atmosphere. Using the observations together with a set of global climate model (GCM) simulations and a hydrologic model (applied to three major hydrological regions of the western US – the California region, the Upper Colorado River basin and the Columbia River basin), we find that the observed trends toward earlier “center ” timing of snowmelt-driven streamflows in the western US since 1950 are detectably different from natural variability

The Northeast Climate Impacts Assessment (NECIA) is a collaboration between the Union of Concerned Scientists (UCS) and a team of independent experts to develop and communicate a new assessment of climate change and associated impacts on key climate-sensitive sectors in the northeastern United States. The goal of the assessment is to combine state-of-the-art analyses with effective outreach to provide opinion leaders, policy makers, and the public with the best available science upon which to base informed choices about climate change mitigation and adaptation. NECIA oversight and guidance is provided by a multidisciplinary Synthesis Team of senior scientists: NECIA Synthesis Team

Using observation-driven simulations of global terrestrial hydrology and a cluster algorithm that searches for spatially connected regions of soil moisture, the authors identified 296 large-scale drought events (greater than 500 000 km 2 and longer than 3 months) globally for 1950–2000. The drought events were subjected to a severity–area–duration (SAD) analysis to identify and characterize the most severe events for each continent and globally at various durations and spatial extents. An analysis of the variation of large-scale drought with SSTs revealed connections at interannual and possibly decadal time scales. Three metrics of large-scale drought (global average soil moisture, contiguous area in drought, and number of drought events shorter than 2 years) are shown to covary with ENSO SST anomalies. At longer time scales, the number of 12-month and longer duration droughts follows the smoothed variation in northern Pacific and Atlantic SSTs. Globally, the mid-1950s showed the highest drought activity and the mid-1970s to mid-1980s the lowest activity. This physically based and probabilistic approach confirms well-known droughts, such as the 1980s in the Sahel region of Africa, but also reveals many severe droughts (e.g., at high latitudes and early in the time period)