Serious economic damages in many regions of the world were caused by the changes in agroclimatic resources during the last 2–3 decades. The Balkan Peninsula is much affected by the temperatures rising, changes in the distribution of precipitation, and the increasing frequency of extreme events—basically, droughts and frosts. Bulgarian agriculture is developed under various agrometeorological conditions. The climate of the country is characterized by the atmosphere and soil moisture deficit in the time of active crop vegetation and yield formation. The aim of this research is to assess the changes in agrometeorological conditions for the growth of the main grain crops and the possibilities for reaction through agro-technologies. Furthermore, the features of contemporary varieties and hybrids of spring and autumn cereals will be taken into account. The next important factor is the specific requirements for hydro-thermal conditions at different phenological phases of agricultural crop development, i.e., sums of the temperatures and precipitations. Agro-technologies react to tendencies in changing agrometeorological conditions. For the adaptation of agro-technologies, the maximum use of natural agroclimatic resources should be included in activities for overcoming unfavorable conditions, as well as the increased frequency of extreme events. A detailed assessment of the agrometeorological conditions is necessary to choose the suitable agro-technology activity. The analysis of the main meteorological elements—temperatures, precipitations, air humidity, wind speed, and solar radiation for thirty years (1986–2015) was used to assess the changes in agrometeorological conditions on agricultural lands in Bulgaria. Appropriate agro-technical activities for growing the main grain crops are proposed in accordance with the observed changes.

Bulgaria is located in an area with insufficient humidification and is characterized by periods of the drought of varying duration and intensity. From the last 15 to 20 years, the limiting factor in agro-meteorological conditions was the drought. Agro-meteorological drought consists of the depletion of available soil water reserves in the root zone. Ultimately, the results of droughts affect the size of yields and the quality of production. The consequences of this extreme condition from a meteorological and agro-meteorological point-of-view phenomenon can be mitigated only by expanding the irrigated areas. The aim of this work was to present the tendencies in the change of the potential evapotranspiration during the studied period 1986–2015 as a result of the climate changes and also the tendencies of the conditions for occurrence of agricultural drought in the future, and also to propose an approach where using certain indicators controls the process of accumulation and consumption of water in the soil. Such approach could find application in adapting agriculture to climate change and the updation of agro-environmental zoning relevant to climatic changes.

A computer programhas been developed for design of surface drip irrigation system. It could be applied for calculation of small scale fields with an area up to 10 ha. The program includes two main parts: crop water requirements and hydraulic calculations of the system. It has been developed in Graphical User Interface in MATLAB and gives opportunity for selecting some parameters from tables such as: agro- physical soil properties, characteristics of the corresponding crop, climatic data. It allows the user of the program to assume and set a definite value, for example the emitter discharge, plot parameters and etc. Eight cases of system layout according to the water source layout and the number of plots of the system operation are laid into hydraulic section of the program. It includes the design of lateral, manifold, main line and pump calculations. The program has been compiled to work in Windows.

Agriculture is one of the most sensitive sectors of the economy. Therefore, climate change has the greatest impact on agricultural production. Despite the achievements of modern agricultural science and the development of agrotechnologies, the importance of meteorological conditions for the size and quality of agricultural products cannot be compensated. Agriculture in Bulgaria is carried out under conditions of limited and insufficient moisture. By the end of the last century, the studied trends of climate change in the area of agricultural production have led to a deterioration of agro-climatic conditions. The temperatures increase and decreasing rainfall and the uneven nature of their distribution cause short-term manifestations of this impact consisting of high variability, including extreme weather events and long-term manifestations consisting of changes in the agro-climatic characteristics of an agricultural area. Since the beginning of the 21st century, we have witnessed annual weather and climate records, both globally and nationally. The frequency and amplitude of extreme weather events is increasing every year. The World Meteorological Organization (WMO) is emphasizing 2019 as the fifth warmest year since the beginning of the 21st century. This paper presents the results of the changes study in agro-climatic conditions in the period 1986-2015 compared to the reference period 1961-1990, as a result of changes in the values of main meteorological elements at the end of the last and the beginning of the present century. The results of the research are necessary for decision-making, both at scientific and management level, in risk assessment and preparation of measures for adaptation to climate change, and directly in agricultural practice - for the choice of crops, varieties and hybrids and in the choice of technological solutions.

Introduction. The condition of the vegetation cover can be traced from Space. Aim of the research. To assess the condition of the vegetation cover in Bulgaria during the last twenty years – its distribution over the country, its change in connection with the typical climatic changes, its seasonal change. Material and methods. The vegetation index NDVI according to NASA data was used to analyze the condition of the vegetation cover in Bulgaria for the years 2000-2020. The methods used were: seasonal data decomposition, t-test, GIS methods for spatial representation of data, Fourier analysis. Conclusions. 1. During the summer months the vegetation in the eastern parts of the territory of Bulgaria is noticeably weaker than in the western parts. The influencing factors-drought and frequent fires are probably related to global warming. 2. For the territory of Bulgaria there is a seasonal rotation of the horizontal gradient of the vegetation index in a counterclockwise direction-from east to west in summer, from northeast to southwest in autumn and from north to south in winter. 3. There is a winter increase in vegetation for Northern Bulgaria and to the greatest extent for Northeastern Bulgaria, as well as for Southwestern Bulgaria. Together with the decreasing snow cover, the winter vegetation contributes to the drought in the eastern parts of the country.