Drought and the 2002-2003 El Niño in the Southwest U.S.

The southwest United States is currently experiencing three years of drought causing water shortages and low lake levels, and now an El Niño event is occurring. This study first assesses the current drought in the southwest United States, and then evaluates whether anticipated hydrologic impacts from the El Niño event are sufficient to end drought conditions. Drought conditions for the Colorado River basin are evaluated using 80 years (1923-2002) of streamflow data from two United States Geological Survey (USGS) stations located in the Upper Colorado River Basin (the Colorado River near Cisco, Utah and the Green River near Green River, Utah). Comparisons of historical cumulative streamflow deficits for droughts during this timeframe are examined. The current El Niño event is forecasted to persist through the end of 2002 and into early 2003 and the anticipated impacts for the Colorado River basin are less than the last El Niño event in 1997-1998. The observed streamflow for water years following the 11 identified El Nino events during 1923-2002 are evaluated to determine if current conditions would be sufficient to end the current drought. The Pacific Decadal Oscillation (PDO) is another factor that affects the hydrologic impacts of an El Niño event. The hydrologic impacts during the different phases of PDO and El Niño events will be evaluated to determine the likelihood of enhanced hydrologic impacts in the next year. The results of this research provide insight to the role of climate variability on drought in the southwes