Comparative analysis of the response of various land covers to an exceptional rainfall event in the central Spanish Pyrenees, October 2012

Abstract

The hydrological and geomorphological effects of an exceptional 14 rainstorm event that occurred in the central Spanish Pyrenees during 19-21 October 15 2012 were studied in five experimental catchments under various land covers: (i) 16 subhumid badlands; (ii) dense forest; (iii) an abandoned farmland area recolonized by 17 shrubs and forest patches; and (iv) subalpine grasslands. Hydrographs and sedigraphs 18 demonstrated that vegetation cover is a major factor affecting the control of floods even 19 during exceptional rainstorms, at least at the spatial scale at which the phenomenon was 20 studied (catchment sizes: 0.3-2.8 km 2 ) and under dry catchment conditions. The 21 combined precipitation over the two days (ca. 250 mm) was the greatest for any two-22 day event recorded since 1950 in the central-western Pyrenees for all but one of the 23 stations in the study. Five pulses of most intense rainfall were recorded. The forested 24 catchment did not react to the two most intense rainfall pulses, because of the very low 25 antecedent level of the water table. The main peak flow occurred only when at least a 26 part of the catchment was saturated. The abandoned farmland catchment had two small 27 peak discharges at the beginning of the event, which were produced by infiltration 28 excess overland flow from eroded areas close to the main stream. During the third most 29 intense rainfall period a large part of this catchment contributed to runoff and a 30 relatively high peak discharge was produced. The badland catchment reacted 31immediately from the beginning of the rainstorm, yielding very high discharges 32 accompanied by high suspended sediment concentrations. The subalpine catchment 33 showed a hydrograph mirroring the hyetograph, with brief but intense hydrological 34 responses to increased precipitation, because of the marked gradients and the presence 35 of bare rock in the headwaters. A high volume of bedload was carried during the peak 36 discharge. Mediterranean region, particularly in coastal areas where rainfall of more than 200 mm 44 in 24 hr is commonly recorded, generally in autumn (López Bermúdez and Romero 45 Díaz, 1993; Poesen and Hooke, 1997; González Hidalgo et al., 2003). These rainstorms 46 are usually caused by warming of the Mediterranean Sea at the end of summer and the 47 occurrence of cold advection at high atmospheric levels, which results in 48 thermodynamically unstable cut-off systems (Nieto et al., 2005) having a duration of 49 two or three days. As a consequence, the most extreme flash floods within Europe tend 50 to occur in the Mediterranean region (Gaume et al., 2009), with some studies reporting 51 a change in flow from zero to hundreds of cubic meters per second in minutes 52 (Camarasa Belmonte and Segura Beltrán, 2001). 53Very large and intense rainstorms also occur in the interior of the Iberian 54Peninsula. These are typically localized and affect relatively small areas. This was the 55 case for the Rivillas ravine in the Guadiana River basin, where a flash ...

Erosion in Mediterranean mountain landscapes during the last millennium: a quantitative approach based on lake sediment sequences (Iberian Range, Spain)

“…However as Lana-Renault et al (2014) showed, catchments that have been subjected to farmland abandonment tend to have hydrological behaviors that are similar to forested catchments, although the hydrological activation of eroded areas, resulting from past agricultural uses, explains a significant contribution of overland flow, and subsequent intense hydrological and sediment responses. Comparing the experimental catchments with the lacustrine watersheds, we found that the Izas catchment -deforested during Medieval times to provide summer grasslands -the Arnás catchment -entirely cultivated until the 1950s -and the San Salvador catchment -covered by an undisturbed vegetal cover -all have similar range of Sy in the catchments.…”

“…The experimental catchment data have indicated that intense but infrequent flood events mainly control the sediment yield (Lana-Renault et al, 2014). For that reason, there is a large uncertainty in the estimation of long-term sediment production from a given catchment, and this is of critical importance for the management of the landscape-associated resources (water reservoirs, land use changes, abandon of cultivated lands, re-vegetation practices, etc.…”

“…It has high values of annual sediment yield (see Table 2). Soils descriptions are found in García-Ruiz et al (2008) and Lana-Renault et al (2014).…”

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

“…En el caso de la urbanización, localizada en Castiello de Jaca, se había desviado un canal del cauce del río Aragón hacia la orilla opuesta y así dar una sensación de seguridad; sin embargo, durante la avenida el río sobreexcavó en la base de una terraza fluvial, que se desplomó sobre el cauce y obligó a éste a retomar el cauce primitivo, a cuyo costado se había construido la urbanización. De esta crecida pudo disponerse además de información detallada en cuatro cuencas experimentales del Instituto Pirenaico de Ecología, pudiéndose comprobar la notable importancia de la cubierta vegetal en la respuesta hidrológica (Lana-Renault et al, 2014a). Así, la cuenca de San Salvador, con un bosque denso no perturbado, esperó hasta el tercer pico de intensidad de lluvia para empezar a reaccionar, y su principal pico de avenida fue re-lativamente moderado en comparación con la cuenca de Araguás, caracterizada por la presencia de cárcavas sobre margas poco permeables.…”

Catchment based hydrology under post farmland abandonment scenarios

“…These findings have enhanced knowledge of the runoff generation processes operating in these catchments under different rainfall and moisture conditions , 2014cSerrano-Muela et al, 2008;Nadal-Romero et al, 2016). These results have also enabled comparisons of their hydrological Nadal-Romero et al, 2016) and sedimentological responses, even under extreme rainfall conditions (Lana-Renault et al, 2014b). The considerable data on meteorological, hydrological and sediment transport variables have been used to test and apply models to simulate soil erosion (Alatorre et al, 2012) and water and sediment yield under different land use scenarios, and to better understand the effect of revegetation on the main hydrological processes (Lana-Renault et al, in review).…”