The article highlights the research results on the assessment of natural moisture supply in Ukraine, the state of water resources and agricultural production in the face of modern climate change taking into account the forecast for the medium and long term prospects. It was established that the rate of air temperature growth for the period of 1975-2019 in Ukraine ranges from 0.61 to 0.82oC, while in neighboring post-Soviet countries (Russia, Moldova, Belarus) – this figure is 0.47 - 0.59oC, and in the northern hemisphere and Europe – it is 0.34 and 0.47oC respectively. These data show that the rate of air temperature rise in Ukraine is much higher compared to European countries and the whole world. The rapid rise in average annual temperature in Ukraine is not accompanied by a significant increase in precipitation. Its amount in Ukraine as well as in some other regions remains virtually unchanged. Due to the steady increase in temperature, the area of ​​Ukraine with a significant deficit of natural moisture supply for the period of 1990-2015 increased by 7%, and with excessive and sufficient natural moisture supply, on the contrary, decreased by 10%. If the current warming rates are kept until 2050 and 2100, the territory of the country with insufficient humidity will increase up to 56 and 71%, respectively. As a result of such changes, there is a high probability of medium and long-term prospects of increasing arable land with insufficient natural moisture supply up to 20.6 million hectares (67%) and up to 24.9 million hectares (80%) with a simultaneous decrease in arable land with sufficient natural moisture supply up to 5.5 - 1.8 million hectares. At present, the potential total evaporation is 40-45 km3/year higher than in 1990. As a result, despite the decrease in water consumption, the total amount of water consumption taken from the territory of Ukraine is 20-25 km3 higher. Further climate change will lead to an increase in the volume of additional water consumption till 2050 by 80 km3, and till 2100 - by almost 150 km3 compared to 1990. Modern climate change has significantly affected the cropping systems and their productivity at regional level. The average yield of grain and legumes in the Forest-Steppe and Polissya compared to 1990 increased by 46-61%, and in the Steppe it decreased by 10%. A similar trend is observed with regard to the changes in the productivity of other major cereals, except corn, the yield of which increased in all areas, but in the Forest-Steppe and Polissya by 71-82%, and in the Steppe - only by 9%. The general increase in the production of grain and legumes in the country for the last years was only due to more humid regions - Polissya and Forest-Steppe. Climate change, which has already taken place, proved to be favorable for the spread of the most economically profitable crops in the north of the country, while limiting their production in the south. Thus, in the face of climate change, the conditions of moisture supply in the territory of Ukraine are the main limiting factor that limits not only the level of crop productivity, but also the use of natural and anthropogenic potential of agriculture.

The article provides an analytical review of the achieved crop yields under irrigation in experimental and production conditions. For today, the best production experience in the use of irrigated land indicates that, subject to all agrotechnical requirements, the yield of early grain crops reaches 8-10 t / ha, corn - 10-14 t / ha, oilseeds - 4-6 t / ha, vegetable crops - over 60 t / ha, which is about 90% of their productivity achieved in the experiments of scientific institutions. The comparative assessment of grain production in different climatic zones of Ukraine for the period of the most intense climatic change shows that over the past thirty years, the share of grain production in the Steppe zone has decreased from 45 to 35% of the total in Ukraine. The analysis of service cost for the transportation of water for irrigation in the southern regions of Ukraine is given. It was revealed that, despite a unified standard method for calculating the cost of water transportation, its price varies significantly by operational units of the State Agency for Water Resources of Ukraine. The main factors of fluctuations in the cost and fees for the transportation services of water for irrigation are the budgetary funding level of operating organizations, providing these services, the number of water transfers, the volume of actual irrigation on irrigated lands, the share of irrigated areas in the service area. The economic assessment of irrigation efficiency when having different water and other technological costs, taking into account the depreciation of capital investments, indicates that having a water price of 4,0-5,0 UAH/m3, the gross profit from growing the most profitable field crops is 35-40 % higher than the efficiency in rainfed agriculture. At the cost of water is 3,0-3,5 UAH/m3 and the use of the production capacity of the inter-farm irrigation network by 60-70%, financial prerequisites will be created for the effective operation of these networks.

Climate change has caused rapid soil dehydration in Ukraine; therefore sustainable agriculture will only be possible applying throughout irrigation or water regulation. Meanwhile, the use of the irrigation and drainage systems potential remains extremely unsatisfactory. In 2019, 532,000 ha were actually irrigated, and water regulation was performed on less than 300,000 ha. The purpose of the research. To analyze the existing state and substantiate the areas of the irrigation and drainage sector development to ensure the sustainable agriculture in the face of a changing climate. Materials and methods of the research. In the work, a set of methods was used: analytical, expert evaluations, surveys, comparisons and analogues, experimental. Observation data from the state meteorological stations network were used to evaluate hydrothermal conditions and the data from the network of hydrological posts of Ukrhydrometcentre were used to evaluate the river condition. To assess the technical condition of the engineering infrastructure, methodological approaches were used in accordance with the requirements of the international and European standards and the normative documents currently in force in Ukraine. To identify the possible ways and mechanisms to restore the irrigation and drainage systems potential, the reasons of the existing state were analyzed and it was determined that the uncompleted land and economic reforms, imperfections in the existing legislation and state support mechanisms, especially in the sector management, caused the long-year underfunding of irrigation and drainage facilities operation and restoration and resulted in the crisis situation in the sector. Conclusions. Based on the study of the world experience and the carried out research, it was established that the restoration and development of irrigation and drainage in Ukraine are possible only along with the implementation of a legal and institutional reform to introduce decentralization, improvement of the existing legislation, modernization of irrigation and drainage systems through the development and implementation of investment projects for restoration and development of irrigation and drainage systems, creation of attractive investment environments, development and introduction of a financing mechanism to cover management, operation and maintenance costs based on a new tariff formation system, introduction of the scientific support and staffing system for the land reclamation sector. The basis for the deployment of irrigation and drainage restoration should be the "Irrigation and Drainage Strategy in Ukraine until 2030", and the appropriate plan of measures, formed on the basis of fundamentally new institutional, scientific, technical and technological, economic, organizational, social and environmental approaches, should become a tool for achieving the goals of the "Strategy ...". Successful implementation of the goals of irrigation and drainage restoration in Ukraine will create the conditions to sustainable and profitable agricultural production in the face of climate change, to restore irrigation on the area of about 1,0 to 1,2 mln. ha and drainage on the area of 1,0 mln. ha and to additionally get up to 10 mln. tons of grain, 8-10 mln. tons of fruit, berries and vegetables annually.

The formation of optimal crop rotations is virtually unsolvable from the standpoint of the classical methodology of experimental research. Here, we deal with a mathematical model based on expert estimates of “predecessor-crop” pairs’ efficiency created for the conditions of irrigation in the forest-steppe of Ukraine. Solving the problem of incorporating uncertainty assessments into this model, we present new models of crop rotations’ economic efficiency taking into account irrigation, application of fertilisers, and the negative environmental effect of nitrogen fertilisers’ introduction into the soil. For the considered models we pose an optimisation problem and present an algorithm for its solution that combines a gradient method and a genetic algorithm. Using the proposed mathematical tools, for several possible scenarios of water, fertilisers, and purchase price variability, the efficiency of growing corn as a monoculture in Ukraine is simulated. The proposed models show a reduction of the profitability of such a practice when the purchase price of corn decreases below 0.81 EUR∙kg –1 and the price of irrigation water increases above 0.32 EUR∙m –3 and propose more flexible crop rotations. Mathematical tools developed in the paper can form a basis for the creation of decision support systems that recommend optimal crop rotation variations to farmers and help to achieve sustainable, profitable, and ecologically safe agricultural production. However, future works on the actualisation of the values of its parameters need to be performed to increase the accuracy.

Relevance of research. Due to ongoing climate change, almost the entire territory of the Steppe of Ukraine by annual humidity factor belongs to the dry and very dry zones, the relative area of ​​which has increased by 13.2% of the total area of ​​the country compared to the 1960-1990s. At the same time, for today in Ukraine only about 500 thousand hectares are actually irrigated, that is 19% of the potential area. Purpose of research. To determine the patterns and trends of climate change in the western part of the dry Steppe of Ukraine and analyze the economic indicators of production activity in the region as to the variable weather conditions. Research methodology. Climate change was estimated on the basis of Climate Water Balance (CWB) and Hydrothermal Coefficient (HTC) values. The analysis of the economic efficiency of agricultural production was carried out by analyzing the statistical data for Odessa region and for the chosen agricultural enterprise. Research results and conclusions. The use of significant heat supply in the dry Steppe zone is limited by insufficient water supply conditions. In the years of 1991-2016 the average annual rainfall was 480 mm and since the early 2000s there has been a slight increase in that. However, even having 500-550 mm of average annual rainfall that has been observed over the past five years, it is not enough for providing high-yield agricultural production. High thermal regime couses high evaporation that in turn, leads to water supply deficit, which at the end of the growing season amounts to 336-436 mm. According to the HTC index in the region 80% of cases show severe and moderately arid vegetation conditions. At the same time, irrigation area in the region has decreased to a minimum, which has led to the domination of winter cereals and sunflower in the cropping system. Under variable weather conditions, winter wheat yields ranged from 19.4 to 38.5 c/ ha (31.4 c/ha on average) and sunflower - from 12.2 to 21.4 c/ha (17.4 c/ha on average), winter rape - from 13.1 to 20.9 c/ha (18.2 c/ha). It was proved a close direct relationship between the sale price of products of all studied crops and their cost price, as well as the inverse relationship of these indicators with the crop yield. The profitability of winter wheat from 2011 till 2016 ranged from 17 to 153 USD/ha with an average value of 86 USD/ha, winter rape - from 39 to 273 USD/ha with an average value of 166 USD ha and sunflower - from 116 to 315 USD/ha with an average value of 192 USD/ha. Corn and soybeans have proven to be unprofitable in some years, which obviously explains rather small areas under these crops in the region. Above mentioned demonstrates the high economic instability of agricultural production in changing weather conditions, which is accompanied by significant risks for producers, especially when attracting credits. This situation, in turn, leads to a limited use of intensification means, in particular mineral fertilizers, which promotes agrochemical soil degradation. Under unstable water supply, the magnitude of net profit variation per hectare of arable land in Odessa region is 33-188 USD/ha (111 USD/ha on average). It is possible to increase these indicators by increasing the share of winter rape in the cropping system. With the optimization of the water and air soil regimes as well as crop rotation factor, the profitability of agricultural production in the region can be increased up to 580-600 USD/ha. Similar results were obtained after analyzing the statistical data from the southern regions within the dry steppe zone.