An exceptional rainfall event in the central western Pyrenees: spatial patterns in discharge and impact

27 páginas, 8 figuras, 3 tablas.- Versión pre-print. - The definitive version is available at: http://onlinelibrary.wiley.com/doi/10.1002/ldr.2221/abstract[EN] An exceptional rainfall and hydrological event occurred on 19–21 October 2012 in the central western Pyrenees and was particularly\ud
signiﬁcant in the Upper Aragón River basin and its tributaries, mainly the Irati River. Analysis of historical records showed that, considered\ud
separately, the event of 19 and 20 October ranked between the second and ﬁfth highest most extreme daily precipitation events. For the two\ud
days combined (with a total between 200 and 260 mm), the precipitation event was the most extreme 2-day event among all observation\ud
stations but one. The consequent ﬂood destroyed part of an urban area, and a long stretch of a national road triggered landslides, enlarged\ud
the alluvial plain and caused generalised soil erosion in cultivated ﬁelds cropped with winter cereals. Badlands in the marls of the Inner\ud
Depression yielded high volumes of sediment. The ﬂoods in the tributaries were relatively moderate (return periods of 14–42 years), whereas\ud
in the Upper Aragón River, the ﬂood corresponded to a return period of approximately 400–500 years and to 142 years at the end of the\ud
Yesa reservoir, although difﬁculties in estimating the discharge increased the uncertainty of these values. The Yesa and Itoiz reservoirs\ud
considerably reduced the intensity of the ﬂood in the middle and lower Aragón River and conﬁrmed the importance of the water level in\ud
the reservoirs when such rainfall events occur. The water storage in the Yesa reservoir increased from 16% to 53% as a consequence of\ud
the event. More integrated studies are necessary to decrease the risks associated with ﬂood hazards. This is particularly the case in mountain\ud
areas, where the steep slopes and longitudinal gradients of the rivers shorten the concentration time of ﬂoods and increase the energy that\ud
erodes channels and riverbanks. Copyright © 2013 John Wiley & Sons, LtdSupport for this research was provided by the projects\ud
INDICA (CGL2011-27753-C02-01 and 02), DISPROSPEC\ud
(CGL2011-24185) and HIDROCAES (CGL2011-27574-\ud
C02-01), funded by the Spanish Ministry of Economy and\ud
Innovation; ACQWA (FP7-ENV-2007-1-212250), ﬁnanced\ud
by the European Commission, and an agreement between\ud
the CSIC and the Spanish Ministry of Environment (RESEL).\ud
The research group on Geomorphology and Global Change\ud
was ﬁnanced by the Aragón Government and the European\ud
Social Fund (ESF-FSE). E. Nadal-Romero and N. LanaRenault beneﬁted from a research contract (Spanish Ministry\ud
of Economy and Innovation, Programme Juan de la Cierva).\ud
The authors acknowledge the free availability of the hydrological information from the Ebro River Authority and the help\ud
provided by the team of the Centro de Proceso de Cuenca\ud
del Sistema Automático de Información Hidrológica de la\ud
Confederación Hidrográﬁca del Ebro. The cartographic help\ud
from Paz Errea and Sergio Valdivielso was also acknowledged.Peer reviewe