Favorability Level Analysis of the Sevastopol Region’s Climate for Viticulture

Abstract

The harvest and quality of vineyards are determined by the climatic conditions of the region. Viticulture is a promising avenue in the agricultural sector of the Sevastopol region. In this study, we provide a comprehensive analysis of the orographic and climatic conditions and microclimate zoning to optimize the placement of vineyards. Meteorological data (air temperature and precipitation) for the period 1985–2018 were used to assess heat and hydration conditions and to calculate agroclimatic indices for a comprehensive evaluation of the effects of the observed climate change on viticulture. The observed upward trends in heliothermic indices and downward trends in precipitation change the conditions and cause a shift in grape-suitable zones. Based on heat supply and frost resistance, microclimatic zoning of the territory was carried out and 13 ecotopes were identified, for each of the grape varieties that were recommended. Our study indicates that the agroclimatic conditions of the Sevastopol region make it possible to grow grape varieties from very early to late ripening.

1. Introduction

The climate plays an important role in the cultivation of grapes and the quality of wine. Grapes (Vítis vinífera L.) are traditionally grown in geographical regions where the average temperature during the growing season (April to September/October for the northern hemisphere) is between 12 °C and 22 °C [1]. The regional climate is an important factor that affects the physiological development of grapes [2], the vegetative growth [3], the phenology [4], the production and thus the quality of wine. Climate dictates the geographical location of vineyards and determines the yield and quality of grape plantations, the orientation, as well as the specifics of agricultural technology and reclamation [5,6]. Variations in weather (air temperature, solar radiation and precipitation) alter productivity. Extreme weather such as hail, freezing or excessive precipitation influences the yield of grapes [7].

Given that vineyards are climate-sensitive, the rising average surface air temperature that has been observed in many regions of the world since the second half of the 20th century [8,9] has likely affected the production of wine. Climate change effects on the production and quality of wine have been studied across Europe [1,10,11,12,13,14], Australia [15,16], North and South America [17,18,19], etc. An investigation [3] of climate, soil and grape variety effects on the quality of wine in Bordeaux (France) had shown that climate is the dominant factor accounting for over 50% of variations when averaged for all the quality parameters. Higher temperatures during the ripening of fruits and berries result in a higher sugar content and lower acidity, which increases the risk of wine spoiling [20] while also producing smaller and lower-weight berries [21].

The projected climate change is expected to have a mostly negative impact on grape and wine production. Cardell et al. [13], Moriondo et al. [22] and Toth and Vegvari [23] predict that winegrowing regions in Europe will shift northward by the mid- or late-21st century due to the upcoming increase in total thermal stress and droughts during growing seasons. Webb et al. [24] for some regions in the Northern and Southern Hemispheres predict significant changes in the distribution of grape production in the specified regions: projections indicating a wetter climate in higher latitude regions (such as the Chinese region, New Zealand, North Oregon), while drier climate conditions are expected in Southern European, South African and Australian regions. The future climate conditions will lead to changes in the structure of the cultivation varieties in Hungary at the end of the century [25]. At the same time, climate changes by the end of the 21st century will prevent Scotland from introducing commercial wine grape production [26].

The natural and climatic conditions of the Sevastopol region determined the priority directions for the development of agriculture—viticulture and winemaking. Sevastopol is the oldest wine-growing region in Russia, the history of viticulture and winemaking here is about 2500 years old. In this regard, agricultural enterprises in the region specialize in the cultivation of grapes, as well as in primary and secondary winemaking. Large wineries are located in the region. Vintage wines produced by the agro-industrial association “Inkerman Vintage Wines Factory” and sparkling wines from the agricultural firm “Zolotaya Balka” and the State Unitary Enterprise Agroindustrial Association “Sevastopol winery” are well known outside the Crimean Peninsula. Wine tourism is developing in Crimea and Sevastopol [27,28]. Investigating how vineyards react to agroclimatic factors and their change in spacetime is of importance for basic science as well as for the applied science of production improvement [29,30]. Sevastopol region’s terroirs feature a different agroclimatic potential, which, along with the variety-specific features, must be borne in mind when planting, even within neighboring areas.

Given the aforementioned climate effects on this plant, it becomes imperative to plan and implement appropriate measures to adapt it to the climate and to mitigate the negative climate impact on wine production. Long-term adaptations to climate change include switching to new varieties and placing vineyards in optimal environmental conditions best suited to utilize the genetic capabilities of each variety. Failure to follow this principle increases yield loss, results in a greater share of substandard product, leads to frosts and diseases damaging the plantings and influences the longevity and productivity of the plants.

The goal hereof is: (1) to comprehensively analyze the orographic and climatic conditions of the Sevastopol region to optimize the placement of vineyards; and (2) to map the microclimate zones in the area, i.e., to perform microclimate zoning.

2. Materials and Methods

2.1. Description of the Region

The region is located in the southwest of the Crimean Peninsula (33°22′–33°54′ E, 44°22′–44°54′ N) (Figure 1). The climate of the region is close to the subtropical climate of the southern coast of Crimea. The region can be divided into two microclimatic subzones: the foothills with a mild marine and moderately continental climate and the south-western coast with its subtropical Mediterranean climate. Towards the southeast, foothill towns become more mountain-like in climate. The total area of agricultural land in the Sevastopol region is about 21 thousand hectares. The agricultural enterprises use more than 5.0 thousand hectares under fruiting perennial plantations (4.3 thousand hectares of vineyards and about 800 hectares of orchards), and 947 hectares of agricultural land is used for growing cereals, legumes and fodder crops. Natural and climatic conditions do not allow grain crops to acquire the properties of food grain [27,28]. The overwhelming share of vineyards is over 25 years old, is highly sparse and requires replacement. The following grape varieties are cultivated in the region: Cabernet Sauvignon, Merlot, Pinot Noir, Aligote and Rkatsiteli, among others. The Socioeconomic Development Strategy of the City of Sevastopol has a scenario that stipulates increasing the area of cultivated vineyards and gardens to 10 thousand hectares by 2030 [31]. There are 17 business entities, three major wineries, primary winemakers, as well as households producing proprietor’s wines in the region. In 2018, the gross harvest of grapes in the Sevastopol region totaled 19.11 thousand tons.

2.2. Research Methods

Meteorological data (air temperature and precipitation) for the period 1985–2018 were taken from the weather station in Sevastopol (44.62 N, 33.53 E). The research materials were: a vector map of the Crimean Peninsula with administrative divisions, the SRTM-3 digital elevation model and the Worldclim 2.0 climate model. The spatial distribution of heat supply was simulated using the Sofroni–Entenzon formula adjusted for the Crimean Peninsula [32]. The spatial variation of the local frost susceptibility was calculated using the author-developed mathematical model [33]. The model utilizes the following parameters: absolute altitude above the sea level for the weather station, relative altitude, aspect and steepness of the slope, distance to the sea and geographical latitude. The models were tested on the territory of the entire Crimean Peninsula using data from 15 weather stations. The model calculates the difference in variables between a location with a known indicator level and the analyzed location based on their differences in relief and other specified parameters.

For a comprehensive evaluation of the effects of observed climate change on viticulture, the authors used special agroclimatic indices recommended by the International Organization of Vine and Wine [34]:

(a)

The Huglin index (HI), a heliothermic index that takes into account daily average and maximum temperatures from April to September. It has a factor that provides adjustment for latitude-dependent daylight hours (40 to 50 degrees N) [35];

(b)

The Winkler index calculated for the grape growing season based on the daily minima and maxima of the temperature, where one degree-day equals an excess of 10 °C over the daily average temperature [36].

These indices describe the accumulation of heat (degree-day indices) and are commonly used in zoning research as well as to determine the suitability of a region for the cultivation of certain varieties [18]. The cool night index (CI) was also calculated. The CI is used to improve the assessment of the qualitative potentials of wine-growing regions [37]. The index is calculated as the minimum air temperature in the month of September (mean of minima) in the Northern Hemisphere [38]. To assess the hydration condition, the authors applied the Selyaninov hydrothermal coefficient (HTC), which describes local access to moisture [14,39]. The spatial distribution of these indices was simulated using the authors’ formulas that had been tested for the Crimean Peninsula and proven reliable [40]. To validate the model, based on data from one of the Crimean meteorological stations, the values of the analyzed indicator were calculated for the locations of the other 14 meteorological stations in the Crimean Peninsula. The calculated data were compared with the actual data. ArcGIS was used for the geoinformation modeling of the spatial and temporal variation of the climate, as well as to visualize the results. The spatial resolution of maps is 80 m. The trends slope estimation and its statistical significance (Students t-test) were performed in XLSTAT.

3. Results and Discussion

3.1. Orographic and Climate Conditions of the Region

GIS technology produced a 3D digital elevation model of the Sevastopol region. Electronic raster maps based on that model were made to show the distribution of the altitude, aspect and steepness of slopes (see Figure 1). The region has diverse terrain. It is a small area that has nearly all kinds of terrain, from plains to mountains. There are seaside plains and areas with strongly dissected relief.

Most of the area (60%) was found to have an altitude of 0 to 200 m (Figure 1). The Sevastopol region mainly slopes towards northwest and west. A total of 50.7% of the area is warm slopes, and 48.1% is cold slopes. The north, center and south of the area are dominated by a southwestern aspect. Most of the area (80%) has a slope of 0 to 12 degrees. All of these call for a very responsible attitude to vineyard placement, as these conditions have a significant impact on whether grapevines will be able to grow, on the vineyard layout and on the industrial specialization. Being complex and diverse, the terrain causes the substantial territorial variation of the agroclimatic resources.

The average annual air temperature of the Sevastopol region was 11.1 °C over the studied period (1985–2018). The average air temperature shows a positive statistically significant trend (p < 0.01), as it grows by 0.5 °C/10 years. The air temperature averaged 17.7 °C over the growing season (April to September), which classifies the region as “warm” [41,42]. Climate variables for the whole year and growing season for the studied period are presented in

Table 1. Climate variables for the Sevastopol region (1985–2018).

Variables	Value (Units)	Trend (Significance)
Average annual air temperature	11.1 °C	+0.5 °C/10 years (p < 0.01)
Average temperature for the growing season	17.7 °C	+0.5 °C/10 years (p < 0.01)
Maximum air temperature for the growing season	23.0 °C	+0.09 °C/10 years
Minimum air temperature for the growing season	13.1 °C	+0.9 °C/10 years (p < 0.01)
Average annual precipitation amount	445 mm	−26 mm/10 years
Precipitation amount for the growing season	198 mm	−25 mm/10 years (p < 0.05)

.

Patterns of the spatial distribution of heat supply in the region were studied in the context of agricultural and environmental factors: absolute altitude, slope aspect and steepness, geographical latitude and solar altitude at apparent noon. Based on the influence of these factors and taking into account the morphometric features of the relief, a digital large-scale cartographic model of the spatial distribution of the sum of active air temperatures above 10 °С was created [29]. According to the obtained data, the Sevastopol region has six zones of heat supply based on the gradation of how much heat different grape varieties need (see Figure 2). More than half of the region is in a zone where the sum of active air temperatures is 3500 to 3900 °C. This makes the area suitable for growing varieties of very early to very late ripening. The fact opens up great opportunities for the placement of grapes of different variety groups on the plains and slopes. In the foothills, the available heat drops to 2000 °C.

Besides the heat requirement of a variety, one should bear in mind its frost resistance and frost susceptibilities [43]. Grapes can survive temperatures down to −15 to −20 °C at rest [44]. Most of the Sevastopol region (72%) has an average absolute minimum above −14°C. The metric drops to −19 °C towards the Crimean Mountains.

Precipitation is an important meteorological factor for growing grapes: insufficient or excessive soil hydration may influence the grapevine, and thus the quality of wine [45,46,47]. Total April-to-September precipitation of 250–350 mm is believed to be optimal for producing high-quality berries [48]. Calculations show that the region has insufficient precipitation during the growing season, although it increases towards southeast, e.g., to the Crimean Mountains. Growing-season precipitation averaged 198 mm in 1985–2018 with a downward trend of −25 mm/10 years (p < 0.05).

3.2. Agroclimatic Indices

Table 2. Agroclimatic indices obtained for the Sevastopol region (1985–2018).

Index (Units)	Class Limits			Area (ha)	Area (%)
Selyaninov hydrothermal coefficient (HTC)	<0.6			37,858	43.9
	0.6–0.7			23,285	27
	0.7–0.8		insufficient hydration	11,909	13.8
	0.8–0.9			6352	7.4
	0.9–1.0			3435	4
	>1.0		normal hydration	3334	3.9
Huglin index (HI, °C)	<1200		Too cool	0.6	0
	1200–1500		Very cool	28	0.03
	1500–1800		Cool	453	0.52
	1800–2100		Temperate	2690	3.08
	2100–2400		Warm temperate	12,962	14.85
	2400–2700		Warm	63,017	72.18
	2700–3000		Very warm	7155	8.19
	>3000		Too hot	1005	1.15
Winkler index (WI, °C)	<850		Too cool	16	0.02
	850–1389		Region 1	5357	6.14
	1389–1667		Region 2	21,886	25.07
	1667–1944		Region 3	57,503	65.86
	1944–2222		Region 4	2418	2.77
	2222–2700		Region 5	130	0.15
	>2700		Too hot	0	0

and Figure 3 show the calculated agroclimatic indices for the Sevastopol region. The calculations apply to the growing season (April through September).

The Selyaninov hydrothermal coefficient sets the threshold of soil hydration that a vine will need to grow, especially in the warm season. Over 70% of the Sevastopol region has an HTC below 0.7 (see Figure 3a), i.e., has insufficient hydration. A total of 25% of the region has HTC values of 0.7 to 1. Only 4% of the area is hydrated enough.

The Huglin index (HI) summarizes the thermal and insolation potential of an area from the standpoints of the ripening of different grape varieties [35]. Calculated for 1985–2018, the HI shows that 80% of the area is warm (HI = 2400–2700 °C) (see Figure 3b). This warm climate (HI+2) has the potential to exceed the heliothermic requirements of varieties, even if these are late-ripening varieties, which carries a risk of stress [49]. Nearly 15% of the region is moderately warm (HI+1, 2100 to 2400 °C), making it unconditionally suitable for the cultivated varieties.

The Winkler index (WI) provides information about the accumulation of heat during the growing season [11]. As for the Winkler index (WI), two-thirds of the region is a Region 3 area ranging from 1667 to 1944 °C (see Figure 3c). The highlands (25% of the area) are Region 2, WI = 1390–1670 °C.

The cool night index (CI) provides additional information on thermal conditions, especially during the ripening period of grapes [37]. The average value of the CI for the period 1985–2018 is 12.7 °C. This is in the CI+1 “cool nights” viticultural climate class.

The regional average series of the sum of active air temperatures, Winkler and Huglin indices for the period 1985–2018 were used for the trends assessment. The indices show positive statistically significant (p < 0.01) trends over the years. The trends vary from 125 °C/10 years for WI to 165 °C/10 years for the sum of active air temperatures. The trends we have identified are also confirmed by the results of other researchers, for instance, in the Mediterranean region [50,51]. The CI trend is positive and statistically significant (1.1 °C/10 years).

3.3. Microclimate Zoning

The detailed analysis of the spatial variation of heat supply and frost susceptibility produced a comprehensive microclimatic map of the region (see Figure 4).

In this map, the Sevastopol region is split into 13 microclimate zones (ecotopes) applicable to grapes (see

Table 3. Ecotopes of the Sevastopol region in relation to grape culture.

Ecotope No.	Average Absolute Minimum, °C	Sum of Active Air Temperatures Above 10 °C	Ecotope Area
			ha	%
1	>−15	>3900	5111	5.855
2	>−15	3500–3900	48,437	55.492
3	>−15	3100–3500	17,409	19.945
4	>−15	2700–3100	5866	6.720
5	−17.5–−15	3500–3900	1714	1.964
6	−17.5–−15	3100–3500	4008	4.592
7	−17.5–−15	2700–3100	1552	1.778
8	−17.5–−15	2300–2700	2170	2.486
9	−20–−17.5	3500–3900	3	0.003
10	−20–−17.5	3100–3500	54	0.062
11	−20–−17.5	2700–3100	165	0.189
12	−20–−17.5	2300–2700	184	0.211
13	<−20	<2700	614	0.703

). Recommendations were made on which varieties to pick for each of the ecotopes. The target was to guarantee high-quality grape yields at least 8–9 years per decade (see

Table 4. Recommended varieties for the isolated ecotopes of the Sevastopol region.

Ecotope No.	Recommended Grape Varieties
	In Terms of Frost Resistance	In Terms of Ripening Time
1	low, medium and high frost resistance	very early to late
2	low, medium and high frost resistance	very early to medium-late
3	low, medium and high frost resistance	very early to mid-season
4	low, medium and high frost resistance	very early to early
5	low and high frost resistance	very early to medium-late
6	low and high frost resistance	very early to mid-season
7	low and high frost resistance	very early to early
8	low and high frost resistance	very early
9	high frost resistance	very early to medium-late
10	high frost resistance	very early to mid-season
11	high frost resistance	very early to early
12	high frost resistance	very early
13	not recommendable

).

According to the zoning results, the most favorable grape farming conditions (heat supply and frost susceptibility) are in Ecotopes 1 to 4, which account for the bulk (88%) of the studied area. The described ecotopes occupy the north and the west of the region, the Baydar Valley and the south coast. These areas are suitable for farming varieties of low, medium and high frost resistance that ripen very early, early, mid-season or late.

Ecotopes 5 to 8 occupy some 11% of the Sevastopol region. These feature average absolute minima from −17.5 to −20 °C and are recommendable for growing grapes of medium to high frost resistance, ripening very early to mid-season. These ecotopes are located in the northeast of the region as well as in the foothills in small inclusions.

Ecotopes 9 to 12 are in the foothills at 500–600 m or higher above sea level. These account for no more than 0.5% of the region’s total area. They are suitable for cultivating highly resistant varieties. Ecotope 13 is not recommendable for industrial grape farming due to unfavorable temperatures with its average absolute minimum below −20 °C and the lack of heat supply.

Thus, the Sevastopol region’s complex terrain coupled with the sea’s influence on the adjacent areas makes for diverse agroclimatic resources in this part of the Crimean Peninsula. With respect to grape farming, there are areas suitable even for non-resistant varieties; however, some areas have such low negative temperatures in winter that open-earth viticulture is not even possible. Heat supply varies broadly, too. The northwest is suitable for varieties that ripen very early to late; at the same time, the sum of active air temperatures in the southeast does not always suffice for stable yearly ripening of even the earliest varieties.

4. Conclusions

Viticulture and winemaking are a specialization of the agricultural sector of the Sevastopol region. The Sevastopol region’s climate and terrain make the area suitable for producing a wide assortment of high-quality wines, which might potentially enable the region to become a world-class winery. More than 4 thousand hectares are planted with vineyards, but most of them require replacement. Grape varieties such as Cabernet Sauvignon, Merlot, Pinot Noir, Aligote and Rkatsiteli, among others, are grown in the region. Varietal selection and locations of vineyards must be carried out taking into account climatic conditions and their changes observed in recent decades.

This paper analyzes the climate conditions of the Sevastopol region using the agroclimatic indices for 1985–2018. Using GIS technologies, the authors have mapped the agroclimatic index distribution with a high spatial resolution. Analysis of heat supply and agroclimatic indices shows that grape varieties can be grown here that ripen very early to late. The observed upward trends in heliothermic indices and downward trends in precipitation alter the conditions and cause a shift in grape-suitable zones. Frost susceptibility and heat supply data were used to perform microclimate zoning of the region. These identified thirteen ecotopes whose agroclimatic conditions are described herein with a list of optimal grape varieties. The most favorable agricultural climate is observed in Ecotopes 1 to 4.

The analysis of the agricultural and ecological resources of the Sevastopol region enables the most optimal placement of vineyards so that the agricultural and ecological conditions of a specific plot suit the biological requirements of the farmed grape varieties. This will produce greater yields of better quality while boosting the winemaking industry without a need for substantial further investment.