Sensitivity of Icelandic river basins to recent climate variations

Abstract

Variations in 22 hydrological variables were considered for 8 watersheds in Iceland to analyse the quantitative impact of variations in climate on hydrology during the period 1971–2006. Observed streamflow characteristics were examined together with information about rain/snow fraction, snow storage, snow and glacier melting derived from gridded precipitation and temperature data using a simple temperature-index melt model. The effect of the observed temperature and precipitation variations was examined by comparing subsets of the data containing the 25\% coldest and warmest and the 25\% wettest and driest years of each series. The seasonality of streamflow of all catchments and timing of hydrological events were found to be sensitive to differences of 1.1–1.4 °C in the annual temperature between the warm and cold data subsets. Snow storage was smaller and depleted earlier and the onset of spring snowmelt was shifted several weeks earlier in warm years, while glacial melt volumes increased by 20–40\%. These changes caused greater discharge in winter and spring and less discharge in summer, except for glacierized catchments where summer flow was maintained by glacier melt. Annual precipitation was 40–58\% greater in the wet compared with the dry data subsets, resulting in substantial seasonal and annual increases of rain, snow storage and snowmelt, streamflow volumes and flood occurrence rate. The seasonal distribution and timing of hydrological events were, however, usually not systematically different. Snow storage and glaciers are found to exert a strong influence on streamflow in Icelandic river catchments, making them sensitive to climate variations. The nature of the hydrological response is not spatially uniform but depends on location, altitude distribution and catchment type.