Master of Engineering Science
Civil and Environmental Engineering
Environment and Sustainability
Najafi, M. Reza
In this study, the impacts of climate and land cover (LC) changes on the hydrologic processes of the Batchawana watershed in Central Ontario are assessed. Batchawana is a snow-dominated forested watershed with coniferous, deciduous and mixed trees and numerous small lakes. A semi-distributed hydrological model, based on the Raven hydrological framework, is calibrated and validated using ground-based observations for 1981-2001 and 2002-2011, respectively. Eight downscaled General Circulation Models (GCMs) that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and three large ensembles (50 members) of Regional Climate Model (RCM) simulations, under the Representative Concentration Pathway (RCP) 8.5, are used to characterize the role of anthropogenic forcing and internal climate variability in projected changes of watershed runoff. Analyses are performed in the historical and future time frames corresponding to global mean temperature increases of 1.5, 2, 2.5, 3, 3.5 and 4 °C compared to the preindustrial (1851-1900) level. The historical trends of land cover changes are extended to develop future LC scenarios including changes from coniferous to deciduous and mixed forests. Besides, to assess the influence of lakes four scenarios are investigated considering 25% lake shrinkage increments. Deciduous and mixed tree cover result in higher flow rates during fall compared to the base model with partial coniferous tree cover. A decrease in the area of lakes can decrease the streamflow in all seasons. Responding to climate change, the snowpack is projected to decline in the future indicating a shift from nival to a rainfall-dominated hydrological regime in a warmer climate. Further, the mean annual streamflow is projected to increase while the annual maximum flow is expected to decline. Analysis of Internal Variability indicates that human-induced climate change, compared with natural variability, will dominate the hydrological changes in the region during the last decade of the 21st century. Overall, the results show significant changes in the hydrological processes of this forested watershed associated with both climate and land cover changes. This will affect the flood and drought hazards and consequently endanger the agriculture, wood industry and lives of indigenous residents of Batchawana.
Summary for Lay Audience
Water is one of the most important resources that humankind needs to collect and use it vigilantly. To manage the water resources, understanding their vulnerability against different threats is essential. Water quality and quantity are affected by human activities, natural random incidents, climate change, etc. To assess and measure the water quantity, understanding the water cycling system, or hydrology, is essential. Hydrology encompasses water storages in a region such as surface water, groundwater, snowpack among others. The basin of study, Batchawana, located in Central Ontario, is mainly covered by three forest types; deciduous, coniferous and mixed forests. Numerous lakes are placed in the basin. Snow is one of the main hydrological contributors in this region as it is ~34% of the total precipitation. Using the satellite imagery techniques this study shows that forest types have changed during the past decades. Also, the total lake area has decreased. Besides, climate change is more tangible in Canada than the global average and its effects on hydrology can be dramatic. To discern the hydrological effects of forest type change, lakes shrinkage and climate change on the Batchawana hydrology, a hydrological model is set up and verified. Two land cover and four lakes scenarios are developed based on the satellite imagery. To apply the climate change scenarios, the outputs of eight global climate models and three regional climate models are used to drive the model to assess the future streamflow changes until the end of the 21st century. Results show that by changing the forest type from deciduous to coniferous, there will be more streamflow for Autumn. Lakes presence is essential for low flows in this forested watershed and by decreasing lakes, streamflow can decrease. Under climate change scenarios, the basin will turn to be a rain-dominated watershed with less annual maximum and more annual mean streamflow. Snowfall and snowpack are expected to decline to result in lower spring snowmelt. In the last decades of the century, the impacts of human activities on streamflow will be more pronounced compared to the effects of internal variability.
Mehdipour, Vahid, "Assessment of the impacts of climate change, land cover transition, and internal climate variability on the hydrology of a forested watershed" (2021). Electronic Thesis and Dissertation Repository. 7698.