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Smith M.,National Oceanic and Atmospheric Administration | Koren V.,National Oceanic and Atmospheric Administration | Zhang Z.,National Oceanic and Atmospheric Administration | Zhang Z.,University Corporation for Atmospheric Research | And 32 more authors.
Journal of Hydrology | Year: 2013

The Office of Hydrologic Development (OHD) of the U.S. National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS) conducted the two phases of the Distributed Model Intercomparison Project (DMIP) as cost-effective studies to guide the transition to spatially distributed hydrologic modeling for operational forecasting at NWS River Forecast Centers (RFCs). Phase 2 of the Distributed Model Intercomparison Project (DMIP 2) was formulated primarily as a mechanism to help guide the U.S. NWS as it expands its use of spatially distributed watershed models for operational river, flash flood, and water resources forecasting. The overall purpose of DMIP 2 was to test many distributed models forced by high quality operational data with a view towards meeting NWS operational forecasting needs. At the same time, DMIP 2 was formulated as an experiment that could be leveraged by the broader scientific community as a platform for the testing, evaluation, and improvement of distributed models.DMIP 2 contained experiments in two regions: in the DMIP 1 Oklahoma basins, and second, in two basins in the Sierra Nevada Mountains in the western USA. This paper presents the overview and results of the DMIP 2 experiments conducted for the two Sierra Nevada basins. Simulations from five independent groups from France, Italy, Spain and the USA were analyzed. Experiments included comparison of lumped and distributed model streamflow simulations generated with uncalibrated and calibrated parameters, and simulations of snow water equivalent (SWE) at interior locations. As in other phases of DMIP, the participant simulations were evaluated against observed hourly streamflow and SWE data and compared with simulations provided by the NWS operational lumped model. A wide range of statistical measures are used to evaluate model performance on a run-period and event basis. Differences between uncalibrated and calibrated model simulations are assessed.Results indicate that in the two study basins, no single model performed best in all cases. In addition, no distributed model was able to consistently outperform the lumped model benchmark. However, one or more distributed models were able to outperform the lumped model benchmark in many of the analyses. Several calibrated distributed models achieved higher correlation and lower bias than the calibrated lumped benchmark in the calibration, validation, and combined periods. Evaluating a number of specific precipitation-runoff events, one calibrated distributed model was able to perform at a level equal to or better than the calibrated lumped model benchmark in terms of event-averaged peak and runoff volume error. However, three distributed models were able to provide improved peak timing compared to the lumped benchmark. Taken together, calibrated distributed models provided specific improvements over the lumped benchmark in 24% of the model-basin pairs for peak flow, 12% of the model-basin pairs for event runoff volume, and 41% of the model-basin pairs for peak timing. Model calibration improved the performance statistics of nearly all models (lumped and distributed). Analysis of several precipitation/runoff events indicates that distributed models may more accurately model the dynamics of the rain/snow line (and resulting hydrologic conditions) compared to the lumped benchmark model. Analysis of SWE simulations shows that better results were achieved at higher elevation observation sites.Although the performance of distributed models was mixed compared to the lumped benchmark, all calibrated models performed well compared to results in the DMIP 2 Oklahoma basins in terms of run period correlation and %Bias, and event-averaged peak and runoff error. This finding is noteworthy considering that these Sierra Nevada basins have complications such as orographically-enhanced precipitation, snow accumulation and melt, rain on snow events, and highly variable topography. Looking at these findings and those from the previous DMIP experiments, it is clear that at this point in their evolution, distributed models have the potential to provide valuable information on specific flood events that could complement lumped model simulations. © 2013.

Steve Sands came with his son Weston to see the rising waters in the Mississippi River as flood waters approach their crest in Greenbelt Park in Memphis, Tennessee January 4, 2016. The risk extends to eastern Texas and the southeastern Coastal Plain, the National Oceanic and Atmospheric Administration (NOAA) said in issuing its spring outlook. Early spring storms fueled by El Nino have already drenched areas of Louisiana, eastern Texas, Mississippi and Arkansas with up to 20 inches (50.8 cm) of rain, causing widespread flooding, said Tom Graziano, acting director of NOAA's National Water Center. "The good news is that once the ongoing river flooding recedes, the risk for additional widespread major flooding is low across the country for the remainder of the spring," Graziano said in a conference call with reporters. "Because of a mild winter and little snow accumulation, the western half of the country, the Upper Midwest, the Middle Atlantic and Northeast all have a low risk of river flooding, which is typically enhanced by snow melt," Graziano said. Following a record-warm winter in the contiguous United States, above-normal temperatures should persist in most of the country through June, except for the southern Plains. "There might be some cool outbreaks from time to time but the general spring outlook is for a warm-weather pattern," said Brad Rippey, a U.S. Department of Agriculture meteorologist on the call. However, he cautioned farmers and gardeners against planting before typical last-frost dates, saying, "you can still have these episodic freezes or cold outbreaks within an overall mild regime." NOAA called for above-normal precipitation through June for the southern half of the United States and an equal chance of above- or below-normal rainfall in the northern Plains, Midwest and Northeast. In California, which has endured a multi-year drought, conditions are improving in the northern half of the state, particularly after storms in the last two weeks. The state's water resources "are more favorable than they have been since 2011," said Rob Hartman, a hydrologist with NOAA's California Nevada River Forecast Center, on the call. But Southern California is still mired in drought that is expected to persist through June. Ending California's drought statewide will take multiple years, Hartman said. "It's going to take a while. Over the last four years prior to this year, we were missing between one and two years of rainfall. That has to be made up in some fashion," Hartman said.

It's official: El Niño is back. This winter is likely to be wetter and warmer than average, thanks to a strong El Niño brewing in the Pacific Ocean that will probably persist through the winter, forecasters said today (Oct. 15) during a news briefing. "We won't be able to officially rank it until it peaks out and ends. But our expectation is that it will be amongst the three strongest," with the other strong El Niño events occurring in the 1997–98 and 1982–83 winter seasons, said Mike Halpert, the deputy director of the Climate Prediction Center, part of the National Oceanic and Atmospheric Administration (NOAA). The strong subtropical weather pattern boosts the odds for rainfall and warm temperatures across the Southern United States and the Eastern Seaboard — including drought-stricken regions such as California and the Southwest. But even if California is inundated with rain, the state's water woes probably won't be eliminated in one season, the experts said. [Infographic: How El Niño Causes Wild Weather Across the Globe] El Niño weather patterns occur when warm water from the western tropical Pacific Ocean shifts toward the equatorial coast of South America, nudging tropical storms eastward. Because moisture-laden air causes thunderstorms, and because the greatest amount of water evaporates from the oceans in the warm, tropical areas, El Niño weather patterns tend to bring high-precipitation thunderstorms and warmer weather to the United States. El Niño and its counterpart, La Niña, are part of the El Niño-Southern Oscillation, or ENSO, cycle. This season, a strong El Niño is in the cards. But that doesn't guarantee warm and soppy forecasts, Halpert said. Other, more unpredictable climate systems such as the North Atlantic and Artic oscillations, as well as local weather events, can also affect winter storms. "The climate system is far more complicated than just El Niño, even a strong one," Halpert said. However, based on the current status, there is about a 60 percent chance for warmer weather than average across the Northern United States, and about a 70 percent chance of wetter weather across the South, he said. Meanwhile, the Rockies, the Great Lakes region, Northern Alaska and Hawaii are expected to face drier-than-average conditions, he said. California is facing its worst drought in hundreds of years, with snowpack at record low levels across much of the state. Nearly half the state faces exceptional drought, with all of the state experiencing some drought, according to the U.S. Drought Monitor. The El Niño could improve the parched conditions, though exactly how much isn't clear, said Allen Haynes, a hydrologist with the California Nevada River Forecast Center. The winter forecast does predict wetter weather across Southern California. However, much of the state's water supply comes from snowpack in Northern California, and weather is only weakly correlated to El Niño events there, Haynes said. In addition, the mountains in the north of the state tend to be lower in elevation, so warmer weather could also mean the storms cause heavy rainfall but do not add to the snowpack, the water storage bank for much of the state, Haynes said. Even if the El Niño brings strong precipitation to Northern California, where it matters most, the soakings are unlikely to erase the four-year deficit in water from the multiyear drought, he said. For instance, the wettest year on record, 1983, brought twice the average yearly precipitation, but completely erasing the current deficit would require between 2.5 and three times the average annual rainfall, he said. "A full recovery is likely to be uneven across the West and is also likely to take more than one season of above-average precipitation," Haynes said. In addition, strong rainfalls could bring flooding, especially in areas scarred by forest fires, which lack the natural barriers that absorb water and slow down runoff, Haynes said. Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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