Spatial distribution of rainfall seasonality in Greece

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1 progress within the last decade has been substantial. Scientists and governments in many countries are working together to design and build a global system for (i) observing the tropical oceans, (ii) predicting El NinÄ o and other irregular climate rhythms, and (iii) making routine climate predictions readily available to those who have need of them for planning purposes (NOAA 1998). We are still learning what an El NinÄ o event can do. No two events are exactly alike so that their impact on worldwide ecologies and economies will also be dissimilar. Caution must be used in attributing any particular anomaly or impact to a specific El NinÄ o because climate-related anomalies can also result from a variety of local and regional conditions, even in the absence of El NinÄ o events. The atmosphere exhibits considerable variability on time-scales ranging from days to seasons to years. This variability often reflects little more than the normal chaotic behaviour of our atmosphere. References Allan, R., Lindesay, J. and Parker, D. (1996) El NinÄ o± Southern Oscillation and climate variability. CSIRO, Australia Fraedrich, K. and MuÈ ller, K. (1992) Climate anomalies in Europe associated with ENSO extremes. Int. J. Climatol., 12, pp. 25± 31 Glantz, M. H., Katz, R. W. and Nicholls, N. (1991) Teleconnections linking worldwide climate anomalies. Cambridge University Press Lander, M. A. (1994) An exploratory analysis of the relationship between the tropical storm formation in the western North Pacific and ENSO. Mon. Wea. Rev., 122, pp. 636± 651 Moron, V. and Ward, M. N. (1998) ENSO teleconnections with climate variability in the European and African sectors. Weather, 53, pp. 287± 295 NOAA (1998) Philander, G. (1998) Learning from El NinÄ o. Weather, 53, pp. 270± 274 Correspondence to: Miss C. Coghlan, 20 Cartmel Drive, Moreton, Wirral CH46 0TE. # Royal Meteorological Society, Spatial distribution of rainfall seasonality in Greece E. A. Kanellopoulou Department of Geography and Climatology, University of Athens Data and analysis Rainfall regimes are of great interest (Ramage 1971; Jackson 1977; Nieuwolt 1974) because knowledge of the rainfall amount in a region defines the degree of vegetation and, generally speaking, the quality of life itself. The seasonal characteristics of rainfall are the parameters which are taken into account for the KoÈ ppen classification (KoÈ ppen and Geiger 1936), while potential evapotranspiration compared with rainfall is also used for climate classification (Thornthwaite 1948; Penman 1963). The relative seasonality of rainfall represents the degree of variability in monthly rainfall throughout the year (Walsh and Lawer 1981). In order to define the seasonal contrasts, the Seasonality Index (SI), which is a function of mean monthly and annual rainfall, is assessed using the following formula: 8 SI ˆ 1 9 >: R >; X12 nˆ1 x n R 12 where x n is the mean rainfall of month n and R is the mean annual rainfall. Theoretically, the SI can vary from zero (if all the months have equal rainfall) to 1.83 (if all the rainfall occurs in one month). 215

2 In the present paper, the climatic data of concern are mean monthly values of rainfall from a network of 30 meteorological stations of the Hellenic Meteorological Service, for the period 1961± 90. Table 1 shows the coordinates of the meteorological stations and the computed values of the SI. The SI varies from to (Fig. 1). Table 1 values The network stations with their geographical coordinates and the representative Seasonality Index (SI) Station Longitude (8E) Latitude (8N) SI 1 Agrinio Alexandoupoli Aliartos Araxos Elliniko Ioannina Iraklio Kalamata Kerkyra Kimi Kithira Kos Kozani Larissa Limnos Methoni Mikra Milos Mitilini Naxos Philadelphia Noa Patra Pyrgos Rhodes Sitia Skyros Trikala Tripolis Xania Fig. 1 Box± whisker diagram of Greek Seasonality Index. The central point shows the mean value, with the box enclosing values within one standard deviation (SD). The extreme values are indicated by the tips of the `whiskers. 216

3 Table 2 shows SI class limits and representative rainfall regimes, while Fig. 2 presents a subdivision of Greece into four classes of SI using the Kriging interpolation method. The first region represents northern Greece, with 0.24SI50.4, that is, the rainfall regime is very equable, but with a definite wetter season. The second region (0.44SI50.6) covers a zone from the north-west to north-east of Greece. The main characteristic of this regime is a short dry season. The third region (0.64SI50.8), where the rainfall appears to be seasonal, includes the south Ionian Sea, the Aegean Sea and the island of Crete. The last region (SI50.8) refers to the south-east Aegean Sea with a long dry season. To illustrate the rainfall regimes, the annual variation of rainfall for four stations, one each from the subdivided regions of Greece, is presented in Fig. 3. Kozani (a continental station), representing the first region, has a biomodal appearance, with maxima in May and November, while minima appear in February and Table 2 Rainfall regime Seasonality Index (SI) classes Very equable Equable but with a definite wetter season 0.20± 0.39 Rather seasonal with a short drier season 0.40± 0.59 Seasonal 0.60± 0.79 Markedly seasonal with a long drier season 0.80± 0.99 Most rain in 3 months or less 1.00± 1.19 Extreme, almost all rain in 1± 2 months August. The mean annual rainfall is mm. Tripolis (from the second region) shows a simple annual variation with a maximum in December and a minimum in August. The mean annual rainfall is mm, while the dry season is limited to the summer months. The third region is represented by Naxos (a marine station) with a maximum in December and a minimum in July. The mean annual rainfall is 349.6mm. Rhodes, from the last region, has a simple annual variation with a long dry season, but with total annual rainfall of mm. SI Fig. 2 Seasonality Index for Greece 217

4 Station: KOZANI (SI=0.212) Station: TRIPOLIS (SI=0.554) Station: NAXOS (SI=0.787) Station: RHODES (SI=0.860) Fig. 3 Rainfall regimes for selected stations of the subdivided regions of Greece Conclusions The SI, which is calculated using mean monthly rainfall data, is used in order to subdivide the Greek area. The spatial distribution of SI is mapped using Kriging and the result is a subdivision of Greece into four regions. The SI varies from to 0.860, but is underestimated using the mean monthly data instead of individual year data (Walsh and Lawer 1981). References Jackson, I. J. (1977) Climate, water and agriculture in the tropics. Longmans, London KoÈ ppen, W. and Geiger, R. (1936) Handbuch der Klimatologie. Gebruder Borntraeger, Berlin Nieuwolt, S. (1974) Seasonal rainfall distribution in Tanzania and its cartographic representation. Erdkunde, 28, pp. 186± 194 Penman, H. L. (1963) Vegetation and hydrology. Technical Communication 53, Commonwealth 218

5 Bureau of Soils Harpenden, Commonwealth Agricultural Bureau Ramage, C. S. (1971) Monsoon meteorology. Academic Press, New York and London Thornthwaite, C. W. (1948) An approach toward a rational classification of climate. Geogr. Rev., 38, pp.55± 94 Walsh, R. P. D. and Lawer, D. M. (1981) Rainfall seasonality: Description, spatial patterns and change through time. Weather, 36, pp. 201± 208 Correspondence to: Prof. E. A. Kanellopoulou, Department of Geography and Climatology, Laboratory of Climatology, Panepistimiopolis GR , Greece. # Royal Meteorological Society, Two UK snow patches last until winter 2001/02 Adam Watson, John Pottie and David Duncan c/o Centre for Ecology and Hydrology, Banchory, Kincardineshire This fifth annual summary follows Watson et al. (2001). Despite a very long winter on the high hills from the end of October till early May, and with far more snowfall than usual, only two patches survived when lasting new snow came on 30 October Both lay in Garbh Choire Mor on Braeriach in the Cairngorms. The winter of 2000/01 Following the first lasting snowfall at patch sites on 28 October 2000, a wet, cold November ensued with continual heavy snow on high hills, leading to an average depth of 1 m on Ben Macdui plateau in late November. Heavy snow fell each month until May, and avalanches were frequent. The main snowfalls came on winds from south-east, east and north-east. A southeast storm on 4/5 February produced 75 cm of snow in Ballater. Even in brief mild spells, snow-cover was near-complete at high altitudes, such as in the Cairngorms above 980 m, throughout April and up to 6 May. The season at Scotland s downhill ski centres was the best since 1995/96 ± also a winter when much snow fell on south-east winds. Glenshee and Cairngorm ski areas had and skier days respectively, and the at Glencoe was the highest there since at least 1983/84. Two US Air Force F-15 jet planes crashed on Ben Macdui on 26 March, ending in the lower Snowy Corrie. Spilled fuel and hydraulic oil threatened pollution to streams, but exceptional snow-cover soaked up most of this and the discoloured snow showed their location. Authorities moved 1200 tonnes of this snow away from streams and flew 260 tonnes of the most polluted snow to Braemar by helicopter (I. Murray, personal communication). This would not have affected later patch survival, for the site was not a long-lying snowbed. Summer snowfalls Fresh snow fell with a north wind on 31 May, lying to 900 m, and a speckling of drifts still showed above 980 m on 3 June. On 7 June, a dusting of snow lay to 900 m on Ben Wyvis, and heavy snow down to 800 m on the Cairngorms and Monadh Liath next day. Ben Nevis, Aonach Mor, Ben Alder, Lochnagar and other southerly hills carried very little, but the high Cairngorms had much until 14 June. Next day, north parts of Ben Avon and Beinn a Bhuird still had a 30% cover with many deep drifts, and small drifts lay down to 890 m, but all new snow had gone on southerly Lochnagar and Cairn Toul. On 18 June, Ben Avon, Braeriach and Cairn Gorm still had a speckling above 1100 m. 219

Individual seasonality index of rainfall regimes in Greece

CLIMATE RESEARCH Vol. 28: 155 161, 25 Published March 16 Clim Res Individual seasonality index of rainfall regimes in Greece I. Livada, D. N. Asimakopoulos* University of Athens, Physics Department, Section