Changes in the Agroclimatic Areas of Slovakia in 1961–2020

The World Meteorological Organisation predicts an increase in average annual temperature. As a result of climate change in Slovakia, one can expect changes in the distribution of precipitation and moisture availability, changes in the temperature availability of crop production, changes in wintering conditions


INTRODUCTION
The last eight years (2016-2022) were globally the warmest in the history of measurements. It was conditioned by constantly increasing concentrations of greenhouse gases as well as heat accumulated in the atmosphere and oceans (Markovič, 2023). The World Meteorological Organisation (WMO) predicts an increase in average annual temperature of between 1.1 °C and 1.7 °C (compared to the 1850-1900 average) for each of the years 2022-2026. The probability that at least one year in this period will be 1.5 °C warmer is 48%. Also, the probability that the five-year average (2022-2026) will be warmer than the last five years (2017-2021) is 93% (WMO, 2022a; Magde, 2022). The temperatures on the European continent have doubled compared to global temperatures over the last 30 years, the highest of any continent in the world. On average, this represents an increase of +0.5 °C per decade (WMO, 2022b). In Slovakia, the average annual temperature is rising about twice as fast as at the global level. Since the mid-20th century, the average annual air temperature has increased by about 2.0 °C. Over the next 15 to 20 years (to 2040), it is expected that air temperatures increase by 1.0-1.5 °C compared to the 1991-2020 climate normal. This means an even more extreme climate and weather pattern, greater and more widespread impacts due to more extreme droughts, heavier rainfall and storms, and the adverse impacts of high temperatures on population health, especially in summer, will become more pronounced (Pecho, Markovič, 2022).
Climate impacts are most extensive in natural ecosystems. As a result of climate change in Slovakia, one can expect, for example, changes in the distribution of precipitation and moisture availability, changes in the temperature availability of crop production, changes in phenological conditions, changes in agroclimatic production potential, changes in wintering conditions, prolongation of the main growing season, and many others (Horák, 2017).
Agriculture, land reclamation and water management are placing increasing demands on the precise characteristics of the environments in which the interests of their activities are concentrated. Such characteristics include studies describing landscape -agroclimatic studies (Šiška et al., 2005).
The aim of this work is the analysis of agroclimatic indicators (temperature indicator, humidity indicator and wintering indicator) for the period 1961-1990 and 1991-2020 to determine the changes in agricultural production areas in Slovakia.

Study area
This study is focused on Slovakia. The country is situated in Central Europe (from 47° 44' 21'' up to 49° 36' 48'' of northern latitude and from 16° 50' 56'' up to 22° 33' 53'' of eastern longitude) with surface area 49,037 km 2 . The territory belongs to Alpine-

Growing season
Plant life is possible within a certain temperature range. The temperature range in which they can develop and grow depends on the individual plant species. Agricultural crops need certain amounts of temperature from sowing to harvesting, which is why the sum of active temperature has been implemented (Kurpelová et al., 1975). In order to determine the sum of active temperatures, it was necessary to calculate the onset and termination date of the main vegetation period (the period with the average daily temperature T d ≥ 10) for each meteorological station according to formulas (Šiška et al., 2005): • termination of temperatures: where: T n -onset temperature (°C); T u -termination temperature (°C); T 1 -the nearest average monthly temperature above the onset or termination of temp. (°C); Figure 1. Location of meteorological stations T 2 -the nearest average monthly temperature below the onset or termination of temp. (°C); R -the difference in days between the middle of the months with the average temperature T 2 and the average temperature T 1 , can be expressed as an average number R = 30; r v -difference in days between the middle of the month with temperature T 2 and the date of onset of temperature T n ; r p -difference in days between the middle of the month with temperature T 2 and the date of termination of temperature T u .

Agroclimatic indicators
The basic factor that differentiates agriculture in Slovakia is temperature. Temperature during the growing season is the dominant criterion for the formation of the basic agroclimatic macro-areas and areas. The second important factor is moisture. On the basis of the climatic indicator of moisture in the summer period, agroclimatic subareas are divided. For fruit trees and winter crops, winter temperatures are the limiting factor. The average of the annual absolute minima helps to distinguish agroclimatic districts (Kurpelová et al., 1975).
Agroclimatic indicator of temperature is defined as the sum of the average daily air temperatures over the main growing season bounded by the onset and termination of the average daily temperature T ≥ 10 °C (TS10). According to TS10, the highest territorial units in Slovakia have been allocated (Kurpelová et al., 1975 Agroclimatic indicator of moisture is given by the difference between potential evaporation (E O ) and precipitation (Z) in the summer months of June-August (K VI-VIII ). According to the climatic indicator K VI-VIII , seven subareas are divided in Slovakia (Kurpelová et al., 1975): 1) Very dry subarea with K VI-VIII ≥ 151 mm; 2) Mostly dry subarea with K VI-VIII 101 -150 mm; 3) Slightly dry subarea with K VI-VIII 51 -100 mm; 4) Slightly wet subarea with K VI-VIII 1 -50 mm; 5) Mostly wet subarea with K VI-VIII -50 -0 mm; 6) Wet subarea with K VI-VIII -100 --51 mm; 7) Very wet subarea with K VI-VIII ≤ -101 mm.

Data processing in GIS
The coordinates of the meteorological stations were uploaded into the Geographic Information System (GIS) program. The observed values of each agroclimatic indicator were assigned to the stations. From the point data, surface values were created by Raster Interpolation tool. Among several interpolation methods, the Topo to Raster tool was chosen. This interpolation method, developed by ESRI, is designed to generate hydrologically correct digital elevation models (DEMs). It is based on the ANUDEM program created by Michael Hutchinson in 1988 and it is optimised to have the computational efficiency of local interpolation methods, as Inverse Distance Weighted interpolation, without losing the surface continuity of global interpolation methods, as Kriging and Spline (Šinka et al., 2015;Igaz et al., 2021;ESRI, 2023). The resulting maps were categorised according to the Agroclimatic indicator of temperature, the Agroclimatic indicator of moisture as well as the Agroclimatic indicator of wintering for periods 1961-1990 and 1991-2020.

RESULTS AND DISCUSSION
When analysing the agroclimatic indicator of temperature (TS10), it can be clearly stated that the zonation of Slovakia has been significantly influenced primarily by the change in temperature regime. The individual analyses presented in Figures 2a and 2b clearly show a significant change in the warm macro-area (TS10 ≥ 2401 °C) in comparison with the years 1961-1990 and 1991-2020, where a shift of this macro-area to higher altitudes is presented. In turn, in 1961-1990 the agroclimatic warm macro-area was located solely in the Danube Lowland and Východoslovenská Lowland, for 1991-2020 this region shifts to the Danube Upland in the west of the country and the Východoslovenská Upland in the east of Slovakia. A similar scenario applies to the slightly warm macro-area (TS10 2001-2400 °C) and the cold macro-area (TS10 1600-2000 °C), where there is a significant shift to higher altitudes.
The agroclimatic indicator of moisture (K VI-VIII ) is also very important and characterises the excess or lack of moisture. Within this assessment ( Figures 3a and 3b), it can be noted that there are also changes in zones. In particular, the areas where the risk of drought is expected to increase (the very dry subarea -K VI-VIII ≥ 151 mm and the mostly dry subarea -K VI-VIII 150-100 mm) areas are increasing. These changes are in close context with increasing average temperature and with uneven distribution of rainfall. The methodology mentions that two climatic normals were compared in the analyses of the agroclimatic indicator of wintering. Specifically, the climatic normal for 1961-1990 and the climatic normal for 1991-2020. The presented map outputs clearly show that the agroclimatic region of mostly mild winter district (T min ≥ -18.1 °C) is shifting to higher altitudes, especially in the southern part of central Slovakia (Figures 4a and  4b). These shifts are noticeable throughout Slovakia. It is similar with the relatively mild winter district (T min -18.1 to -20.0 °C), the moderately cold winter district (T min -20.1 to -22.0 °C) and the mostly cold winter district (T min -22.1 to -24.0 °C). In these districts, over the last thirty-year normal period (1991-2020), mainly due to global warming, the zones have been shifting to higher altitudes throughout Slovakia. At the highest altitudes (areas not used for agricultural activities or in limited quantities), where is the mostly cold winter district (T min ≤ -24.0 °C), refers significant changes in absolute minima have been recorded (e.g., Oravská Lesná -T min -27. 2 °C in 1961-1990 and T min -24.7 °C in 1991-2020). However, these changes were not significantly reflected in the changes on zones of the area.
Increasing average temperatures in Slovakia leads to an earlier onset and later termination of  decade (Olszewski, Żmudzka, 2000). With higher temperatures, there is a visible increase in the number of hot days, what they claim in Montenegro (Burić et al., 2014) or in Serbia (Unkašević et al., 2013). Agricultural production is sensitive to high temperatures and lack of precipitation. In recent years, prolonged periods without rainfall alternating with extreme rainfall have become increasingly common, causing floods, destroying crops, and eroding agricultural land (USDA, 2013). Increasing temperatures also affect winters. In recent years in Slovakia, there has been almost no snow cover in winter in the southern regions. Also, Popov et al. (2017) in Bosnia and Herzegovina found from the analysis a decrease in frosty days since 1990.

CONCLUSIONS
Climate change affects everyday life around the world. In Europe, climate change is the most pronounced of all continents, which also affects agriculture the most. Therefore, the aim of this paper was the evaluation of agroclimatic indicators. The results showed a prolongation of the onset and termination of temperatures ≥ 10 °C, which also increased the sums of temperatures in the growing season. The increase in temperature affected the values of evaporation and precipitation, which resulted in a change in the zones of the agroclimatic indicator of moisture; There are higher temperatures, moderate winters and absolute minimum temperatures, which is seen especially in the southern regions of Slovakia. With climate change, it is necessary to change the strategy of agricultural production, and owing to such outputs, the options for agricultural producers can be proposed.