A return-period analysis of annual peak spring break-up and open-water levels for 136 Water Survey of Canada hydrometric stations was used to classify rivers across Canada and to assess the physical controls on peak break-up water-levels. According to the peak water-level river-regime classification and subsequent analysis, 32% of rivers were classified as spring break-up dominated, characterized by low elevations and slopes and large basin sizes while 45% were open-water dominated and associated with alpine environments of high elevations and channel slopes, and smaller basin sizes. The remaining 23% of rivers were classified as a mixed regime. A spatial and temporal analysis (1969-2006) of the river ice break-up season using hydrometric variables of timing and water levels, never before assessed at the northern Canada-wide scale, revealed significant declines in break-up water levels and significant trends towards earlier and prolonged break-up in western and central Canada. The spatial and temporal influence of air temperature on break-up timing was assessed using the spring 0°C isotherm, which revealed a significant positive relationship but no spatial patterns. In the case of major ocean/atmosphere oscillations, significant negative (positive) correlations indicate that break-up occurs earlier (later) during the positive phases of the Pacific North American Pattern (El Niño Southern Oscillation) over most of western Canada. Fewer significant positive correlations show that break-up occurs later during the positive phases of the Arctic Oscillation and North Atlantic Oscillation in eastern Canada. / Graduate

Memoria para optar al título de Geógrafo / El planeta se enfrenta a nuevos escenarios climáticos, y Chile no se encuentra ajeno. Aumentos de temperatura y disminución en las precipitaciones son algunos de los fenómenos que se están dando con mayor frecuencia, en donde la isoterma 0°C toma un rol importante al encontrarse vinculado estrechamente con las variaciones de temperatura. Es así como se propone un método de determinación de isoterma 0°C mediante datos de radiosonda lanzados en territorio chileno, así como también una validación de sus resultados. Los datos de radiosonda son limpiados y llevados a una macro, en donde se automatiza el cálculo de la altura de la isoterma 0°C mediante una regresión polinómica, cuyos resultados son espacializados en el territorio chileno a nivel estacional. Por otro lado, estos datos son analizados temporalmente según Makesens y contrastados con resultados arrojados por un modelo alternativo, utilizando datos de una base mundial denominada Terraclimate. La isoterma 0°C se ubica principalmente en la cordillera de Los Andes, abarcando mayor superficie en la zona norte y centro del país. A grandes rasgos, las tendencias señalan un aumento en la altura de isoterma 0°C en la zona norte, centro y sur, siendo en los meses de verano en donde existe un mayor grado de significancia. La altura de la isoterma 0°C en días de precipitación presenta un alza en la zona norte y centro del país, mientras que en la zona austral se destaca la tendencia negativa. / The planet is facing to new climate stages, and Chile isn't so far of that. Temperature increase, decrease in rainfall, are just some of the phenomenon that happens more frequently, where 0°C isotherm takes an important role to be closed linked with temperature variations. This Is how a 0°C isotherm variations method is proposed using radiosonde data launched in Chilean territory, as well as a validation of their results. The radiosonde data are cleaned and taken to a macro, where the calculation of the 0°C isotherm height is automated by a polynomial regression, the results of which are spatialized in Chilean territory at the seasonal level. On the other hand, these data are temporarily analyzed according by Makesens and contrasted with results produced by an alternative model, using data from a global database called Terraclimate. The 0°C isotherm is located mainly in the Andes mountain range, covering a larger area in the northern and central part of the country. Broadly speaking, the trends indicate an increase in the height of 0°C isotherm in the north, center and south zone, being in the summer months where there is more significance. The height of the 0°C isotherm on rainy days shows an increase in the north and center of the country, while in the southern zone the negative trend is noted.