Title: PESETA III – Task1: Climate change projections, bias-adjustment, and selection of model runs
Authors: DOSIO ALESSANDRO
Publisher: Publications Office of the European Union
Publication Year: 2018
JRC N°: JRC113745
ISBN: 978-92-79-97261-4 (online)
ISSN: 1831-9424 (online)
Other Identifiers: EUR 29444 EN
OP KJ-NA-29444-EN-N (online)
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC113745
DOI: 10.2760/44883
Type: EUR - Scientific and Technical Research Reports
Abstract: Global warming will greatly affect the climate at regional and local scale through, e.g., the increase of intensity and frequency of extreme weather events (floods, droughts, heat waves, etc.). In order to assess the impact of climate change at such scale (on, e.g., the hydrological cycle or crop production) it is necessary to attain meteorological information with a spatial detail much finer than that provided by global climate models (GCMs). High-resolution climate projections are usually obtained by employing regional climate models (RCMs), which are able to better resolve small-scale features such as topography and heterogeneous land use. When compared to present-day observations, however, the results of climate models can present large biases; in order to be used as an input for process-based impact models (like in PESETA III) outputs from RCMs are usually further post-processed by means of statistical techniques known as bias-correction (or bias-adjustment). Here, we describe the projections of climate change used in PESETA III and the bias-adjustment method applied to them, focusing on the analysis of a series of climate change indices for both the mean climate and extreme events (such as the number of frost days, of the number of consecutive dry days) relevant for impact assessment studies. Results show that, under the RCP8.5 emission scenario, at the end of the Century, maximum temperature is expected to increase, in winter, between about 2.5∘C over the British Isles and 4.8∘C over Scandinavia. In summer, the projected change ranges between 2.5∘C over Britain and 4.7∘C over the Iberian Peninsula. Winter precipitation is projected to increase over most of central and northern Europe in both frequency, and intensity, with a consequent increase of the number of consecutive wet days, and reduction of consecutive dry days. The change in precipitation frequencies distribution is not uniform, though, and a reduction in low precipitation intensity is accompanied by an increase of extreme events, even for the Mediterranean regions where total precipitation is projected to decrease. In summer, a general reduction in precipitation is projected for all regions except Scandinavia and Eastern Europe; as for winter, there is a tendency toward less frequent but more severe precipitation episodes. A set of 12 RCMs’ bias-adjusted climate change projections is provided to the PESETA III impact modellers; the use of such a large ensemble of runs is essential to quantify the uncertainty in climate projections (the so-called inter-model variability). In fact, each model’s run (driven by the same emission scenario) represents an equally plausible projection of the future evolution of the climate. However, due to differences in the models’ formulation and physical parameterization, the climate change signal projected by different models may present significant differences. Due to resource limitations, some impact model groups may not be able to use all the 12 provided runs; in this case, a sub-set of 5 runs is selected to be used by all impact models (compulsory core runs). The sub-set of core runs needs to be able to reproduce, as accurately as possible, the inter-model variability of the entire ensemble. The selection of the sub-set has been performed by means of Principal Component Analysis (PCA) on the bias adjusted climate change indices. Finally, the PESETA III protocol also requires investigating the impacts of a 2ᵒC global warming, compared to the preindustrial period. Here for each RCM run, the timing of reaching 2ᵒC warming is provided following the same procedure used in the FP7 project IMPACT2C, namely: - It is assumed that the climate in a +2ᵒC world is comparable irrespective of when and how fast this warming is reached - An RCM is defined to project a 2ᵒC global warming when the corresponding driving GCM reaches the 2ᵒC threshold, under RCP8.5 emission scenario - For each GCM-RCM run, the +2ᵒC period is defined as the 30 year period centred around the year when the 2ᵒC global warming is first reached
JRC Directorate:Space, Security and Migration

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