Editing IPCC:AR6/WGI/Chapter-10 (section)

==== 10.6.4.7 Future Climate Information From Regional Downscaling ====

<div id="h3-79-siblings" class="h3-siblings"></div>

To unravel the complex interactions and feedbacks over the region on a range of spatial and temporal scales, regional downscaling projects are being developed to provide more comprehensive and detailed information on the future of the Mediterranean. The importance of regional downscaling for investigating the subregional details caused by the complex morphology of the Mediterranean region is a well-known issue in the literature ( [[#Planton--2012|Planton et al., 2012]] ), which has been addressed in many studies since AR5. Recent examples of dynamical downscaling are EURO-CORDEX ( [[#Jacob--2014|Jacob et al., 2014]] ) and Med-CORDEX ( [[#Ruti--2016|Ruti et al., 2016]] ; [[#Somot--2018|Somot et al., 2018]] ), but earlier activities have included ENSEMBLES ( [[#Déqué--2012|Déqué et al., 2012]] ; [[#Fernández--2019|Fernández et al., 2019]] ), PRUDENCE ( [[#Christensen--2002|Christensen et al., 2002]] ), CIRCE ( [[#Gualdi--2013|Gualdi et al., 2013]] ) and ESCENA ( [[#Jiménez-Guerrero--2013|Jiménez-Guerrero et al., 2013]] ).

From an analysis of CORDEX results, studies showed that southern Europe is projected to face a robust non-linear increase in temperature larger than the global mean ( [[#Zittis--2019|Zittis et al., 2019]] ), EURO-CORDEX projections, that are driven by CMIP5 global models, project a less pronounced warming than that of CMIP6 ( [[#Coppola--2021|Coppola et al., 2021]] ; see Figure 10.21c). The non-linear increase is especially evident for both hot and cold extremes ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ; [[#Maule--2017|Maule et al., 2017]] ; [[#Jacob--2018|Jacob et al., 2018]] ; [[#Kjellström--2018|Kjellström et al., 2018]] ). In particular, [[#Dosio--2018|Dosio and Fischer (2018)]] showed that in many places in southern Europe and the Mediterranean, the increase in the number of nights with temperature above 20°C is more than 60% larger under 2°C warming compared to 1.5°C. Over the region, the projected temperature increase, including a higher probability of severe heatwaves ( [[#Russo--2015|Russo et al., 2015]] ), is accompanied by a reduction in precipitation ( [[#Jacob--2014|Jacob et al., 2014]] ; [[#Dosio--2016|Dosio, 2016]] ; [[#Rajczak--2017|Rajczak and Schär, 2017]] ), resulting in projected increases of drought frequency and severity ( [[#Spinoni--2018|Spinoni et al., 2018]] , 2020; [[#Raymond--2019|Raymond et al., 2019]] ). Also, the frequency and severity of marine heatwaves of the Mediterranean Sea are projected to increase ( [[#Darmaraki--2019|Darmaraki et al., 2019]] ; see [[IPCC:Wg1:Chapter:Chapter-12#12.4|Section 12.4]] and Atlas.8.4).

Only a limited number of RCM simulations for the MENA domain are currently available. For the southern and eastern Mediterranean, they project a mean warming ranging from 3°C for RCP4.5 to 9°C for RCP8.5 at the end of this century compared to its beginning ( [[#Bucchignani--2018|Bucchignani et al., 2018]] ; [[#Ozturk--2018|Ozturk et al., 2018]] ). The frequency and duration of heatwaves and annual number of extremely hot days (i.e., those with maximum temperature &gt;50°C) in the southern Mediterranean will increase substantially. For 2070–2099 with respect to 1971–2000 the latter might even reach 70 days for RCP8.5 ( [[#Lelieveld--2016|Lelieveld et al., 2016]] ; [[#Almazroui--2019|Almazroui, 2019]] ; [[#Driouech--2020|Driouech et al., 2020]] ; [[#Varela--2020|Varela et al., 2020]] ).

Despite the large efforts of these regional downscaling projects, the global model–RCM matrix is still sparse and lacking a systematic design to explore the uncertainty sources (e.g., global model, RCM, scenario, resolution) ( [[#10.3|Section 10.3]] ). Focusing on the Iberian peninsula, [[#Fernández--2019|Fernández et al. (2019)]] argued that the driving global model is the main contributor to uncertainty in the ensemble. Physically consistent but implausible temperature changes in RCMs can occur. An example is a strong temperature increase over the Pyrenees due to excessive snow cover in the present climate ( [[#Fernández--2019|Fernández et al., 2019]] ). Based on an older set of RCM simulations (ENSEMBLES), [[#Déqué--2012|Déqué et al. (2012)]] also argued that the largest source of uncertainty in the temperature response over southern Europe is the choice of the driving global model (whereas for summer precipitation the choice of the RCM dominates the uncertainty). Finally, [[#Boé--2020a|Boé et al. (2020a)]] found that over a large area of Europe, including parts of the Mediterranean, RCMs project a summer warming 1.5°C–2°C colder than in their driving global models for the end of the 21st century. This is caused by differences in solar radiation related to the absence of time-varying anthropogenic aerosols in RCMs ( [[#Boé--2020a|Boé et al., 2020a]] ; [[#Gutiérrez--2020|Gutiérrez et al., 2020]] ), which also affects the noted differences in cloud cover between global models and RCMs ( [[#Bartók--2017|Bartók et al., 2017]] ).

Statistical downscaling studies for the Mediterranean confirm the results from global model and RCM studies, with large agreement among future projections showing lower rates of warming in winter and spring, and, in most cases, higher ones in summer and autumn ( [[#Jacobeit--2014|Jacobeit et al., 2014]] ).

<div id="10.6.4.8" class="h3-container"></div>

<span id="storyline-approaches-1"></span>