Analysis of Trends and Persistence in Hydrologic Records

The issue of global warming has prompted an examination of hydrologic time series for trends. Trend assessment is pursued here in conjunction with an assessment of flow series persistence. The analysis of trend and persistence is carried out in the Upper Mississippi and Missouri River basins. In the investigation, flood sequences are considered as elements of the spectrum of extreme flows, where the spectrum extends from the low to the high flows. Most gages in the Upper Mississippi basin show significant positive trends and persistence in low flows, with larger trends in the more northern part of the basin. There is also a consistent pattern of significant positive trends and persistence in the annual mean flows throughout the basin. Longer-duration high flows showed less propensity toward trend and persistence. There is not a strong propensity toward trend and persistence in the 1-day high flow.