Streamflow Forecast

This past winter’s La Niña event left a dry imprint on the Southwest. The spring–summer streamflow forecast issued May 1 by the Natural Resources Conservation Service (NRCS) for the Southwest predicts below-average flows for all basins in New Mexico and above-average flows for most of the Upper Colorado River Basin (Figure 13). These forecasts are based principally on snow accumulation in the mountains from which most of the water originates. The NRCS and the Colorado Basin River Forecast Center do not issue streamflow forecasts for Arizona after April 1. On April 1, forecasts for the Salt and Upper Gila rivers called for very low probabilities that flows will be near average. Forecasts indicated a 50 percent chance that streamflow in the Salt and Verde rivers during the April–May period will be equal to or less than about 15 and 43 percent of average, respectively.

In New Mexico, many gaging stations are falling into the 10th to 24th percentiles for streamflow, which is considered below average, while some of the mainstream gages are falling into the 25th to 74th percentiles, which is considered average. Some stations along the Pecos and Upper Rio Grande tributaries are reporting well below-average flows, as are some points on the Gila and San Juan rivers. It should be noted that although snowpack levels dropped throughout April, streamflow volumes have not consistently increased accordingly, indicating sublimation and infiltration losses are occurring.