Large-scale drivers of the Mediterranean climate change hot-spot

2021 ◽  
Author(s):  
Roman Brogli ◽  
Silje Lund Sørland ◽  
Nico Kröner ◽  
Christoph Schär
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Hot Spot ◽  
Regional Climate ◽  
Lapse Rate ◽  
Summer Climate ◽  
Climate Simulations ◽  
Summer Warming ◽  
The Mediterranean ◽  
Circulation Changes

<div> <p><span>It has long been recognized that the Mediterranean is a ‘hot-spot’ of climate change. The model-projected year-round precipitation decline and amplified summer warming are among the leading causes of the vulnerability of the Mediterranean to greenhouse gas-driven warming. We investigate large-scale drivers influencing both the Mediterranean drying and summer warming in regional climate simulations. To isolate the influence of multiple large-scale drivers, we sequentially add the respective drivers from global models to regional climate model simulations. Additionally, we confirm the robustness of our results across multiple ensembles of global and regional climate simulations.</span></p> </div><div> <p><span>We will present in detail how changes in the atmospheric stratification are key in causing the amplified Mediterranean summer warming. Together with the land-ocean warming contrast, stratification changes also drive the summer precipitation decline. Summer circulation changes generally have a surprisingly small influence on the changing Mediterranean summer climate. In contrast, changes in the circulation are the primary driver for the projected winter precipitation decline. Since land-ocean contrast and stratification changes are more robust in global climate simulations than circulation changes, we argue that the uncertainty associated with the projected climate change patterns should be considered smaller in summer than in winter.</span></p> </div><div> <p><span>References:</span></p> </div><div> <p><span>Brogli, R., S. L. Sørland, N. Kröner, and C. Schär, 2019: Causes of future Mediterranean precipitation decline depend on the season. Environmental Research Letters, 14, 114017, doi:10.1088/1748-9326/ab4438.</span></p> </div><div> <p><span>Brogli, R., N. Kröner, S. L. Sørland, D. Lüthi and C. Schär, 2019: The Role of Hadley Circulation and Lapse-Rate Changes for the Future European Summer Climate. Journal of Climate, 32, 385-404, doi:10.1175/JCLI-D-18-0431.1</span></p> </div>

scholarly journals Causes of future Mediterranean precipitation decline depend on the season

2020 ◽  
Author(s):  
Roman Brogli ◽  
Silje Lund Sørland ◽  
Nico Kröner ◽  
Christoph Schär
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Lapse Rate ◽  
Environmental Research ◽  
Economic Sectors ◽  
Climate Simulations ◽  
The Mediterranean ◽  
Circulation Changes

<p>The Mediterranean is among the global 'hot-spots' of climate change, where severe consequences of climate change are expected. Changes in the atmospheric water cycle are among the leading causes of the vulnerability of the Mediterranean to greenhouse gas-driven warming. Specifically, precipitation is projected to decrease year-round, which is expected to have major impacts on hydrology, biodiversity, agriculture, hydropower, and further economic sectors that rely on sufficient water supply.</p><p>We investigate possible causes of the Mediterranean drying in regional climate simulations. To isolate the influence of multiple large-scale drivers on the drying, we sequentially add the respective drivers from global models to regional climate model simulations. We show that the causes of the Mediterranean drying depend on the season. We will present in detail how the summer drying is driven by the land-ocean warming contrast, lapse-rate and other thermodynamic changes, while it only weakly depends on circulation changes. In contrast, changes in the circulation are the primary driver for the projected winter precipitation decline. Since land-ocean contrast, thermodynamic and lapse-rate changes are more robust in climate simulations than circulation changes, the uncertainty associated with the projected drying should be considered smaller in summer than in winter.</p><p>Reference: Brogli, R., S. L. Sørland, N. Kröner, and C. Schär, 2019: Causes of future Mediterranean precipitation decline depend on the season. Environmental Research Letters, 14, 114017, doi:10.1088/1748-9326/ab4438.</p>

scholarly journals Why Is the Mediterranean a Climate Change Hot Spot?

2020 ◽  
Vol 33 (14) ◽  
pp. 5829-5843 ◽  
Author(s):  
A. Tuel ◽  
E. A. B. Eltahir
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Hot Spot ◽  
Winter Precipitation ◽  
Sea Temperature ◽  
Circulation Change ◽  
The Mediterranean ◽  
The Stability ◽  
Regional Land ◽  
Circulation Changes

AbstractHigher precipitation is expected over most of the world’s continents under climate change, except for a few specific regions where models project robust declines. Among these, the Mediterranean stands out as a result of the magnitude and significance of its winter precipitation decline. Locally, up to 40% of winter precipitation could be lost, setting strong limits on water resources that will constrain the ability of the region to develop and grow food, affecting millions of already water-stressed people and threatening the stability of this tense and complex area. To this day, however, a theory explaining the special nature of this region as a climate change hot spot is still lacking. Regional circulation changes, dominated by the development of a strong anomalous ridge, are thought to drive the winter precipitation decline, but their origins and potential contributions to regional hydroclimate change remain elusive. Here, we show how wintertime Mediterranean circulation trends can be seen as the combined response to two independent forcings: robust changes in large-scale, upper-tropospheric flow and the reduction in the regional land–sea temperature gradient that is characteristic of this region. In addition, we discuss how the circulation change can account for the magnitude and spatial structure of the drying. Our findings pave the way for better understanding and improved modeling of the future Mediterranean hydroclimate.

scholarly journals CECILIA Regional Climate Simulations for Future Climate: Analysis of Climate Change Signal

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Michal Belda ◽  
Petr Skalák ◽  
Aleš Farda ◽  
Tomáš Halenka ◽  
Michel Déqué ◽  
...  
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Global Scale ◽  
Climate Change Signal ◽  
Northwestern Part ◽  
Climate Simulations ◽  
Climate Analysis

Regional climate models (RCMs) are important tools used for downscaling climate simulations from global scale models. In project CECILIA, two RCMs were used to provide climate change information for regions of Central and Eastern Europe. Models RegCM and ALADIN-Climate were employed in downscaling global simulations from ECHAM5 and ARPEGE-CLIMAT under IPCC A1B emission scenario in periods 2021–2050 and 2071–2100. Climate change signal present in these simulations is consistent with respective driving data, showing similar large-scale features: warming between 0 and 3°C in the first period and 2 and 5°C in the second period with the least warming in northwestern part of the domain increasing in the southeastern direction and small precipitation changes within range of +1 to −1 mm/day. Regional features are amplified by the RCMs, more so in case of the ALADIN family of models.

scholarly journals Evaluation of convective parameters derived from pressure level and native ERA5 data and different resolution WRF climate simulations over Central Europe

2021 ◽  
Author(s):  
Ákos János Varga ◽  
Hajnalka Breuer
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Wrf Model ◽  
Environmental Parameters ◽  
Pressure Level ◽  
Lapse Rate ◽  
Strong Suppression ◽  
Climate Simulations ◽  
Multiple Variables

AbstractThe mean climatological distribution of convective environmental parameters from the ERA5 reanalysis and WRF regional climate simulations is evaluated using radiosonde observations. The investigation area covers parts of Central and Eastern Europe. Severe weather proxies are calculated from daily 1200 UTC sounding measurements and collocated ERA5 and WRF pseudo-profiles in the 1985–2010 period. The pressure level and the native ERA5 reanalysis, and two WRF runs with grid spacings of 50 and 10 km are verified. ERA5 represents convective parameters remarkably well with correlation coefficients higher than 0.9 for multiple variables and mean errors close to zero for precipitable water and mid-tropospheric lapse rate. Monthly mean mixed-layer CAPE biases are reduced in the full hybrid-sigma ERA5 dataset by 20–30 J/kg compared to its pressure level version. The WRF model can reproduce the annual cycle of thunderstorm predictors but with considerably lower correlations and higher errors than ERA5. Surface elevation differences between the stations and the corresponding grid points in the 50-km WRF run lead to biases and false error compensations in the convective indices. The 10-km grid spacing is sufficient to avoid such discrepancies. The evaluation of convection-related parameters contributes to a better understanding of regional climate model behavior. For example, a strong suppression of convective activity might explain precipitation underestimation in summer. A decreasing correlation of WRF-derived wind shear away from the western domain boundaries indicates a deterioration of the large-scale circulation as the constraining effect of the driving reanalysis weakens.

Mediterranean Marine heatwaves: On the comparison of the physical drivers behind the 2003 and 2015 events

2020 ◽  
Author(s):  
Sofia Darmaraki ◽  
Samuel Somot ◽  
Robin Waldman ◽  
Florence Sevault ◽  
Pierre Nabat ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Large Scale ◽  
Climate Model ◽  
Heat Budget ◽  
Hot Spot ◽  
Regional Climate ◽  
Detection Algorithm ◽  
Heat Fluxes ◽  
Basin Scale ◽  
The Mediterranean

<p>Over the last decade, an intensification of extreme warm temperature events, termed as marine heatwaves (MHWs), has been reported in the Mediterranean Sea, itself a “Hot Spot” region for climate change. In the summer of 2003, a major MHW occurred in the Mediterranean with abnormal surface temperature anomalies of 2-3 Cº persisting for over a month. In 2015, an undocumented but more intense summer MHW affected almost the entire Mediterranean Sea with regional temperatures anomalies reaching 4-5 Cº. Here, we apply a MHW detection algorithm for long-lasting and large-scale summer events, on the hindcast output of a fully-coupled regional climate model (RCSM). We first examine the spatial variability and temporal evolution of both the 2003 and 2015 events. Then a basin-scale analysis of the mixed layer heat budget during each MHW is performed. The ocean and atmospheric components’ contribution is investigated separately during the onset, peak, and decay phases of both events, in order to disentangle the dominant physical processes behind each event. On the large-scale, our results indicate a key role of the wind forcing and the air-sea heat fluxes, while advection processes become more important at local scales. This study provides a comparison of the underlying mechanisms behind the two most intense MHW detected in the Mediterranean Sea during the last decade, constituting key information for the marine ecosystems of the region.</p>

scholarly journals Impact of air–sea coupling on the climate change signal over the Iberian Peninsula

2021 ◽  
Author(s):  
Alba de la Vara ◽  
William Cabos ◽  
Dmitry V. Sein ◽  
Claas Teichmann ◽  
Daniela Jacob
Keyword(s):  
Climate Change ◽  
Iberian Peninsula ◽  
Mediterranean Sea ◽  
Large Scale ◽  
Regional Distribution ◽  
Coupled Model ◽  
Climate Change Signal ◽  
The North ◽  
The Mediterranean ◽  
The Impact

AbstractIn this work we use a regional atmosphere–ocean coupled model (RAOCM) and its stand-alone atmospheric component to gain insight into the impact of atmosphere–ocean coupling on the climate change signal over the Iberian Peninsula (IP). The IP climate is influenced by both the Atlantic Ocean and the Mediterranean sea. Complex interactions with the orography take place there and high-resolution models are required to realistically reproduce its current and future climate. We find that under the RCP8.5 scenario, the generalized 2-m air temperature (T2M) increase by the end of the twenty-first century (2070–2099) in the atmospheric-only simulation is tempered by the coupling. The impact of coupling is specially seen in summer, when the warming is stronger. Precipitation shows regionally-dependent changes in winter, whilst a drier climate is found in summer. The coupling generally reduces the magnitude of the changes. Differences in T2M and precipitation between the coupled and uncoupled simulations are caused by changes in the Atlantic large-scale circulation and in the Mediterranean Sea. Additionally, the differences in projected changes of T2M and precipitation with the RAOCM under the RCP8.5 and RCP4.5 scenarios are tackled. Results show that in winter and summer T2M increases less and precipitation changes are of a smaller magnitude with the RCP4.5. Whilst in summer changes present a similar regional distribution in both runs, in winter there are some differences in the NW of the IP due to differences in the North Atlantic circulation. The differences in the climate change signal from the RAOCM and the driving Global Coupled Model show that regionalization has an effect in terms of higher resolution over the land and ocean.

Mediterranean climate change projections: an update from CMIP5 and CMIP6.

2021 ◽  
Author(s):  
Josep Cos ◽  
Francisco J Doblas-Reyes ◽  
Martin Jury
Keyword(s):  
Climate Change ◽  
21St Century ◽  
Hot Spot ◽  
Weighting Scheme ◽  
Temperature And Precipitation ◽  
High Emission ◽  
The Mediterranean ◽  
Model Ensembles ◽  
Projected Changes ◽  
Model Weighting

<p>The Mediterranean has been identified as a climate change hot-spot due to increased warming trends and precipitation decline. Recently, CMIP6 was found to show a higher climate sensitivity than its predecessor CMIP5, potentially further exacerbating related impacts on the Mediterranean region.</p><p>To estimate the impacts of the ongoing climate change on the region, we compare projections of various CMIP5 and CMIP6 experiments and scenarios. In particular, we focus on summer and winter changes in temperature and precipitation for the 21st century under RCP2.6/SSP1-2.6, RCP4.5/SSP2-4.5 and RCP8.5/SSP5-8.5 as well as the high resolution HighResMIP experiments. Additionally, to give robust estimates of projected changes we apply a novel model weighting scheme, accounting for historical performance and inter-independence of the multi-member multi-model ensembles, using ERA5, JRA55 and WFDE5 as observational reference. </p><p>Our results indicate a significant and robust warming over the Mediterranean during the 21st century irrespective of the used ensemble and experiments. Nevertheless, the often attested amplified Mediterranean warming is only found for summer. The projected changes vary between the CMIP5 and CMIP6, with the latter projecting a stronger warming. For the high emission scenarios and without weighting, CMIP5 indicates a warming between 4 and 7.7ºC in summer and 2.7 and 5ºC in winter, while CMIP6 projects temperature increases between 5.6 and 9.2ºC in summer and 3.2 to 6.8ºC in winter until 2081-2100 in respect to 1985-2005. In contrast to temperature, precipitation changes show a higher level of uncertainty and spatial heterogeneity. However, for the high emission scenario, a robust decline in precipitation is projected for large parts of the Mediterranean during summer. First results applying the model weighting scheme indicate reductions in CMIP6 and increases in CMIP5 warming trends, thereby reducing differences between the two ensembles.</p>

scholarly journals Simulating future precipitation extremes in a complex Alpine catchment

2013 ◽  
Vol 13 (2) ◽  
pp. 263-277 ◽  
Author(s):  
C. Dobler ◽  
G. Bürger ◽  
J. Stötter
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Precipitation Extremes ◽  
Climate Projections ◽  
Research Station ◽  
Climate Change Scenarios ◽  
Station Data

Abstract. The objectives of the present investigation are (i) to study the effects of climate change on precipitation extremes and (ii) to assess the uncertainty in the climate projections. The investigation is performed on the Lech catchment, located in the Northern Limestone Alps. In order to estimate the uncertainty in the climate projections, two statistical downscaling models as well as a number of global and regional climate models were considered. The downscaling models applied are the Expanded Downscaling (XDS) technique and the Long Ashton Research Station Weather Generator (LARS-WG). The XDS model, which is driven by analyzed or simulated large-scale synoptic fields, has been calibrated using ECMWF-interim reanalysis data and local station data. LARS-WG is controlled through stochastic parameters representing local precipitation variability, which are calibrated from station data only. Changes in precipitation mean and variability as simulated by climate models were then used to perturb the parameters of LARS-WG in order to generate climate change scenarios. In our study we use climate simulations based on the A1B emission scenario. The results show that both downscaling models perform well in reproducing observed precipitation extremes. In general, the results demonstrate that the projections are highly variable. The choice of both the GCM and the downscaling method are found to be essential sources of uncertainty. For spring and autumn, a slight tendency toward an increase in the intensity of future precipitation extremes is obtained, as a number of simulations show statistically significant increases in the intensity of 90th and 99th percentiles of precipitation on wet days as well as the 5- and 20-yr return values.

scholarly journals The Effect of Explicit Convection on Couplings between Rainfall, Humidity, and Ascent over Africa under Climate Change

2020 ◽  
Vol 33 (19) ◽  
pp. 8315-8337 ◽  
Author(s):  
Lawrence S. Jackson ◽  
Declan L. Finney ◽  
Elizabeth J. Kendon ◽  
John H. Marsham ◽  
Douglas J. Parker ◽  
...  
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Hadley Circulation ◽  
Moist Convection ◽  
Rain Belt ◽  
Adaptation To Climate Change ◽  
Convective Scale ◽  
Mean Climate

AbstractThe Hadley circulation and tropical rain belt are dominant features of African climate. Moist convection provides ascent within the rain belt, but must be parameterized in climate models, limiting predictions. Here, we use a pan-African convection-permitting model (CPM), alongside a parameterized convection model (PCM), to analyze how explicit convection affects the rain belt under climate change. Regarding changes in mean climate, both models project an increase in total column water (TCW), a widespread increase in rainfall, and slowdown of subtropical descent. Regional climate changes are similar for annual mean rainfall but regional changes of ascent typically strengthen less or weaken more in the CPM. Over a land-only meridional transect of the rain belt, the CPM mean rainfall increases less than in the PCM (5% vs 14%) but mean vertical velocity at 500 hPa weakens more (17% vs 10%). These changes mask more fundamental changes in underlying distributions. The decrease in 3-hourly rain frequency and shift from lighter to heavier rainfall are more pronounced in the CPM and accompanied by a shift from weak to strong updrafts with the enhancement of heavy rainfall largely due to these dynamic changes. The CPM has stronger coupling between intense rainfall and higher TCW. This yields a greater increase in rainfall contribution from events with greater TCW, with more rainfall for a given large-scale ascent, and so favors slowing of that ascent. These findings highlight connections between the convective-scale and larger-scale flows and emphasize that limitations of parameterized convection have major implications for planning adaptation to climate change.

scholarly journals Regional Climate Model Emulator based on Deep Learning: Concept and First Evaluation of a Novel Hybrid Downscaling Approach

2021 ◽  
Author(s):  
Antoine Doury ◽  
Samuel Somot ◽  
Sébastien Gadat ◽  
Aurélien Ribes ◽  
Lola Corre
Keyword(s):  
Climate Change ◽  
Network Architecture ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Future Climate ◽  
Near Surface ◽  
The Way

Abstract Providing reliable information on climate change at local scale remains a challenge of first importance for impact studies and policymakers. Here, we propose a novel hybrid downscaling method combining the strengths of both empirical statistical downscaling methods and Regional Climate Models (RCMs). The aim of this tool is to enlarge the size of high-resolution RCM simulation ensembles at low cost.We build a statistical RCM-emulator by estimating the downscaling function included in the RCM. This framework allows us to learn the relationship between large-scale predictors and a local surface variable of interest over the RCM domain in present and future climate. Furthermore, the emulator relies on a neural network architecture, which grants computational efficiency. The RCM-emulator developed in this study is trained to produce daily maps of the near-surface temperature at the RCM resolution (12km). The emulator demonstrates an excellent ability to reproduce the complex spatial structure and daily variability simulated by the RCM and in particular the way the RCM refines locally the low-resolution climate patterns. Training in future climate appears to be a key feature of our emulator. Moreover, there is a huge computational benefit in running the emulator rather than the RCM, since training the emulator takes about 2 hours on GPU, and the prediction is nearly instantaneous. However, further work is needed to improve the way the RCM-emulator reproduces some of the temperature extremes, the intensity of climate change, and to extend the proposed methodology to different regions, GCMs, RCMs, and variables of interest.

Sign in / Sign up

Export Citation Format

Share Document