Vladimir Djurdjevic

Mediterranean extreme precipitation: a multi-model assessment

Exploiting the added value of the ensemble of high-resolution model simulations provided by the Med-CORDEX coordinated initiative, an updated assessment of Mediterranean extreme precipitation events as represented in different observational, reanalysis and modelling datasets is presented. A spatiotemporal characterisation of the long-term statistics of extreme precipitation is performed, using a number of different diagnostic indices. Employing a novel approach based on the timing of extreme precipitation events a number of physically consistent subregions are defined. The comparison of different diagnostics over the Mediterranean domain and physically homogeneous sub-domains is presented and discussed, focussing on the relative impact of several model configuration features (resolution, coupling, physical parameterisations) on the performance in reproducing extreme precipitation events. It is found that the agreement between the observed and modelled long-term statistics of extreme precipitation is more sensitive to the model physics, in particular convective parameterisation, than to other model configurations such as resolution and coupling.

Assessment of meteorological climate models as inputs for coastal studies

Modeling studies of future changes in coastal hydrodynamics, in terms of storm surges and wave climate, need appropriate wind and atmospheric forcings, a necessary requirement for the realistic reproduction of the statistics and the resolution of small scale features. This work compares meteorological results from different climate models in the Mediterranean area, with a focus on the Adriatic Sea, in order to assess their capability to reproduce coastal meteorological features and their possibility to be used as forcings for hydrodynamic simulations. Five meteorological datasets are considered. They are obtained from two regional climate models, implemented with different spatial resolutions and setups and are downscaled from two different global climate models. Wind and atmospheric pressure fields are compared with measurements at four stations along the Italian Adriatic coast. The analysis is carried out both on simulations of the control period 1960–1990 and on the A1B Intergovernmental Panel for Climate Change scenario projections (2070–2100), highlighting the ability of each model in reproducing the statistical coastal meteorological behavior and possible changes. The importance of simulated global- and regional-scale meteorological processes, in terms of correct spatial resolution of the phenomena, is also discussed. Within the Adriatic Sea, the meteorological climate is influenced by the local orography that controls the strengthening of north-eastern katabatic winds like Bora. Results show indeed that the increase in spatial resolution provides a more realistic wind forcing for the hydrodynamic simulations. Moreover, the chosen setup and the global climate models that drive the regional downscalings appear to play an important role in reproducing correct atmospheric pressure fields. The comparison between scenario and control simulations shows a small increase in the mean atmospheric pressure values, while a decrease in mean wind speed and in extreme wind events is observed, particularly for the datasets with higher spatial resolution. Finally, results suggest that an ensemble of downscaled climate models is likely to provide the most suitable climatic forcings (wind and atmospheric pressure fields) for coastal hydrodynamic modeling.

Evaluation of simulated decadal variations over the Euro-Mediterranean region from ENSEMBLES to Med-CORDEX

Med-CORDEX simulations over the period 1979–2011 are evaluated with regard to their capability to represent observed decadal variations over the Euro-Mediterranean region and improve upon previous generation simulations from the ENSEMBLES project in their various experimental set-ups. Such an evaluation is needed to inform the use of these simulations and also future model development. For temperature, both Med-CORDEX and ENSEMBLES simulations tend to provide comparable results: they generally capture the sign and timing of the anomalies but not the amplitude. In general, no clear stratification appears when considering different types of Med-CORDEX regional modeling systems. Rather, it is remarkable that certain periods are poorly represented by all systems with a general underestimation of the observed long-term temperature trend, mostly in the summer season, even with respect to the corresponding global drivers. For precipitation, the Med-CORDEX simulations are closer to observations than the other datasets, with some improvement with respect to ENSEMBLES dataset. In general, all the systems experience difficulties in representing anomalies during specific periods or for specific regions. These appear in part due to limitations in the reanalysis boundary forcing data. For instance, in the second part of 1980s, the spatial patterns of surface air temperature during DJF/MAM are generally poorly represented, as well as the regionally averaged MAM/JJA surface air temperature decadal anomalies. Overall, the evaluation suggests limited improvement in Med-CORDEX simulations compared to ENSEMBLES, and a lack of sensitivity to resolution or coupling configuration, with persisting problems in part likely related to the representation of surface processes that could also affect the viability of future projections (e.g. the estimation of temperature trends). A set of decadal variability evaluation metrics, as applied in this study, could be useful in the context of a broader evaluation framework.

Some Indicators of the Present and Future Climate of Serbia According to the SRES-A1B Scenario

According to the last IPCC report, there are several indications that the area of Southeastern Europe might experience large climate changes due to the increase of the concentration of greenhouse gases. These include results of several regional climate studies. In order to objectively study the climate change, precipitation and temperature indices can be used. Climate indices can be calculated either from the local observations of temperature and precipitation or from climate simulations. In this study, we use the results of dynamical downscaling of global simulations obtained by the atmosphere–ocean global circulation model SINTEX-G (AOGCM SX-G/INGV) using a regional climate model, the EBU-POM. The EBU-POM is the combination of the Eta/NCEP as the atmospheric component and Princeton Ocean Model (POM) as the ocean component. Global simulations were done for the very long period 1771–2100, while downscaling was done for the 1961–1990 and 2071–2100 periods according to the SRES-A1B scenario.

Method for efficient prevention of gravity wave decoupling on rectangular semi-staggered grids

Generation of short gravity wave noise often occurs on semi-staggered rectangular grids as a result of sub-grid decoupling when there is a strong forcing in the mass field. In this study a numerical scheme has been proposed to prevent the generation of the gravity wave decoupling. The proposed numerical method provides efficient communication between decoupled gravity wave finite-difference solutions by a simple averaging of a term in the height tendency in the continuity equation. The proposed method is tested using a shallow water sink model developed for the purpose of this study. It has been demonstrated that this method outperforms other existing approaches. The new scheme is time efficient, based on explicit time integration and can be easily implemented. The proposed method is applicable in hydrodynamic models specified on semi-staggered B or E grids.