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Hydrological balance and biogeochemical processes in watershed are significantly influenced by changes in land use land cover (LULC) and climate change. Those changes can influence interception, evapotranspiration (ET), infiltration, soil moisture, water balance and biogeochemical cycling of carbon, nitrogen and other elements at regional to global scales. The impacts of these hydrological disturbances are generally reflected in form of increasing runoff rate and volume, more intense and frequent floods, decreasing groundwater recharge and base flow, elevated levels of sediments and increase in concentration of nutrients in both streams and shallow groundwater. Water quality of Sudbury, Assabet and Concord (SuAsCo) watershed in Massachusetts is also compromised because of influx of runoff, sediments and nutrients. There is a crucial need to evaluate the synergistic effects of LULC change and climate change on the water quality and water quantity in a watershed system. A watershed simulation model is used to simulate hydrologic processes and water quality changes in sediment loads, total nitrogen (TN), and total phosphorus (TP). The model is calibrated and validated with field-measured data. Climatic scenarios are represented by downscaled regional projections from Global Climate Model (GCM) models and regional built out scenarios of LULC are used to assess the impacts of projected LULC and climate change on water quality and water quantity. Simultaneous changes in LULC and climate significantly affect the water resources in the SuAsCo River watershed. Change in climate increased ET (4.7 %) because of high temperature, but independent change in land cover reduced ET (6.5%) because of less available vegetation. Combined change in land cover and climate reduced ET (2.1%) overall, which indicates that land cover change has significant impact on ET. Change in climate increased total run off (6%) and this increase is more significant as compared to 2.7 % increase in total runoff caused by land cover change. Change in land cover increased surface runoff more significantly (69.2%) than 7.9 % increase caused by climate change. Combined change in land cover and climate further increased the average storm peak volume (12.8 percent) because of high precipitation and impervious area in future. There is a potential for reducing runoff, sediments and nutrients loads by using conservation policies and adaptation strategies. This research provides valuable information about the dynamics of watershed system, as well as the complex processes that impair water resources.

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<p>The thesis aims to investigate the impact of climate change on the hydrology of four semi-urban watersheds in southern Ontario. The study is mainly concerned with future changes in climate variables and flow regimes. The study also assesses future changes in the frequency and magnitude of peak and low flows. The hydrologic effects of climate change were assessed using a couple of climate and hydrological models. Three regional climate models (RCMs), namely, Canadian Regional Climate Model (CRCM), United States Regional Climate Model 3 (RCM3), United Kingdom Hadley Regional Model 3 (HRM3) were used to extract raw climate variables. The raw RCM data were corrected using a bias correction method. The method performance statistics and the nonparametric test results revealed that the bias corrected climate variables followed the patterns of the observed climate variables for all weather stations. Future climate scenario was then simulated and analyses show increases in annual precipitation about 5-8% and increases in mean annual daily mean temperature about 2.6-3.2 oC. Three hydrological models (namely HBV, MAC-HBV, and SAC-SMA) were used for flow simulation. The models' validation results show a good agreement with the observed flow with a Nash Sutcliffe efficiency around 0.49-0.75 and a correlation coefficient of around 0.7-0.8 for all sub-basins. The three hydrologic models coupled with the bias corrected RCMs data were used to simulate current and future flow. For future period (2050s), the models predicted increasing winter flow and decreasing spring, summer and autumn flows. Mean annual flow shows slight to moderate changes. Significant increases in peak and low flow magnitude are predicted for higher return periods (20-100 years). Overall, the effects of projected future changes in precipitation and temperature clearly govern the significant changes in seasonal and annual flows, peak and low flow magnitudes and frequencies. Using three hydrologic and three climate models projections, a comprehensive picture of probable hydrologic impact of climate change was assessed in the study area. The wide range of predicted changes will have significant implications for future water resources development in the selected semi-urban watersheds.</p> / Master of Applied Science (MASc)