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This study identifies significant periodicities in streamflow dynamics across western Europe using a hydrological database encompassing 1874 monthly series from catchments in Ireland, the United Kingdom, France, Spain and Portugal, spanning the years 1962 to 2012. Significant and synchronous periodicities with the main atmospheric mechanisms over the North Atlantic sector are also identified using Cross Wavelet Transform and Wavelet Coherence analysis. Principal Components Analysis (PCA) were applied to the different Wavelet transforms analysis in order to summarize the results. These show the occurrence of a 7-years streamflow cycle in a large proportion of catchments within the study domain since the mid 1980's that was not present in earlier periods. The significance, intensity and persistence of the observed regional cycle follows a spatial gradient around the English Channel. We show how the transitive coupling of key atmospheric mechanisms is an influencing factor causing the general change observed. These results suggest the occurrence of a regional change in the periodicities of streamflow across the western European domain. Our results emphasize the non-stationary interaction between streamflow and atmospheric circulation during recent decades and the prominent role of the North Atlantic Oscillation in the newly stablished streamflow cycles.

This work analysed the changes in air temperature in 25 meteorological stations in the Altiplano and the surrounding Andean slopes of Bolivia and Peru, and their relationship with El Niño-Southern Oscillation (SO) and the Pacific Decadal Oscillation (PDO). The analysis focused on annual, warm season (DJF) and cold season (JJA) maximum and minimum temperatures. All analyses were undertaken during 1965-2012, but some analyses were also from 1945 and 1955 when data were available. Principal component analysis was applied to the annual and seasonal series to identify spatial differences of changes in maximum and minimum air temperature. There was an overall increase of temperatures since the mid-20th century. The most intense and spatially coherent warming was observed for annual and warm season maximum temperature, with warming rates from 0.15 to 0.25 °C decade-1. Changes in the cold season maximum temperature were more heterogeneous, and statistically significant trends were mostly in the Bolivian Altiplano. Minimum temperatures increased, but there was higher spatial variability and lower rates of warming. Maximum temperature was negatively correlated with the Southern Oscillation index (SO) in the warm season, and positively correlated with the SO in the cold season; there were less statistically significant correlations with the PDO, that exhibited inverse sign than those for SO. The strongest correlations were in the region near Lake Titicaca. The negative correlation of minimum temperatures with SO and the positive correlation of minimum temperatures with PDO were lower than the observed for maximum temperature. The changes in temperature and correlations with SO and PDO were highly dependent on the selected period, with stronger trends in the last 30-40 years. This suggests reinforcement of warming rates that cannot be only explained by SO and PDO variability. Por pares

Streamflows in five Mediterranean mountain headwaters in the central Spanish Pyrenees were projected under various climate and land use change scenarios. Streamflows were simulated using the Regional Hydro-Ecologic Simulation System (RHESSys). The results show that changes in precipitation and temperature could cause a decline of annual streamflow between 13% and 23%, depending on the considered catchment. When the effect of increased forest cover in the basins is added to climate change effects, the decrease in annual streamflow is enhanced up to 19% and 32%. The largest hydrological changes resulting from environmental change are projected mainly in early spring, summer and autumn, when the decline may exceed 40%. Winter is the least affected season by environmental change because of increased runoff as a consequence of reduced storage of water in the snowpack and an earlier onset of the snowmelt, and the lower consumption of water by vegetation during the cold season. The magnitude of hydrological change as a result of the assumed environmental change scenarios may lead to serious impacts on water management and ecology of the studied region, as well as the water availability in the Ebro basin., Se han simulado los caudales de cinco cabeceras de ríos en los Pirineos centrales españoles, considerando diferentes escenarios de cambio climático y de uso del suelo. Los caudales fueron simulados utilizando el modelo hidroecológico RHESSys (Regional Hydro-Ecologic Simulation System). Los resultados muestran que los cambios proyectados por un conjunto de modelos climáticos regionales en precipitaciones y temperaturas en el siglo XXI podrían causar una disminución del caudal anual entre el 13% y el 23%, dependiendo de la cuenca considerada. Cuando se añade a los efectos del cambio climático el efecto del aumento de la cubierta forestal en las cuencas, la disminución de los caudales anuales oscila entre el 19% y el 32%, dependiendo de la cuenca estudiada. Los mayores cambios hidrológicos se producirían a principios de primavera, verano y otoño, cuando la disminución puede superar el 40% respecto a los valores actuales. El invierno es la estación menos afectada como consecuencia del aumento de la escorrentía debido a una reducción del agua acumulada en forma de nieve y a un inicio más temprano de su fusión, así como por que durante los meses fríos el consumo de agua por parte de la vegetación es menor. La magnitud del cambio hidrológico, resultado de los escenarios de cambio ambiental, puede afectar seriamente a la gestión de los recursos hídricos y a las comunidades vegetales del Pirineo central, así como a la disponibilidad de agua en el conjunto de la cuenca del Ebro.