A part of the study of future climate changes is based on the forecast provided by Global Circulation Models (GCM). Testing GCM output for the past is therefore a major issue for climate studies. Different approaches are possible, based... more
A part of the study of future climate changes is based on the forecast provided by Global Circulation Models (GCM). Testing GCM output for the past is therefore a major issue for climate studies. Different approaches are possible, based on comparison between numerical output and atmospheric and oceanic measurements. More recently, another approach has been proposed, which makes use of
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We describe the development of a non-hydrostatic version of the regional climate model RegCM4, called 9 RegCM4-NH, for use at convection-permitting resolutions. The non-hydrostatic dynamical core of the Mesoscale 10 Model MM5 is... more
We describe the development of a non-hydrostatic version of the regional climate model RegCM4, called 9 RegCM4-NH, for use at convection-permitting resolutions. The non-hydrostatic dynamical core of the Mesoscale 10 Model MM5 is introduced in the RegCM4, with some modifications to increase stability and applicability of the model 11 to long-term climate simulations. Newly available explicit microphysics schemes are also described, and three case 12 studies of intense convection events are carried out in order to illustrate the performance of the model. They are all 13 run at convection-permitting grid spacing of 3 km over domains in northern California, Texas and the Lake Victoria 14 region, without the use of parameterized cumulus convection. A substantial improvement is found in the simulations 15 compared to corresponding coarser resolution (12 km) runs completed with the hydrostatic version of the model 16 employing parameterized convection. RegCM4-NH is currently being used in ...
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In this work, a new Italian precipitation dataset is used to evaluate two different European regional climate simulations within the EURO-CORDEX framework: one driven by the ERA-Interim reanalysis and one by the HadGEM global climate... more
In this work, a new Italian precipitation dataset is used to evaluate two different European regional climate simulations within the EURO-CORDEX framework: one driven by the ERA-Interim reanalysis and one by the HadGEM global climate model. These are the latest simulations available with the RegCM regional climate model, version 4.6.1. The evaluation is also compared with that carried out with two existing datasets: E-OBS, covering the whole study area, and the Alpine high-resolution dataset EURO4M-APGD.
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The new version of RegCM4 has been used in a configuration where the model is global in the zonal direction but bounded in the meridional direction over the tropical region: the tropical belt. A multiple year perfect boundary simulation... more
The new version of RegCM4 has been used in a configuration where the model is global in the zonal direction but bounded in the meridional direction over the tropical region: the tropical belt. A multiple year perfect boundary simulation has been completed and the model climatology has been validated against the CRU temperature observation and TRMM precipitation derived product from satellite. The lateral boundary conditions are taken from the most recent reanalysis product form ECMWF, the ERA-interim dataset and the model resolution is 50 km, 25 km and 10km. The RegCM4-belt configuration sees a double convection scheme implemented one for the ocean and one over land. In particular the Emanuel convection scheme is adopted over the ocean and the Grell-FC is used over the continental areas. The model is able to reasonably reproduce the strength and the position of the ITCZ and its seasonal migration. The JJA season shows a cold bias uniformly distributed over the tropical region but li...
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Tropical countries are already experiencing the adverse impacts of climate change. This study presents projections of climate change-driven variations in hydrology and sediment loads in the Kalu River Basin, Sri Lanka. Bias-corrected... more
Tropical countries are already experiencing the adverse impacts of climate change. This study presents projections of climate change-driven variations in hydrology and sediment loads in the Kalu River Basin, Sri Lanka. Bias-corrected climate projections (i.e., precipitation and temperature) from three high resolution (25 km) regional climate models (viz., RegCM4-MIROC5, MPI-M-MPI-ESM-MR, and NCC-NORESM1-M) are used here to force a calibrated hydrological model to project streamflow and sediment loads for two future periods (mid-century: 2046–2065, and end of the century: 2081–2099) under two representative concentration pathways (i.e., RCPs 2.6 and 8.5). By the end of the century under RCP 8.5, all simulations (forced with the three RCMs) project increased annual streamflow (67–87%) and sediment loads (128–145%). In general, streamflow and sediment loads are projected to increase more during the southwest monsoon season (May–September) than in other periods. Furthermore, by the end ...
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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... more
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.
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We use an unprecedented ensemble of regional climate model (RCM) projections over seven regional CORDEX domains to provide, for the first time, an RCM-based global view of monsoon changes at various levels of increased greenhouse gas... more
We use an unprecedented ensemble of regional climate model (RCM) projections over seven regional CORDEX domains to provide, for the first time, an RCM-based global view of monsoon changes at various levels of increased greenhouse gas (GHG) forcing. All regional simulations are conducted using RegCM4 at a 25 km horizontal grid spacing using lateral and lower boundary forcing from three General Circulation Models (GCMs), which are part of the fifth phase of the Coupled Model Inter-comparison Project (CMIP5). Each simulation covers the period from 1970 through 2100 under two Representative Concentration Pathways (RCP2.6 and RCP8.5). Regional climate simulations exhibit high fidelity in capturing key characteristics of precipitation and atmospheric dynamics across monsoon regions in the historical period. In the future period, regional monsoons exhibit a spatially robust delay in the monsoon onset, an increase in seasonality, and a reduction in the rainy season length at higher levels o...
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We evaluate the performance of a large ensemble of Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) over South America for a recent past reference period and examine their projections of... more
We evaluate the performance of a large ensemble of Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) over South America for a recent past reference period and examine their projections of twenty-first century precipitation and temperature changes. The future changes are computed for two time slices (2040–2059 and 2080–2099) relative to the reference period (1995–2014) under four Shared Socioeconomic Pathways (SSPs, SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5). The CMIP6 GCMs successfully capture the main climate characteristics across South America. However, they exhibit varying skill in the spatiotemporal distribution of precipitation and temperature at the sub-regional scale, particularly over high latitudes and altitudes. Future precipitation exhibits a decrease over the east of the northern Andes in tropical South America and the southern Andes in Chile and Amazonia, and an increase over southeastern South America and the northern Andes—a ...
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The potential changes in the strength and location of five low-level jets (LLJs) located within four Coordinated Regional Climate Downscaling Experiment (CORDEX) domains are examined for present and future climate conditions using an... more
The potential changes in the strength and location of five low-level jets (LLJs) located within four Coordinated Regional Climate Downscaling Experiment (CORDEX) domains are examined for present and future climate conditions using an ensemble of simulations conducted with the RegCM4 regional model at a 25 km horizontal grid spacing. Lateral and lower boundary forcing fields are from three General Circulation Models (GCMs), and we analyse a historical period (1995–2014) along with two future periods (2041–2060 and 2080–2099) under the Representative Concentration Pathways 2.6 and 8.5. The RegCM4, as driven by the GCMs, is capable of capturing most of the observed climatological features of the LLJs, both in terms of spatial location and seasonal evolution. 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 warming scenarios. The Monsoon and West African westerly LLJs exhibit a northward shift, while the Caribbean and South American LLJs present a westward expansion. The use of an ensemble of high-resolution simulations is found to provide a key element for a robust assessment of changes in LLJs associated with future global warming scenarios.
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The interannual variability of the boreal winter (DJF) subtropical jet stream (STJ) is analyzed over the Coordinated Regional Downscaling Experiment—Central America, Mexico, and Caribbean domain (CORDEX-CAM) during 1980–2010. We use... more
The interannual variability of the boreal winter (DJF) subtropical jet stream (STJ) is analyzed over the Coordinated Regional Downscaling Experiment—Central America, Mexico, and Caribbean domain (CORDEX-CAM) during 1980–2010. We use simulations with the regional climate model RegCM4 (version 7) at 25 km resolution driven by ERA-Interim (RegERA) and three global models (RegGCMs). The simulations are evaluated using zonal winds at 200 hPa level from ERA-Interim and MERRA2, which show similar results, and no significant trends in the STJ. Despite some biases, RegERA captures the STJ variability and its relationship with several teleconnections. The polarities of the principal mode of variability of the Pacific and Atlantic jets are significantly anti-correlated; they represent the longitudinal extension/retraction and the poleward/equatorward migration of the jet cores, respectively. During El Niño and the + PNA (Pacific North America), the North Pacific jet exit region and the North Atlantic jet show maximum speeds equatorward of their climatological positions. During these conditions, there is an extended and strong STJ over the domain; this pattern also tends to occur during the negative phases of the Arctic and North Atlantic oscillations. The RegGCMs simulate better the principal modes of the Atlantic jet variability than those of the Pacific jet exit region; nevertheless, they reproduce the observed sign of the variations of the jet speeds and their latitudinal changes in the two basins. They also partially capture the sign of the temperature and precipitation anomalies in the domain, which respond to the STJ polarities and their interaction with the teleconnections.
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This study evaluates the projected changes in the atmospheric water budget and precipitation under the RCP8.5 scenario over two CORDEX-CORE domains: South America (SAM) and Europe (EUR). An ensemble of five twenty-first century... more
This study evaluates the projected changes in the atmospheric water budget and precipitation under the RCP8.5 scenario over two CORDEX-CORE domains: South America (SAM) and Europe (EUR). An ensemble of five twenty-first century projections with the Regional Climate Model version 4 (RegCM4) and their driving Global Climate Models (GCMs) are analyzed in terms of the atmospheric water budget terms (precipitation, P; evapotranspiration, ET; and moisture flux convergence, C). Special focus is on four subregions: Amazon (AMZ), La Plata basin (LPB), Mid-Europe (ME) and Eastern Europe (EA). The precipitation change signal in SAM presents a dipole pattern, i.e. drier conditions in AMZ and wetter conditions in LPB. Over the two European regions a seasonality is evident, with an increase of ~ 25% in precipitation for DJF and a decrease of ~ 35% in JJA. The atmospheric water budget drivers of precipitation change vary by region and season. For example, in DJF the main drivers are related to the large-scale moisture flux convergence, while in JJA over the AMZ atmospheric moisture flux convergence plays only a minor role and local processes dominate. For JJA in the GCMs the high values of the residual term do not allow us to assess which mechanisms drive the precipitation change signal over the AMZ and LPB, respectively. Same conclusions are found for the RegCM4 JJA simulations over the LPB and EA. This points to the importance of the spatial resolution of climate simulations and the role of parameterization schemes in climate models. Our work illustrates the usefulness of analyzing regional water budgets for a better understanding of precipitation change patterns around our globe.
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Renewable energy is key for the development of African countries, and knowing the best location for the implementation of solar and wind energy projects is important within this context. The purpose of this study is to assess the impact... more
Renewable energy is key for the development of African countries, and knowing the best location for the implementation of solar and wind energy projects is important within this context. The purpose of this study is to assess the impact of climate change on solar and wind energy potential over Africa under low end (RCP2.6) and high end (RCP8.5) emission scenarios using a set of new high resolution (25 km) simulations with the Regional Climate Model version 4 (RegCM4) produced as part of the CORDEX-CORE initiative. The projections focus on two periods: (i) the near future (2021–2040) and ii) the mid-century future (2041–2060). The performance of the RegCM4 ensemble mean (Rmean) in simulating relevant present climate variables (1995–2014) is first evaluated with respect to the ERA5 reanalysis and satellite-based data. The Rmean reproduces reasonably well the observed spatial patterns of solar irradiance, air temperature, total cloud cover, wind speed at 100 m above the ground level, p...
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The information of when and where region-specific patterns in both mean and extreme temperatures leading to heat stress will emerge from the present-day climate variability is important to plan adaptation options, but to date studies on... more
The information of when and where region-specific patterns in both mean and extreme temperatures leading to heat stress will emerge from the present-day climate variability is important to plan adaptation options, but to date studies on this issue still remain limited and fragmented. Here, we estimate the time of emergence (TOE) of temperature and wet-bulb temperature (Tw), a better indication of heat stress, using fine-scale, long-term regional climate model projections under the RCP2.6 and RCP8.5 scenarios across six different domains. Differently from previous studies, the TOE is determined using three methods applied on impact-relevant variables: two different signal-to-noise frameworks based on summer mean temperature and Tw and a statistical test to identify significant differences in daily extreme distributions. The TOE response to RCP2.6 and RCP8.5 with respect to the end of 20th century variability differs significantly regardless of which TOE metric is applied. For summer mean temperature, the land fraction reaching TOE is expected to exceed 90% by the 2050s under the RCP8.5, whereas the increase rate of land exposure to TOE tends to stagnate over time under the RCP2.6 so that more than 40% of land will not experience TOE by the end of the 21st century. Compared to temperature, the TOE of Tw is reached earlier in most of the wet tropics but is delayed in hot and dry regions because of the nonlinear response of Tw to humidity. For both temperature and Tw, the TOE appears earlier in regions with low baseline variability, such as in the tropics. Despite the uncertainties arising from the choice of TOE metrics, the vast majority of regions in Africa and southeast Asia experience TOE in the early 21st century under both the RCP2.6 and RCP8.5 scenarios, which stresses the urgent need for developing adequate adaptation strategies in these regions.
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The regional climate model version 4.5 (RegCM4.5) is used to investigate thermal and dynamical processes associated with the Indian summer monsoon rainfall. The RegCM4.5 is run over the South Asia COordinated Regional Climate Downscaling... more
The regional climate model version 4.5 (RegCM4.5) is used to investigate thermal and dynamical processes associated with the Indian summer monsoon rainfall. The RegCM4.5 is run over the South Asia COordinated Regional Climate Downscaling Experiment (CORDEX) domain during 1990 to 2014 (25 years). The model realistically simulates the Indian summer monsoon rainfall (ISMR), tropospheric temperature and its gradient, and circulation patterns over the Indian region. The effect of Arabian Sea moisture transport on the ISMR is studied. It is argued that the weaker inward zonal transport and stronger outward meridional moisture transport from the Arabian Sea to the Indian subcontinent lead to reduced precipitation (dry bias) over India. The soil moisture over the Indian land points is significantly positively correlated to the precipitation over the region. The water budget analysis reveals that the moisture flux convergence values are slightly underestimated as compared to the precipitation minus evapotranspiration values over India. It is shown that the RegCM captures the eddy heat flux (EHF) and eddy momentum flux (EMF) variability over the Indian monsoon region. The model exhibits a distinct EHF dipole pattern between central India (20° N–30°N) and northern India (> 35° N) during the JJAS in the lower atmosphere. The monthly variability of the EMF over the Indian region suggests that EMF propagates northwards and upwards and becomes weaker from March onwards up to May. The EMF remains lowest during the monsoon season. The EMF again becomes stronger from Oct onwards with propagation of eddies in the opposite direction.
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The European CORDEX (EURO-CORDEX) initiative is a large voluntary effort that seeks to advance regional climate and Earth system science in Europe. As part of the World Climate Research Programme (WCRP) - Coordinated Regional Downscaling... more
The European CORDEX (EURO-CORDEX) initiative is a large voluntary effort that seeks to advance regional climate and Earth system science in Europe. As part of the World Climate Research Programme (WCRP) - Coordinated Regional Downscaling Experiment (CORDEX), it shares the broader goals of providing a model evaluation and climate projection framework and improving communication with both the General Circulation Model (GCM) and climate data user communities. EURO-CORDEX oversees the design and coordination of ongoing ensembles of regional climate projections of unprecedented size and resolution (0.11° EUR-11 and 0.44° EUR-44 domains). Additionally, the inclusion of empirical-statistical downscaling allows investigation of much larger multi-model ensembles. These complementary approaches provide a foundation for scientific studies within the climate research community and others. The value of the EURO-CORDEX ensemble is shown via numerous peer-reviewed studies and its use in the develo...
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Seasonal precipitation forecast over Mexico based on a hybrid statistical-dynamical approach
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The mountain cryosphere is recognized to have important impacts on a range of environmental processes. This paper reviews current knowledge on snow, glacier, and permafrost processes, as well as their past, current and future evolution in... more
The mountain cryosphere is recognized to have important impacts on a range of environmental processes. This paper reviews current knowledge on snow, glacier, and permafrost processes, as well as their past, current and future evolution in mountain regions in mainland Europe. We provide a comprehensive assessment of the current state of cryosphere research in Europe and point to the different domains requiring further research to improve our understanding of climate–cryosphere interactions, cryosphere controls on physical and biological mountain systems, as well as related impacts. We highlight advances in the modeling of the cryosphere, and identify inherent uncertainties in our capability of projecting changes in the context of a warming global climate.
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Testing Numerical Prediction Models (NPM) is a major issue for climate studies. Different approaches are possible, based on comparison between numerical output and atmospheric and oceanic measurements, such as air temperature, humidity,... more
Testing Numerical Prediction Models (NPM) is a major issue for climate studies. Different approaches are possible, based on comparison between numerical output and atmospheric and oceanic measurements, such as air temperature, humidity, sea surface temperature. More recently, another approach has been proposed [Haskins et al, 1995; 1997; 1998; Goody et al., 1998], which make use of direct observations, such as
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L’Aquila, a distributed grid-based hydrological model (CHYM) has been developed to provide a general purpose model for operational flood warning activity. This paper presents two new cellular automata (CA) algorithms used respectively for... more
L’Aquila, a distributed grid-based hydrological model (CHYM) has been developed to provide a general purpose model for operational flood warning activity. This paper presents two new cellular automata (CA) algorithms used respectively for drainage network extraction and rainfall data assimilation. The first is a cellular automaton-based algorithm for the extraction of a drainage network from an arbitrary digital elevation model. It has been implemented and tested on a large number of different domains. This algorithm is able to define the flow direction at every point on the digital elevation model where singular points are present (pits or flat areas). The second is a CA-based numerical technique for assimilating different data sources of rainfall to rebuild the rainfall field on a grid. This technique has been shown to produce a reasonable rainfield shape without any geometrical artefacts that often produce unrealistic rain gradients in the rainfield. Key words hydrological model; cellular automata; CHYM; drainage network extraction Algorithmes d’automates cellulaires pour l’extraction du réseau de drainage et l’assimilation de données pluviométriques Résumé Depuis 2002, dans le cadre du centre d’excellence Cetemps à l’université de L’Aquila, un modèle hydrologique distribué maillé (CHYM) a été développé pour fournir une modélisation générale