Statistical relations of precipitation and stream runoff for El Niño and La Niña periods, Texas Hill Country


The Texas Hill Country is threatened by devastating long-duration droughts and short-duration floods, either of which can occur at any time. In Central Texas, El Niño and La Niña conditions each occur about one-quarter of the time. Long-term precipitation data for the area reveal that greater rainfall generally occurs during La Niña periods for summer months but greater rainfall typically occurs during El Niño periods for other months. Annual streamflow peaks cannot be attributed to El Niño or La Niña conditions, but typically occur during the hurricane season (June through November), especially for the largest peaks. Additionally, El Niño period runoff volumes exceed those during La Niña at all runoff-gaged streams in the area. For the streams in the northern part of the Hill Country, El Niño period runoff only slightly exceeds La Niña period runoff. However, for the streams in the southern part of the area, El Niño period runoff greatly exceeds La Niña period runoff.