Multi-decadal variations in annual maximum peak flows in semi-arid and temperate regions of Chile

In determining the possible influence of climate change, it is important to understand the temporal and spatial variability in streamflow response for diverse climate zones. Thus, the aim of this study was to determine the presence of changes in annual maximum peak flow for two climate zones in Chile over the past few decades. A general analysis, a flood frequency analysis and a trend analysis were used to study such changes between 1975 and 2008 for a semi-arid (29 degrees S-32 degrees S) and a temperate (36 degrees S-38 degrees S) climatic zone. The historic annual maxima, minima and mean flows, as well as decadal mean peak flow, were compared over the period of record. The Gumbel distribution was selected to compare the 30-year flood values of two 15-year intervals, which showed that streamflow decreased by an average of 19.5% in the semi-arid stations and increased by an average of 22.6% in the temperate stations. The Mann-Kendall test was used to investigate the temporal changes in streamflows, with negative trends being observed in 87% of the stations analysed in the semi-arid zone, and positive trends in 57% of those analysed in the temperate zone. These differences in streamflow response between climate zones could be related to recent documented increases in altitude of the zero-degree isotherm in the Andes Mountains of Chile, since most of the significant positive and negative changes were detected in first-order rivers located closer to this mountain range.Editor D. Koutsoyiannis; Associate editor H. LinsCitation Pizarro, R., Vera, M., Valdes, R., Helwig, B., and Olivares, C., 2013. Multi-decadal variations in annual maximum peak flows in semi-arid and temperate regions of Chile. Hydrological Sciences Journal, 59 (2), 300-311. ResumePour determiner l'influence possible du changement climatique, il est important de comprendre la variabilite temporelle et spatiale de la reponse en debits pour diverses zones climatiques. Ainsi, l'objet de cette etude etait de determiner l'existence de changements dans le debit de pointe maximum annuel de deux zones climatiques du Chili au cours des dernieres decennies. Une analyse generale, une analyse de la frequence des crues et une analyse de tendances ont ete utilisees pour etudier les changements des valeurs du debit de pointe maximal annuel entre 1975 et 2008 pour la zone semi-aride (29 degrees S a 32 degrees S) et la zone temperee (36 degrees S a 38 degrees S). Les maximums, minimums et moyennes historiques annuels, ainsi que le debit de pointe decennal ont ete compares sur la periode d'observation. Nous avons choisi la distribution de Gumbel pour estimer les valeurs des crues tricennales (30 ans) de deux intervalles de 15 ans, ce qui a montre que la valeur de ce debit a diminue en moyenne de 19,5% dans les stations semi-arides et augmente en moyenne de 22,6% dans les stations temperees. Le test de Mann-Kendall a egalement ete utilise pour etudier les changements temporels des debits. Des tendances a la decroissance sont observees dans 87% des stations de la zone semi-aride, et des tendances a la croissance dans 57% de celles de la zone temperee. Ces differences de la reponse en debit entre zones climatiques pourraient etre liees a une elevation recemment mise en evidence de l'isotherme zero degre dans la Cordillere des Andes du Chili, puisque la plupart des changements positifs et negatifs significatifs ont ete detectes dans des rivieres du premier ordre proches de cette chaine de montagnes.