Assessment of Impacts of Upstream Developments and Climate Change on Carp River Watershed
Creators: name: Zango, Baba-Serges
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2021
Subjects: Carp River watershed
Climate Change
Hydrological modelling
SWAT
Urbanization

description: A SWAT hydrological model is developed to evaluate the individual and combined impacts of urbanization and climate change on water quantity (discharge) and quality (N and P) of the watershed of Carp River in Ontario, Canada. Seven numerical experiments (scenarios) were developed to represent the different configurations of the watershed in terms of land use (either current or projected) and climate regime (current or future, observed or simulated). The reference period is 1990-2018, and the future period is 2021-2050. The 2017 land use was used to represent the reference period. The future land use is the projected 2050 land use obtained from the City of Ottawa. The future climate was obtained by downscaling the outputs of nine (9) Regional Climate Models (RCMs) under two Representative Concentration Pathways (RCPs): RCP4.5 and RCP 8.5. The developed scenarios are the following: • S0o (baseline scenario) corresponding to the current land use map and the observed climate regime on the reference period • S0m is similar to S0o except that RCM outputs are used instead of the observed climate on the reference period • S1 corresponds to the future land use and historical climate regime on the reference period. • S0M45/S0M85 corresponds to the current land use and the future climate regime under RCP4.5 (S0M45) and RCP8.5 (S0M85) • S1M45/S1M85 corresponds to the future land use map and future climate regime under the two RCPs. The changes or impacts on quantity and quality in each scenario were estimated by comparing the results with the baseline scenarios S0o/m (reference) at two levels: globally (at the main outlet) and locally (at the outlet of an upstream sub-watershed). For a consistency purpose, S0o is used when assessing land-use change scenario while S0m was the reference in climate change and combined effects scenario. This allowed the comparison to be consistent with the same climate data frame. The results showed that climate change is likely to be the most dominant factor affecting discharge and nitrogen, while urbanization will control the quantity of phosphorus. Unsurprisingly, the combined effect had a more significant impact on water quantity and quality. However, the impact is not additive, and the relationship is not linear. Compared with S0, the annual average discharge increased by 1.57%, 5.49%, 7.52%, 6.75%, and 9.34% in S1, S0M45, S0M85, S1M45, and S1M85, respectively. In comparison, the change for annual N load was estimated at -1.88%, 29.62%, 2.03%, 24.84%, and -1.20% respectively. Change in annual average P was respectively 26.49%, 1.07%, -4.49%, 23.81% and 19.15%. Local impact assessment indicates the impact in upstream sub-watersheds may differ from the main outlet's impact in terms of magnitude and direction of change. Therefore, only considering global change may lead to a wrong interpretation of the impacts over the watershed. It is, therefore, necessary to evaluate the impacts at the local level as well.