Monday, 10 January 2005: 5:00 PM
Using NWSRFS ESP for Making Early Outlooks of Seasonal Runoff Volumes into Lake Powell
The Colorado Basin River Forecast Center (NOAA/NWS) is responsible for providing operational daily river forecasts and seasonal streamflow volumes for Lake Powell in the Upper Colorado River Basin. The Lake Powell forecast is extremely important to the USBR, States, Mexico and other water users. Forecasts are typically issued beginning on January 1 and updated every 15 days through the spring runoff season. During the past 15 years the runoff into Lake Powell has experienced two protracted lower than normal periods, 1988-1992 and 2000-2004. During the most recent drought, the lake level in Lake Powell has dropped to the lowest level since the lake completely filled in 1980. Published and local studies indicate that the observed streamflow over time is becoming more variable. At the same time, users are asking for earlier outlooks of spring runoff. To accommodate these requests, the CBRFC has explored creative ways of utilizing forecasts of climate variability in the forecast process. All of this provides interesting challenges for an operational forecast center. Currently the CBRFC utilizes two classes of models to provide outlooks and forecasts for seasonal volumes into Lake Powell: (1) multiple linear and non-linear regression using various types of variables and (2) the Ensemble Streamflow Prediction System, part of the NWS River Forecast System. The later incorporates an updating soil-moisture model, capabilities for pre-adjustment of input (precipitation and temperature ensembles) and post adjustment of output (streamflow) ensembles using climate forecasts and/or a variety of observed climate indices. Several other techniques such as Holt-Winters Analysis and statistical analogs have also been investigated for early outlooks made in the late summer and early fall. A description and application of the forecasts techniques for Lake Powell are presented.
Supplementary URL: http://www.cbrfc.noaa.gov