Title

Long-range streamflow forecasting in the Columbia River Basin and the El Niño-Southern Oscillation

Document Type

Presentation

Publication Date

1997

Description

Long-range forecasting of streamflow is important to hydrologists and water resource planners for the maintenance of a diverse ecosystem and for optimal operation of water resource systems. In the Western U.S., there is a significant relationship between streamflow and the El Nino-Southern Oscillation (ENSO). The Southern Oscillation Index (SOI) and the Wright Sea Surface Temperatures (SST) are used here to study the lag relationship between Western U.S. streamflow and ENSO indices. Preliminary research has shown that the North (Montana, Northern Idaho, Eastern Washington) experiences below normal spring-summer runoff during ENSO events while the South (New Mexico, Arizona, Southern California) experiences above normal spring- summer runoff. In both of these regions, the spring- summer runoff is significantly correlated with the prior summer and autumn SOI and SST values. These six to nine month lag correlations are important in making long- range streamflow forecasts. A long-range seasonal streamflow forecasting model is developed and tested on the Columbia River Basin, Washington State. A probabilistic streamflow forecast is made from an optimal linear combination of climatology, persistence, SOI Phase, SST Phase, and SOI Linear Discriminant Analysis (LDA), and SST LDA forecasts. The climatology forecast is based on the natural probabilities of receiving below normal (30\%), normal(40\%), or above normal conditions(30\%). The persistence forecast uses the previous three-month average streamflow value to make a probabilistic forecast of the next season streamflow. The influence of ENSO in the generation of streamflow is accounted for in the SOI Phase, SST Phase, LDA SOI, and LDA SST forecast models. The optimal linear combination of the six models is the forecast that minimizes the mean square error (Half- Brier score) and is the forecast with the best overall skill. This final combination forecast is referred to as a "consensus forecast."

Keywords

Columbia River Basin; Washington State; El Nino-Southern Oscillation (ENSO); Long range streamflow forecast modeling; Precipitation; Runoff; Water supply forecasting

Disciplines

Environmental Sciences | Fresh Water Studies | Meteorology

Comments

Presented at the Fourteenth Annual Pacific Climate (PACLIM) Workshop, Two Harbors, California, April 6-9.

Permissions

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