27/04/2005

The National Observatory of Athens (NOA), in an effort to study the impact of climate changes on Greece and the surrounding region in the coming years, installed the PRECIS regional climate model in late 2003 and adapted it for the region of the Eastern Mediterranean. This is the first time that climate simulations (experiments) have been carried out by a Greek scientific body.

The PRECIS model was developed at the Hadley Centre (Meteorological Office, Great Britain) and is based on the latest edition of the HadCM3 global climate model. All computer simulations are carried out with a horizontal resolution of 25 km, which is considered to be the highest resolution used to date for climate predictions in the region of Greece. It should be noted that climate simulations are an especially time-consuming process, since they refer to 30-year "runs" and produce a huge volume of data. For example, each of the three experiments produced ~600 Gb of data.

Specifically, the experiments that were carried out are the following: a) climate simulation for the period 1961-1990 (which is internationally taken to be a reference period), b) climate simulation for the period 2071-2100 for scenario A2 of the Intergovernmental Panel for Climate Change (IPCC), c) climate simulation for 2071-2100 for scenario B2 of the IPCC.

Scenarios A2 and B2 which were used for the above-mentioned predictions concern the anticipated increases in greenhouse gas emissions over the next 100 years. The scenarios differ in their assumptions on world population change, globalisation of the economy and spread of technology. Although not extreme cases, they still lead to an emissions increase of 250% (A2) and 62% (B2) by 2100. The results of the climate simulation for scenario A2 are the following:

With regard to mean maximum temperature changes for the period 2071-2100, compared to the figures for the period 1961-1990, in the month of July a substantial increase in temperature is forseen throughout the region, and in the Balkan countries in particular, where the mean maximum temperature increases by up to 12 degrees Celsius compared to present-day values. In Greece the increase is around 7-8 degrees in the southern regions (including Attica), whereas in Central and Northern Greece the increase ranges between 8 and 10 degrees. As with maximum temperature, the average minimum temperature also increases throughout the region of the Eastern Mediterranean, and in the Balkan countries in particular, where the mean minimum temperature in the month of July increases by up to 9 degrees compared to present-day values. In Greece the increase is around 6-7 degrees in the southern regions (including Attica), whereas in Central and Northern Greece the increase ranges between 7 and 8 degrees.

With regard to rainfall change for the months of December and July, the results are as follows: In December (at present the rainiest month in most regions of Greece) there is a substantial decrease in rainfall, particularly over the sea areas of the Eastern Mediterranean and also in Western Greece, where mean rainfall for the period 2071-2100 ranges from about 60% to 70% of present-day rainfall. In North-eastern Greece, the islands of the Eastern Aegean and Crete, the decrease is smaller.

In summer (July) the decrease in rainfall is quite substantial, in Northern Greece and the Balkans in particular. Mean rainfall in these regions in the period 2071-2100 ranges from around 20% to 30% of present-day rainfall. In the regions of Yugoslavia, Bulgaria and Romania where at present rainfall in the summer months is quite substantial, the decrease is extremely large and disturbing, because rainfall in these areas supplies water to large rivers which also flow through Greece. The decrease in rainfall is also quite substantial in regions of Northern Greece where at present substantial storm activity is observed during the summer. In Southern Greece the predicted decrease in rainfall is also great, but it is well known that even today these areas are characterised by scant rainfall in the summer months.

Of particular interest are the temperature predictions for four large Greek cities. Mean maximum temperature in Athens shows an increase for all months, but particularly the summer months, when the increase exceeds 7 degrees. A similar upward trend is seen in the mean minimum temperature, with the greatest increase during the summer months. At the same time, mean monthly precipitation decreases substantially, following the general trend towards a transition to a drier climate. Furthermore, as far as the change in mean maximum temperature for Thessaloniki, Larissa and Iraklio is concerned, in all three of these large cities, the increase in maximum temperature is highest during the summer months.