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Hazardous weather related to the occurrence of severe thunderstorms including tornadoes, high-winds, and hail cause significant damage globally to life and property every year. Yet the impact on these storms from a warming climate remains a difficult task due to their transient nature. In this study we investigate the change in large-scale environments in which severe thunderstorms form during twenty-first century warming (RCP2.6 and RCP8.5) in a group of RegCM CORDEX-CORE simulations. Severe potential is measured in terms of Convective Available Potential Energy (CAPE) and vertical wind-shear during the severe seasons in three regions which are known to currently be prone to severe hazards: North America, subtropical South America, and eastern India and Bangladesh. In every region, environments supportive for severe thunderstorms are projected to increase during the warm season months in both the RCP2.6 and RCP8.5 scenarios during the twenty-first century. The number of days supportive for severe thunderstorms increases by several days per season over the vast majority of each region by the end of the century. Analyzing the CAPE and shear trends during the twenty-first century, we find seasonally and regionally specific changes driving the increased severe potential. Twenty-first century surface warming is clearly driving a robust increase in CAPE in all regions, however poleward displacement of vertical shear in the future leads to the displacement of severe environments over North America and South America. The results found here relate that severe impacts in the future cannot be generalized globally, and that regionally specific changes in vertical shear may drive future movement of regions prone to severe weather.

The added value of using regional climate models (RCMs) to downscale data from general circulation models (GCMs) has often been questioned and researched. Although several studies have used different methods to identify (and in some cases quantify) the added value, there is still a need to find a general metric that quantifies the added value of any variable. This paper builds on past studies to propose a new metric of added value in the simulation of present-day climate which measures the difference in the probability density functions (PDFs) at each grid-cell between a model and an observation source, and then compares the results of the RCM and GCM in order to spatially compute the added value index. The same method is also adapted to quantify the climate change downscaling signal in a way that is consistent with the present-day metric. These new metrics are tested on the daily precipitation output from the EURO-CORDEX and CORDEX-CORE projection ensembles and reveal an overall positive added value of RCMs, especially at the tail-end of the distribution. Higher added value is obtained in areas of complex topography and coast-lines, as well as in tropical regions. Areas with large added value in present-day climate are consistent with areas of significant climate change downscaling signal in the RCP 8.5 far future simulations, and when the analysis is repeated at a low-resolution. The use of different resolution observations shows that the added value tends to decrease when models are compared to low-resolution observation datasets.

The characteristics of tropical cyclone (TC) activity over 5 TC basins lying within four Coordinated Regional Downscaling Experiment (CORDEX) domains are examined for present and future climate conditions using a new ensemble of projections completed as part of the CORDEX-CORE initiative with the regional climate model RegCM4. The simulations were conducted on a 25 km horizontal grid spacing using lateral and lower boundary forcing from three CMIP5 global climate models (GCMs) under two Radiative Concentration Pathways (RCP2.6 and RCP8.5). The RegCM4 is capable of capturing most features of the observed TC climatology over the different basins and exhibits a much-improved simulation of TC statistics compared to the driving GCMs. Analysis of the influence of global warming on TC activity indicates significant increases in their frequency over the North Indian Ocean, the Northwest Pacific and Eastern Pacific regions. These changes are consistent with an increase in mid-tropospheric relative humidity. On the other hand, the North Atlantic and Australasia regions show a decrease in TC frequency, mostly associated with an increase in wind shear. We also find a consistent increase in future storm rainfall rates associated with TCs and in the frequency of the most intense TCs over most domains. Our study shows robust and statistically significant responses often, but not always, in line with previous studies, still implying the presence of significant uncertainties. A robust assessment of TC changes requires analyses of ensembles of simulations with high-resolution models capable of representing the response of different TC characteristics to key atmospheric factors.

Dangerous weather related to severe thunderstorms including tornadoes, high-winds, and hail cause significant damage globally to life and property every year. Yet the impact on these storms from a warming climate remains a difficult task due to their small scale and transient nature. Here, we present a study in which the changes to the large-scale environments in which severe thunderstorms form were investigated during 21st century warming (RCP2.6 and RCP8.5) in a group of RegCM CORDEX-CORE simulations. Severe potential is measured in terms of CAPE (Convective Available Potential Energy) and shear during the severe seasons in three regions which are known to currently be prone to severe hazards: North America, the southeastern coast of South America east of the Andes, and eastern India and Bangladesh. In every region environments supportive for severe thunderstorms are projected to increase during the warm season months in both RCP2.6 and RCP8.5 during the 21st century. The number of days supportive for severe thunderstorms increases by several days per season over the vast majority of each region by the end of the century. In the case of RCP2.6, where greenhouse gas forcing is relatively weak compared to RCP8.5, there is still a consistent positive trend in the impact on severe days. The simulations using RCP8.5 forcing show large changes to the annual cycle of severe weather as well as the number of days supportive for severe weather per season. In some regions, like for example Northern Argentina along the Andes mountains, the number of days with severe conditions present increases by nearly 100% by the end of the century. Analyzing the CAPE and shear trends during the 21st century we find seasonal and regionally specific changes driving the increased severe potential. 21st century surface warming is clearly driving a robust increase in CAPE in all regions, however poleward displacement of vertical shear in the future leads to the movement of severe environments over North America and South America. We would also like to present a preliminary look at the next phase of this project which will apply similar methods to an ensemble of 11o Euro-CORDEX simulations to investigate severe conditions over the European region in the future.

The CORDEX-CORE initiative was developed with the aim of producing homogeneous regional climate model (RCM) projections over domains world wide. In its first phase, two RCMs were run at 0.22° resolution downscaling 3 global climate models (GCMs) from the CMIP5 program for 9 CORDEX domains and two climate scenarios, the RCP2.6 and RCP8.5. The CORDEX-CORE simulations along with the CMIP5 GCM ensemble and the most recently produced CMIP6 GCM ensemble are analyzed, with focus on several temperature, heat, wet and dry hazard indicators for present day and mid-century and far future time slices. The CORDEX-CORE ensemble shows a better performance than the driving GCMs for several hazard indices due to its higher spatial resolution. For the far future time slice the 3 ensembles project an increase in all temperature and heat indices analyzed under the RCP8.5 scenario. The largest increases are always shown by the CMIP6 ensemble, except for Tx > 35 °C, for which the CORDEX-CORE projects higher warming. Extreme wet and flood prone maxima are projected to increase by the RCM ensemble over the la Plata basin in South America, the Congo basin in Africa, east North America, north east Europe, India and Indochina, regions where a better performance is obtained, whereas the GCM ensembles show small or negligible signals. Compound hazard hotspots based on heat, drought and wet indicators are detected in each continent worldwide in region like Central America, the Amazon, the Mediterranean, South Africa and Australia, where a linear relation is shown between the heatwave and drought change signal, and region like Arabian peninsula, the central and south east Africa region (SEAF), the north west America (NWN), south east Asia, India, China and central and northern European regions (WCE, NEU) where the same linear relation is found for extreme precipitation and HW increases. Although still limited, the CORDEX-CORE initiative was able to produce high resolution climate projections with almost global coverage and can provide an important resource for impact assessment and climate service activities.

The new Coordinated Output for Regional Evaluations (CORDEX-CORE) ensemble provides high-resolution, consistent regional climate change projections for the major inhabited areas of the world. It serves as a solid scientific basis for further research related to vulnerability, impact, adaptation and climate services in addition to existing CORDEX simulations. The aim of this study is to investigate and document the climate change information provided by the CORDEX-CORE simulation ensemble, as a part of the World Climate Research Programme (WCRP) CORDEX community. An overview of the annual and monthly mean climate change information in selected regions in different CORDEX domains is presented for temperature and precipitation, providing the foundation for detailed follow-up studies and applications. Initially, two regional climate models (RCMs), REMO and RegCM were used to downscale global climate model output. The driving simulations by AR5 global climate models (AR5-GCMs) were selected to cover the spread of high, medium, and low equilibrium climate sensitivity at a global scale. The CORDEX-CORE ensemble has doubled the spatial resolution compared to the previously existing CORDEX simulations in most of the regions (25$$\,\mathrm {km}$$km(0.22$$^{\circ }$$∘) versus 50$$\,\mathrm {km}$$km(0.44$$^{\circ }$$∘)) leading to a potentially improved representation of, e.g., physical processes in the RCMs. The analysis focuses on changes in the IPCC physical climate reference regions. The results show a general reasonable representation of the spread of the temperature and precipitation climate change signals of the AR5-GCMs by the CORDEX-CORE simulations in the investigated regions in all CORDEX domains by mostly covering the AR5 interquartile range of climate change signals. The simulated CORDEX-CORE monthly climate change signals mostly follow the AR5-GCMs, although for specific regions they show a different change in the course of the year compared to the AR5-GCMs, especially for RCP8.5, which needs to be investigated further in region specific process studies.

Regional Climate Models (RCMs) have undergone substantial development, resulting in increasingly reliable high-resolution simulations. Despite this, the added value of these simulations compared to their driving General Circulation Models (GCMs) has been a recurring issue. Past studies have used different techniques to quantify the added value of a RCM. A new method is now being presented, based on these past studies, that quantifies the added value and presents it spatially. The method was also adapted to assess the Downscaling Signal (DS) in climate change simulations and compare this to the added value.This new method has been used to assess the daily precipitation of the 55-model EURO-CORDEX ensemble and the CORDEX-CORE ensemble, focusing especially on the higher-end of the PDFs. This revealed an overall positive added value across all domains, especially in areas of complex topography, cost-lines, and tropical regions. This DS was similar to that of the added value when looking at RCP 8.5 far-future simulations.

Five of the most prominent low-level jets (LLJs) around the world – the Monsoon Low-Level Jet, Caribbean Low-Level Jet, West African Westerly Jet, Great Plains Low-Level Jet and South American Low-Level Jet – are examined for future climate conditions relative to the present using an ensemble of Regional Climate Model (RCM) simulations under the Coordinated Regional Downscaling Experiment (CORDEX) initiative. The simulations were conducted on a 25 km horizontal grid spacing using lateral and lower boundary forcing from three Coupled Model Inter-comparison Project 5 (CMIP5) global climate models (GCMs) for a near-present historical period (1995–2014) and two future periods (2041–2060 and 2080–2099) under the Representative Concentration Pathway 8.5 (RCP8.5). The RCM is capable of capturing most of the observed climatological features of the LLJs and exhibits a much greater capacity to represent their positioning and core strength compared to the driving GCMs. Analysis of the influence of global warming on the LLJs shows a consistent strengthening of the jets and a shift in their location under both future scenarios. The Monsoon and West African LLJs exhibit a northward shift, while the Caribbean and South American LLJs undergo a westward expansion. The use of an ensemble of high-resolution simulations provides a key element in a robust assessment of changes in LLJs associated with future global-warming scenarios.

Dangerous weather related to severe thunderstorms including tornadoes, high-winds, and hail cause significant damage globally to life and property every year. Yet the impact on these storms from a warming climate remains a difficult task due to their transient nature. In this study we investigate changes in the large-scale environments in which severe thunderstorms form during 21st century warming (RCP2.6 and RCP8.5) in a group of RegCM CORDEX-CORE simulations. Severe potential is measured in terms of CAPE (Convective Available Potential Energy) and shear during the severe seasons in three regions which are known to currently be prone to severe hazards: North America, the southeastern coast of South America east of the Andes, and eastern India and Bangladesh. In every region environments supportive for severe thunderstorms are increasing during the warm season months in both RCP2.6 and RCP8.5 during the 21st century. The number of days supportive for severe thunderstorms increases by several days per season over the vast majority of each region by the end of the century. In the case of RCP2.6, where greenhouse gas forcing is relatively weak compared to RCP8.5, there is still a consistent positive trend in the impact on severe days. The simulations using RCP8.5 forcing show large changes to the annual cycle of severe weather as well as the number of days supportive for severe weather per season. In some regions, like for example Northern Argentina along the Andes mountains, the number of days with severe conditions present increases by nearly 100% by the end of the century. Analyzing the CAPE and shear trends during the 21st century we find seasonal and regionally specific changes driving the increased severe potential. 21st century surface warming is clearly driving a robust increase in CAPE in all regions, however poleward displacement of vertical shear in the future leads to the movement of severe environments over North America and South America. The results found here relate that severe impacts in the future cannot be generalized globally, and that regionally specific changes in vertical shear may drive future movement of regions prone to severe weather.