Precipitation and streamflow variability in northwestern Oklahoma, 1894-2003

This paper utilizes time-series analysis to examine precipitation and streamflow variability in northwestern Oklahoma over the period 1894-2003. Trends and periodicities in the hydroclimatic variables were investigated using, respectively, Mann-Kendall test and continuous wavelet transform (CWT) methods. Statistically significant trends were found in annual precipitation at individual gauging stations but with no spatial coherence to suggest evidence of large-scale climatic forcing. No significant trends were found for the regionalized average annual or seasonal precipitation. Annual streamflow exhibited declining trends upstream of Woodward. The CWT analysis revealed interannual to decadal modes of variability in precipitation. Similar but less sustained cycles are also found in streamflow. Correlation of precipitation with the El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) indices suggests precipitation for northwestern Oklahoma is associated with Pacific sea surface temperatures (SST).