An Exceptional Rainfall Event in the Central Western Pyrenees: Spatial Patterns in Discharge and Impact

Abstract

An exceptional rainfall and hydrological event occurred on 19-21 October 2012 in the central western Pyrenees and was particularly significant in the Upper Aragón River basin and its tributaries, mainly the Irati River. Analysis of historical records showed that, considered separately, the event of 19 and 20 October ranked between the second and fifth highest most extreme daily precipitation events. For the two days combined (with a total between 200 and 260 mm), the precipitation event was the most extreme 2-day event among all observation stations but one. The consequent flood destroyed part of an urban area, and a long stretch of a national road triggered landslides, enlarged the alluvial plain and caused generalised soil erosion in cultivated fields cropped with winter cereals. Badlands in the marls of the Inner Depression yielded high volumes of sediment. The floods in the tributaries were relatively moderate (return periods of 14-42 years), whereas 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 Yesa reservoir, although difficulties in estimating the discharge increased the uncertainty of these values. The Yesa and Itoiz reservoirs considerably reduced the intensity of the flood in the middle and lower Aragón River and confirmed the importance of the water level in the reservoirs when such rainfall events occur. The water storage in the Yesa reservoir increased from 16% to 53% as a consequence of the event. More integrated studies are necessary to decrease the risks associated with flood hazards. This is particularly the case in mountain areas, where the steep slopes and longitudinal gradients of the rivers shorten the concentration time of floods and increase the energy that erodes channels and riverbanks.

Erosion in Mediterranean landscapes: Changes and future challenges

“…However, extremely intense rainstorms can occur, with precipitation of >200 mm occurring in only a few hours (Llasat and Puigcerver, 1992;López-Bermúdez and Romero-Díaz, 1993). Such events sometimes trigger large floods (Poesen and Hooke, 1997;Wainwright and Thornes, 2004;Gaume et al, 2009) that change channel morphology and affect bridges, roads and human lives, and have major geomorphological effects (Thornes, 1976;White and García-Ruiz, 1998;González-Hidalgo et al, 2007;Nadal-Romero et al, 2012a;Serrano-Muela et al, 2013). Gaume et al (2009) noted that, in the context of Europe, the most extreme flash floods occur in the Mediterranean region.…”

Los efectos geoecológicos del cambio global en el Pirineo Central español: una revisión a distintas escalas espaciales y temporales

“…(i) Las lluvias del 19 al 21 de octubre de 2012 afectaron sobre todo a la cuenca alta del río Aragón, donde la suma de lluvia de los días 19 y 20 fue el evento más extremo registrado en dos días en todos los observatorios de la cuenca excepto uno (Serrano-Muela et al, 2013). La consiguiente avenida, que en algunos aforos correspondió a un periodo de retorno de 400 a 500 años, destruyó parte de una urbanización, ensanchó notablemente algunos tramos del río Aragón, provocó varios deslizamientos profundos y una intensa erosión en campos de cultivo recién sembrados de cereal.…”

The effects of rainfall intensity and rock fragment cover on soil hydrological responses in Central Chile

“…In Central and South Chile 5-8% of the annual precipitation (from 500 to 2500 mm y -1 ) has a high kinetic energy and the range of erosivity oscillates between 27 and 35 Mega joule ha -1 mm -1 (Ellies, 2000). Rainfall intensity has been found to be one of the most important factors affecting soil erosion and surface runoff (Serrano-Muela et al, 2013), especially in the case of extreme events, which may produce high levels of soil erosion over short periods (Cerdá et al, 2016).…”