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North Dakota State University (2015)

Impact of climate variability on streamflow and water quality in the north central United States

Ryberg, Karen Renee

Titre : Impact of climate variability on streamflow and water quality in the north central United States

Auteur : Ryberg, Karen Renee

Université de soutenance : North Dakota State University

Grade : Doctor of Philosophy (PhD) 2015

Résumé
Long-term precipitation, temperature, and streamflow records were used to compare changes in precipitation and potential evapotranspiration to changes in runoff within 25 stream basins. Historical changes in the region appear to be more consistent with complex transient shifts in seasonal climatic conditions than with gradual climate change. Annual peak streamflow data were divided into two populations, snowmelt/spring and summer/fall, to test the hypotheses that, because of changes in precipitation regimes, the odds of summer/fall peaks have increased and, because of temperature changes, snowmelt/spring peaks happen earlier. The odds of summer/fall peaks occurring have increased across the study area. In northern portions of the study region, snowmelt/spring peaks are occurring earlier by 8.7 to 14.3 days. Tree-ring chronologies and historical precipitation data in a region around the Souris River Basin, were analyzed to model past long-term variations of precipitation. Results show that precipitation varies on multi-decadal time scales.
The Red River of the North drains much of eastern North Dakota and northwestern Minnesota and flows north into Manitoba, Canada, ultimately into Lake Winnipeg, so phosphorus transport is an International concern. Phosphorus changes over time were determined and phosphorus concentrations at the International border, when adjusted for variability in streamflow (flow-normalized), have generally increased from 1972-2012 ; however, most of that increase happened in the 1970s. Flux, the total amount of phosphorus transported, has increased dramatically in recent decades ; however, when adjusted for streamflow variability (so that flux is from variation caused by the occurrence of high- or low-flow conditions), the flow-normalized flux has declined in recent years. This indicates that an important reason for increased flux is climatic – the wet conditions experienced since 1993.
These changes have implications for water interests, such as potential changes in lead-time for flood forecasting or changes in the operation of flood-control dams or wastewater treatment plants. Results suggest that the recent wet period may be a part of natural variability on a very long time scale and that this not only has implications for flood risk, but for nutrient export to Canada.

Mots Clés : Climate, Precipitation, Runoff, Streamflow, Variability, Water quality

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