Weather types, runoff and sediment yield in a Mediterranean mountain landscape

ABSTRACT The relationship between the synoptic weather types (WTs), runoff and sediments in a Mediterranean mountain landscape was analysed. The study was performed between 2005 and 2012 using one of the most complete and extensive daily databases of rainfall, runoff and sediment recorded in the Spanish Pyrenees, coupled with WTs defined from the National Meteorological Center/National Center for Atmospheric Research (NMC/NCAR) 40-Year Reanalysis Project. The results show that the three wettest WTs accounted for 30% of rainy days and 46% of rainfall, but comprised only 13% of total daily records. To obtain a much more robust association between WTs and rainfall an analysis was carried out using a longer rainfall record (1989-2011). The analyses confirmed that the results obtained from the Araguas catchment are representative of a longer time span. The cyclonic, north-westerly and westerly WTs play an important role in runoff generation, coinciding with the wettest WTs. Extreme floods are commonly associated also with south-westerly and westerly airflows, whereas less flooding was generated under cyclonic circulations. Sediment transport was concentrated in 2.9% of total time mainly related to westerly WTs. Seasonal differences exist in WT frequency. In winter and spring north-west and West are the most prominent WTs related to rainfall, water and sediment yield, although in spring cyclonic frequency was higher. During autumn north-west and south-west were the most frequent, but sediment yield was produced nearby under south-west flow. In summer the WTs that produce sediment are north and west. A magnitude-frequency analysis shows the different behaviour of WTs according to their efficiency in producing runoff and sediment. A study with different monitored areas around the Iberian Peninsula and the Mediterranean basin would be very valuable in providing information for hydrological and sediment behaviour under the current conditions of global climate change. Copyright (c) 2013 John Wiley & Sons, Ltd.