MULTI-YEAR PRECIPITATION VARIATIONS AND WATER RESOURCES IN WEST-CENTRAL OKLAHOMA

Persistent, multi-year departures in annual precipitation from mean have been observed in central Oklahoma. Precipitation departures caused by a sequence of predominantly wet or dry years and lasting 5 or more years are called wet or dry periods, respectively. Impacts of wet and dry periods on water yield from an 800 km2 mixed-agricultural watershed in west central Oklahoma were investigated. Precipitation and water yield observations and estimates were available for 1940 through 2007, and several wet and dry periods were identified over this time span. Mean annual precipitation and water yield were calculated separately for wet and dry periods. A comparison of mean precipitation between wet and dry periods showed a difference of about 30% based on mean annual precipitation, whereas the corresponding difference in annual water yield was about 100% based on mean annual water yield. A similar response to precipitation variations was also observed in stream flow of the much larger Washita River basin in south west Oklahoma. These two examples illustrate that small or moderate multi-year precipitation variations can amplify into comparatively large water yield variations. The non-linearity and sensitivity of the cause-effect relationships linking annual precipitation and water yield, and the presence of multi-year precipitation variations suggest that care should be taken when selecting a representative climate and stream flow record for design of water infrastructure and water resources management.