Online

Guilbert, Justin

Civil and Environmental Engineering

2016

PhD

Shifting climatic regimes can increase or decrease the frequency of extreme hydrologic events (e.g., high and low streamflows) causing large societal and environmental impacts. The impacts are numerous and include human health and safety, the destruction of infrastructure, water resources, nutrient and sediment transport, and within stream ecological health. It is unclear how the hydrology of a given region will shift in response to climate change. This is especially the case in areas that are seasonally snow covered as the interplay of changing temperature, precipitation, and resulting snowpack can lead to an increased risk of flood or drought. This research aimed to understand the ways temperature and precipitation are changing using general circulation models and observed weather station data in the northeastern United States. With the knowledge that general circulation models do not accurately represent precipitation statistics and trends from the historical period, a large network of climate stations was utilized to further investigate shifts in precipitation. A hydrology model was utilized for further study of regional hydrology. The model used was the Regional Hydro-Ecologic Simulation System, which was calibrated to snow coverage and streamflow for a historical time period. The hydrology model was used to investigate the relationship of snow and streamflow in a changing climate. We characterized climate change and related impacts in the northeastern United States and estimated a decrease in snowfall of 50% and the number of days below freezing by 45 days by the end of the century. We also showed that precipitation is not only becoming more intense, but it is also more persistent - a finding that may have significant hydrological implications including increased flood risk throughout the year. The 95th percentile of daily precipitation has increased by 0.5 mm per day per decade, while the probability of successive days with precipitation increased by 0.6 percent per decade. We also explored the role of snowpack in a changing climate. We found that temperature plays a larger role than precipitation in shifting hydrologic regime, because the warming-induced reduction of snowpack reduced the maximum flows more than the increasing precipitation increased the maximum flows. However, because of the increasing intensity and persistence of precipitation, instantaneous peak flows occurring outside of the snowmelt season will likely continue to increase during all times of the year. We shed light on the complexity of the modes of climate change and the interactions that increases in temperature and precipitation can have on the hydrology of a region.