Statistical modelling of extreme precipitation indices for the Mediterranean area under future climate change

Abstract

Projected changes of extreme precipitation in the Mediterranean area up until the end of the 21st century are analysed by means of statistical downscaling. Generalized linear models are used as downscaling technique to assess different percentile-based indices of extreme precipitation on a fine-scale spatial resolution. In the region under consideration extreme precipitation is related to anomalies of the large-scale circulation as well as to convective conditions. To account for this, predictor selection encompasses variables describing the large-scale circulation (geopotential heights of the 700 hPa and 500 hPa levels, u-and v-wind components of the 850 hPa level) as well as thermo-dynamic parameters (specific humidity of the 850 hPa and 700 hPa levels, Showalter-Index, convective inhibition). In the scope of the statistical downscaling approach a specific statistical ensemble technique is applied in order to allow for non-stationarities in the predictors-predictand relationships. Consequently, the statistical ensembles include a range of possible future evolutions of extreme precipitation. Two different emission scenarios (A1B and B1), multiple runs for each scenario, and output of two different general circulation models (ECHAM5 and HadCM3) are applied to assess extreme precipitation under enhanced greenhouse warming conditions. The results yield mainly decreases over many parts of the Mediterranean area in spring. In summer increases are assessed around the Tyrrhenian Sea, the Ionian Sea, and the Aegean Sea, whereas decreases are projected for most of the western and northern Mediterranean regions. In autumn reductions of heavy rainfall occur over many parts of the western and central areas. In winter distinct increases are widespread in the Mediterranean area. Beyond the assessments using all predictors it is shown in the present contribution that different predictor variables can lead to varying statistical downscaling results. It points to distinct impacts of the change of specific atmospheric conditions on local extreme precipitation.

An intercomparison of a large ensemble of statistical downscaling methods over Europe: Results from the VALUE perfect predictor cross‐validation experiment

“…The data set includes a reduced number of commonly used predictors, degraded to a common 2 grid and postprocessed by computing daily means from the original 6hourly fields when required (see Table 2). This reference data set includes most of the circulation and thermodynamic predictors at different pressure levels (including some surface predictors), typically used in downscaling applications in different European regions (Benestad, 2002;Gutiérrez et al, 2013;Hanssen-Bauer, Achberger, Benestad, Chen, & Førland, 2005;Hertig et al, 2014;Huth, 1999Huth, , 2002Huth, , 2005San-Martín et al, 2017;Timbal, Dufour, & McAvaney, 2003), excluding redundancy as much as possible. For instance, vorticity and divergence have been considered as potential predictors in the literature (see, e.g., Hessami, Gachon, Ouarda, & St-Hilaire, 2008), but they were excluded from the standard set because they reported similar results to geopotential or wind directions in some studies (Gutiérrez et al, 2013).…”

Review Article: Atmospheric conditions inducing extreme precipitation over the eastern and western Mediterranean

“…In an attempt to quantify the relative contribution of each of these mechanisms to the possible evolution of extreme precipitation, Hertig et al (2014) used two general circulation models to assess the projected changes of extreme precipitation in the MR until the end of the twenty-first century by means of statistical downscaling. They found that large-scale circulation plays an important role in the generation of extreme precipitation events in the transitional seasons.…”

Adaptability of Mediterranean Agricultural Systems to Climate Change. The Example of the Sierra Mágina Olive-Growing Region (Andalusia, Spain). Part I: Past and Present

“…In Mediterranean regions, the most common climate change scenarios foresee an increase in temperatures and a decrease in rainfall (Christensen et al 2007;Stocker et al 2014;Giorgi and Lionello 2008;Magnan et al 2009;Gualdi et al 2013), and an increase in extreme episodes (Hertig et al 2013), with potential consequences for agricultural yields (FAO 2008) and natural resources. In this context, we must look beyond the question of sustainable development and risk and incorporate the concepts of vulnerability, adaptation, and the resilience of socioeconomic systems facing environmental change.…”