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Published February 27, 2013
Streamflow Forecast(for spring and summer)
Data Source(s): National Water and Climate Center
The spring–summer streamflow forecast for the Southwest, issued on February 1 by the Natural Resources Conservation Service (NRCS), calls for below-average flows in most river basins in Arizona and New Mexico (Figure 12). Based on the accumulated precipitation through February 1, there is only a 50 percent chance that the Salt River, measured near Roosevelt Lake, and the Gila River, measured at the inflow of San Carlos Reservoir, will exceed 63 and 44 percent of the February–May average, respectively. The 50 percent likelihood can be considered the best estimate. In these probabilistic forecasts, lower likelihoods are accompanied by a higher percent of average streamflows, and vice versa. For example, the Salt River has only a 30 percent chance of exceeding 84 percent of average flows.
For Lake Powell, there is only a 50 percent chance that spring inflow will exceed 52 percent of the 1971–2000 average for April–July, or about 3.75 million acre-feet. The forecast also indicates only a 10 percent chance that Lake Powell inflow will be more than 91 percent of average, providing an indicator that above-average flows are very unlikely. The Verde River is the only watershed in Arizona in which spring streamflows are likely to be above average.
Below-average precipitation has fallen this winter in the Rio Grande headwaters in southern Colorado. Consequently, there is a 50 percent chance that the March–July flow in the Rio Grande, measured at Otowi Bridge in New Mexico, will be 47 percent of average, the same as last month. If this occurs, irrigators in the Elephant Butte Irrigation District could experience another season with below-average allotments. As of February 1, Elephant Butte Reservoir contains only 8 percent of its full storage. Also, the projected inflow into the El Vado Reservoir, on the Rio Grande north of Otowi Bridge, is only 64 percent of average; El Vado contains only 8 percent of average storage.
Water supply forecasts for the Southwest are coordinated between the National Water and Climate Center, part of the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS), and the Colorado Basin River Forecast Center (CBRFC), part of NOAA. The forecast information provided in Figure 12 is updated monthly by the NWCC. Unless otherwise specified, all streamflow forecasts are for streamflow volumes that would occur naturally without any upstream influences, such as reservoirs and diversions. The coordinated forecasts by NRCS and NOAA are only produces for Arizona between January and May, and for New Mexico between January and May.
The NRCS provides a range of forecasts expressed in terms of percent of average streamflow for various exceedance levels. The forecast presented here is for the 50 percent exceedance level, and is referred to as the most probable streamflow. This means there is at least a 50 percent chance that streamflow will occur at the percent of average shown in Figure 12. The CBRFC provides a range of streamflow forecasts in the Colorado Basin ranging from short fused flood forecasts to longer range water supply forecasts. The water supply forecasts are coordinated monthly with NWCC.
For state river basin streamflow probability charts, visit :
For information on interpreting streamflow forecasts, visit:
For western U.S. water supply outlooks, visit:
Southwest Climate Outlook Staff
- Michael Crimmins, UA Extension Specialist
- Stephanie Doster, Institute of the Environment Editor
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, Managing Editor, CLIMAS Associate Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Dollin, CLIMAS Publications Assistant
- Dave Dubois, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
The CLIMAS Web site contains official and non-official forecasts, as well as other information. While we make every effort to verify this information, please understand that we do not warrant the accuracy of any of these materials.... Read full disclaimer