National Research Program
Hydrologic Variability and Trends
Using long-term data records, this project is focused on two problems of importance to water resources managers. First, long-term streamflow records are being used to a) identify broad regional to national trends in floods and low-flows and relate them to possible causes (climate change, water management changes, land-cover changes, and ground-water level change) and b) determine whether there are patterns that relate to watershed size or climate characteristics. It is often stated in the popular press and in official publications on global climate change that we can expect increased variability, including larger and/or more frequent floods, and deeper and longer droughts, as a result of greenhouse warming. This research will use the long-term historical records of streamflow at USGS streamgages to explore the empirical evidence for such statements. The second area of research is related to long-term changes in nutrient concentration and transport in major rivers. Although water resources managers have been attempting to control nutrients in our Nation's waters through efforts such as point source pollution control, non-point source best-management-practices, and air quality controls to limit atmospheric deposition, the question on how effective these efforts are remains unclear. The scientific complexities of this problem include consideration of: time lags between control measures and expected results, the potential that different control measures will have a different type of impact at low versus high flows or during some seasons and not others, and the potential for hysteresis in relationships between concentration and flow. The answer to this seemingly simple question is difficult to determine because surface-water quality is so highly dependent on the natural interannual variability of flow conditions.
REPORTS PUBLISHED 2008- 2012
Hirsch, R.M., and Ryberg, K.R. 2012 (web publication 10/24/11), Has the magnitude of floods across the USA changed with global CO2 levels?: Hydrological Sciences Journal, v. 57, no, 1, p. 1-9. (on-line abstract of journal article)
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