Impacts of climate change on the hydrology of extreme summer floods

Abstract

The examination of the impacts of climate change on extreme hydroclimate events has received a great deal of interest, as a rise in these events will impact floods and droughts. These events can harm human and animal and also cause damage to property and infrastructure. It is essential to have a thorough comprehension of the characteristics and distribution of extreme precipitation, as well as the timing, magnitude, and frequency of extreme flow, in order to effectively plan and manage our water resources systems, including dams, reservoirs, and irrigation systems. Recent studies have indicated that there may be an increase in the intensity of extreme precipitation events, such as convective precipitation, in the future due to the effects of climate change. This could result in higher amounts of rain or snowfall within a shorter period of time, which could potentially bring about an increase in flooding and other weather-related challenges. This study endeavors to examine the variations in the intensity and frequency of short and long-term hydroclimatic variability, with a specific focus on extreme precipitation and streamflow in the Eastern and Northeastern regions of the United States. Additionally, the study delves into the uncertainty associated with diurnal cycle biases and internal climate variability for future hydroclimatic variability. The overall aim of this research is to enhance our understanding of how future extreme events will develop with a focus on their relationship to catchment size, in order to better prepare for the changing climate. This study utilized the 50-member ClimEx large ensemble, which is a Single Model Initial condition Large Ensemble (SMILE) operating under the Representative Concentration Pathway 8.5 scenario. ClimEx offers high spatial resolution (0.11o ) and temporal resolution (1-hour) and was derived by dynamically downscaling the 50-member Canadian Earth System Model (CanESM2) across a northeastern America domain. As the hydrometeorological modeling done in this study was at the sub-daily time step, a first step was to investigate the need and impact of a diurnal cycle bias correction method on climate variables, such as temperature and precipitation, and its effect on simulated streamflow. In the second step of the study, the progression of hydrological extremes across 133 catchments was examined by investigating the relationship between catchment size, rainfall duration (ranging from 1 to 72 hours), return periods (between 2 and 300 years) and streamflow. Finally, the study sought to understand the significance of internal climate variability for identifying changes in streamflow by analyzing the timing of emergence This analysis aimed to shed light on how internal climate variability can influence the detection of changes in streamflow and the reliability of the results. The study revealed that the utilization of multivariate diurnal cycle bias correction methods can effectively adjust sub-daily biases in temperature and precipitation, in terms of both timing and magnitude, when compared to actual observations. These corrections lead to small yet systematic improvements in the simulation of streamflow quantiles, particularly in smaller catchment areas. As the climate changes, the study also found an increase in extreme precipitation across all durations and return periods. The projected increase in extreme precipitation is closely correlated with the duration, frequency, and size of the catchment area. The areas that are expected to experience the largest relative increases in rainfall are those with the shortest durations, largest return periods, and smaller catchment areas. The study determined that the time of emergence of climate change on extreme floods and droughts occurs later than those on average flow levels, but the changes in floods and droughts are more pronounced. The timing of these changes is related to the size of the catchment area, with smaller catchments displaying an earlier emergence for floods and a later one for droughts. The findings of this study imply that in the future, smaller catchments will be disproportionately affected by the increases in extreme rainfall. This emphasizes the need for further research on the impacts of climate change on extreme floods and droughts, particularly in relation to the timing of these effects and how it is influenced by the size of the catchment area.

Date	8 Jun 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	François Brissette (Supervisor)