Regional Earth System Modeling
A number of regional climate model (RCM) systems have been developed during the last two decades in order to downscale the output from large scale global climate model simulations and produce fine scale regional climate change information useful for impact assessment and adaptation studies (e.g. Giorgi 2006a).
To date most RCMs have been essentially composed by an atmospheric component coupled to a land surface scheme and driven over ocean areas by prescribed sea surface temperature (SST). Although such a RCM can be sufficient for many applications, there are cases in which the fine scale feedbacks associated with air-sea interactions can substantially influence the spatial and temporal structure of regional climates.
The development of a Regional Earth System Model has been one of the main objective of the Regional climate variability research area of ENEA. Our main focus is the Mediterranean climate variability, together with the simulations of the African climate.
- Modelling the Mediterranean coupled system
- Mediterranean ocean variability
- Land-surface atmosphere interaction
- River modeling
- Impact modeling
- African climate
Modelling the Mediterranean coupled system
We developed an atmosphere-ocean regional climate model (AORCM) for the Mediterranean basin, called the PROTHEUS system, composed by the regional climate model RegCM3 as the atmospheric component and by a regional configuration of the MITgcm model as the oceanic component. The model is applied to an area encompassing the Mediterranean Sea and compared to a stand-alone version of its atmospheric component. An assessment of the model performances is done by using available observational datasets.
Despite a persistent bias, the PROTHEUS system is able to capture the inter-annual variability of seasonal SST and also the fine scale spatio-temporal evolution of observed SST anomalies, with spatial correlation as high as 0.7 during summer. The close inspection of a 10-day strong wind event during the summer of 2000 proves the capability of the PROTHEUS system to correctly describe the daily evolution of SST under strong air-sea interaction conditions. As a consequence of the model's skill in reproducing observed SST and wind fields, we expect a reliable estimation of air-sea fluxes. The model skill in reproducing climatological land surface fields is in line with that of state of the art regional climate models.
This activity is carried out in collaboration with ICTP
Within the CIRCE-EU project, we performed regional climate scenarios for the Mediterranean region.
Figure. SST anomalies (degrees C) for 09/07/2000 in CPL scale observations.
Figure. SST anomalies (degrees C) for 09/07/2000 in fine scale observations.
Mediterranean ocean variability
The oceanic component of the PROTHEUS system is firstly validated comparing the sea level variability reproduced by the model with altimeter data and then used to study the interannual variability of the Mediterranean Sea and to extrapolate future behavior using the A1B scenario of IPCC.
Please note that this work is in progress.
The validation with data shows that the fully coupled model (C4, panell upper right on the figure below) bette represents the 'strange' sea level behavio observed between 1993 and 1998 in the Eastern Mediterranean. Probably due to the cooncomitant Eastern Mediterranean Transient, the sea level in the 90's in the EM shown a complicate behavior with apparent oscillation of the sea level height both in space and time.
Figure. Sea level trend observed between 1993 and 1998 in the EM from AVISO data (upper left panel) fully copled experiment (upper right panel), oceanic stand-alone experiment (lower left panel) and partly coupled experiment (lower right panel, this experiment is equal to C4 except the interactive river run off scheme)
Land-surface atmosphere interaction
We investigate the impact of land cover changes on regional climate over the Euro Mediterranean area. Land use and Land Cover Changes (LCC) affect the local, regional and global climate system through biogeophysical and biogeochemical processes that modify both surface-atmosphere exchanges of momentum, energy and greenhouse gases and surface roughness.
The feedback mechanisms between the land surface and the atmosphere have been increasingly investigated during last decade due to the increasing computational power. Therefore, in order to study the potential impacts of LCC on local climate, the simulations performed by General Circulation Models (GCMs) have been complemented by the use of Regional Climate Models (RCMs): in fact, the coarse resolution of the GCMs limits their capability to capture mesoscale features that play a pivotal role in regional dynamics.
Figure. Differences of deforestated and control simulations of horizontal wind vectors (arrows, m/s) and temperature (shaded area, K) at 960 hPa over the summer season (JJA). The contour lines indicate where these differences are statistically significant (t test for 90% confidence level).
River discharge data analysis
River discharge is one of the five components of the Mediterranean Sea water budget, together with the net inflow of Atlantic water through the Strait of Gibraltar that from the Black Sea at the Dardanelles Strait, evaporation, and precipitation. In terms of absolute values, river discharge (R) represents the smallest contributionto this budget. In fact, climatological annual mean discharge is less than 20% of the atmospheric water budget evaporation minus precipitation (E - P), and the amplitude of its seasonal cycle is almost negligible with respect to the seasonal cycle of E-P. Nevertheless, discharge together with precipitation is the only freshwater input into the basin, and during spring the two basin-integrated components E -P and R are fairly comparable.
We collected historical river discharge monthly series from different hydrological database in order to assess the river discharge contribution to the Mediterranean fresh water input. We identified 68 rivers discharging into the Mediterranean and we estimated the climatological annual mean Mediterranean discharge with an accuracy of about 78%, see Fig.1
Fig. 1 Climatological seasonal cycle of total discharge into the Mediterranean Sea and its decomposition by continent of origin. Represented here is at least 78% of the actual Mediterranean totals (solid line), 76% of discharge from Europe (short dashed), 40% of that from the Middle East (dotted), and 86% of discharge from North Africa (long dashed). (Values are in m3/s.) From "River Discharge into the Mediterranean Sea: Climatology and Aspects of the Observed Variability" , M.V. Struglia, A. Mariotti, A. Filograsso, Journ. Clim. Vol.17 (2004), No. 24 pp. 4740-4751.
Regional projections of river discharge in the Mediterranean catchment
Among all the possible physical impacts of climate change in the Mediterranean area, the one related to the availability of water resources is crucial both for natural equilibrium of biological ecosystems and for social and economic activities of the inhabitants of the Mediterranean countries. Projected variations in river discharge deriving from altered rainfall distribution will dramatically affect both natural equilibriums and people, as some areas are liable to experience large increases in flood flows, whereas others will be subject to water stress.
We developed IRIS (Interactive River Scheme) which is a numeric tool to estimate river discharge from modelled total runoff fields. Runoff fields are computed by atmospheric models via a soil parameterization scheme, which accounts for energy and water fluxes at the atmosphere-biosphere-land interfaces, thus determining the moisture content of soil, the quantity of water returned to the atmosphere through evapo-transpiration and the excess rainfall that goes into runoff.
Fig.2 Mediterranean and Black Sea catchments in IRIS. Reconstruction based on TRIP datase
On sufficiently long time scales, vertical balance between the four components of the terrestrial hydrological cycle should be achieved:
where P is the cumulated precipitation, E is the cumulated evaporation, ΔS is the soil storage variation and R is the cumulated total runoff. Therefore, river discharge can be easily calculated by spatially integrating the simulated time mean total runoff field over distinct catchment basins. Such a simple approach is allowed only when climatic scales are concerned as the relevant variables can be derived as long term means of those computed for forecast purposes.
IRIS is based on the Total Runoff Integrated Pathway (TRIP) dataset, which maps information on land water flow directions onto a 0.5°x0.5° regular global grid.
The above figure shows the results of the hind-cast run. The blue line is the modelled seasonal cycle from the runoff fields of the hind-cast run of the Protheus coupled model, forced with the ERA-40 reanalysis , years 1958-1997. For comparison, we also show the observed climatology for the same years (red line), computed from river discharge time series. Only in the case of the Danube river the plotted climatology refers to the period 1958-1984, for which observations are available.
Designing adaptation strategies requires a fundamental understanding of regional climate change and its impact on productive sectors. The main objectives of our research is the applications of weather-driven physiologically based demographic models (PBDMs) used to analyze a major Mediterranean crop-pest system, namely olive (Olea europaea) and the olive fruit fly (Bactrocera oleae) (Center for the Analysis of Sustainable Agro-ecological Systems).
The Mediterranean Basin is expected to be particularly vulnerable to climate change including pronounced climate warming and desertification. The tight co-evolution links of drought-resistant olive and its major pest the olive fly, and their wide distribution makes the system a suitable model for climate change studies.
Figure. Olive yield (kg dry matter tree-1) in the Mediterranean Basin: average (a, b) and standard deviation (c, d) for the period 1958-1967 and 1988-1997.
The West African Monsoon is a climatological feature of major social importance to populations whose economy relies on agriculture. Therefore, understanding its dynamics, variability at various timescale and evolution contribute toward food security and stability of the region.
The monsoon is a large-scale circulation characterized by a seasonal reversal of winds due primarily to the land-sea temperature contrast. Within this circulation is embedded a number of rainfall producing systems such as African Easterly Waves (AEWs), squall lines and tropospheric jets: African Easterly Jet (AEJ) centered approximately at 600 hPa and the Tropical Easterly Jet (TEJ) centered at about 200 hPa. The intensity of these systems and their latitudinal location influence not only the amount of rainfall but also its variability over West Africa.
Our research aims to understand the intraseasonal and the interannual variability of rainfall and the related atmospheric circulation over West Africa and to evaluate our capability to correctly reproduce them.
Figure. Averaged 1989-2005 Precipitation (in mm/day and shaded) from CRU (Upper Panels), GPCP Superimposed are ERAIM Wind Vectors at 925 hPa (Middle Panels) and RegCM3 Superimposed its 925 hPa Wind Field (Lower Panels) on DJF (Left) and JJA (Right)