Assessment of the aridity index of various agro-climatic regions of the Republic of Azerbaijan

. The issue of updating information about the aridity index AI for various agro-climatic regions of the Republic of Azerbaijan is considered in the article. It has been found out that the irrigated lands are mainly concentrated in arid zones with an aridity (hydrothermal) index AI = 1.3...3.0 (for soils with different degrees of salinity and with different intensity of erosion processes). The humidity (water) deficit D is on average 199...800 mm. It is noted that the obtaining of guaranteed yields of agricultural crops is possible with reclamation measures only. The maps-schemes of agro-climatic regions and aridity index zoning of the Republic of Azerbaijan are presented in the article.


Introduction
Based on the analysis of long-term data  for various regions of the Republic of Azerbaijan, it was found that on reclaimed lands during the growing season the depth of groundwater varies within 1.5...2.0 m.The active influence of groundwater in plant nutrition forms semi-hydro-morphic and hydromorphic regimes on irrigation lands in the regions of the Republic of Azerbaijan taking into account the soil properties (granulometric composition, degree of drainage, capillary rise, etc.) [1,2].The adjustment of irrigation norms of water is very important for agricultural practice against the background of these regimes.
According to the UN classification, the Republic of Azerbaijan belongs to the countries experiencing shortage of water.The future balance of the republic's water resources will be affected by the intensive melting of glaciers, which forms the main rivers of the region, and other aspects of climate change, as well as the growing water needs of the population and the growth of irrigated lands.The climate changes such as an increase of the average temperature of the environment, especially during hot periods of the year, increases in the frequency of low-water years and other natural phenomena are the main challenges today for this region.It is assumed that the reduction of water availability by 10...20% can have serious consequences for the size of irrigated areas and employment of the population, and will lead to a decrease in gross national income.The creation of conditions to meet the effective management and use of water resources, the reclamation condition of irrigated lands and food security in conditions of increasing water scarcity, as well as global climate change are the determining factors of optimal life of this region.
The purpose of this research was to update information about the hydrothermal conditions of the irrigated zones of the Republic of Azerbaijan.
The climatic conditions vary over the years significantly, therefore the irrigation regimes of plants will be different in different years.Zonal heat and moisture availability can be estimated by averaged annual indicators of the radiation balance R and the sum of atmospheric precipitation P at the same time [3].It should be noted that the aridity index AI is used by many researchers and practitioners to assess the conditions for obtaining the required yield in rain-fed and irrigated conditions.Mohammad Bannayan and et al [4] established a relationship between climate indices, the aridity index AI and the yield of rainfed crops in northeastern Iran.The authors note that there is a correlation between hydrothermal coefficients AI and the yield of barley and wheat.Fahime Mohamadzade and et al [5] note that crop yields in arid and semiarid areas directly depend on irrigation to ensure efficient economic production and food security.
It should also be noted that the aridity index AI can be determined by various methods each of which is characterized by its own range of reference values.For example, there are De Martonne aridity index [6,8], Pinna combinative index [6] (depending on the amount of precipitation and air temperature), Thornthwaite's index [8].It is widely known and is used the Food and Agriculture Organization aridity index (IFAO) also [7].
The aridity index AI has become widely used in climate studies [9,10,11].Such studies help to assess the possible level of water deficit.Such studies are the basis for the development of projects to improve the efficiency of agricultural production too.The aridity index AI is one of the indicators for localization of water scarcity regions as well.

Research methodology
Hydrometeorological parameters necessary in reclamation practice to adjust and optimize irrigation norms (or irrigation regimes) in order to assess the needs of soil formation and soil reclamation conditions are used to determine the hydrothermal coefficient or aridiry index AI according to the dependence of M.I.Budyko [3,12]: where: L -the latent heat of vaporization, kJ/cm 3 per year; R -radiation balance of the water surface, kJ/cm 2 per year; P -the amount of precipitation per year, mm.
In assessing the process of soil formation, one of the most important factors is the amount of solar energy spent on soil formation.Based on long-term data radiation balance of the water surface R for the conditions of the Republic of Azerbaijan is about 168…240 kJ/cm 2 or 40…61 kcal/cm 2 .In this study based on the actual values of evaporation and precipitation the radiation balance index R (kJ/cm 2 ) is determined by the formula of M.I.Budyko and B.K. Davydova: R = 0.58P 0.26 E0 0.74 , (2) where: Е0 -total evaporation, mm.
The latent heat of vaporization L (kJ/cm 3 ) is calculated according to the following dependence: It is known that soil types and their properties are subject to hydrothermal zonality.According to the degree of balance of thermal and water resources, several zones are distinguished.It is known that the value of the index AI = 0.9 ...1.4 is characteristic of the zone of sufficient and unstable humidification.The balance of heat and moisture creates the best conditions for soil formation.Plowing of soils increases their radiation balance by R = (0.15…0.25)R.Therefore, the additional moistening of soils is necessary to restore the balance of heat and moisture.
The soil characteristics in this study were carried out according to the soil map of the Republic of Azerbaijan (1991, the Main Directorate of Geodesy and Cartography under the Council of Ministers of the USSR).
For calculations, data of meteorological conditions with a retrospective of 15 years (2007-2022) were used.

Results of research
The results of the studies are shown in Table 1 and in Figures 1 and 2. The soils of areas with AI = 1.0 are rich in humus, have a sufficiently high content of silty fraction, due to which they have a high degree of cation exchange capacity (CECe) and a waterproof structure.Soils of areas with AI = 2.0 have low fertility, evaporation far exceeds the amount of precipitation during the growing season in this zone, biological yield decreases in conditions of moisture deficiency, organic residues of agricultural crops are rapidly mineralized (with resulting in a shortage of humus), and CECe decreases.The soils of subtropical zones with AI = 0.8 are characterized by deterioration of soil properties due to intensive leaching of mineral and organic compounds despite the high biological yield.The Absheron-Gobuastan climatic region is characterized by the values of the hydrothermal index AI = 4.2.This indicates an acute shortage of humidity in this zone.The zone is mainly represented by gray soils and chestnut soils.There are degraded soils with oil pollution and mining.In the southern part of the region there are solonetz, salt marshes and eroded soils.There are sands on the coast.The main irrigated area is located east of Baku.The Northeastern slope of the Greater Caucasus (AI = 1.3...2.0), Kura-Araks (AI = 2.9) and Nakhchivan (AI = 2.9...3.0) are agro-climatic regions which characterized by aridity index values in the range AI = 1.4...3.0.This also indicates a high humidity deficit.The soils of the North-Eastern slope of the Greater Caucasus are represented by mountain-forest, closer to the coast by irrigated heavy loamy chestnut meadow soils.
Most of the irrigated soils of the Kura-Araks agro-climatic region are located in its central part (south of the Mingechaur reservoir).Basically, the soils have a medium-loamy granulometric composition and are represented by chestnut (including weak and mediumsaline), gray soils and meadow soils.Closer to the coast of the Caspian Sea there are sands and meadow-swamp soils.In the northern part of the agro-climatic region there are irrigated slightly eroded heavy loamy meadow soils.Meadow and gray-earth soils of varying degrees of salinity are located on the irrigated areas of the Nakhichevan agro-climatic region.The zones of the Lesser Caucasus are characterized by sufficient and unstable moisture (AI = 1.1...1.2) with mountainous brown, yellow-earth and brown soils.There are no irrigated lands.The Talysh agro-climatic region is characterized by AI = 0.7...1.6(sufficient and unstable moisture).Irrigated lands are located on podzolic yellow soils.The southern slope of the Greater Caucasus is characterized as humid with AI = 0.7...0.9.Soils are represented by mountain-meadow heavy loamy eroded types.There are no irrigated lands.
In most agro-climatic regions of the Republic of Azerbaijan the amount of evaporating moisture exceeds the precipitation that falls during the growing season, therefore the main reclamation measures should be aimed at restoring, preserving and rational use of moisture.This is typical for the Kura-Araks, the northeastern slope of the Greater Caucasus, the Absheron-Gobustan, the Lesser Caucasus and the Nakhchivan agro-climatic regions.These zones are characterized by a moisture deficit of about 50...800 mm on average.In the zone of the Southern slope of the Greater Caucasus, there is an excess of moisture according to observations and averages 50...350 mm.It is humid zone with AI < 0.9.According to separate data for the Talysh agro-climatic region, a moisture deficit at the level of 330 mm and an excess of humidity up to 448 mm is also possible.This area is characterized by a type of climate with relatively excessive moisture.Precipitation in the growing season exceeds evaporation and therefore, reclamation measures consist in saving and economical use of moisture.Irrigation norms are calculated taking into account the mineralization and depth of groundwater.Table 2 shows data on the humidity deficits D.

Conclusions
As a result of this research the values of aridity index AI (hydrothermal coefficients) were calculated and the information of the agro-climatic zoning of the Republic of Azerbaijan was updated.It was found that irrigated lands are mainly concentrated in arid zones with an aridity index AI = 1.3...3.0 (for soils with different degrees of salinity and with different intensity of erosion processes).The humidity deficit D is on average 199...800 mm.This indicates that obtaining of guaranteed yields of agricultural crops is possible with reclamation measures only.

Fig. 1 .
Fig. 1.Agro-climatic regions of the Republic of Azerbaijan: and 1 -Kura-Araks; -the Greater Caucasus; 2 -northeastern slope of the Greater Caucasus; 3 -the southern slope of the Greater Caucasus; 4 -Absheron-Gobuastan; -Lesser Caucasus; 5 -the northern slope of the Lesser Caucasus; 6 -the lower slope of the Lesser Caucasus; 7 -the eastern slope of the Lesser Caucasus; and 8 -Talysh; and 9 -Nakhchivan; -the state border of Azerbaijan; -boundaries of agro-climatic regions

Table 1 .
The hydrometric parameters of agro-climatic regions of the Republic of Azerbaijan.

Table 2 .
Humidity deficits D of various agro-climatic regions of the Republic of Azerbaijan.