نوع مقاله : مقاله پژوهشی
نویسندگان
1 استادیار بخش تحقیقات خاک و آب، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان کرمانشاه، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرمانشاه، ایران.
2 دانشیار، بخش تحقیقات آبیاری، موسسه تحقیقات خاک و آب، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران.
3 محقق، بخش تحقیقات آبیاری، مؤسسه تحقیقات خاک و آب، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران.
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Reference evapotranspiration, as one of the important components of the hydrologic cycle, is an important factor in field irrigation planning, drought assessment and climate change (Li et al., 2017). Reference evapotranspiration represents the maximum amount of water transferred from the land surface to the atmosphere (Yang et al., 2020). Determining this parameter is the first step in estimating the water requirements of plants and irrigation water management (Yassen et al., 2020). Research on temporal and spatial changes of reference evapotranspiration is very important in order to understand climate change and its effects on hydrologic processes and water resources (Liu and Zhang, 2013). Knowledge of reference evapotranspiration change trends can help agricultural irrigation management and support decision makers involved in water resources management in the future (Yang et al., 2020). In many regions with a shortage of water resources, such as Kermanshah province, the study of reference evapotranspiration changes can help to understand the spatial distribution and temporal changes of water. The purpose of this research is to determine the temporal variations of reference evapotranspiration and the factors affecting it in 10 synoptic meteorological stations of Kermanshah province. The information obtained from this research can provide guidance for agricultural water requirements, irrigation planning and sustainable water resource management under climate change conditions.
کلیدواژه‌ها [English]
Methodology
The study area is Kermanshah province. This province is located in the geographical coordinates of 33° 41ʹ to 35° 17ʹN and 45° 25ʹ to 48° 6ʹE. The area of this province is 2.44 million hectares, which is about 1.5% of the total area of Iran. Its average height is 1200 meters above sea level. The meteorological data used include minimum and maximum temperature, average temperature, minimum and maximum relative humidity, wind speed, net radiation input to the surface, and daylight hours in the statistical period of 1999 to 2022. The water requirement system of plants which is the result of the Penman Monteith method of FAO was used to determine the reference evapotranspiration. This reference evapotranspiration estimation method is proposed in FAO publication No. 56 as the best method compared to other reference evapotranspiration estimation methods (Sumner and Jacobs, 2005). Pettitt's test of XLSTAT software was used to determine the possible changes in reference evapotranspiration and climatic factors affecting it. Pettitt's test was first presented by Pettitt (Pettitt, 1979). Pettitt's test is a non-parametric test that does not require any assumptions about the data distribution. This test is an adaptation of the Mann-Whitney test, which allows identifying the time in which the change occurs.
Results and Discussion
The results of Pettitt's test for reference evapotranspiration in the synoptic meteorological stations of Kermanshah province are shown in Table (1). In Table (1), when the p-value is < 0.05, Pettitt's test is significant at the 5% probability level and indicates the sudden changes of reference evapotranspiration in the investigated time series. The results of Table (1) showed that the changes of monthly and annual reference evapotranspiration time series were significant in 42 and 60% of the studied stations, respectively, at the 5% probability level and indicated the existence of a sudden change in these variables.
Table 1-The results of Pettitt's test for reference evapotranspiration in synoptic meteorological stations of Kermanshah province
The year and amount of reference evapotranspiration change in the synoptic meteorological stations of Kermanshah province are presented in Table (2). The results of Table (2) showed that the meteorological station of Gilan Gharb had sudden incremental changes in reference evapotranspiration in all months of the year. Eslamabad-e-Gharb, Kermanshah, Gilan Gharb, Javanrud and Hersin stations had sudden incremental changes in annual reference evapotranspiration. Gilan Gharb station had the highest amount of this change with 429 mm. In order to find the reason for the biggest increase in annual reference evapotranspiration at Gilan Gharb station, the time series of each of the parameters affecting the annual reference evapotranspiration was investigated by Pettitt's test. The results showed that although the maximum annual temperature had a sudden decrease, but with an increase in the average minimum annual temperature, wind speed, daylight hours and net radiation, and a decrease in the maximum relative humidity, the reference evapotranspiration increased in this station. The research results of Fu et al. (2022) in China showed that the increase in temperature and wind speed and the decrease in relative humidity had positive and large effects on the increase in evapotranspiration, which agrees with the results of the present study. Ravansar station had a sudden decrease in evapotranspiration of annual reference amounting to 183 mm. In order to find the reason for the reduction of annual reference evapotranspiration at Ravansar station, the time series of each of the parameters affecting the annual reference evapotranspiration was investigated by Pettitt's test. The results showed that although the average temperature, minimum temperature and maximum annual temperature had a sudden increase, but with the increase in the average maximum relative humidity and the decrease in wind speed and annual daylight hours, the annual reference evapotranspiration in this station decreased. In the study of Jhajharia et al. (2012) also pointed out the contradiction of increasing temperature while reducing evapotranspiration. The research results of Liu and Zhang (2013) showed that a significant reduction in wind speed dominates the change of reference evapotranspiration and neutralizes the effect of increasing air temperature that increases the reference evapotranspiration and leads to its reduction. This result agrees with the findings of the present study.
Table 2-The year and value of reference evapotranspiration change (mm) in synoptic meteorological stations of Kermanshah province
Conclusions
The results of this study show that, in general, from 2003 to 2015, sudden incremental changes in reference evapotranspiration and have occurred in most meteorological stations of Kermanshah province. Sudden incremental changes in reference evapotranspiration indicate an increase in the water requirement of plants. Therefore, water resources should be providing to the agricultural sector with a more appropriate planning, and the farmers, considering the amount of evapotranspiration, should act with better planning regarding the crop selection.
Acknowledgments
The authors of this article express their appreciation and gratitude to the officials of the Water Requirement System of Plants (NIAZAB), Soil and Water Research Institute (SWRI), and the I.R. of Iran Meteorological Organization (IRIMO) for their cooperation and providing the data needed for this study.
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