Cent. Eur. J. Geosci. • 1(2) • 2009 • 176-182 DOI: 10.2478/v10085-009-0013-8 Central European Journal of Geosciences Continental and oceanic precipitation régime in Europe Research Article Katerina Mikolaskova∗ Charles University in Prague, Department of Physical Geography and Geoecology, Albertov 6, 128 43, Praha 2, Czech Republic Received 24 February 2009; accepted 20 April 2009 Abstract: This work considers continentality from the point of view of an annual course of precipitation. It assesses conti- nentality according to percentage of precipitation in summer and winter half year, ratio of precipitation in summer to winter half year and the period of half year precipitation in the area of WMO Region VI (Europe). Region VI can be divided into five main regions according to their annual course of precipitation. These regions are: Northwest- ern Europe with precipitation in all seasons, a predominance of winter precipitation and maximum precipitation in December and January; Central Europe with precipitation in all seasons, a predominance of summer precipita- tion and maximum precipitation in July; Eastern Europe with less precipitation over the year than in Northwestern Europe, a predominance of summer precipitation and maximum precipitation in July; the Mediterranean region with a predominance of winter precipitation, a dry season in summer and maximum precipitation in November and December; and Western Asia with a variable climate, a predominance of winter precipitation and maximum precipitation in December and January. Continentality from the point of view of precipitation rises towards the east. In comparison with thermal continentality, according to Gorczynski, it unexpectedly reaches its maximum in the centre of Europe (especially in northeast of the Czech Republic and south of Poland). Keywords: Climate • continentality • Europe • the Mediterranean climate • precipitation © Versita Warsaw 1. Introduction Climate continentality is difficult to quantify because it is governed by a wide range of factors and for this rea- son some simplifications are used. Frequently climate continentality is quantified from two basic viewpoints – Climate continentality is one of the basic characteristics of temperature and precipitation; with temperature the most climate. It represents a degree to which a particular place common. is influenced by land or by ocean. It is a consequence Thermal continentality is characterized by a high annual of the transformation of air mases during their transfer temperature range, which (generally over 15.6°C) [1] in- from the ocean to the mainland or from the mainland to creases eastward and reaches the maximum in the area of the ocean. Climate continentality is characterized by a Russia. In the case of continentality from the precipita- specific course and degree of climate elements such as tion point of view the situation seems to be different. The temperature, precipitation, cloudiness, pressure etc. distribution of temperature over the Earth is dependent on fluxes in radiation, heat and moisture which results ∗E-mail: [email protected] from the distribution of solar radiation with latitude [2]. 176 Katerina Mikolaskova Energy fluxes across the air/land and air/water interfaces are another factor which influences temperature ranges. These fluxes are controlled by the thermal properties of the interface substances and it is suggested that above the land there is a much bigger annual temperature range than above the sea. Thus the increase in the annual range of temperature inland is the most remarkable effect of con- tinental surface. The distribution of temperature does not have as complex pattern as the distribution of precipita- tion, which is more influenced by local factors. In general, coastal areas have maritime climates, which means cli- mate influenced by the ocean. The air saturates above the ocean and is then transferred to the mainland where the water vapour condenses; as a result there is abun- dant precipitation in coastal areas. Maritime air does not penetrate far inland and the total amount of precipitation decreases the further inland. On the other hand there are significant differences in the amount of precipitation and Figure 1. Major climatic regions in Europe and the position of sta- its distribution among climate zones, as precipitation is tions. generated from different mechanisms. In spite of this it is still possible to classify climate continentality according to annual courses of precipitation in Europe. However, if we measure climate continentality in this way we may get falls, counted in moderate climate from 1st April (in north- different results than if we use temperature. ern hemisphere). As the degree of climate continentality increases the period of half year precipitation gets shorter (prevailing precipitation in summer months), reaching 9 2. Data and methods of analysis months in areas of oceanic climate and 3 months in areas of continental climate [6]. The analysis used monthly means of precipitation from Neither of these indicators considers the exact location of the period of 1961 – 1990, which were obtained from 321 the station from the point of view of altitude or orientation stations distributed across Europe and part of western (leeward/windward side) in case of mountain stations. The Asia (WMO Region VI). All records were taken from World aim of this work was to define a divide between oceanic Weather Records 1961 – 1970, 1971 – 1980, 1981 – 1990 and continental climate in Europe, so that inaccuracies (Compiled by WMO). Stations without continuous mea- caused by not including these factors are insignificant. surements for at least 20 years were excluded [3–5]. All map analyses were done in ArcMap 9.1. from ESRI The seasonal distribution of precipitation was the most using Kriging interpolation. important feature of these analyses. The first indicator of analyses is: summer half year precipitation 3. Distribution of precipitation in R = , winter half year precipitation Europe where the summer half year is defined as a period from 1st April to 30th September and the winter half year as a pe- Europe and Western Asia can be divided into several major riod from 1st October to 31st March. If R is higher than 1 regions according to the amount of precipitation, their an- it means prevailing precipitation in the summer half year nual course and the factors they are caused by. These ma- (result of convectional rainfalls), and thus a continental jor regions, which were estimated according to the above climate. If R is smaller than 1 it means prevailing precip- features, are: Northwestern Europe, Central Europe, East itation in the winter half year (result of cyclonic rainfalls) Europe, the Mediterranean and Western Asia. The most and thus an oceanic climate. The second indicator – pe- important features are the amount of precipitation and its riod of half year precipitation (H) was arranged by Hru- distribution among summer and winter months. The driest dicka [6]. This indicator expresses the time (counted in and the rainiest months were also considered. The main months) in which half of the total amount of precipitation climatic regions are depicted in Figure 1. 177 Continental and oceanic precipitation régime in Europe 3.1. Northwestern Europe maximum changes from autumn months (September, Octo- ber) in Norway to winter months (December, January) in Precipitation in Northwestern Europe is abundant both Great Britain and France. R decreases southward, with in summer and winter. The total amount of precipitation a value of 0.81 in Norway, 0.72 in Great Britain and 0.66 ranges from 600 to 900 mm per annum. Most of it falls in the north of Spain (Table 1). The driest month is gen- in winter owing to the extension of Icelandic low pressure erally April but February is the second driest in Ireland system, to the north-east of the pressure centre in Ice- and Great Britain. Slightly continental climate can be land. This system causes northeasterly winds which are found in French basins (Paris, Garonne) where the mini- very strong and brings heavy rainfalls in winter. In summer mum precipitation occurs in February. The influence of the the Azore anticyclone extends to the north-east of its pres- Atlantic Ocean is blended with influence of the Mediter- sure centre and prevailing winds are westerlies and north- ranean climate in the south of France. The influence of westerlies with less precipitation. The most precipitation the Atlantic Ocean can be observed in the maximum pre- falls in the west of Scandinavian mountains (2061 mm in cipitation in December and January and influence of the Bergen), on islands of Ireland (1430 mm in Valentia) and Mediterranean climate in minimum precipitation in July Great Britain (1529 mm in Eskdalemuir). Moving south and August. the total amount of precipitation decreases and the winter Table 1. Distribution of precipitation in Northwestern Europe. Altitude Annual Spring Summer Autumn Winter Summer Winter H R mean half half (months) precipitation year year (m) (mm) (%) (%) (%) (%) (%) (%) BERGEN (NORWAY) 40 2061.4 16 21 38 25 43.83 56.17 7 0.78 VALENTIA (IRELAND) 9 1430.4 21 18 30 31 38.78 61.22 7 0.63 EDINBURGH (SCOTLAND) 35 667.4 21 26 30 23 49.73 50.27 6 0.99 BORDEAUX (FRANCE) 6 923.9 24 17 28 31 41.18 58.82 7 0.7 Table 2. Distribution of precipitation in Central Europe. Altitude Annual Spring Summer Autumn Winter Summer Winter H R mean half half (months) precipitation year year (m) (mm) (%) (%) (%) (%) (%) (%) BERLIN-TEMPELHOF (GERMANY) 48 597.6 23 33 23 21 58.17 41.83 5 1.39 TRIER-PETRISBERG (GERMANY) 265 784.3 23 27 25 25 50.27 49.73 6 1.01 KLODZKO (POLAND) 316 591.3 23 44 21 12 70.72 29.28 5 2.42 BISTRITA (ROMANIA) 366 677.2 25 37 19 19 63.09 36.91 5 1.71 BOURGAS (BULGARIA) 28 533.4 25 22 27 26 47.27 52.73 7 0.90 WROCLAW-STRACHOWICE (POLAND) 120 587.2 21 42 22 15 66.61 33.39 5 1.99 DEBRECEN (HUNGARY) 111 564.5 24 36 20 20 61.06 38.93 5 1.57 3.2.