Africa: Coupled regional modelling of land-atmosphere-ocean interactions over western-southern Africa under climate change
Contact person Francois Engelbrecht FEngelbrecht@csir.co.az
The climate system of western-southern Africa is highly coupled and exhibits intricate interactions between the land, atmosphere and ocean. The dominating biome is the African savannahs, where complex tree-grass interactions are shaped by fire and land-use.
It has been postulated that under future climate change rising CO2 levels and increasing temperatures may favor trees over grasses in the savannah, leading to bush encroachment at the expense of biodiversity and grazing potential. However, given that that much of southern Africa is likely to become drier and significantly warmer under climate change (a conclusion of the Africa Chapter of AR5) it is plausible that mega-fire events may occur more frequently in savannahs, effectively favoring grasses over trees.
Complex dynamic vegetation models including realistic descriptions of savannah fire events, coupled to RCMs, are required to gain more insight into the future of the African savannahs under climate change. Fire in the savannahs, and the consequent release of biomass-burning aerosols into the atmosphere, are potentially important towards reducing uncertainties regarding one of the most intriguing open questions in climate science: climate sensitivity. The role of these aerosols on the stratocumulus (Sc) cloud deck over the Atlantic remains largely unexplored, but given that the southern African region is the largest source of biomass-burning aerosols in the world, it is a potentially important role.
Prognostic aerosols schemes in RCMs, combined with suitably sophisticated microphysical schemes will enable the study of both aerosol direct and indirect effects on the Sc cloud deck. Of particular interest is the role of climate change and land-use change on biomass-burning, with potential consequences for the Sc cloud deck and therefore climate sensitivity, through altered aerosol attributes and aerosol transport patterns.
Another fascinating aspect of the western-southern African climate system is the Benguela upwelling regime on the western coastal areas of South Africa and Namibia, and the related occurrence of Benguela-Niño events along the African west coast. Potential changes in this upwelling regime under climate change will be of crucial importance to ocean productivity and fisheries along these coastal areas.
Moreover, the rich biodiversity of the Namib desert depends largely on the inland penetration of fog as a source of water, and the formation of such fog events in turn depend on the location of upwelling patterns. High-resolution and coupled RCMs are needed to project the effects of regional climate change on the prevailing southeasterlies that blow along the west coast of southern Africa, and how such changes may impact on the formation of upwelling zones and fog. In fact, the more realistic simulation of African west-coast upwelling may be important towards reducing the significant biases most GCMs exhibit in simulating SSTs along the African west coast.
Similarly, the more realistic simulation of aerosol and Sc radiative effects may result in reducing this problem that has plagued GCMs in both AR4 and AR5. The above arguments build a convincing case to apply coupled RCMs to the western-southern African region, towards tackling a key open problem in climate science, reducing one of the most important biases common to current climate models, and to better anticipate and prepare for climate change impacts on this fascinating and complex coupled climate regime.
Five FPS propsals, out of nine, were selected from the first round of submissions and announced at the last day of the ICRC-CORDEX 2016 conference;
South America: Extreme precipitation events in Southeastern South America: a proposal for a better understanding and modeling
Contact person Maria Bettolli email@example.com
Southeastern South America (SESA) is a highly populated region where socio-economic activities are mainly based on rainfed agriculture and cattle rising, for both domestic consumption and exports. The hydroelectric power utilities are also very important as they supply energy to the region and rivers provide the water for consumption.
SESA has been characterized by a remarkable increment in the frequency and intensity of heavy precipitation events, particularly during the late 20th century. The region is particularly vulnerable to extreme events due to adaptation measures have not been performed at the same rate as changes in these extreme events. However, it is still a challenge to better identify the factors and mechanisms that determine the location, intensity and frequency of the precipitation extremes and their large hydrologic impacts.
The main objectives of the SESA-FPS are to study multi-scale processes and interactions (convection, local, regional and remote processes, including the co-behaviour of processes) that result in these extreme precipitation events; and to develop actionable climate information from multiple sources (statistical and dynamical downscaling products) based on co-production with the impact and user community.
This initiative seeks to promote inter-institutional collaboration and further networking, integrating not only South American research communities but also European communities, taking into account that, in the recent years, there have been little or scattered activities related with inter-institutional coordinated regional climate modeling.
Multi-scale aspects, processes and interactions that result in extreme precipitation events will be investigated using dynamical models (high resolution, convection permitting and coupled models) and statistical models. ESD and RCM products will be compared and validated exploring the added value of downscaling. This will allow for a strengthened cooperation between ESD and RCM communities to jointly tackle key issues of regional climate change research. The impact of heavy precipitations on flooding and soil moisture conditions will be assessed using a water balance model, and hydrological models will be used to simulate ground water and soil moisture to drive crop models. In this context, an increased cooperation and integration of RCM, ESD and VIA communities is expected towards a distillation of actionable information from multiple sources of downscaled products.
Data from RELAMPAGO, CHUVA and SALLJEX field campaigns will be available to perform the proposed studies, providing highly temporal-spatial resolution data to characterize the synoptic scale, mesoscale, and convective scale flows in the region. Observed long records from surface meteorological and hydrological stations from different local institutions and the CLARIS-LPB initiative as well as a net of meteorological stations which includes the measurement of soil moisture at different levels will be available for calibration and validation of models (ESD, RCM, impact models.
Europe+ Mediterranean; Convective phenomena at high resolution over Europe and the Mediterranean
Damaging weather events are often associated with extreme convective precipitation (Ducrocq et al. 2014). Convective cells occur due to rapidly ascending motions in areas of moisture convergence in regions of conditionally unstable atmospheric stratification. They can form anywhere in Europe and in Mediterranean areas, over homogeneous plains, or can develop from orographic barriers, land/sea or urban/rural contrasts. Convection induces a variety of potentially severe consequences such as heavy rainfall, flash floods, short-lived windstorms, hail and/or lightning.
Climate change potentially alters convection, making extreme precipitation more extreme, and also potentially modifying large-scale conditions (atmospheric circulation and stratification) making convection less or more favorable. This induces changes in return periods of precipitation extremes.
The study of convective precipitation events and their evolution under human-induced climate change is therefore of particular importance, and it is also timely:
- Large field campaigns dedicated to the study of heavy precipitation events such as HyMeX (Ducrocq et al., 2014) and gridded high-resolution precipitation datasets (typically hourly, kilometer scale) , often merging station and radar data (Wüest et al. 2010, Delrieu et al. 2014) now provide a wealth of observations;
- Computer capacity and model development now allow limited-area convection-permitting climate simulations at longer time-scales (Kendon et al., 2012, 2014; Ban et al., 2014, 2015, Leutwyler et al., http://www.c2sm.ethz.ch/research/crCLIM.html), enabeling a quantum jump in atmospheric climate modeling;
- Homogeneous observation data sets collected over the years now unveil emerging trend signals in most extreme precipitations, particularly at sub-daily time scales (Westra et al., 2014) and in Mediterranean and Alpine mountain ranges (Vautard et al., 2015; Scherrer et al. 2016)
- Several issues linked to detection, attribution, and downscaling of the very localized consequences of extreme convective events can now benefit from recent progress in advanced statistical methods combined with advances in dynamical modeling (Beaulant et al., 2011).
Convective extreme events are a priority under the WCRP Grand Challenge on climate extremes, because they carry both society-relevant and scientific challenges that can be tackled in the coming years. Further, “coordinated modeling programs are crucially needed to advance parameterizations of unresolved physics and to assess the full potential of CPMs” (Prein et al., 2015)
The proposal reflects a number of FPS criteria and aims to enlist research groups beyond the current CORDEX community. Present and future convective extremes and their processes will be investigated with models at convection-permitting resolutions over selected sub-regions of Europe and the Mediterranean. Advanced statistical techniques will also be employed in parallel to evaluate the performance of dynamical models and to, potentially, serve as emulators of convective extremes, as well as detect and attribute their changes. The added value of fine scale representation of convection will be rigorously evaluated with respect to both coarser resolution simulations up to GCM scales and VIA applications. The availability of observational datasets at very high resolutions in both space and time allows unprecedented evaluation opportunities. The FPS mobilizes the Euro- and Med-CORDEX communities and is also open to new partners who bring fresh perspectives and expertise to bear on issues surrounding convective phenomena.
Europe; Impact of land use changes on climate in Europe across spatial and temporal scales
Contact person Diana Rechid firstname.lastname@example.org
We propose the Flagship Pilot Study “LUCAS” (Land Use & Climate Across Scales) for Europe, as a EURO-CORDEX & LUCID initiative supported by WCRP CORDEX and the GEWEX-GLASS international program. The spatial fragmentation of land use dynamics in Europe requires fine-scale modelling techniques, and their biophysical impacts on climate are often dominant on local to regional scales. Our overall objective is to identify robust biophysical impacts of land use changes (LUC) in Europe on climate across regional to local spatial scales and at various time scales from extreme events to multi-decadal:
- Can local LUC attenuate negative impacts of climate change, e.g. extreme events in Europe?
- What is the effect of spatial resolution on the magnitude and robustness of LUC-induced climate changes?
- How large is the contribution of LUC to detected past and potential future climate trends in Europe?
In order to derive robust answers, we want to initiate a new era of coordinated regional climate model (RCM) ensemble LUC experiments on high spatial resolutions based on consistent land use dynamics for the past and the future. We include a new generation of RCMs, which couple regional atmosphere interactively with further components of the regional earth system, e.g. terrestrial biosphere and hydrosphere. The multi-model experiments shall be conducted over multiple gridded nests to refine the continental simulations down to resolutions below 5 km. Pilot regions are carefully chosen to a) evaluate the validity of coupled atmosphere-land simulations, b) better resolve the heterogeneity of land use changes in Europe and its local impacts on climate.
RCMs have been applied individually for investigating impacts of LUC on regional climate in different world regions (e.g. see reviews of Pielke et al. 2011, Mahmood et al. 2014). Most results are model specific and therefore do not allow one to derive robust conclusions and strategic directions. In this new initiative, for the first time an ensemble of RCMs will be used in coordinated experiments to inter-compare their sensitivities to LUC. Essential variables and fine-scale processes will be evaluated against multi-variable observations from flux towers, satellite sensors and new airborne and spaceborn radar techniques.
In our context, LUC refer to anthropogenic land cover changes as well as land management changes, as suggested by Luyssaert et al. (2014). The topic is of high societal relevance with respect to mitigation of global greenhouse gas emissions, e.g. through reforestation, and adaptation to local consequences of climate change, e.g. through irrigation of croplands. de Noblet-Ducoudré et al. (2012) demonstrated that regional impacts can be at least as important as greenhouse gas forcings, but biophysical feedbacks of land use changes on regional climate are still uncertain in magnitude and sign. There is an urgent need for robust information, which may help to prevent decisions on land management from unintended consequences.
We are prepared to build further collaborations with modelling activities over other CORDEX regions towards coordinated LUC experiments over multiple world regions.
Mediterranean; Role of the natural and anthropogenic aerosols in the Mediterranean region: past climate variability and future climate sensitivity
Aerosols strongly affect the Mediterranean basin located at the crossroads of air masses carrying both natural and anthropogenic particles making the basin an ideal testbed for aerosol effects on climate. The aerosols have strong effects on the regional climate fluctuations from daily to multi-decadal scales due to their direct, semi-direct and indirect effects on radiation, atmospheric circulation and cloud cover. Aerosols also represent one of the main sources of uncertainty in past climate change attribution and future climate change projections at global and regional scales. Due to their relatively short life-time, aerosols influencing the Mediterranean area are mostly produced in nearby regions and therefore they constitute a regional climate forcing of regional origin. In addition, the aerosols show a hig spatio-temporal variability and are influenced by numerous fine-scale processes. The use of high-resolution RCMs therefore fits well to address the four main scientific questions of the proposed FPS:
(1) Can we fully characterize the Mediterranean aerosol past variability and future evolution at climate scales ? in particular using RCMs.
(2) Can we understand the role of the Mediterranean aerosols on the past regional climate variability? including issues related to regional climate change attribution and aerosols representation in climate models (GCM, RCM).
(3) Can we determine the role of regionally-born aerosols in the Mediterranean future climate sensitivity ? in particular using RCMs as complementary approach to GCMs.
(4) What is the aerosol role in shaping the Mediterranean extreme events ? (e.g. heat waves, heavy precipitation events)
The proposed FPS will be facilitated by recent observation efforts such as the ChArMEx programme, long-term multi-variable super-sites, availability of new homogenized datasets for AOD and surface shortwave and longwave radiations from in-situ coordinated networks (AERONET, GEBA, BRSN) and climate-aware satellite initiatives (ESA-CCI).
The representation of aerosols and their effects in RCMs is still very crude and uncertain and a multi-model approach is therefore requested to bring robust answers to the scientific questions CORDEX then constitutes an adequate framework to propose scientifically-based and well-coordinated simulation protocols involving RCMs with various aerosol representations
The proposed FPS targets in particular a better understanding of solar radiation variability and future changes. This is required to anticipate potential energy production or to understand the level of production of existing sites. The FPS may therefore leads to new and innovative climate services for energy producers over the Euro-Mediterranean area. Another outcomes of the FPS concerns the marine biogeochemistry of the oligotrophic Mediterranean Sea ecosystem as particles constitute one of the main sources of regional nutrients.
Besides, this FPS will contribute to several WCRP Grand Challenges, to the CORDEX Challenge about the coupled regional climate models and to the climate modelling activities of the Mediterranean regional programmes of Gewex (HyMeX) and CLIVAR (Med-CLIVAR).
Mediterranean; Role of the air-sea coupling and small scale ocean processess on regional climate
The mechanisms through which air-sea coupling can modify the regional climate will be investigated in this FPS, with special emphasis on the role of small scale ocean processes and waves. This FPS is a natural continuation of the activities of MedCORDEX, HyMeX and MedCLIVAR. The selected region is the area surrounding the Mediterranean Sea, which is often referred to as an ocean in miniature due to the variety of processes occurring therein. These include strong air-sea interactions, active mesoscale and submesoscale dynamics and a permanent thermohaline overturning circulation. Moreover, this area is one of the best observed regions in the world. Besides the dense observational network of meteorological stations over Europe, the Mediterranean Sea is regularly sampled by different monitoring programs (e.g HyMeX, the regional component of Gewex) providing observations of the ocean-atmosphere coupled system over the last decades (Jordà et al., 2016). The Mediterranean region is therefore a particularly suitable candidate for this FPS.
Ocean mesoscale in the Mediterranean Sea is characterized by a Rossby deformation radius of 5-10 km. In consequence, the SST often shows narrow and sharp fronts (e.g. in upwelling regions) as well as filaments with associated strong temperature gradients that can significantly modify the air-sea interaction (Chelton et al., 2004) and affect the climate evolution (Artale et al., 2009). Ocean mesoscale also plays a crucial role in the main mechanism of heat uptake by the ocean, namely dense water formation, which modelling requires both atmospheric (~25 km) and oceanic (~5-10 km) high spatial resolution that present GCMs are not able to achieve. Last, the Mediterranean wind-wave climate is characterized by high temporal and spatial variability due to the channeling of winds acting over the sea by the orography (Lionello et al. 2005). Wave effects on the turbulent heat fluxes are known to be important and the inclusion of this interaction in regional models is also expected to have a significant impact on long term simulations.
A detailed analysis of how air-sea coupling at high resolution can modify the regional climate, and consequently the global climate, is still missing in the literature. There are some indications that it can provide an added value to RCMs in both present climate (Artale et al 2009, Nabat et al., 2015) and future scenarios (Somot et al., 2008), but the mechanisms nderlying such impact are not completely understood. Global climate modelling should therefore benefit from this FPS as it will give clues for the future design of GCMs.
This FPS will moreover provide to the broad community focusing on the impacts of climate change on marine environments (e.g. marine ecosystems, fisheries and coastal infrastructures including harbour operations, ocean energy harvesting, tourism activities and beach management ) a database of regional ocean and atmosphere projections which consistency will be insured by the common robust protocol used for the simulations. ). This FPS should therefore have a great potential in terms of funding opportunities while insuring an efficient transfer of knowledge, insofar as many of end-users are already familiar with climate information.