Étude des variations climatiques (1921-1990) des Prairies canadiennes à partir de la classification de Köppen : une application des SIG dans l'étude des changements environnementaux.

The primary objective of this thesis was to study climatic variations that occurred in the Grassland Ecoclimatic Province (Canadian Prairies), between 1921 and 1990, using a geographic information system (GIS). DBASE IV was used to establish the Koppen classification. The annual classification showed important climatic variations within the study period. No station could be associated to only one climatic classification, but to many categories. For example, the climate for Medicine Hat cannot be considered as purely semiarid (31 years classified as BSk) because it also has many years classified as Dvb (12) and Dsb (11). The climatic maps, representing each decade, showed much more information, concerning the spatial variations of the Prairies climate. The 1981-90 period had the most important surface classified as semiarid (BSk), this classification representing 7.73% of the total area covered by this study (579 800 km$\sp2$). This semiarid area, generally situated around Medicine Hat, completely disappeared if not almost between 1931 and 60. The 1931-40 map did not show the presence of very dry conditions reported for the Prairies during the Dust Bowl period (1936-38). Yearly maps created for this important dry spell, agreed with some of the information published by Phillips (1990) and Jones (1991), concerning the areas affected by the Dust Bowl droughts. However, the map for 1936 showed no station classified as BSk, despite the fact that it was very dry that year. The use of the Koppen's classification permitted a climatic analysis based on critical thresholds of temperatures and precipitation, which favor or limit vegetation growth. The use of a GIS, helped to easily process large amounts of data, in order to create climatic maps according to this climatic classification. (Abstract shortened by UMI.