Climate impacts on hydrometric variables in the Mackenzie River Basin
The research described in this thesis examines how the hydrologic cycle is affected by climate changes in the Mackenzie River Basin (MRB) in northern Canada. The study focuses on five hydro-meteorological variables; runoff, evapotranspiration, storage, temperature and precipitation. Two different climate input data sets were used: Environment Canada gridded observed data and the European Center for Medium range Weather Forecasting (ECMWF) Re-Analysis climate data (ERA-40). In both data sets, runoff and evapotranspiration were modelled using the WATFLOOD hydrological model for the period of 1961 to 2002 on a 20 by 20 km grid. Trends were assessed on a monthly and annual basis using the Mann-Kendall non-parametric trend test. The hydrologic cycle in the MRB appears to be strongly influenced by climate change. The results reveal a general pattern of warming temperatures, and increasing precipitation and evapotranspiration. Overall decreases in runoff and in storage were detected from the Environment Canada data set while increases in runoff and in storage were detected from the ECMWF data set. The trends in runoff and evapotranspiration reflected changes in both precipitation and temperature. The spatial pattern of changes in runoff followed the pattern of change in precipitation very closely in most of the months, with the exception of March and October. The effect of changes in temperature is much more noticeable than that of changes in precipitation in March and October. The change in spatial distribution of evapotranspiration, on the other hand, matched the pattern of changes in temperature better; yet its seasonal pattern follows more closely to that of precipitation. The sensitivity of annual runoff to changes in climate was also estimated using a nonparametric estimator. Among the most important findings are: 1) runoff was more sensitive to precipitation and less sensitive to temperature; 2) runoff was positively correlated with precipitation and evapotranspiration; 3) runoff was negatively correlated with temperature, implying any increase in melt runoff from glaciers caused by increases in temperature were offset by losses due to evapotranspiration within the basin; 4) soil moisture storage may play an important role in the runoff and evapotranspiration processes; and 5) the sensitivity of mean annual runoff to changes in precipitation and evapotranspiration is typically lower along the Rocky Mountain chain, higher in the central zone of the Interior Plain, and highly varied in the Canadian Shield region in the basin. Correlation analysis suggested that the agreement between the two data sets is very weak at the grid-cell level. However, there was broad degree of consistencies in the seasonal and spatial patterns of trends between the two data sets, suggesting that the data are more reliable for identifying hydrological changes on a regional scale than at grid-cell level.