Showing 29 results for Evapotranspiration
H. Modabberi, M. Mirlatifi, M. A. Gholami,
Volume 18, Issue 67 (6-2014)
Abstract
Since more than 75% of the rice fields in Iran are located in the Northern provinces i.e. Mazandaran, Guilan, and
Golestan identifying the crop water requirement of rice fields is essential for water resources planning in the Northern
provinces. The objective of this research was to ascertain the crop water requirement of two rice cultivars namely
Hashemi and Khazar in Guilan province during 1389 growing season. Four iron barrels with diameter of 56 cm were
used as lysimeters to grow the cultivars mentioned. According to a simple volume balance approach the crop water use
of the four lysimeters were determined during the growing season. The elements of volume balance approach such as
the depths of drainage, precipitation, and irrigation were recorded daily and the average of 5-day and 10-day periods
were reported. The daily rice crop water use during the growing season was found to range from 2.4 to 6.3 mm/day with
a seasonal crop water use ranging from 430 to 470 mm for Hashemi and Khazar cultivars, respectively. Daily reference
evapotranspiration was computed by the FAO-Penman-Montith equation and accordingly rice crop coefficients were
computed. The crop coefficient of Hashemi variety was found to be 1.1, 1.3, and 1.1 during the initial, mid, and end
growth stages, respectively. In addition, the aforementioned parameters for Khazar variety were 1.2, 1.3, and 1.1.
M. Kiani, M. Gheysari, B. Mostafazadeh-Fard, M. M. Majidi and E. Landi, , , , ,
Volume 18, Issue 67 (6-2014)
Abstract
The purpose of this study was to measure daily and seasonal evapotranspiration and daily crop coefficient of two common varieties of sunflower (Sirna and Euroflor) via drip-tape irrigation system. For this purpose, the sunflower water use was determined by daily monitoring of soil moisture at the depths of 10, 20, 30, 40 and 60 cm, and the crop evapotranspiration (ETC) was measured using volume balance method. According to the equation recommended by FAO, the obtained value of KC for Euroflor and Sirna varieties at the initial stage was 0.32. According to volume balance method, the Euroflor KC value for development, middle, and late stages were found to be 0.75, 1.18 and 0.9 and for Sirna were found to be 0.72, 1.15 and 0.84 respectively. Seasonal amount of evapotranspiration for Euroflor and Sirna varieties was equal to 601 and 575 mm, which was 26 and 30 percent less than seasonal ET0 in Isfahan. The average value of during the sunflower growing season was 0.77, which was greater than that offered by Doorenbose and Pruitt (0.55). As the crop coefficients of two varieties were different during the growing season and they were also different from FAO KC, measuring the actual amount of KC as a function of growing degree days can increase the accuracy of the estimated ETc and help develop the crop models in order to improve the irrigation management.
N. Moshtagh, R. Jafari, S. Soltani , N. Ramezani,
Volume 19, Issue 73 (11-2015)
Abstract
Spatial estimation of evapotranspiration (ET) rates is essential for agriculture and water resources management. This study aimed to estimate ET v an ET estimation algorithm called Surface Energy Balance Algorithms for Land (SEBAL) and also by using TM June 2009 satellite data in Damaneh region of Isfahan province. To calculate the ET, all the energy balance components and related parameters including net radiation, surface albedo, incoming and emitting shortwave and longwave radiation, surface emissivity, soil heat flux, sensible heat flux, NDVI vegetation index, Leaf Area Index(LAI), and surface temperature were extracted from the geometrically and radiometrically corrected TM images. Results showed that ET rate was about 7.2 mm day-1 in agricultural areas, which was almost equal to 6.99 mm day-1 extracted from the FAO Penman-Monteith method in the synoptic weather station of Daran. Results here indicate that the extraction of ET rate which is almost equal to plant water requirements from remote sensing data can be used in selecting appropriate plants for agriculture and rehabilitation purposes in extensive arid and semi-arid regions of Isfahan province where severe droughts and water shortage are major problems.
M. J. Zareian, S. S. Eslamian, H. R. Safavi,
Volume 20, Issue 75 (5-2016)
Abstract
This study investigated the effects of climate change on the evapotranspiration amount and water balance in the Zayandeh-Rud river basin. Two important weather stations; Isfahan and Chelgerd stations, located in the East and West of the basin respectively, were selected for investigation in this study. The combination of 15 GCM models were created based on the weighting method and three patterns of climate change including the ideal, medium and critical were defined. Using the proposed patterns, the effects of climate change on temperature and evapotranspiration in Isfahan station and precipitation in Chelgerd station were estimated under the A2 and B1 emissions scenarios. Two indices were considered to determine the sustainability of agricultural water consumption in the study area. Ratio of evapotranspiration in the East part of the basin to precipitation in the West part was defined as EPR index (Evapotranspiration-Precipitation Ratio), and the ratio of maximum agricultural water deficit to the amount of agriculture water need, was considered as maximum deficit index (MD). Results showed that the annual temperature would increase between 0.63-1.13°C in the eastern part of the basin. The west precipitation in the basin would reduce between 6.5-30% in the ideal to critical patterns. Summer season, showed the most amount of increase in the temperature, and winter season, showed the most amount of decrease in precipitation. The A2 emission scenario showed more temperature increase and more precipitation decrease in comparison with the B1 emission scenario and also indicated that the potential evapotranspiration would increase by 3.1 to 4.8% in the basin. The EPR index will increase between 13-52% and MD index will increase between 9-35% in Zayandeh-Rud river basin under different climate change patterns. The results revealed the imbalance between agricultural water use in eastern part and the precipitation in the western part of the basin. In other words, in these conditions, appropriate management strategies and planning should be implemented to ensure the sustainability of water resources in Zayandeh-Rud River Basin.
Sh. Zand-Parsa, S. Parvizi, A. R. Sepaskhah, M. Mahbod,
Volume 20, Issue 77 (11-2016)
Abstract
In agricultural development many factors such as weather conditions, soil, fertilizer, irrigation timing and amount are involved that are necessary to be considered by the plant growth simulation models. Therefore, in this study, the values of soil water content at different depths of soil profile, dry matter production and grain yield of winter wheat were simulated using AquaCrop and WSM models. The irrigation treatments were rain-fed, 0/5, 0/8, 1 and 1/2 times of full irrigation conducted in Agricultral College of Shiraz University during 2009-2010 and 2010-2011. The models were calibrated using measured data in the first year of experiment and validated by the second year data. The accuracy of soil water simulation was used to refer to the accuracy of simulated evapotranspiration. The accuracy of soil water content at different layers of root depth in the validation period was good for the WSM model (Normalized Root Mean Squer Error, NRMSE= 0/14). But the AquaCrop model showed less accuracy for soil water content (NRMSE=0/26). However, the values of predicted and measured crop evapotranspiration were close together at full irrigation treatment, the accuracy of AquaCop predictions was decreased with inceasing water stress. WSM model has had a good estimation of the dry matter and grain yield simulation with NRMSE of 0/15 and 0/18, respectively. However, they were simulated with less accuracy in the AquaCrop model with NRMSE of 0/19 and 0/39.
O. Babamiri, Y. Dinpazhoh,
Volume 20, Issue 77 (11-2016)
Abstract
Accurate estimation of ET0 in any region is very important. The aim of this study is to compare and calibrate the 20 empirical methods of estimating evapotranspiration (ET0) based on three categories in monthly timescale at the Urmia Lake watershed. These categories are: 1) temperature-based models (Hargreaves (HG), Thornthwaite (TW), Blaney-Criddle (BC), Linacre (Lin)), 2) radiation-based model (the Doorenbos-Pruitt (DP), Priestly-Taylor (PT), Makkink (Mak), Jensen-Haise (JH), Turc (T), Abtew (A), McGuinness-Bordne (MB)) and 3) mass transfer-based model (Meyer (M), Dalton (D), Rohwer (R), Penman (P), Brockamp-Wenner (BW), Mahringer (Ma), Trabert (Tr), WMO and Albrecht (AL)). For this purpose, the information of 10 synoptic meteorological stations during the period of 1986-2010 was used. Results from the above mentioned methods were compared with the output of the FAO Penman-Monteith (PMF-56) method. Performance of the methods evaluated using the R2, RMSE, MBE and MAE statistics. The best and worst methods of each category were determined for the study area. The best methods of each category were calibrated for the area under study. Results indicated that there is a significant difference between the results of selected methods of each category and the PMF-56 method. Performance of the selected methods remarkably increased after calibration. Among the temperature-based group, the HG method having the median R2 value of 0.9597 was recognized as the best method. After calibration the medians of RMSE, MBE, and MAE were 72.09, 3.14 and 10.70 mm/ month, respectively. After HG, the Lin and BC found to be the best second and third methods in the study area. The TW showed Large error, therefore, it was not a suitable method for ET0 estimation in study area. Among the radiation-based group, the DP model was selected as the best method in the study area. Furthermore, the median of R2 values was 0.982. In this method, the medians of RMSE, MBE and MAE after calibration were 7.89. -0.62 and 6.03 mm/month, respectively. Following DP, the PT method was recognized as the 2nd best one. The methods namely M, JH, T, A and MB were put in the 3rd to seventh rank of the radiation category. Finally, among the mass transfer-based group, having R2=0.8945, the Meyer method was selected as the best method of this group for the study area. In the mentioned method (after calibration) the medians of RMSE, MBE, and MAE were 21.8, -8.7 and 17.3 mm per month, respectively. From mass transfer based group, the D method was found as the second best method in the study area. The methods namely R, P, BW, Ma, Tr, WMO and A were ranked 3rd to 7th, respectively. In general, the performance of radiation based methods was superior than others in Urmia Lake basin. Temperature based methods and mass transfer based methods were ranked second and third, respectively. Further examination of the performance resulted in the following rank of accuracy as compared with the PMF-56: DP (Radiation based), HG (Temperature based) and Meyer (Mass transfer). In general, it can be concluded that after calibration the DP method is suitable to estimate reference crop evapotranspiration among 20 selected methods in the Urmia Lake basin.
A. Morshedi, M. Naderi, S. H. Tabatabaei, J. Mohammadi,
Volume 21, Issue 3 (11-2017)
Abstract
This study was designed to investigate the possibility of using the surface energy balance algorithm for land (SEBAL) and mapping evapotranspiration at high resolution with internalized calibration (METRIC) models to estimate evapotranspiration (ET) in Shahrekord plain (Chaharmahal va Bakhtiari province, Iran). Two sets of Landsat ETM+ data dated June 30th and August 21st, 1999 were provided to estimate and compare reference evapotranspiration (alfalfa) at regional scale using Landsat ETM+ data to ET estimations by five mathematical methods (experimental and combined) known as standardized Penman-Monteith by American Society of Civil Engineers (ASCE-stPM), Penman-Monteith (F56PM), Blaney-Cridle (F24BC), Hargreaves-Samani (HS) and evaporation pan (F24P). Results showed that ET at cold anchor pixel for SEBAL were 6.97 and 6.77 millimeters per day and for METRIC were 10.27 and 9.31 millimeters per day, on days when the satellite passed over. Hargreaves-Samani ET values, as the suitable mathematical model for the studied area, were 8.0 and 7.5 millimeters per day, respectively, on two satellite passes. Results showed that, in the first pass all statistical indices for SEBAL were less than the second pass, maybe due to higher air temperature and wind speed. On the other way, statistical indices in METRIC on the alternate pass, however, showed higher values over the corresponding values in SEBAL. ET values on two satellite passes for anchor pixels were 5.65 and 5.93 mm/day in SEBAL, and 5.22 and 6.65 mm/day in METRIC, respectively. ET values on the same days of satellite overpass for Hargreaves – Samani (HS) were 8.0 and 7.5 mm/day. Consequently, based on the results, both RS-ET models were comparable to empirical models such as (HS). Generally, the results showed that SEBAL had higher accuracy than METRIC, presumably due to lack of accurate weather data (hourly data), so SEBAL is recommended in similar conditions. Generally, the results showed that SEBAL had higher accuracy in comparison to HS and lysimeters data than METRIC, so SEBAL is recommended in similar conditions.
. A. A. Sabziparvar1, S. Ebrahimzadeh2, M. Khodamoradpour3,
Volume 21, Issue 4 (2-2018)
Abstract
The most important factor in determining crop water requirement is estimation of evapotranspiration (ET). Majority of the methodsestimate ET apply series of relatively complex formula,which is then used to determine crop evapotranspiration (ETc). The parameters used in aforesaid methods are: Solar radiation, wind speed, humidity, etc. Unfortunately, in Iran and many countries, long-term records of these parameters are not readily available. The purpose of this study is to calculate the Selianinov Hydrothermic Index that merely requires daily temperature and precipitation data in order to determine correlation coefficients (r) versus ET and Crop Water Requirement (CWR) of some agricultural crops of Iran. First, the Selianinov index is calculated from daily precipitation and temperature during the growth season. Further, the results are correlated against both ETc and CWR. The model results indicate inverse (negative) strong exponential and polynomial relations between the dependent and independent variables. Coefficient of determination (R2) for polynomial equations (on average 0.84) in all crops was better than exponential equations (on average 0.72). Correlation between Selianinov index and CWR indicates that coefficient of determination in both equations was close together (0.83 for polynomial equations and 0.82 for exponential equations).
S. Ekhtiary Khajeh, F. Negahban, Y. Dinpashoh,
Volume 23, Issue 2 (9-2019)
Abstract
In this study, drought characteristics of Arak, Bandar Anzali, Tabriz, Tehran, Rasht, Zahedan, Shiraz and Kerman stations during the statistical period of 1956 to 2015 were studied by Reconnaissance Drought Index (RDI) and Standardized Precipitation Index. Precipitation and temperature data were needed to calculate RDI. Precipitation data was also required to estimate SPI. In this study, Drinc software was used to calculate RDI, SPI and potential evapotranspiration (PET). The software calculated PET by the Thornthwaite method. One of the main challenges in drought monitoring is to determine the indicator that has a high reliability based on its monitoring purpose. Therefore, in this research, two methods used for selecting the appropriate index based on the minimum rainfall and normal distribution were evaluated. The results of the evaluation of the minimum rainfall method for selecting the appropriate index showed that most drought indices with the occurrence of minimum rainfall level indicated severe or very severe drought situations; in most cases, it could not lead to selecting an exact and unique index. Based on the results of the normal distribution method for the stations of Arak, Tabriz, Rasht, Zahedan, Shiraz and Kerman, SPI index, and for the stations of Bandar Anzali and Tehran, RDI index were selected as the most appropriate ones.
M. Saeidipour, F. Radmanesh, S. Eslamian, M. R. Sharifi,
Volume 23, Issue 2 (9-2019)
Abstract
The current study was conducted to compute SPI and SPET drought indices due to their multi-scale concept and their ability to analyze different time-scales for selected meteorological stations in Karoon Basin. Regionalization of SPI and SPEI Drought indices based on clustering analysis was another aim of this study for hydrological homogenizing. Accordingly, to run test through data and determine similar statistical periods, 18 stations were selected. SPI and SPEI values were plotted in the sequence periods graphs and their relationships were analyzed using the correlation coefficient. The results were compared by Pearson correlation coefficient at the significance level of 0.01. The results showed that correlation coefficients (0.5-0.95) were positive and meaningful for all stations and the correlation coefficient between the two indices were increased by enhancing the time-scales. Also, time-scales enhancement decreased the frequency of dry and wet periods and increased their duration. Through regionalization of basin stations based on clustering analysis, the stations were classified into 7 classes. The results of SPEI regionalization showed that the frequency percentage of the normal class was more than those of dry and wet classes.
H. Ghamarnia, Z. Jalili, D. Kahrizy,
Volume 23, Issue 3 (12-2019)
Abstract
Exactly estimating of water requirement is essential for water balance studies, design and management of irrigation systems and water resources management. Because of limited soil and water resources in Iran, for optimal use of water resources in the agricultural sector, it is necessary to determine the amount of water requirement by different plants in different climatological conditions. In order to determine the water requirement and crop coefficients of Stevia, six lysimeter numbers were used in three replications for stevia and reference plant (grass). The reference Stevia plant evapotranspiration was measured on a daily basis. The results showed that during the 537 day period of Stevia cultivation, the maximum and minimum water requirement in the first and second year of cultivation was respectively 9.85 and 1.69 mm per day, and for the reference plant was obtained as 6.54 and 1.84 mm per day. In this study, the Kc coefficients in initial, development, intermediate and final stages of growth in 2016 were 0.76, 1.11, 1.46 and 1.05 and in 2017 at growth stages, were 0.76, 1.18, 1.52 and 1.29 respectively. The average of individual Stevia plant growth factors for four growth stages in two years of research was obtained as 0.76, 1.15, 1.49, and 1.17, respectively.
H. Karimi Avargani, A. Rahimikhoob, M. H. Nazarifar,
Volume 23, Issue 3 (12-2019)
Abstract
In recent years, a lot of research has been done on the Aquacrop model, the results show that this model simulates the product performance for deficit irrigation conditions. But this model, like other models, is sensitive to values of independent variables (model inputs). In this research, the sensitivity of the Aquacrop model was analyzed for 4 input parameters of reference evapotranspiration, normalized water productivity, initial canopy cover percentage and maximum canopy cover for barley. Irrigation treatments included full irrigation and two deficit irrigation treatments of 80% and 60%, the experiment was done in 2014-15 growing season in the field of Abourihan College. The values of measured biomass were used as the base values for treatments. The Beven’s method (Beven et al., 1979) was used for sensitivity analysis of Aquacrop model. The results showed that the model is most sensitive to the reference crop evapotranspiration, So the sensitivity coefficient for this parameter for full irrigation treatments, 80% full irrigation and 60% full irrigation were -1.1, -1.2 and -2.3 respectively. The negative sign indicates that if the value of reference evapotranspiration input is exceeded the actual value into the model, Yield performance is simulated less than actual value. In the meantime, the higher the degree of deficit irrigation, the greater the sensitivity of the model.
B. Noori, H. Noori, Gh. Zehtabian, A. H. Ehsani, H. Khosarvi, H. Azarnivand,
Volume 23, Issue 4 (12-2019)
Abstract
Due to the impact of climate change on the plant water demand and the availability of water, especially in drylands, it is vital to estimate the evapotranspiration rates accurately. In this study, the vegetation status in the marginal desert areas of Varamin Plain was studied, and the actual evapotranspiration and water demand of intercropped farms were assessed. This study also evaluated the potential relationship between the evapotranspiration of different agricultural lands and their vegetation index using remote sensing techniques. A collection of satellite images from Landsat 7 in consecutive seasons was used to determine the greenness rate of marginal desert areas during 2013 and 2014. ENVI software was used for the image processing, which included geometric corrections and atmospheric corrections, to develop NDVI maps. Also, weather data and crop properties of Varamin Plain were collected, and the actual evapotranspiration rate of plant cover was estimated using CropWat. The correlation between NDVI extracted from satellite images and the evaluated evapotranspiration rate was assessed. The results showed a strong relationship between evapotranspiration of heterogeneous agricultural lands and NDVI. This confirmed that the NDVI derived by remote sensing approach could be a useful index to evaluate vegetation status and water demand of farmlands in the desert borders.
Sh. Zand-Parsa, F. Ghasemi Saadat Abadi, M. Mahbod, A. R. Sepaskhah,
Volume 24, Issue 2 (7-2020)
Abstract
Due to the limited water resources and growing population, food security and environmental protection have become a global problem. Increasing water productivity of agricultural products is one of the main solutions to cope with the difficulties. By optimizing applied water and nitrogen fertilizer, the pollution of groundwater could be deceased and the water productivity could be increased. The aim of this research was to determine the relationships between water productivity (IRWP) and water use efficiency (WUE) and different amounts of applied water (irrigation + rain fed) and nitrogen (applied and residual). This study was conducted on wheat (Triticum aestivum L., cv. Shiraz) in Shiraz University School of Agriculture, based on a split-plot design with three replications, in 2009-2010 and 2010-2011 periods. Irrigation treatments varied from zero to 120% of full irrigation depth, and nitrogen fertilizer treatments varied from zero to 138 kg ha-1 under basin irrigation system. The experimental data of the first and second years were used for the calibration and validation of the proposed relationships, respectively. The calibrated equations using the dimensionless ratios of irrigation depth plus rainfall, actual evapotranspiration and nitrogen fertilizer plus soil residual nitrogen to their amounts in full irrigation and maximum fertilizer amounts were appropriate for the estimation of water productivity and water use efficiency. The values of the determination coefficient (R2) for water productivity and water use efficiency (0.88 and 0.93, respectively), and the values of their normalized root mean square error (NRMSE) (0.2 and 0.13, respectively) showed a good accuracy for the estimation of IRWP and WUE.
J. Jalili, F. Radmanesh, A. A. Naseri, M. A. Akhond Ali, H. A. Zarei,
Volume 24, Issue 3 (11-2020)
Abstract
Agricultural water management studies require accurate information on actual evapotranspiration. This information must have sufficient spatial detail to allow analysis on the farm or basin level. The methods used to estimate evapotranspiration are grouped into two main groups, which include direct methods and indirect or computational methods. Basics of the indirect methods are based on the relationship between meteorological parameters, which impedes the use of these data with a lack or impairment. On the other hand, this information is a point specific to meteorological stations, and their regional estimates are another problem of uncertainty of their own. To this end, the use of remote sensing technology can be a suitable approach to address these constraints. Real evapotranspiration can be estimated by satellite imagery that has short and long wavelengths and is estimated using surface energy equations. Examples of such algorithms include SEBAL, METRIC, SEBS. Among the above mentioned algorithms, SEBAL and SEBS have been used. Among the factors of superiority of the SEBAL and SEBS algorithms, in comparison with other remote sensing algorithms, is a satellite imagery analysis algorithm based on physical principles and uses satellite simulation and requires minimum meteorological information from ground measurements or air models.
N. Salamati, A. Danaie,
Volume 24, Issue 4 (11-2020)
Abstract
In order to study and evaluate the drought stress indices in surface irrigation by furrow method on grain yield, the yield components and water use efficiency, an experiment was conducted at Behbahan Agricultural Research Station in 2014-16. The experiment was conducted as a split plot in a randomized complete block design with 4 replications. Irrigation at two levels (irrigation after 100 and 200 mm evaporation from Class A pan, respectively) was evaluated as the main factor and corn cultivar was considered at 6 levels as the sub-factor. Comparison of the mean water use efficiency in irrigation and cultivar interactions showed 100 mm evaporation from Class A pan and cultivars V4 (PH1), V5 (PH3) and V2 (SC Mobin) were ranked the first and foremost, respectively, with the yields of 1.353, 1.299 and 1.296 kg of corn per kg of water consumed, respectively. The mean water consumed in 2014 of the experiment in 100 and 200 mm evaporation from Class A pan was 521.2 and 462.4 mm, respectively. Pearson correlation coefficient results also showed that with increasing the yield components, such as the number of grains per row and number of rows, the 1000-grain weight was increased due to the highly significant correlation coefficient of 1000-grain weight with grain yield (r = 0.8776). Consequently, grain yield was also increased. The highest values of SSI, STI, MP, TOL, GMP HM and YI indices were calculated in V4 (PH1). The higher values of the above indices in cultivar V4 (PH1) than other cultivars caused this treatment to be introduced as the superior one. The decreasing trend of corn yield, which was caused by water deficit stress, increased SSI, STI, MP, TOL, GMP and YI indices, while it decreased corn yield, leading to incremental changes in the YSI indices.
S. Banihashemi , S. S. Eslamian, B. Nazari,
Volume 25, Issue 2 (9-2021)
Abstract
The upcoming climate change has become a serious concern for the human society. These changes, caused and aggravated by the industrial activities of the international community and the increase in the concentration of greenhouse gases in the atmosphere, are seen as a threat to the food security and environment. Temperature change and precipitation are studied in the form of different probabilistic scenarios in order to have an outlook for the future. The present study was conducted to address the effects of climate changes on temperature and precipitation in Qazvin plain in the form of five AOGCMs including Hadcm3, CSIRO-MK3, GFDL, CGCM3 and MICROC3.2, and 3 greenhouse gas emission scenarios of A1B, A2 and B1, based on different possible scenario combinations in the next 30 years, 2021-2050 and 2051-2080 (near and far future). On basis of the study results, all 4 target stations, on average, will have experienced a change between two ratios of 0.5 and 1.4 of the observed precipitation period by the end of 2050, and the mean temperature will have had a change between -0.1 to 1.6 °C, relative to the observed period. By the end of 2080, the precipitation will also have fluctuated between the two proportions of 0.5 and 1.7 times of the observed precipitation period and the mean temperature will touch an increase between 0.6 and 2.6 °C. Both SPI and SPEI indices suggest the increment in the number of dry periods in the near and far future. However, the total number of negative sequences differed considering the 3, 12 and 24-month intervals at the stations level. Given the SPEI index, as compared to the base period, the total negative sequences of drought and number of dry periods will increase at 3 stations of Avaj, Bagh-Kowsar and Shahid-rajaei-powerhouse and decrease at Qazvin station in the future; however, SPI gives different results, such that for Bagh-Kowsar, there will be an increase in both total negative sequences of drought and number of dry periods, as compared to the baseline period; three other stations will have more dry periods, specifically, but less total negative sequences. The results reported that the drought events would become severe, and the wet events would become extreme in the future.
Y. Sabzevari, M. Saeidinia,
Volume 25, Issue 2 (9-2021)
Abstract
The FAO Penman-Monteith is a baseline method to estimate reference evapotranspiration. In many cases, it is difficult to access all data, so replacing simpler models with lower input data and appropriate accuracy is necessary. The purpose of this study is to investigate the capability of the experimental models, gene expression programming, stepwise regression, and Bayesian network in estimating reference evapotranspiration. In this research, daily information of the Boroujerd synoptic station in the period of 1996 -2017 was used as model inputs. Based on the correlation between input and output parameters, six input patterns were determined for modeling. The results showed that the Kimberly-Penman model has the best performance among the experimental models. Gene expression programming with fourth pattern and Default Model Operators (R2 = 0.98 and RMSE = 0.9), Bayesian Network with sixth pattern (R2=0.91 and RMSE = 1.01), and stepwise regression with sixth pattern have the most accurate patterns at R2 = 0.91 and RMSE = 0.9 in the training stage. Comparison of the performance of the three models showed that the gene expression programming model was superior to the other two models with the Average Absolute Relative Error (AARE) of 0.12 and the Mean Ratio (MR) of 0.94. The results showed that gene expression programming had an acceptable ability to estimate reference evapotranspiration under the weather conditions of Boroujerd and could be introduced as a suitable model.
H. Ahmadzadeh, A. Fakheri Fard, Mohammad Ali Ghorbani, M. Tajrishy,
Volume 26, Issue 3 (12-2022)
Abstract
Determining the actual evapotranspiration value and analyzing its temporal trend is essential for optimal water resources management in a basin. In the present paper, the actual evapotranspiration time series is simulated and its trend is analyzed according to the trend of climatic variables and land use in the Ajichi basin during the period of 2015-1987. The comprehensive SWAT model was set up, calibrated, and validated for the Ajichi basin. Also, the average of simulated actual evapotranspiration of crops (in wet years) was compared with similar values in the National Water Document. The results of the Mann-Kendall trend test showed that the annual rainfall in most meteorological stations had a decreasing trend and the rainfall trend in the ten stations decreased significantly. While the annual maximum temperature at all stations and the annual minimum temperature in most of them have significantly increased. Investigation of land use maps illustrated that the irrigated land area of the basin has increased by a 39% during the study period. According the study's results, the potential evapotranspiration of the basin has had a significant increasing trend with a rate of 2.54 mm per year. The results indicated that despite the increasing trend of potential evapotranspiration and irrigated land area, the actual evapotranspiration of the basin had a significant decreasing trend with a rate of 2.2 mm per year due to the decrease in rainfall.
F. Zolfaghari, S. Eslamian, A.r. Gohari, M.m. Matinzadeh, S. Azadi,
Volume 29, Issue 2 (7-2025)
Abstract
Drought represents one of the most critical natural disasters, exerting profound impacts on agriculture, society, the economy, and water resources. Various indices are used to monitor drought and its effects. This study aims to monitor drought in the Zayandeh-Rud Basin using the Standardized Precipitation Index (SPI), the Standardized Precipitation-Evapotranspiration Index (SPEI), the Evaporative Demand Drought Index (EDDI), the Palmer Drought Severity Index (PDSI), and the Reconnaissance Drought Index (RDI). All these indices are based on potential evapotranspiration, incorporating parameters such as precipitation, temperature, relative humidity, wind speed, and sunshine duration. These five indices were calculated and evaluated during the statistical period of 1993–2023 for meteorological stations in Isfahan, East Isfahan, Kabootarabad, Daran, Shahreza, Najafabad, and Mobarakeh. After calculating the indices and using spatial zoning maps, the studied stations were compared in terms of these indices. The continuity of dry and wet periods, as well as the intensity of droughts and wet spells, was analyzed. Subsequently, drought intensities during different years in these stations were ranked using the TOPSIS model based on factors such as precipitation, potential evapotranspiration, and station elevation. The results showed that in stations with a dry climate (such as Isfahan, East Isfahan, and Shahreza), drought occurrences (as indicated by higher rankings) have been consecutive over multiple years. Comparing the performance of the indices in the studied stations using spatial zoning maps revealed that the intensity of droughts and wet spells in regions with dry and semi-dry climates was not very significant. However, in areas with humid climates, the fluctuations in drought and wet spell intensities were quite substantial. The findings indicate that the PDSI and EDDI indices are more suitable for evaluating drought in dry climates.
