ZONING OF CLIMATE IN RIGA CITY

ZONING OF CLIMATE IN RIGA CITY Anita Kalnina*, Marita Cekule**, Lita Lizuma* *Faculty of Geography and Earth Sciences, University of Latvia, Riga, Latvia ** Institute of Geodesy and Geoinformation, University of Latvia, Riga, Latvia Abstarct City environment creates the diversity of climatic conditions. The mesoclimatic mapping of Riga city (location close to the Gulf of Riga, Baltic Sea coast 56 57'00'' N and 24 06'45'' E and total area 307 km²) was performed basing on the analysis of physiogeographical and social conditions and the results of several thousands of microclimatic observations. A definite microclimatic spectrum is characteristic for each district. The building disposition, relations between the green belt and buildings, horizontal and vertical disunity of the active surface and the other factors determine it. The estimation of the possible factors that form microclimate is given. It gives a possibility to express the microclimatic contrasts of territory in a numerical form. In prospect it could enable to define more exactly the borders of mesodistricts. Key words: urban climate, mesoclimatic mapping, Riga city 1. INTRODUCTION 1 In the case of urban environment it is both possible to define the city as one single ecosystem or to see the city as composed of several individual ecosystems (Rebele, 1999). Each of these individual ecosystems generate the climatic conditions which are depends on land-use/land-cover. The ecological research of the city environment is tightly connected with its climate that has an important role in the planning of the city sustainable development. One of the main tool for urban planners are climate maps presenting broad spectra of urban climate features. (Scherer et al, 1999. Lazar and Podesser, 1999). It is possible to distinguish four classes of urban climate maps: analytical maps showing geographical distribution of various elements of climate, syntactical maps showing the deviation of areas investigated into particular topoclimates, applied maps showing usefulness of existing climate conditions of practical purposes and prognostic maps showing expected modification of local climate (Paszynski, 1991). This investigation is the first effort to create the syntactical climate map for Riga city. Riga is the largest city of Latvia located near the Baltic Sea (56 º 57 00 N and 24 º 06 45 E) with population approximately 800 000 and the total area 307 km ². It is characteristic the plain relief with the absolute marks 6-8 m above the sea level to the territory of the city. The climate is humid continental with cool summers. Annual mean air temperature in Riga is 7,3 º C annual precipitation is 705 mm. The wind direction changes according to seasons. In the territory of the city there are located several rivers, the bigger of which the Daugava crosses the territory of the city, canals, lakes, ponds. Approximately (3 000 ha) of the city territory are occupied by parks and gardens. 2. MATERIAL AND THE METHODS The mesoclimatical division into districts of Riga is done on the base of the following: Evaluation of the city s environmental conditions Types of anthropogenic landscapes Analysis of the factors forming the microclimate Multitude microclimatical observations (about 10 000 measurements) On dividing the mesoclimatical districts there is taken into account the district s geographical condition towards the following: the Riga Sea bay; the river Daugava that crosses the city in the direction of Southeast Northwest, North; overall water surfaces in the North-East, East part of the city (Kishezers, Jugla Lake, Baltezers); the location of the city close to large areas of forest Corresponding author address: Marita Cekule**, Institute of Geodesy and Geoinformation, University of Latvia, Rainis blvd. 19, LV-1856, Riga, Latvia; e-mail: cekule@one.lv, Lita Lizuma*, Faculty of Geography and Earth sciences, University of Latvia, Rainis blvd. 19, LV-1856, Riga, Latvia; e-mail: lital@lanet.lv

3. RESULTS To the inner structure of the Riga City it is characteristic the following: the dense building zone in the central part of the city with large territories of parks the new districts of various planning in the peripheral part of the city, which often borders directly upon the outside landscapes of the city the industrial complexes often forms the zones or separate sectors between the central part of Riga and the districts (built in the years of 60 s and 80 s) the territories of detaches houses between the dense constructed areas with the tendency to diminish and negatively influence the microclimate the multiformity and dynamism of the city the reciprocal changes of the environment s interactions depending on the weather content (especially on the wind direction and speed, the cloudiness) the influence of the active surfaces depending on the season (in summer green areas, asphalt, concrete plates, tin, etc. in winter the uniformity of the surface) and on the types of the weather Taking into account these conditions there were divided 13 mesoclimatically local districts (figure 1, table 1). In every mesoclimatical district there is the possibility to divide the territories with different climatical indices. Taking into account the multiformity of the nature and sociogene conditions of each climatical district and its territorial disintegration it is more correct to speak about the spectrum of mesoclimatical conditions. The districts with diverse and different natural and sociogene conditions form a diverse microclimatical spectrum. For example, in the mesoclimatical district XIII the climatical differences are formed as a result of different big, wide, with closed tree crowns, relatively old parks, squares, tree avenues, different construction density, big, open squares, differently oriented streets and in the influence of the near located Daugava. This district is characterised by a broad contrast of microclimatical spectra. Viewing the mesoclimatical district VII it should be concluded that there are only three main landscapes in it, which set up the microclimatical spectrum, i.e. pine-tree forest, the industrial construction sector with the plots of garden and the main vehicle roads. The landscape structure in each divided district sets up the contrast of the microclimatical display. In the districts with a big multiformity of sociogene landscapes there will form diverse territorially disintegrated microclimates. In the districts with homogeneous landscapes also the microclimatical spectrum is little and the differences are less differentiated. The inner climatical peculiarities of each divided district are reflected in the chart. The first sector of it shows the air temperatures (t º ), the second the speed of the wind (w), the third normally equivalent effective temperature s (reference) (NEET º ) character towards the indices outside the city. These indices can be increased (>), decreased (<) or equal (=) to the corresponding indices outside the city. The fourth sector shows the multiformity of the district s microclimatical spectrum or the microclimatical contrast, which can be stated weakly (1), mean (2), strongly (3). The mesoclimatical districts of Riga Table 1 The region I II III IV V Name of Mesoclimatical District North-West seacoast district The valley district of Daugava- Vecdaugava North-East lake bank district The little urbanized district of Bolderaja. construction district of Bolderaja with the industrial The Main Factors of the Climatical elements Differentiation Direct border with the Riga Sea bay. Location in the NW part of Riga The closeness to Riga Sea bay. The direct influence of the Daugava. The direct border with lakes. The Location in the NE part of the city. The broad tracts of forest in the N, W, NE, part. The location in the W periphery of the city. Large proportion of large tracts of forest. The location in the NW part of the city. Surrounding of large tracts of forest. The wide spreading of the air-polluting enterprises. The Dynamics of Borders The shift of S, SE borders at the winds of N, NW (their repetition in the period May- August 30 %) The unstability of N, NW borders at the winds of NW, W. The shift of SW border at the winds of NE. The Mesoclimatical Types Characteristic to the District construction of forest, non-forest plains; water surfaces Island coast constructions; water surfaces forests. The recreation zones of lake coasts. forests. The recreation zones of lake coasts. The industrial forests. The manystoried areas.

VI VII VIII IX X XI XII XIII accent. enterprises. areas. The location between the construction and Daugava, its branches and industrial district of Kishezers. The closeness of large tracts of forest. Daugava- Vecdaugava. Mezaparks and the district of the individual construction. of industrial and territories of district Chiekurkalns. construction district of the Daugava right bank valley. buildings and the recreational territories of the Daugava left bank. buildings and offices of the Daugava left bank. buildings and offices the Old part of Riga. The centre district with the dense many-storied buildings and parks. The proportion of all-round large tracts of forest. The location in the W coast of Kishezers. The small density of construction. The borders with the Kishezers in the NE part. The concentration of industrial enterprises in the E, NE part. The location in the E part of the city. Location between the Daugava and the Jugla Lake. The direct border with the central district. The relatively big existence of large tracts of forest in the E part. The peculiarities of planning. The location in the W part of the city. The forests in the territory outside the city. The direct influence of The Daugava. The density of the construction. The little proportion of green belt. The location in the city centre. The density of the construction. The little proportion of green belt. The location in the city centre. The interchanges of the dense construction and green belt. The E borders are unstable at the circulation of breezes. The NE border is unstable in 20% of cases. Unstable in the W part at the NW, W, SW winds in the influence of the city centre. In the E part at the E winds in the influence of the city outside. The unstable W border at the NE, SE winds. The change of border on the big main vehicle roads at the different wind directions. areas and many-storied industrial buildings. Green belts. Little individual constructions. The massives of graveyards. constructions. The industrial construction. The few-storied houses with the gardens. constructions. Densely populated many-storied buildings, the main vehicle roads and the industrial enterprises. The new many-storied areas of Jugla, Plavnieki, Purvciems, Mezhciems, Kengarags. The allround large tracts of forest. areas of Imanta, Zolitude. houses. Green belts. Many-storied industrial objects; Densely constructed areas. Dense many-storied constructions. The grounds overall covered with stones. buildings and offices. Parks of different kind. 4. CONCLUSION The mesoclimatical division into districts of Riga city is stated as a relative one because it includes the dynamics of the divided districts borders, the shift at the certain conditions (Table 1, Column 4). The mesoclimatical division into districts of the Riga City is not to be considered as the finished. In the perspective it could be formed as the series of mesoclimatical division into districts, which would reflect the displays of warm and cold seasons peculiarities in the multiform variations of the weather and as well as the changes of the city environment conditions.

Figure 1. Mesoclimatical regions of Riga city References Rebele F., 1999, Urban ecology and spacial features of urban ecosystems. Glob. Ecol. Biogeography Lett., 4, 173-187 Scherer D., U. Fehrenbach, H.-D. Beha, E. Parlow, 1999, Improved concepts and methods in analysis and evaluation of the urban climate for optimizing urban planning process. Atmos. Environment., 33, 4185-4193 Lazar R., A. Podesser, 1999, An urban climate analysis of Graz and its significance for urban planning in the tributal vallays est of Groz (Austria), Atm. Environm., 33, 4195-4209 Paszynski I., 1991, Mapping urban topoclimates, Energy and Building, 16 (3-4), 1059-1062