THE ROLE OF RELIEF AND LAND USE IN SHAPING THERMAL CONDITIONS OF LOCAL CLIMATE IN THE YEARS 2006–2007

Joanna Kopcińska¹, Barbara Skowera^2
1 Department of Applied Mathematics, University of Agriculture in Kraków, Poland
² Department of Ecology, Climatology and Air Protection, Faculty of Environmental Engineering and Land Surveying, University of Agriculture in Kraków, Poland

ABSTRACT

In this article the authors analyzed the impact of relief and land use on air temperature, which incidentally is one of the basic characteristics of local climate. Climatological research was performed in a sample area in the southern part of the Krakowsko-Częstochowska Plateau. The location was chosen because of its diversified relief and land use. Air temperature measurements were carried out in the years 2006–2007, in a series of observations which lasted for several weeks. These measurements were taken at different meteorological sites including hilltop, valleys and slopes (western, southern and northern exposures) as well as on various types of land cover (cultivated land, forest and meadow). Climate diversity on a local scale is best seen during radiation type weather. Therefore, daily courses of air temperature were analyzed for selected high pressure and synoptic situations.

The results of this study indicate that most favorable thermal areas in the studied region are the slope sites (southern and western) and the high land site. Meanwhile the valley has slightly less favorable conditions for agricultural development due to the frequent occurrence of temperature inversions. The most statistically significant (α = 0.05) impact  of relief and land use on the dynamic changes of air temperature occurs in the warmer half of the year (especially during summer and late spring). During autumn and winter months this impact is much lower and is conditioned by the inflow of solar radiation. The most stable weather conditions were observed in the forest area throughout the whole time the research was conducted. The results of this research indicate that the most favorable thermal areas for cultivation plants in the upland region under observation are the slope sites (southern and western) and the hilltop area. Meanwhile the valley has slightly less favorable conditions especially for vegetable crops and orchards due to the frequent occurrence of temperature inversions. It should be noted that temperature inversions are closely associated with ground frosts, which are very hazardous for plants especially in the early vegetation phase.

Key words: meteorological observations, Krakowsko-Częstochowska Plateau, cultivation plants.

INTRODUCTION

Knowledge of the characteristics of the local climate is crucial for the optimal use of natural resources for both agricultural production and land use planning. The principal features of the Krakowsko-Częstochowska Plateau are diversified relief and abundant vegetation. These factors are responsible for a clear and pronounced variability of both micro-climatic and meso-climatic conditions in places that are several miles apart [3, 6]. In order to describe the mesoclimate (local climate or topoclimate) climatologists apply the daily course of air temperature during insolation weather [11, 8, 10]. There are many articles referring to local climate conditions, but to fulfill economic needs, local studies are determining the specific features of the area [7, 12, 13].

Field studies and meteorological observations, of which the primary goal is to comprehend the peculiarity of local climates, are carried out in relatively small areas. They are usually limited to short temperature series measured in standard weather screens (2 meters above the surface) during days with clear weather. Days with clear weather are characterized by little cloud cover and low wind velocities. During such days we may encounter  the greatest variability of meteorological conditions, which result from a chain of interactions between relief, plant cover and soil. The authors of this article decided to use days with clear weather that prevail in the Upper Vistula river basin in order to analyze the thermal conditions in Garlica Murowana, which is a typical fruit-growing region. Understanding of the variability of thermal conditions of land relief may have broad practical significance that is often associated with agriculture, fruit-growing industry and land use planning.

The goal of this research is to determine the quantitative impact of relief and land use on the variability of thermal conditions during high-pressure synoptic situations in the upland terrain.

STUDY AREA

Research was conducted in the years 2006–2007 on a fruit-growing farm in Garlica Murowana, a small rural village situated in the southern part of the Krakowsko-Częstochowska Plateau. The area studied was relatively small (~80ha); nevertheless it was characterized by distinct variability of relief and land use, which is typical for that part of the Plateau.

Weather stations were situated on various types of land use terrain and topographical forms typical of an agricultural region. It should be mentioned that this area is used by the Department of Fruit Farming and Apiculture Agricultural University in Kraków (Fig. 1).

RESEARCH METHODS AND MATERIALS

In order to determine the quantitative impact of land relief and land use on thermal conditions the authors established a set of 6 weather stations equipped with miniature temperature recorders Hobo (property of Hobo Company). These are the miniature battery temperature loggers with Pt100 platinum sensors. Recorders are designed to measure temperatures in the range -30°C to +70°C. They have the potential long-term recording of temperature in given time intervals. For the benefit of this experiment the temperature was recorded every hour. The data from the recorders were processed using a computer program LoogBook for Windows. These recorders were placed in anti-radiation shields 2 meters above the ground. Meteorological measurements were carried out from July 2006 until May 2007. It should be emphasized that the temperature series was performed in the following seasonal order: spring, summer, autumn and winter. Mean, maximum and minimum temperature as well as temperature amplitudes are displayed in charts, while the daily course of temperature is shown in graphs.

The selection of weather stations was conditioned by the type of land use and topographic form. Land use terrain included cultivated land (vegetable cultivars), meadow whilst topographical forms included hilltop, valley and terrain relief with both western and southern exposures. Deciduous forest was aged of about 40–50 years.

Only the temperature series with insolation type weather was selected for analysis. It should be noted that this particular weather condition is typical for high-pressure synoptic situations. In order to select days with insolation weather the authors employed the synoptic situation and mass advection calendar which was devised for the upper Vistula river basin and was readily available for this research project [9].

The selected temperature series from each season was analyzed by a non-parametric Kruskall-Wallis (K-W) variance and median test. Statistical analysis was performed at the significance level equal 0.05. The test K-W is a non-parametric test (equivalent to analysis of variance in a single classification) and the test is weaker than the parametric test. This test does not require the assumption of a normal distribution of the sample. Therefore, this test can be used in any environment, however, so as to detect the differences between the characteristics, it requires a long series of observations [4].

STUDY AND DISCUSSION OF RESULTS

The impact of relief and land use is presented on the basis of selected daily courses of air temperature during spring, summer, autumn and winter (Figs 2–5). These figures indicate clear differences between individual weather stations. However, it should be pointed out that only during summer does the Kruskall-Wallis test confirm a statistically significant impact of relief and land use on the course of temperature for the following land types: western slope, meadow, cultivated land and forest. The calculated probabilities ranged from 0.027 to 0.028.

There is no indication of statistically significant differences in the daily course of air temperature between individual weather stations. The calculated probability equaled 0.681 in spring, whilst in autumn it ranged between 0.205 and 0.727. It should be noted that the lowest probability was encountered when the air temperature distribution between upland and valley was compared (0.205). The highest probability was attained during winter months (0.998). Statistical analyses which were performed lead to the conclusion that both relief and land use show no indication of statistically significant impact on the variability of courses of air temperature during autumn, winter and spring. Nevertheless, during spring months, along with increasing solar radiation and development of vegetation there is a marked impact of relief and land use on thermal conditions. This is especially visible when the maximum temperature and temperature amplitudes are examined.

Between 1st May and 3rd May 2007 there was a brief and strong incursion of arctic air from the Scandinavian Peninsula, which was associated with a high-pressure system situation. During that time frequent frosts occurred, which created hazards for cultivated plants that were entering an early phase of vegetation. These frosts were also hazardous for the blooming of fruit orchards.

Figure 2 presents the course of air temperature during spring months. There is a clear indication of large variability of extreme temperatures. The highest maximum temperatures as well as temperature amplitudes occurred in the valley (Tab. 1). The lowest minimum temperatures (below -4.8°C) were noted in the valley, while the highest were noted in the forest. Wide spread frosts which occurred for 4 nights in a row in nearly every part of Poland, caused severe damage to fruit orchards (it should be noted that this coincided with the period of apple blossoming). Fruit orchards situated in valleys were most susceptible to freezing of blossoms. It should be added that valley terrain is favorable for the occurrence of temperature inversions and frost hollows.

Figures 2 and 3 indicate a clear variability of thermal conditions during afternoon hours on both the slopes and upland terrain. The aforementioned weather stations are characterized by slightly lower temperature amplitudes compared with valley forms (Tab. 1). The analyses of the temperature plot during spring months confirm that the valley forms are the most susceptible to highest temperature variability and temperature inversions. During summer the variability of mean temperatures and daily temperature amplitudes was higher than in any other season. During summer daily temperature amplitudes were the highest in the valley. It should be noted that they were clearly higher than in winter and autumn (Figs 3–5). Nocturnal decline of temperature was marked especially in the valley. It should be added that temperature declines lasted the longest at this station and similarly to spring a temperature inversion occurred. The temperature distribution on the slopes and the upland (covered with grassy vegetation) showed many similarities. Whereas, the forest area dominated by deciduous forest stand was characterized by lower temperature amplitudes throughout the entire year. It should be added that forest stand acted as a sort of protective umbrella, which decreased insulation during the day while decreasing heat radiation during the night (Figs 2–5).

During autumn and winter relief and land use have no statistically significant impact on the differences in the daily course of air temperature between individual weather stations. In the aforementioned seasons considerably higher day to day temperature variability is indicated compared with the warm period (Figs 4, 5). On the other hand in autumn and winter a slightly lower variability of mean and extreme temperatures was observed in comparison with summer and spring. It should be added that at individual weather stations temperature differences did not exceed 1°C (Tab. 1).

The climatological research which was performed and verified with the Kruskall-Wallis statistical test indicates that both relief and land use pose the greatest impact on thermal conditions during the summer period. The above-mentioned factors reveal a strong association with daily temperature amplitudes. In the valley the temperature amplitudes were slightly higher than on the slopes and the hilltop, whilst grassy surfaces on the southern slope and the hilltop were characterized by lower temperature amplitudes compared with the western slope and the valley. The western slope was the warmest during afternoon and early evening hours (Figs 2–5, Tab. 1).

The weather station located in the valley has distinctly more severe thermal conditions compared with the hilltop and slope stations. This fact is of great importance for an agricultural region, specifically when we consider the selection of plants that are particularly susceptible to fluctuating thermal conditions. During spring months a significant hazard for cultivated plants is the occurrence of thermal inversions, when very frequently night temperatures fall below freezing (Fig. 2). The occurrence of thermal inversions is a typical feature in mountainous terrain, especially during the period of negative radiation balance [1, 5, 12]. It is not recommended to establish fruit orchards and cultivate staple vegetables in valley basins since there exists a considerable threat that plants will freeze and sustain damage.

The results of this research have been confirmed by other studies performed in mountainous regions in southern Poland as well as in the Eastern Carpathians, which are situated in Ukraine [7, 8]. The role of relief and land use in shaping local climate is emphasized in many national and international scientific papers. Some scholars emphasize the impact of surface properties on the exchange of energy via radiation [1, 5, 12]. Others point out that the surface layer especially during summer months has an impact on differences in thermal conditions between forest habitats, grassy areas and built-up terrain [2, 5]. Yoshino [13] emphasizes the fact that relief conditions and incoming solar radiation affect local circulation. The research of the above-mentioned authors corresponds with the results presented in this work.

CONCLUDING REMARKS

Statistically significant impact of relief and land use on the variability of  the daily course of air temperature has been confirmed for all weather stations during summer months. The results of this research indicate that the most favorable thermal areas for cultivation plants in the upland region under observation are the slope sites (southern and western) and the hilltop area. Meanwhile the valley has slightly less favorable conditions especially for vegetable crops and orchards due to the frequent occurrence of temperature inversions. It should be noted that temperature inversions are closely associated with ground frosts, which are very hazardous for plants especially in the early vegetation phase.

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.