This paper documents the occurrence of significant glacier and hydroclimatic changes in northwestern Patagonia during the past century. Drastic, widespread glacier recession is documented by repeat photography of some of the earliest glacier images from southern South America. Linear trends in regionally-averaged annual and seasonal temperature and precipitation records indicate significant warming and decreasing precipitation over the 1912-2002 interval. A climatic index is developed, based on winter precipitation and summer temperature records, that mimics glacier mass balance relationships and shows a strong negative trend which agrees with the drastic glacier recession shown by the photographic comparisons. Short positive periods of this climatic index broadly correspond with known evidence of glacier advances in the region. Regionally-averaged mean annual streamflow records east of the mountains were used in an independent verification check of the climatic series used in this study. This regional runoff record shows a strong negative trend, remarkable similarities with the climatic index, and highly significant positive (negative) correlations with the regional precipitation (temperature) series. This highlights the existence of a strong, regionally coherent hydroclimatic signal across this region and supports the utility of these records as environmental indicators for northwestern Patagonia between ca. 38° and 45°S. Given the significant socio-economic importance of rivers and glaciers in this area, further research is needed to evaluate the full range of natural hydroclimate variability and improve understanding of potential impacts of the future warmer and drier climates projected for this region.
