Large-scale patterns of daily precipitation extremes on the Iberian Peninsula

Abstract

The study of weather extremes is critical because of their great impact on the environment, economy and society. The identification of areas at greater risk of extreme conditions, and of meteorological situations that give rise to such conditions, enhances the understanding of climate risks and helps establish measures to reduce adverse impacts. In the current paper, precipitation extreme events (PEEs) in Spain between 1960 and 2011 were analysed. Thresholds for determining event severity were defined using 99th percentiles. First, regions of extreme weather risk were identified and then trends of extreme precipitation index were analysed using the Mann–Kendall test. To better understand atmospheric processes associated with extreme weather events in each season, synoptic‐scale fields of events exceeding the 99th percentile were analysed. By applying non‐hierarchical K‐means clustering, we defined six large‐scale atmospheric patterns that largely explain the spatiotemporal distribution of PEEs in the study area. PEEs on the western Iberian Peninsula mainly occurred with zonal flow, with a long Atlantic fetch generating moisture advection towards that area. On the eastern peninsula, the most important pattern for PEE production is characterized by a cutoff low at mid‐levels together with easterly moisture flow. The relationship of PEEs with teleconnection patterns, such as the North Atlantic Oscillation (NAO), Mediterranean Oscillation (MO) and Western Mediterranean Oscillation (WeMO), showed that nearly all the events over the southwestern peninsula were during the NAO‐ and MO‐negative phases. However, on the Mediterranean coast, the negative WeMO phase had greater influence. By contrast, the northwestern peninsula and eastern Cantabrian coast showed weaker relationships between these indices and PEEs. The results show a clear ability to identify regions exposed to extreme precipitation hazards. The correct identification of synoptic patterns associated with each type of weather extreme will assist the prediction of such events, thereby providing useful information for decision making and warning systems.

SPREAD: a high-resolution daily gridded precipitation dataset for Spain – an extreme events frequency and intensity overview

“…Some previous works in Spain that used a lower spatial resolution and a lower number of observatories (Herrera et al, 2012;Merino et al, 2015) showed overestimated values in extreme precipitation indices in some areas (especially in the north-west area of the Iberian Peninsula) but smoothing in others (e.g. Central Range).…”

“…But they are also suitable to analyse spatial patterns in daily characteristics of precipitation through extreme indices that allow comparisons between regions. In Spain, these indices have been applied to mainland Spain (Martín-Vide, 2004;Herrera et al, 2012;Merino et al, 2015) and to specific regions (Casas et al, 2007;Martínez et al, 2007;Rodrigo and Trigo, 2007;Lopez-Moreno et al, 2010). All of these datasets used the precipitation estimations to compute climatic indices.…”

Meteorological Driving Mechanisms and Human Impacts of the February 1979 Extreme Hydro-Geomorphological Event in Western Iberia

“…The most severe events are mainly associated with flash floods that are often produced by a sudden thunderstorm that usually develops into a mesoscale convective system. In addition, [26] studied the large-scale patterns of daily precipitation extremes on the Iberian Peninsula, where it was found that extreme precipitation events on the Western Iberian Peninsula mainly occurred under strong zonal flow, with a long Atlantic fetch generating moisture advection towards that area. On the eastern sector of the Iberian Peninsula, the most important pattern associated with extreme precipitation is characterized by a cut-off low system at mid-levels together with easterly moisture flow from the Mediterranean.…”

An updated review on recent trends in observational surface atmospheric variables and their extremes over Spain

“…Cortesi et al (2012) assessed the statistical structure of daily precipitation over Europe from 1971 to 2010 using the daily precipitation concentration index (CI), suggesting significant positive trends in most of observatories south of Spain and along the Mediterranean coasts. More recently, Merino et al (2016) defined regions that exposed to extreme precipitation hazards over the Iberian Peninsula and assessed trends of extreme precipitation index from 1960 to 2011, based on the 99 th percentile of daily precipitation distribution.…”