Topoclimatic and Microclimatic Differences in the Braşov Town-Area

8/12/2019 Topoclimatic and Microclimatic Differences in the Braov Town-Area

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SEMINARUL GEOGRAFIC D. CANTEMIR NR. 26 / 2006

Topoclimatic and Microclimatic Differences in the Braov Town-Area

Sterie Ciulache

ResumLa spcificit du topoclimat urbain de Brasov, qui sinscrit comme une le de chaleur

gnre par les caractristiques anthropiques de sa surface active, est complique par lasuperposition des particularits du climat de dpression, caractris par des inversions

thermiques frquentes et persistantes.Le territoire de la ville de Brasov inclut un mosaque de

microclimats, parmi lesquels, par la gnralisation des types relativement homognes desurface active, on peut identifier 5 microclimats distincts : le microclimat de la ville mdival

compact , le microclimat de la ville rsidentielle ancienne (avec des maisons, cours et jardins) ,

le microclimat de la ville rsidentielle nouvelle (avec des immeubles collectifs et de petitsespaces verts) , le microclimat de la ville industrielle et le microclimat de la ville verte (forme

des parcs et jardins avec une vgtation forestire).

Mots-cls: diffrences thermiques, surface active artificielle, impermabilit, inversion

thermique, le de chaleur, rchauffement artificielle, topoclimat urbain, mosaque de microclimats.

Greatly changing the natural characteristics of the active surface they develop

on, the towns exert largely modifying influences on all the meteorological elements,accordingly creating specific urban topoclimates that are sensibly different from the

climate of the surrounding open spaces, both concerning the values of various

meteorological parameters and their distribution in time. The Braov city is not

excepted from the rule. Ranking as one of Romanias big cities and lying over a pretty

large area with close buildings and compact street-pavements, it suggestively

expresses the role that the artificial active layer plays in the creation of specific urbantopoclimates. But the specific character of the respective topoclimates gets even more

complicated since, in the particular case of the Braov city, they superimpose on a

climate of intermountainous depression, which is characteized not only by a far greater

spatial extention, but also by larger quantitatively differences in the daily and annual

variations of all meteorological elements. The specific depressionary climate also

exerts different influences on the various microclimates developing within the urbanarea of the Braov city. As these microclimates are better evidenced on clear and calm

skies, it results that, in the Braov town area, they get less evident because of the

lower frequency of clear skies, on one side, but get more evident because of the higher

frequency of calm weather. Nevertheless, besides the specific microclimates that may

form due to the particular characteristics of the various urban active layer-types, the

temperature inversions getting very frequent during the cold season, may also generate

further different microclimates, due mostly to the greater relative height of the relief

forms, than to the other nature characteristics of the underlying active layer.

Therefore, it is far more difficult to highlight the topoclimatic characteristics of

the Braov town area in comparison to the climatic characteristics of the Braov

Depression, than to do the same for a town lying in a plain area, as the Ploieti city for


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Lucrrile Seminarului Geografic D. Cantemir nr. 26, 2006

44

example, simply because the former one is not only located on the bottom of a large

depressionary area, but also because it extends on the slopes of the surrounding

mountains. Consequently, the differences of the main climatic characteristics between

the inner and the outer parts of the town-area might be either positive or negative

when compared to the values obtained from an outer weather station (meaning that the

air-temperatures in the town-area might as well be higher than those recorded at a

weather station located in the floodplain area of the Olt River, but lower than thoserecorded at a weather station located on the slopes of the nearby Tmpa or Post varu

Mts. In the latter case, if the height difference is large, the higher air-temperatures in

the Braov town area dont make an exception from the rule of decreasing air-

temperature with altitude (although sometimes, the town areas lying below the level of

the persistent air-temperature inversions, may be colder than the upper parts of the

mountain slopes raising above it).

The specific topoclimates of the Braov town area may convincingly be

evidenced by simply comparing the weather data recorded at the Braov-town weather

station (609 m above sea level) to those recorded at Ghimbav (534 m above sea level).

The value and the sign (positive or negative) of the differences between the two

weather stations are largely modified by the two local factors of influence: the

artificial active layer inside the town area, on one side, and the specific depressionaryrelief forms, on the other side.

The analysis of various air-temperature parameters over a 30 yrs. period is quite

relevant in this respect (Fig. 1).

The annual air-temperature of 7.70C at the Braov-town station, and of 7.50C at

the Ghimbav station, clearly indicate the important role that the temperature inversions

play in the depressionary areas. The mean annual range of only 0.20C may seeminsignificant, but we must keep in mind that this value is largely attenuated because

when computing the annual means, we have to take into account both the periods of

the year (the months of the warm season) and the intervals of the day (the noon and

after-noon hours) when the temperature inversions are either weak or absent. The

mean annual range increases to 0.80C in the coldest month of the year (January), when

the mean air-temperature value decreases to -3.7

0

C at the Braov-town station, and to-4.50C at the Ghimbav station. The temperature inversions are most clearly evidenced

by comparing the mean values of the daily minimum air-temperatures in January. The

difference of 1.80C (-7.00C at the Braov-town station and -8.80C at the Ghimbav

station) seems quite substantial when referring to monthly average values, even if they

have been obtained from the daily means of the minimum temperatures. The

parameter of reference still reflects the influence of temperature inversions even

during the hottest month of the year (July), when the difference between the Braov-

town station (11.50C) and the Ghimbav station (10.90C) reaches 0.60C in favour of the

former weather station, despite its location at a higher altitude.


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During the period of analysis, the differences between the absolute minimum

air-temperature values that have been recorded at the Braov-town (-26.30C) and at the

Ghimbav (-32.30C) weather stations, perfectly fit into the logic of the inversion

processes, the value of 6.00C being quite impressive if taking into account the distance

and the difference of altitude between the two weather stations.

The topoclimatic consequences of the air-temperature inversions are also

evidenced by the annual means of specific air-temperature parameters from the wholedata series. For example, the mean annual number of freezing days (Tmin 0

0C) is

lower with 9.4 days in Braov (130.9 days) than in Ghimbav (140.3 days); the mean

annual number of frosty nights is lower with 8.2 nights in Braov (23.1) than in

Ghimbav (31.3) etc.

As air-temperature inversions are largely influenced by the presence of

anticyclonic air-pressure forms and greatly favoured by the depressionary relief forms

or by the existence of the snow-layer cover, they have low frequencies, durations and

depths during the warm period of the year, when the intervals with direct air-

temperature stratification are getting more dominating, especially in the lower

troposphere. Consequently, the air-temperature parameters strictly referring to this

period have a spatial distribution that perfectly corresponds to the general rule of their

value decreasing with altitude. For example, the mean air-temperature in the hottestmonth (July) is 0.20C higher at Ghimbav (17.70C) than in Braov (17.50C) and the

mean value of the daily maximum air-temperatures at Ghimbav (24.60C) is 0.60C

higher than the corresponding value recorded in Braov (24.00C) during the same

month. The direct air-temperature stratification during the warm season largely

compensates the influence of the air-temperature inversions during the whole year

only when dealing with the mean annual value of daily maximum air-temperatures(13.80C at Ghimbav and 13.50C at Braov) or with the mean annual number of

summer days (51.5 at Ghimbav and 47.3 in Braov).

The greater decrease of air-temperature as result of the stronger influence of

winter air-temperature inversions and the larger increase of the values of the same

weather parameter as result of the more prevalent direct air-temperature stratification

in summer, clearly reveal why the air-temperature ranges are sensibly higher atGhimbav than in Braov. For example, the mean annual temperature range in

Ghimbav is 22.20C, while in Braov, it hardly reaches 21.20C; the mean annual range

of daily extreme air-temperatures is 11.60C at Ghimbav and 10.40C at Braov; the

mean annual range of monthly extreme air-temperatures is 33.40C at Ghimbav and

30.60C at the Braov-town weather station. Logically, the absolute range of the whole

period of analysis is also higher at Ghimbav (67.70C) than in Braov (61.70C). The

lower values of the air-temperature ranges clearly reflect the decreasing temperature

continentalism with increasing altitudes. However, the decreasing values of this

indicator, which are getting sensibly lower than it would have been expected for the


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altitude difference of only 75 m between the two weather stations, are more than

relevant for the influence of the frequent and persistent air-temperature inversions.

The higher rates of the referred-to thermal continentalism may easily be explained,

especially on condition that between the Ghimbav (534 m) and the Braov-town weather

stations (609 m) there appears a difference of 233 days (64%) with air-temperature

inversions, as referred to the minimum air-temperature values, and a difference of 212

days (58%), as referred to maximum air-temperature values.

The topoclimatic characteristics of the Braov town-area, as presented above by

means of specific air-temperature features, are obviously inconsistently analyzed in

the absence of a convenient volume of meteorological data resulted from simultaneous

measurements in representative stationary points or stations of observations, located

both inside and outside the town-area, or from field measurements along pre-

established routes, during the relatively stable intervals of either minimum or

maximum air-temperatures occurence.

Episodic measurements made by both (stationary and expeditionary) methods

during the summer months of the 2000-2005 period, especially on calm and clear

weather, on anticyclonic conditions, have clearly revealed the towns thermal

superiority over the open spaces around it, even if they are lying at similar or at lower

altitudes. The towns heat surplus, which is mainly due to the various building

materials (with specific heat and heat conductibility or permeability highly differing

from the ones of the open spaces with vegetation cover lying outside the town-area), to

the towns prophile (largely increasing the absorbtion-emission surface of radiation

flows) and to the sewerage system (that rapidly evacuates the rainfall water, thus

greatly diminishing evaporation), gets more evident during the warm season, even

when comparing the Braov-town data to those obtained from the lower areas of the

Braov Depression, including to those recorded at Ghimbav, which, as it has been

previously mentioned, are fairly higher than those in the Braov town-area. Although

episodic, the respective measurements indicate the fact that, in the area of interest, the

influence of the urban active surface is stronger than that due to altitude, that is simply

overcompensates it, and therefore, the air-temperatures recorded in the Townhall

Square lying in the heart of the Braov city, on clear and calm weather, in summer, are

constantly higher than those obtained at Ghimbav, despite that the latter weather

station lies at a 75 m lower altitude (Table 1). However, most measurements have

generally been made on calm and clear weather, in anticyclonic pressure-field

conditions, in order to obtain the highest differences in the periods when the annual

maximum air-temperatures are most likely to occur. This is, in fact, what it actually

happened in July, 5th, 2000, when the Ghimbav weather station recorded the highest

air-temperature value from that specific year (37.30C) and the absolute maximum air-

temperature value of the 1912-2000 period. The data resulted from the measurements

that have been made at the observation point in Braovs Townhall Square, during the


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same day, over a practically impermeable active surface (street pavement), surrounded

by compact fronts of several storey-high buildings, are more than relevant for the role

of the town area as a modifying factor of climatic (thermal) conditions specific of the

region the town lies in (Table 1).

Table 1. Air-Temperature (0C) Evolution at Braov and Ghimbav (July, 5th, 2000)

Observation pointObservation hour

05 06 07 08 09 10 11 12 13

Ghimbav 23.6 25.0 28.5 29.4 31.5 33.1 34.0 36.3 35.8

Braov Townhall Square 25.4 26.5 29.8 30.4 32.3 33.7 34.6 36.8 36.2

Difference + 1.8 + 1.5 + 1.3 + 1.0 + 0.8 + 0.6 + 0.6 + 0.5 + 0.4

Observation pointObservation hour

14 15 16 17 18 19 20 21 22

Ghimbav 34.9 34.9 34.9 33.8 32.6 30.6 27.2 25.6 21.8

Braov Townhall Square 35.2 35.4 35.5 35.5 34.2 32.7 29.6 28.8 24.5

Difference + 0.3 + 0.5 + 0.6 + 1.2 + 1.6 + 2.1 + 2.4 + 3.2 + 2.7

These values are constantly higher than those recorded inside the shelter on the

standard meteorological platform of the Ghimbav weather station. The highest

differences are characteristic of the interval of daily maximum air-temperaturesoccurrence, that is between 1200 and 1500hrs., when they are low (ranging between

0.30C and 0.50C), and in the evening , between 2000 and 2200hrs. (when they range

between 2.40C and 3.20C). The most important role in this apparently paradoxical

daily evolution of the air-temperature differences between the inner and the outer parts

of the Braov town-area falls to the massive heat accumulations of the compact

buildings in the Townhall Square during the day, as well as to the crossed emissions of

heat radiations that have greatly diminished the cooling processes in the evening. On

the contrary, in the outer parts of the town-area, the active surface loses the heat

accumulated during the daytime more rapidly, consequently emitting upwards the

infrared (heat) radiations, without receiving any other kind of radiations, except the

atmospheres radiation, which gets almost insignificant during the clear nights.

In their annual evolution, the highest differences between the inner and the outerparts of the town-area appear in winter, on anticyclonic weather conditions. They may

sometimes reach 70C -80C, mainly because of the artificial heating of the ground, due to

the combined action of more factors that transform the town-area into a heat island, and

because of specific synoptic situations that place the Ghimbav weather station below the

upper levels of thermal inversions (often accompanied by fog) and the Braov-town

station, above them, thus receiving important heat flows from direct sunlight. In such

cases, the effect of the thermal inversions juxtaposes over the artificial heating effect, so

that the air-temperatures differences greatly increase in the built-in areas.


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By lacking special instrumental observations in the Townhall Square area, all

over the years months, we just couldnt adequately evidence the yearly evolution of the

air-temperature differences describing the specific urban topoclimate of the Braov city.

However, we could identify and delimit the main topoclimatic areas of the

Braov city mainly by analyzing the various types of active surfaces inside the town-

area, on account of the episodic measurements that have been made on clear and calm

weather, during summertime, especially in July and August. Unlike the plain towns,

the area of Braov city is highly heterogenous from the point of view of the density

and the particular characteristics of the various buildings, as well as of landforms. That

is why the range of potential microclimates is highly diversified and their spatial

distribution is extremely complicated. Nevertheless, we could group them into 5

distinct types of microclimates (Fig. 2), with relatively stable and consistent

instrumental and sensing differences.

1. The microclimate of the compact, mediaeval Braov town-area with impermeableactive surface layers, both at the upper level of the tile-roofs and at the lower level

of the narrow streets, with compact buildings and close inner courtyards, with

practically almost no plant-cover.

2. The microclimate of the old, residential Braov town-area, with less high houses(groundfloor or groundfloor plus one floor), closely aligning along both street-

sides, but with backyards full of vegetation and (fruit)-trees.

3. The microclimate of the new, residential Braov town-area, with 4-10 storey-highblocks of appartments, separated by narrow green spaces.

4. The microclimate of the industrial Braov town-area, with large production halls,warehouses, stacks releasing important amounts of heat energy and pollutants and

access roads actively interacting with the air-environment.

5. The microclimate of the green-spaced Braov town-area, represented by all theparks, gardens and woodland remains stretching over the slopes of the surrounding

hills and mountains.

The thermometrical determinations that have been simultaneously performed in

five characteristic points of the five relatively homogenous, yet distinct, types of

active surface areas, are presented in Table 2. Despite the given conditions of high

atmospheric stability in which the measurements have been made, the values show

clear differences of air heating processes, mostly due to the different interaction

patterns between solar radiation and the active surface layer.

The analysis of the respective data confirms the major influence of the fully

artificialized active surface in the Townhall Square area, which records air-

temperatures that are constantly higher than any of those recorded in the five distinct

types of microclimatic areas inside the Braov town. The air-temperatures measured in

the industrial areas of the Braov city (13 December Street, separating the two big

industrial units: Tractorul (Tractor) and Rulmentul (Bearing) Works), were very


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similar to those recorded in the Townhall Square area, mostly due to the same factors

and processes of influence, but the temperature values recorded in the Nicolae

Titulescu Park area (lying in the northern part of the compact, mediaeval Braov town-

area) were much lower.

Intermediary values have been recorded in the Latin Street, namely on the

crossroads area with Cpt. Ilie Birt Street, from the Schei District, as well as in the

Figure 2. The Specific Microclimates of the Braov Town Area

1. The microclimate of the compact, mediaeval Braov town-area2. The microclimate of the old, residential Braov town-area3. The microclimate of the new, residential Braov town-area4. The microclimate of the industrial Braov town-area5. The microclimate of the green-spaced Braov town-area

Limit of microclimates


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Independena Street, lying in the center of the Tractorul block-of-flats district. The

green gardens at the back of the Schei houses and the green strips among the blocks of

flats have largely diminished, through active evaporation and improved air-ventilation,

the temperature values, as compared to those in the Townhall area.

Air-temperature distribution in the Braov town-area, as resulting from the data

presented in Table 2, is, nevertheless, more complicated, due to the influence of the

complex relief-forms within the settlement area, the varying altitudes, the sheltering

effects of the buildings, the local thermal circulations etc., which greatly alter the

interaction pattern with the active surface layers.

Table 2. Air-Temperature (0C) Evolution at Braov, on different types of active surface layers

(July, 5th, 2000)

Microclimate

Type

Observation Point

Observation Hour

06 07 08 09 10 11 12 13

1. Townhall Square 25.5 29.8 30.4 32.3 33.7 34.6 36.8 36.2

2. Latin Street 25.6-0.9

28.9-0.9

29.6-0.8

31.7-0.6

33.1-0.6

34.1-0.5

36.3-1.5

35.8-0.4

3. Independena Street 25.2 28.4 29.2 31.4 33.0 34.0 36.1 35.7

4. 13 December Street 25.3 28.5 29.3 31.7 33.2 34.3 36.5 35.95. N. Titulescu Park 26.1 29.3 29.9 31.7 32.9 33.8 35.9 35.2

Microclimate

Type

Observation Point

Observation Hour

14 15 16 17 18 19 20 21

1. Townhall Square 35.2 35.4 35.4 35.0 34.2 32.7 29.6 28.8

2. Latin Street 34.9

-1.3

34.9

-0.7

34.6

-0.9

34.0

-1.0

33.0

-1.2

31.2

-1.5

28.0

-1.6

27.0

-1.8

3. Independena Street 34.9 34.6 34.7 34.0 33.2 31.4 28.4 27.5

4. 13 December Street 35.0 35.0 34.0 34.2 33.8 31.7 28.7 27.9

5. N. Titulescu Park 34.1 34.2 34.0 33.6 31.6 31.3 28.2 27.0

References

Huber Viorela- (2001) Cercetri asupra regimului meteo-climatic al spaiului montan (nCarpaii de la Curbur), Tezde doctorat, Universitatea din Bucureti.

Mihai Elena (1975) - Depresiunea Braov. Studiu climatic., Editura Academiei Romne,

Bucureti.Neaca O. i colab. (1972) Studiul climatologic al oraului Braov i al zonei sale

preoreneti, Culegere de lucrri ale Institutului Metorologic, Bucureti.

Documents

Topoclimatic and Microclimatic Differences in the Braşov Town-Area