Abstract
Spain, one of the most mountainous countries in Europe, suffers from frequent river flooding due to specific climatic and topographic features. Many headwaters of the largest rivers in Spain are located in mountainous areas of mid-to-high elevation. These include the Pyrenees, the Central System, and the Cantabrian mountains, that have a sustained snowpack during the winter months. Most previous research on flood generation in Spain has focused on intense rainfall events, and the role of snowmelt has been ignored or considered marginal. In this paper we present a regional-scale study to quantify the relative importance of rainfall versus snowmelt in the largest floods recorded in mountain rivers in Spain during the last decades (1980–2014). We further analyzed whether catchments characteristics and weather types may favor the occurrence of rainfall or snowmelt induced floods. Results show that in 53% of the 250 analyzed floods the contribution of rainfall was larger than 90%, and in the rest of events snowmelt contribution was larger than 10%. Floods where snowmelt was the main contributor represented only 5% of the total events. The average contribution of snowmelt represents 18% of total runoff in floods that were analyzed. The role of snowmelt in floods, rather than triggering the event, was usually amplifying the duration of the event, especially after the peak flow was reached. In general, the importance of snowmelt in floods is greater in catchments with characteristics that favor snow accumulation. However, this does not apply to floods where contribution of snowmelt was larger than 90%, which tend to occur at catchments at mid-elevations that accumulate unusual amounts of snow that melt rapidly. Floods were more frequent under both cyclonic and anticyclonic synoptic situations over the Iberian Peninsula, as well as under advection of western and eastern flows. Our results contribute to the ongoing improvement of knowledge about the role of snow in the hydrology of Spanish rivers and on the importance of mountain processes on the hydrology of downstream areas.
Highlights
Mountains are important for water resources across the world [1]
The objectives of the research are (1) to determine whether the major floods are derived from rain, snowmelt, or a combination of rain and snowmelt; (2) to quantify the relative contribution of each on the total flooding streamflow; (3) to explore the main characteristics of the floods hydrographs [27,28] according to the relative contribution of rainfall and snowmelt and (4) to determine whether the geographical characteristics of the catchments, and atmospheric circulation over the Iberian region can explain the relative importance of rainfall and snowmelt in triggering major floods
We explored the characteristics of hydrographs for each type of flood to discern whether the relative contribution of rainfall and snowmelt involve different shapes in the flood hydrograph
Summary
Mountains are important for water resources across the world [1]. They constitute the headwaters of major fluvial systems, storing water in the form of snow, ice, groundwater, or lakes. Both the quantity and the timing of water flowing downstream depend on the elevation, drainage area, and other geographical characteristics of mountains. Mountains facilitate adiabatic uplift of air masses, and convective precipitation [2] and the steep slopes enable surface runoff and rapid water routing, increasing the potential for flood generation [3,4]. Greater damage to society usually occurs downstream, where most of the population is concentrated, and where water from different tributaries converges in the main stream, causing a substantial increase in streamflow and potential risk
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