Evaluation of streamflow trends in the Pacific Northwest using Wavelet Analysis

Abstract:

Streamflow is one of the key components of hydrologic cycle. Understanding the variability and trends in streamflow can help in water resources planning, especially management of floods and droughts. Pacific Northwest US is unique due to its geographical location, having Pacific Ocean on the west and Rocky mountains on the east. Recent climate studies in the area show increase in temperatures and decline in snow water equivalent. In this study, a series of sequential Mann-Kendall tests and continuous wavelet analysis are performed on 39 Hydro-Climatic Data Network (HCDN) streamflow stations with available data between 1951 - 2010. The results from sequential M-K tests and continuous wavelet analysis reveal the trends observed in the Pacific Northwest region at 5% significance level. Scale-averaged power spectra are used to relate the streamflow time series and interannual variability at the 39 streamflow stations. Mann-Kendall tests show a significant negative trend. Spatial analysis for these stations is done using Time-Latitude Hovmoller plot. It is observed that for 8-16 years period, there is high variance between 1975 to 2002 in the northern region and the variance decreases towards south. For 4-8 year period, increasing variance is observed in the southern part between 1987-1997. For 2-4 year period, significant variance is observed between 1970-1975 and 1998-2002 for all the stations in the study area.