| dc.description.abstract | 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 leadtime
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. | en_US |
