The Analysis of Climate-Based Conditions on Irrigation in the Baˇcka Region (Northern Serbia) †

: Since climate conditions in a certain region have a signiﬁcant role in setting irrigation practices, an optimized use of natural resources is needed. Therefore, climate elements, which have the most effect on plant growth and development, must be considered. This study aimed to create an indicator for irrigation applications using historical climate data for the Baˇcka region, characterized by a moderate continental climate. Considering daily temperature, precipitation, and evapotranspiration data from 1964 to 2012, this study examined the need for irrigation according to different climate conditions. Finally, three irrigation suggestions were provided, using the method for assigning the weights.


Introduction
The impact of climate change on the environment, especially agriculture, presents an essential problem in the 21st century.According to the United Nations Intergovernmental Panel on Climate Change [1], climate change and global warming considerably reduce water and food for a million people around the world, hindering efforts to achieve Sustainable Development Goals.
Facing unmerciful climate changes and providing more food, irrigation presents a critical component of future agriculture.Due to the already high pressure on freshwater resources, it is anticipated that pressure will be higher, leading to more uncertainty in agricultural production, a sharp increase in water demand, and alterations in the hydrological cycle [2].Understanding water demand in different climate scenarios is necessary for water resource planning, development, and management.Thus, the analysis of climate-based conditions on irrigation is a first step towards sustainable agricultural production.
Despite the fact that irrigation is strongly influenced by climate-based conditions, there has been limited attention to the analysis of climate-based factors and their effects on farmers' decisions [3][4][5][6].Analyzing the climate conditions can help identify the key factors that impact irrigation, such as rainfall, temperature, and evapotranspiration, and develop strategies for effective irrigation management.Temperature is a key factor that affects irrigation demand.Rising temperatures can increase crop evapotranspiration rates, making crops more water-stressed and thus increasing irrigation demand [7].Precipitations are another significant factor in climate-based analysis.During periods of high rainfall, irrigation demand may be lower, while during dry periods, irrigation demand may be much higher.Understanding these patterns and how they vary over time can help farmers to plan their irrigation schedules and optimize water use.
In order to help farmers in making irrigation decisions, this research investigated historical climate data with the aim to design a climate-based irrigation framework.This framework would be of great importance for future irrigation applications, considering that it should be applied in certain climatic conditions when it is really necessary.Thus, climatic factors, such as temperature, precipitation, and evapotranspiration on a daily basis for 49 years, were considered.These climate elements were used to set different conditions and finally to assign the weights that determine the level of need for irrigation.

Research Area
The study area is the Bačka region, which presents one of the main agricultural regions in Serbia.It is located in the northern part of the country where the western, southern, and eastern borders are the great rivers of Danube and Tisza, while the northern part is the continental border.This region is characterized by a moderately continental climate where winters are cold and summers are hot and humid (the warmest month is July with T = 21-23 • C) with irregular distribution of rainfall and extreme temperatures [8,9].The average annual precipitation is approximately 600 mm [10].

Materials and Methods
In this section, the materials and methods used in this research will be described.

Data
For this study historical meteorological data was used to determine the need for irrigation according to different climate conditions during the historical period.The daily values of mean temperature and precipitation for the period of 1964-2012 were obtained for all three meteorological stations in the Bačka region: Sombor (44 • 37 N, 20 • 95 E), Novi Sad (45 • 33 N, 19 • 85 E), and Bečej (45 • 61 N, 20 • 06 E) (Figure 1).These data were downloaded from the database of the Republic Hydrometeorological Service of Serbia [11].Temperature data was used to calculate evapotranspiration which can provide an objective estimation of plants' water needs.The missing values in the database, i.e., missing dates, were filled by the mean values of climate elements for surrounding dates.
be much higher.Understanding these patterns and how they vary over time can help farmers to plan their irrigation schedules and optimize water use.
In order to help farmers in making irrigation decisions, this research investigated historical climate data with the aim to design a climate-based irrigation framework.This framework would be of great importance for future irrigation applications, considering that it should be applied in certain climatic conditions when it is really necessary.Thus, climatic factors, such as temperature, precipitation, and evapotranspiration on a daily basis for 49 years, were considered.These climate elements were used to set different conditions and finally to assign the weights that determine the level of need for irrigation.

Research Area
The study area is the Bačka region, which presents one of the main agricultural regions in Serbia.It is located in the northern part of the country where the western, southern, and eastern borders are the great rivers of Danube and Tisza, while the northern part is the continental border.This region is characterized by a moderately continental climate where winters are cold and summers are hot and humid (the warmest month is July with T = 21-23 °C) with irregular distribution of rainfall and extreme temperatures [8,9].The average annual precipitation is approximately 600 mm [10].

Materials and Methods
In this section, the materials and methods used in this research will be described.

Data
For this study historical meteorological data was used to determine the need for irrigation according to different climate conditions during the historical period.The daily values of mean temperature and precipitation for the period of 1964-2012 were obtained for all three meteorological stations in the Bačka region: Sombor (44°37′ N, 20°95′ E), Novi Sad (45°33′ N, 19°85′ E), and Bečej (45°61′ N, 20°06′ E) (Figure 1).These data were downloaded from the database of the Republic Hydrometeorological Service of Serbia [11].Temperature data was used to calculate evapotranspiration which can provide an objective estimation of plants' water needs.The missing values in the database, i.e., missing dates, were filled by the mean values of climate elements for surrounding dates.

Evapotranspiration Calculation
In this study, the Hargreaves equation was used as a common method for estimating reference evapotranspiration (ET 0 ).The equation was developed by Dennis Hargreaves in 1985 and recommended by the FAO [12] as an alternative to the more complex and dataintensive Penman-Monteith method.The Hargreaves equation uses temperature and solar radiation data to estimate ET 0 .It has been widely used and validated in various regions of the world, particularly in areas with limited data on weather parameters.An advantage of this equation is its simplicity and ease of use, requiring only the abovementione parameters.
For the ET 0 calculation, the Python programming language and built-in function from the PyET 0 package 2.0 were used.Parameters T min , T max , T mean and extraterrestrial solar radiation were used as inputs for the following equation [13]: where: ET 0 -reference evapotranspiration (mm d −1 ); 0.0023-empirical Hargreaves coefficient (HC); R a -extraterrestrial solar radiation above the atmosphere on the 15th day of each month (MJ m −2 d −1 ); T mean -mean daily temperature ( • C); 17.8-empirical temperature Hargreaves constant (TH); T max -maximum daily temperature ( • C); T min -minimum daily temperature ( • C); 0.5-empirical Hargreaves exponent.

Setting Conditions and Assigning the Weights
The initial step included preparation and refining the dataset that contained information related to climate elements (temperature, precipitation, and evapotranspiration).After that, certain conditions were established to determine irrigation suggestions.These conditions were based on combining the reference values of the climate elements, determined by the optimal plant requirements in the research area.Comparing the actual values from the dataset to these conditions, it would be possible to determine which condition(s) each data point fell into.By applying the assigned weights to the conditions, the system could provide three different irrigation suggestions for each data point: 3-need to be irrigated, 2-could be irrigated and 1-should not be irrigated.For example, the combination where the mean temperature was above 20 • C, precipitation values were below 5 mm and evapotranspiration were above 2.5 mm d −1 , belongs to the irrigation suggestion number 3, which means there is a need for irrigation.The suggestions were designed to guide irrigation decisions and optimize plant growth in the research area.Knowing the real-time climate trends and using these suggestions, farmers could make decisions more confidently.These suggestions are part of the research framework and represent the basis for further research.

Results and Discussion
Figure 2 shows the frequencies of daily weights aggregated by months (expressed in %) in the Bačka region.As in moderate climate areas, winters are cold, crop types are adjusted to the climate and an artificial water supply is not necessary.Thus, the period from late autumn (November) to early spring (March) is not further analyzed in this research.
According to Figure 2 and Table 1, it is evident that June, July, and August have the highest number of days when irrigation needs to be applied (42%, 63%, and 59%, respectively).The results show that the transitional period among seasons (May and September) still has a need for irrigation (~20% of the days/months).This indicates that climate conditions in these months tend to be dryer, with less precipitation necessary for plants growing.An artificial water supply will be more frequent, leading to higher pressure on water resources.On the other hand, results for June show that there are a higher number of days that should not be irrigated.This can be explained due to the recent climate changes and irregular distribution of precipitation in the research area during the investigated period.According to Figure 2 and Table 1, it is evident that June, July, and August have the highest number of days when irrigation needs to be applied (42%, 63%, and 59%, respectively).The results show that the transitional period among seasons (May and September) still has a need for irrigation (~20% of the days/months).This indicates that climate conditions in these months tend to be dryer, with less precipitation necessary for plants growing.An artificial water supply will be more frequent, leading to higher pressure on water resources.On the other hand, results for June show that there are a higher number of days that should not be irrigated.This can be explained due to the recent climate changes and irregular distribution of precipitation in the research area during the investigated period.However, it should be kept in mind that these results are climate-based, where the type of crop and exact irrigation water requirements are not considered.Further research should include previously mentioned information, giving more detailed information about irrigation suggestions for specific crop types in specific climate conditions.
Finally, we can consider this research as the first step for irrigation management improvement and as the easiest way to create some basic suggestions for farmers who still lack applicative measures of smart irrigation in the research area, but who also still provide a lot of attention to the deductive determination of weather conditions before irrigation.

Conclusions
Considering that irrigation needs to be applied in certain climatic conditions when it is really necessary, this research investigates historical climate data in order to propose a climate-based irrigation framework to help farmers in making future irrigation decisions.Climate factors, such as temperature, precipitation, and evapotranspiration on a daily ba- should not be irrigated could be irrigated need to be irrigated  However, it should be kept in mind that these results are climate-based, where the type of crop and exact irrigation water requirements are not considered.Further research should include previously mentioned information, giving more detailed information about irrigation suggestions for specific crop types in specific climate conditions.
Finally, we can consider this research as the first step for irrigation management improvement and as the easiest way to create some basic suggestions for farmers who still lack applicative measures of smart irrigation in the research area, but who also still provide a lot of attention to the deductive determination of weather conditions before irrigation.

Conclusions
Considering that irrigation needs to be applied in certain climatic conditions when it is really necessary, this research investigates historical climate data in order to propose a climate-based irrigation framework to help farmers in making future irrigation decisions.Climate factors, such as temperature, precipitation, and evapotranspiration on a daily basis for 49 years, were examined.These climate elements were used to set different conditions and to assign the weights that determine the level of need for irrigation.Results showed that, in the Bačka region, irrigation is most necessary during June, July, and August, as well as in the transitional period among seasons (May and September).

Figure 1 .
Figure 1.Geographical location of the Bačka region and meteorological stations used in this study.

Figure 1 .
Figure 1.Geographical location of the Bačka region and meteorological stations used in this study.

5 Figure 2 .
Figure 2. Percentage representation of the number of days per month (for all three stations) for each irrigation suggestion.

Figure 2 .
Figure 2. Percentage representation of the number of days per month (for all three stations) for each irrigation suggestion.

Table 1 .
Sum of suggested numbers of days/months for each irrigation suggestion according to historical climate data (1-should not be irrigated; 2-could be irrigated; 3-need to be irrigated).

Table 1 .
Sum of suggested numbers of days/months for each irrigation suggestion according to historical climate data (1-should not be irrigated; 2-could be irrigated; 3-need to be irrigated).