Browsing by Subject "Trends"

Now showing 1 - 3 of 3
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    Exploring Hydroclimatic Variability on the Red River of the North, the Least Stationary River of the United States
    (2022-12) Avila, Judith
    Nation-wide surveys of hydrological trends have described the Red River of the North as the least stationary river in the continental United States. In this study, I examine first, how the Red River has varied across the spectrum of high, median, and low flows and second, how mean climatology across the watershed and the broader region has behaved before and after an abrupt increase in streamflow. For those gauges with more than 50 years of daily observations, minimum flows on the Red River increased between 3% and 28% per year, median flows from 3% to 10% per year, and maximum flows from 1% to 5%. For most time periods tested (315/420), discharge on the Red River had a positive and statistically significant (p≤0.05) increase. There were no significant trends for tests with start years after 1980. Change-point analysis revealed a cluster of upwards shifts in basin-wide streamflow in the early 1990s. After 1992, daily flows on the Red River have been higher throughout the year and the river has exhibited novel secondary peaks in June and November. Since the onset of this new regime, the northeastern Great Plains have been both warmer and wetter. These changes have been most prominent in the summer and fall, with temperatures 0.6°C to 1.0°C warmer and rainfall increasing between 39 to 85 mm. I expected the observed increase in regional temperature might have caused the spring snowmelt pulse to happen earlier, but the daily flow data did not show any significant changes in the timing of peak flow on the river. The coincidence between higher flows in the Red River and warmer and wetter conditions after the early 1990s suggests the strong non-stationary behavior of the river could be due, at least in part, to climate change and variability.
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    Temporal Variations on the Allocation of Time
    (Transportation Research Board, 1995) Levinson, David M; Kumar, Ajay
    This study investigates the allocation of time and trip-making across time-of-day, day-of-week, and month-of-year, as well as over the past forty years. Some interesting findings result. People are working much more, shopping somewhat more on weekends, and stay at home less today than forty years ago. Time spent in travel on each weekend day (Saturday or Sunday) exceeds that on any weekday, as it did forty years ago. Time spent shopping on a typical day in the busiest month (December) is more than double that in the least busy month (September). Monthly variations in daily time in travel exceed 10 percent. The time of day patterns of shop and other trips for workers and nonworkers are both rational: nonworkers peak in mid-day away from rush hour while workers peak just after work, indicating trip chaining.
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    Trends in Total Phosphorus Concentrations in Urban and Non-Urban Environments
    (2017-01) Halbach, Ann
    A study of lake trends was conducted across Minnesota and Wisconsin to determine the effects of actions to improve water quality. A comparison between urban and non-urban environments helped determine drivers of change, as many factors contribute to water quality and they differ between environments. Though evidence of both increasing and decreasing trends in phosphorus were observed, there were more lakes with decreasing trends than increasing trends, especially in the urban environment. Similar trend patterns were not found with nitrogen. Trends in nitrogen were more often positive, and trends in N:P were generally strongly positive. Climatic and morphometric factors were not significantly related to trends, but there was a connection between the amount of lawn at lake edge and phosphorus reduction. The results indicate that phosphorus concentrations in the study lakes are improving more frequently than not. This may be due to the adoption of phosphorus control measures.