This special issue of Climatic Change contains a series of research articles documenting coordinated work carried out within a 3-year European Union project 'Prediction of Regional scenarios and Uncertainties for Defining European Climate change risks and Effects' (PRUDENCE). The main objective of the PRUDENCE project was to provide high resolution climate change scenarios for Europe at the end of the twenty-first century by means of dynamical downscaling (regional climate modelling) of global climate simulations. The first part of the issue comprises seven overarching PRUDENCE papers on: (1) the design of the model simulations and analyses of climate model performance, (2 and 3) evaluation and intercomparison of simulated climate changes, (4 and 5) specialised analyses of impacts on water resources and on other sectors including agriculture, ecosystems, energy, and transport, (6) investigation of extreme weather events and (7) implications of the results for policy. A paper summarising the related MICE (Modelling the Impact of Climate Extremes) project is also included. The second part of the issue contains 12 articles that focus in more detail on some of the themes summarised in the overarching papers. The PRUDENCE results represent the first comprehensive, continental-scale intercomparison and evaluation of high resolution climate models and their applications, bringing together climate modelling, impact research and social sciences expertise on climate change.In Europe, as elsewhere in the world, there is a growing demand from decision-makers in the public and private sectors, from non-governmental organisations (NGOs), from researchers and from the general public for detailed information on future climate. Only

Between November 1999 and April 2000, two major field experiments, the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) and the Third European Stratospheric Experiment on Ozone (THESEO 2000), collaborated to form the largest field campaign yet mounted to study Arctic ozone loss. This international campaign involved more than 500 scientists from over 20 countries. These scientists made measurements across the high and middle latitudes of the Northern Hemisphere. The main scientific aims of SOLVE/THESEO 2000 were to study (1) the processes leading to ozone loss in the Arctic vortex and (2) the effect on ozone amounts over northern midlatitudes. The campaign included satellites, research balloons, six aircraft, ground stations, and scores of ozonesondes. Campaign activities were principally conducted in three intensive measurement phases centered on early December 1999, late January 2000, and early March 2000. Observations made during the campaign showed that temperatures were below normal in the polar lower stratosphere over the course of the 1999–2000 winter. Because of these low temperatures, extensive polar stratospheric clouds (PSC) formed across the Arctic. Large particles containing nitric acid trihydrate were observed for the first time, showing that denitrification can occur without the formation of ice particles. Heterogeneous chemical reactions on the surfaces of the PSC particles produced high levels of reactive chlorine within the polar vortex by early January. This reactive chlorine catalytically destroyed about 60% of the ozone in a layer near 20 km between late January and mid‐March 2000, with good agreement being found between a number of empirical and modeling studies. The measurements made during SOLVE/THESEO 2000 have improved our understanding of key photochemical parameters and the evolution of ozone‐destroying forms of chlorine.

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The long-term precipitation series ) from a 10 rain gauge station network in the Marathon area, Greece, have been statistically examined for trends. Application of the Mann-Kendall rank statistic test to the annual time series revealed a significant decreasing trend in the precipitation over the area. Similar decreasing trends are observed in neighbouring regions to the Marathon area (Athens basin and Beotia). The differences in precipitation trends during the transitional seasons among the three areas seem to be caused by the urbanization process. The seasonal variations and the periodicities of precipitation in the study areas also are examined. Finally, the spatial distribution of precipitation and the relation of precipitation amounts to the station height in the Marathon area are discussed.

SUMMARYA statistical evaluation of the air pollution situation in Athens for the year 1982 is presented. This analysis refers to NOz, NO, O3 and SO, concentration levels measured at the National Observatory of Athens (NOA) with a fully automatic monitoring station. The seasonal, weekly and daily variations of the above pollutants are in agreement with the corresponding activities in the city which are responsible for these emissions. Auto-and cross-correlation techniques are applied to the pollutants for January and July. It is found that all pollutants exhibit a well defined oscillatory behaviour because of their diurnal peaks in both months, except for NO2 in January whose auto-correlation function shows no regular shape. For the same reason the January NO-NO2 cross-correlation function behaves in the same way; the pairs NO-03 and N02-03 exhibit a clear oscillatory pattern. The spectral estimate method is also employed to the above pollutants for the two months in question. The energy content of 03, for instance, in July shows to be concentrated around a frequency corresponding to a periodicity of 24 hours.