Assessing spatial pattern of irrigation hydromodule under different crop patterns in northwestern Iran

Abstract

Introduction

As the population continues to grow, the significance of boosting food production becomes increasingly evident. Consequently, it is imperative to find solutions to address water limitations and enhance food production in regions facing water scarcity. In this context, it is proposed to implement strategies that involve expanding cultivated areas and optimizing the utilization of available water resources, particularly in scenarios where irrigation is restricted. Successful water engineering projects necessitate precise estimation of plants' water requirements across various regions. The goal is to maximize the efficiency of water usage per unit volume to ensure optimal agricultural output. This study aims to explore fluctuations in the water requirements and hydromodule of crops within different cultivation patterns in selected regions of northwest Iran, in response to climatic variables.



Materials and Methods

The objective of this study is to evaluate the variations in plant water needs in cultivation patterns across different regions in northwest Iran, taking into account climatic parameters. Initially, meteorological data from stations in Tabriz, Kalibar, Parsabad, Germi, and Bukan were collected from the national meteorological organization.

Cultivation pattern of agricultural plants in the investigated stations was extracted from the Jihad Agricultural Organization of the respective province. Considering the vastness of the studied areas and the impossibility of detailed soil investigation, the soil of the areas was considered medium. According to Ministry of Energy researches, the irrigation efficiency for all the studied areas averagely was considered to 60%.

Subsequently, utilizing CROPWAT 8.0 software based on the FAO56 equation, factors such as evapotranspiration of grass (used as a reference plant), solar radiation, and effective rainfall were determined for the selected stations. The hydromodule, representing water requirements, was then calculated monthly for the desired cultivation patterns in the respective areas. Finally, employing the Weibull transformation coefficient, the irrigation hydromodule with various return periods was derived for the study region.



Results and Discussion

The results indicated that the average potential evapotranspiration of grass, serving as the reference plant, was calculated as 4.12, 3.03, 2.86, 3.32, and 3.86 mm per day for the Tabriz, Kalibar, Parsabad, Germi, and Bukan stations, respectively. Furthermore, the average irrigation hydromodule for these stations was determined as 0.73, 0.35, 0.6, 0.7, and 0.62 liters per second per hectare, respectively. Utilizing the linear variation function, the average irrigation hydromodule for return periods of 2, 5, 10, 25, 50, 100, and 200 years for the aforementioned stations were obtained as 0.813, 0.552, 0.707, and 0.721 liters per second per hectare, respectively. Similarly, using the exponential function, the corresponding values were extracted as 0.818, 0.632, 0.719, 1, and 0.73 liters per second per hectare, respectively. Specifically, for the Tabriz, Kalibar, Parsabad, Germi, and Bukan stations, the irrigation hydromodule values with a return period of 2 years, employing the linear function, were calculated as 0.742, 0.439, 0.622, 0.821, and 0.67 liters per second per hectare, and with the exponential function, they were determined as 0.74, 0.444, 0.618, 0.829, and 0.672 liters per second per hectare, respectively. Additionally, for these stations, with a return period of 200 years, using the linear function, the calculated irrigation hydromodule values were 0.851, 0.613, 0.754, 1.015, and 0.748 liters per second per hectare, while employing the exponential function, they were determined as 0.862, 0.749, 0.777, 1.1, and 0.762 liters per second per hectare, respectively.



Conclusion

The irrigation hydromodule values in the Tabriz station increased by 0.851 liters per second per hectare, which is equivalent to a 10.88 percent increase compared to the average. Similarly, in the Kalibar, Parsabad, Germi, and Bukan stations, the increases were 0.613, 0.754, 1.01, and 0.748 liters per second per hectare, respectively, representing increments of 8.44, 13.17, 38, 19.7, and 7.78 percent compared to the average. Utilizing the exponential changes function, when the return period was adjusted from 2 years to 200 years and the probability of occurrence was reduced, the irrigation hydromodule increased by 0.862 liters per second per hectare in the Tabriz station, which corresponds to a 12.23 percent increase relative to the average. Similarly, in the Kalibar, Parsabad, Germi, and Bukan stations, the increases were 0.749, 0.777, 1.1, and 0.762 liters per second per hectare, respectively, representing rises of 30.5, 15.82, 09, 27.04, and 9.04 percent compared to the average. Given the water scarcity in various regions of the country, it is recommended to use the minimum values of functions (linear or exponential) to estimate the irrigation hydromodule for different return periods. With respect to linear function changes, and considering that the irrigation hydromodule does not decrease significantly (around 20% on average) with an increase in the return period (up to 200 years), it is advisable to design and implement storage facilities, transfer systems, and water distribution networks in the studied plains with a low probability of occurrence (high return period). This approach minimizes the increase in costs and reduces risks during water transfer and distribution operations.