Research Article
Irrigation
M.R. Alashti; M. Khoshravesh; F. Sadegh-Zadeh; H.M. Azamathulla
Abstract
Introduction
The rapid growth and development of urban communities, coupled with the increased industrial and economic activities in recent years, have led to the production and release of various pollutants into the environment. These pollutants have adverse effects on human health, living organisms, ...
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Introduction
The rapid growth and development of urban communities, coupled with the increased industrial and economic activities in recent years, have led to the production and release of various pollutants into the environment. These pollutants have adverse effects on human health, living organisms, and the overall environment. With limitations in water resources, insufficient rainfall, the looming risk of water crises in many countries, and the escalating pollution of surface and underground water, there is a pressing need for environmental solutions to mitigate these issues. It is important to acknowledge that wastewater often contains pollutants that may render it unsuitable for certain applications. The utilization of biochar derived from cost-effective materials and innovative technologies such as ultrasonics is one avenue that warrants exploration for enhancing water quality. In this approach, a nitrate solution is exposed to both an adsorbent and ultrasonic waves. This dual treatment induces changes in the physical and chemical properties of water, thereby offering potential improvements in water quality.
Materials and Methods
This study aimed to explore the impact of utilizing biochar derived from rice straw, which was coated with iron(III) and zinc cations, and subjected to ultrasonication, on the nitrate adsorption process from aqueous solutions. In order to produce biochar, cheap materials of rice straw were used. The chopped straw was placed in the electric furnace and heated for one hour to reach the desired temperature. Then it was kept at that temperature for 2 hours. After that, the obtained biochar was washed three times with distilled water at a ratio of 1:20 and dried in an oven at 70°C for 24 hours. In this study, two temperature levels, 350 °C and 650 °C, were used for biochar production. Based on the results from pre-tests, it was found that biochars produced at 650 °C exhibited higher nitrate removal efficiency. These biochars were then used for the continuation of the experiments. To optimize the adsorbent dose, pre-tests were conducted using doses of 0.1, 0.3, 0.5, 0.8, and 1 gram of the adsorbent with 40 ml of nitrate solution. The concentrations of nitrate solution tested were 20, 45, 80, 100, 150, and 200 mg L-1. The research involved conducting experiments to determine the optimal parameters for each treatment, with three repetitions conducted in the water quality laboratory of Sari agricultural sciences and Natural Resources University during the years 2021 and 2022. The treatments comprised biochar (B), biochar and ultrasonic (BU), biochar with iron(III) coating (BF), biochar with iron(III) coating and ultrasonic (BFU), biochar with zinc coating (BZ), and biochar with zinc coating and ultrasonic (BZU). In this investigation, Langmuir and Freundlich adsorption isotherms were examined.
Results and Discussion
The results indicated that the BF and BFU treatments exhibited a higher maximum adsorption capacity. The Freundlich isotherm demonstrated higher correlation coefficients for BF, BFU, BZ, and B, suggesting a superior fit of the Freundlich model in these treatments. The better fit of the Freundlich adsorption isotherm indicates the heterogeneity of biochar surface adsorption sites, which means that the adsorption process is not confined to a single constituent layer. Nitrate adsorption on biochar surface is probably influenced by electrostatic adsorption and ion exchange. Conversely, the BZU and BU treatments showed a better fit with the Langmuir model. In the analysis of the Freundlich isotherm, nf values revealed that BF, BFU, and BZ treatments exhibited a favorable adsorption state with a desirable curve shape. The B treatment displayed a normal adsorption state with a linear curve shape, while BU and BZU treatments showed a weak adsorption state with an unfavorable curve shape. The elevated values of adsorption capacity (KF) obtained for BF, BFU, and BZ, namely 1909.414, 1484.22, and 386.63 ((mg g-1)(L mg-1)1/n), respectively, underscore the high nitrate adsorption capacity of these treatments. Also, biochars coated with iron(III) and with iron solution concentration of 10000 mg L-1 had a very good performance in removing nitrate from aqueous solutions. The new ultrasonic technology was able to improve the performance of the tested adsorbents in a period of 5 minutes without the need to stir the mixture of biochar and nitrate solution in the obtained equilibrium times, which were between 60 and 120 minutes. Application of this technology can be effective and useful in increasing the economic benefits of using limited water resources and increasing the efficiency of water consumption.
Conclusion
The utilization of cost-effective biochars derived from rice straw, along with the application of ultrasonic technology, can substantially decrease nitrate levels in aqueous solutions. In the case of biochar with iron(III) coating, biochar with iron(III) coating combined with ultrasonic treatment, and biochar combined with ultrasonic treatment, there is a notable affinity for nitrate to be adsorbed onto the surface of the adsorbent.
Research Article
Irrigation
A. Zahiri; Kh. Ghorbani; H. Feiz Abady; H. Sharifan
Abstract
IntroductionReservoirs are crucial for water supply to human societies, making their proper and planned management essential. Dams serve multiple purposes, including urban water supply, agricultural irrigation, flood control, and hydroelectric power generation. In order to properly manage and monitor ...
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IntroductionReservoirs are crucial for water supply to human societies, making their proper and planned management essential. Dams serve multiple purposes, including urban water supply, agricultural irrigation, flood control, and hydroelectric power generation. In order to properly manage and monitor the consumption of these important reserves, it is inevitable to know their capacities. Using water stage and the reservoir's initial volume-area-elevation curve, which is prepared with the hydrographic operations, is a common method for estimating the storage capacity of reservoirs at different water levels. Over time, the occurrence of numerous sedimentations, often due to factors such as floods, can alter the initial volume-area-elevation curve of a reservoir, requiring it to be updated. Hydrographic operations, using tools like eco-sounders, are conventional methods for updating this curve; however, these methods are both expensive and time-consuming. In recent years, various studies have focused on remote sensing techniques aimed at estimating the volume of water stored in reservoirs, using water levels to establish the surface area-elevation curve. The basis of these studies is the separation of water-land masks using spectral indices, the calculation of water levels, and the development of reservoir surface area-elevation curves through linear or polynomial relationships. However, the main limitation of these methods is the inaccuracy of linear or polynomial relationships in fitting the surface area-elevation curves at the beginning and end points of the water stage change interval, which correspond to the empty or full states of the reservoir. This inaccuracy arises due to factors such as drought or flood events. In this research, the limitation of linear and polynomial relationships in accurately predicting the points of the reservoir surface area-elevation curves, where observational data are unavailable due to non-occurrence, was addressed by using the Modified Strahler method to draw the hypsometric curve. This method allows for the calculation of the storage capacity of the reservoir between successive water levels and the determination of the final volume of water stored in the reservoir. By comparing the volumes of water stored at the present and initial reservoir capacities, the sedimentation rate and the useful life of the Negarestan Dam reservoir were estimated. Material and MethodsNegarestan Dam (Kabudval) is located on the Qarasu (Zarin Gol) river, 45 km east of Gorgan in the Golestan Province. This dam is used for purposes such as supplying urban water to Aliabad city and supplying water needed for the agricultural irrigation network of Qarasu. In this study, landsat8 satellite images were used to estimate the useful life of the Negarestan reservoir. The required images of the ROI were downloaded through the USGS database and pre-processed in Envi5.3 software. Using visible and infrared spectral bands, water indices NDWIMCFeeters, NDWIGao, MNDWI, AWEISh and TCWet were calculated to separate land-water masks. After evaluating the accuracy of the obtained water level results by comparing it with the initial volume-area-elevation curve of Negarestan reservoir, the MNDWI index was used as the most accurate index to calculate water levels. In this study, the modified Strahler method was used to obtain the hypsometric curve of the surface area-elevation of the reservoir, which has high accuracy in extrapolating the beginning and end points of the curve. By using the hypsometric curve, water levels were extracted for arbitrary water levels, and with the help of the prismoidal method, the volume between consecutive water levels was calculated. The sum of these volumes equaled the current storage capacity of the reservoir. To estimate the sedimentation rate of the Negarestan Dam reservoir, the current storage capacity was compared with the initial storage capacity in 2015. Based on this comparison, the useful life of the reservoir was accurately predicted. Results and DiscussionValidation results for calculating water surface areas using NDWIMCFeeters, NDWIGao, MNDWI, AWEISh and TCWet water indices showed that the MNDWI index with an average water surface areas calculation error equal to 5% is more accurate than other indices. Therefore, the MNDWI index was used in this study. Additionally, the comparison of the volume of water stored in the Negarestan reservoir with its initial storage capacity at the time of operation revealed that, over a period of 9 years, the storage capacity of the reservoir (at a water level of approximately 189.5 meters), which is close to the overflow crest level, had significantly decreased. It has decreased from about 24 to 20 million cubic meters, based on which the average annual sedimentation rate of the reservoir was estimated, to about 1.6%. The results showed that in a period of 9 years, the average level of the bathymetry of Negarestan reservoir has increased by 10 meters due to the accumulation of sediments, and the minimum level of the batymetry has reached from 160 to about 170 meters. According to the statistics of the International Commission on Large Reservoirs (ICOLD), the average annual sedimentation rate of the world's reservoirs is reported to be about 0.95%, and the results show that this amount in the Nagaristan Dam reservoir is almost 2 times the average rate. It is universal. According to the results obtained from this research and assuming constant climatic conditions, the useful life of the Nagarestan dam reservoir was estimated to be about 53 years from the beginning of 2024. ConclusionConsidering the increasing importance of water resources management, including dam reservoirs, this study employed a fast and cost-effective method based on remote sensing to calculate the volume of water stored in dam reservoirs and estimate their useful life. In addition to providing appropriate accuracy, this method was able to overcome the limitations of previous approaches in estimating the volume of accumulated sediment in the deeper parts of the reservoir. As a result, it offers a reliable tool for the effective management of water resources.
Research Article
Irrigation
N. Bahremand; H. Aroiee; A. Aien
Abstract
Introduction
Watermelon (Citrullus lanatus) is a widely recognized product with high demand, nutritional value, and export potential worldwide. Since the ultimate goal of agricultural production systems is to maximize plant yield, providing sufficient water to the plant is one of the most critical factors ...
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Introduction
Watermelon (Citrullus lanatus) is a widely recognized product with high demand, nutritional value, and export potential worldwide. Since the ultimate goal of agricultural production systems is to maximize plant yield, providing sufficient water to the plant is one of the most critical factors influencing yield. Therefore, investigating the effects of water limitation is an essential and undeniable necessity. On the other hand, deficit irrigation has been introduced as an approach to increase water productivity. Therefore, it is essential to consider the effects of this water-saving method on plant production, which highlights the need for further research. Deficit irrigation involves supplying only a portion of the plant's water requirements, while regulated deficit irrigation is a specific type of deficit irrigation that can be applied in various ways, such as irrigation based on growth stages, or allocating water to stages that are more sensitive to drought. It is important to recognize that plant response to water deficit depends on several factors, including climatic conditions, plant type, the intensity and method of deficit irrigation application, soil condition, and management practices.
Materials and Methods
In order to determine the effect of deficit irrigation and regulated deficit irrigation on yield and water productivity of the watermelon, an experiment in the form of randomized complete blocks with 8 treatments including three irrigation levels of 100, 70 and 50 % of the plant's water requirement (evapotranspiration estimated by the FAO-Penman-Monteith method) and 5 regulated deficit irrigation levels including 50% of the water requirement in the stages of seedling, vine, flowering, fruit expansion and fruit maturity were carried out with three replications under black plastic mulch, during 2020-2022, in the Research and Education Center of Agriculture and Natural Resources in the south of Kerman province. Irrigation as the main plot at three levels of 100, 70 and 50% of water requirement and mulching at three levels of crushed date palm leaf, black plastic and no mulch, as the sub-plot, were considered. Crimson B 34 watermelon seeds produced by Seminis company, were planted on January 2021, in plots with the size of 13.5 × 7 m, on furrows and ridges planting system (the width of furrows and ridges were 0.5 and 4 meters, respectively). After planting, bow-shaped wires were put on the planting rows and a transparent plastic was placed as a tunnel on them. In the first year, the total depth of the irrigations in aforesaid treatments were respectively 444, 321, 237, 413, 389, 435, 345 and 425, and in the second year 427, 303, 223, 395, 373, 416, 331 and 405 mm.
Results and Discussion
The results showed that the highest and lowest yield were observed in full irrigation and irrigation 50 % (60.1 and 16.3 t ha-1 respectively). Among the regulated deficit irrigation treatments, irrigation 50% at the seedling stage was the closest to full irrigation, and the irrigation 50 % at the fruit expansion stage had the lowest yield. The highest water productivity belonged to the irrigation 50 % in the seedling and vine stages (15.9 and 1.15 kg m-3 respectively). Irrigation 50% at fruit maturity stage despite half irrigation, improved Qualitative characteristics such as soluble solids, vitamin C, dry matter, lycopene and fruit taste.
Conclusion
Applying deficit irrigation led to a significant decrease in watermelon yield compared to full irrigation (control). Water productivity remained nearly constant, and there was no significant improvement in the quality of the edible part. However, treatments involving regulated deficit irrigation, such as irrigation during the seedling stage, showed similar yield to full irrigation, while the 50% irrigation during the vine stage resulted in higher water productivity. Additionally, 50% irrigation during the fruit maturity stage produced superior fruit quality compared to the control. Overall, regulated deficit irrigation yielded better results than deficit irrigation due to less yield reduction, increased water productivity, and improved fruit quality, especially under water-restricted conditions. Finally, it is recommended that milder intensities of deficit irrigation that seem to have more favorable results in this plant should be investigated in the next studies.
Research Article
Soil science
A. Sarabchi; H. Rezaei; F. Shahbazi
Abstract
Introduction
High-resolution satellite imagery data is widely utilized for Land Use/Land Cover (LULC) mapping. Analyzing the patterns of LULC and the data derived from changes in land use caters to the increasing societal demands, improving convenience, and fostering a deeper comprehension of the interaction ...
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Introduction
High-resolution satellite imagery data is widely utilized for Land Use/Land Cover (LULC) mapping. Analyzing the patterns of LULC and the data derived from changes in land use caters to the increasing societal demands, improving convenience, and fostering a deeper comprehension of the interaction between human activities and environmental factors. Although numerous studies have focused on remote sensing for LULC mapping, there is a pressing need to improve the quality of LULC maps to achieve sustainable land management, especially in light of recent advancements made. This study was carried out in an area covering approximately 8000 hectares, characterized by diverse conditions in LULC, geomorphology and pedology. The objective was to investigate the potential for achieving maximum differentiation and accurate mapping of land features related to LULC. Additionally, the study assessed the impact of various spectral indices on enhancing the results from the classification of Landsat 8 imagery, while also evaluating the efficacy of support vector machine (SVM) and maximum likelihood algorithms in producing maps with satisfactory accuracy and precision.
Materials and Methods
As an initial step, LULC features were identified through fieldwork, and their geographic coordinates were recorded using GPS. These features included various types of LULC, soil surface characteristics, and landform types. Following the fieldwork, 12 types of LULC units were identified. Subsequently, the LULC pattern in the study area was classified using the RGB+NIR+SWIR1 bands of Landsat 8, employing both SVM and maximum likelihood classifiers. To assess the impact of various spectral indices on improving the accuracy of the LULC maps, a set of vegetation indices (NDVI, SAVI, LAI, EVI, and EVI2), bare soil indices (BSI, BSI3, MNDSI, NBLI, DBSI, and MBI), and integrated indices (TLIVI, ATLIVI, and LST), and digital elevation model of study area were successively incorporated into the classification algorithms. Finally, the outcomes from the two classification algorithms were compared, taking into account the influence of the applied indexes. The classification process continued with the selected classifier and indices until reaching the maximum overall accuracy and kappa coefficient.
Results and Discussion
Field observations revealed that the study area could be categorized into 12 primary LULC units, including irrigated farms, flow farming, dry farming, traditional gardens (with no evident order observed among planted trees), modern gardens (featuring regular rows where soil reflectance is visible between tree rows), grasslands, degraded grasslands, highland pastures (covered by Astragalus spp., dominantly), lowland pastures (covered by halophyte plants), salt domes (with no or very poor vegetation), outwash areas (River channel with many waterways), and resistant areas. The results of image classification indicated that the performance of the SVM algorithm across different band combinations is superior to that of the maximum likelihood method. Using SVM resulted in an increase in overall accuracy and Kappa coefficient by 3-8% and 0.03-0.08, respectively. For the map generated using RGB+NIR+SWIR1 bands and employing SVM, overall accuracy and Kappa coefficient were determined to be 76.6% and 0.72, respectively. Among the vegetation indices used in the SVM algorithm, LAI had the most significant impact, increasing the classification accuracy by 2.64%. Among the soil indices, BSI and MBI indices demonstrated the best performance; with BSI increasing the classification accuracy by 1.95% and MBI by 1.64%. Among the integrated indices, LST and ALTIVI enhanced the classification accuracy by 2.75% and 2.35%, respectively. It should be noted that the inclusion of the digital elevation model did not significantly improve the classification accuracy when using the support vector machine algorithm; in fact, it led to a decrease in accuracy when applied to the maximum likelihood classification. The probable reason for this issue is the different nature of DEM data compared to the other input data, as well as the limitations of parametric statistical approaches to effectively integrating data from diverse sources. Finally, the classification process was executed using the three visible bands, NIR, and SWIR1, in conjunction with selected indices (LAI, BSI, MBI, LST, and ALTIVI). Results indicated that using these spectral indices significantly improved classification accuracy, particularly for the DF, DGL, MG, O, and IF land cover/use classes. The calculated accuracies for these classes increased by 11.62%, 18.57%, 20.06%, 29.39%, and 33.19% respectively. Consequently, the accuracy of the classification and the Kappa coefficient (using support vector machine algorithm) increased to 85.24% and 0.82, respectively.
Conclusion
In this research, we aimed to accurately map various land use/land covers by utilizing Landsat 8 imagery and incorporating three group of spectral indexes. Despite spectral interferences and overlaps among various phenomena related to LULC, the utilization of different spectral indices resulted in significant differentiation among LULC classes. Finally, considering the limitations of modelling in ENVI software, it is recommended to investigate the effectiveness of other models for classification in more specialized software, such as R.
Research Article
Soil science
M. Malehmir Chegini; AHMAD GOLCHIN
Abstract
Introduction
Soil contamination with heavy metals significantly threatens both environmental and human health. Anthropogenic activities, including chemical fertilizers and pesticides, industrial processes, wastewater disposal, and mining, contribute to the accumulation of heavy metals in soil. Plants ...
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Introduction
Soil contamination with heavy metals significantly threatens both environmental and human health. Anthropogenic activities, including chemical fertilizers and pesticides, industrial processes, wastewater disposal, and mining, contribute to the accumulation of heavy metals in soil. Plants can then taken up these contaminants and enter the food chain, causing various health problems. Soil amendments such as biochar and activated carbon offer a promising strategy for reducing the mobility and bioavailability of heavy metals in soil. This study investigated the effectiveness of biochar and activated carbon derived from organic waste materials (wheat straw, walnut shells, and almond shells) in immobilizing lead (Pb), zinc (Zn), and cadmium (Cd) and promoting corn (Zea mays. L.) growth in a greenhouse setting using contaminated soil.
Materials and Methods
Three types of organic waste wheat straw, walnut shells and almond shells were pyrolyzed at two temperatures (300 °C and 500 °C) under oxygen-free conditions for two hours to produce six types of biochar. The resulting biochars were then activated with phosphoric acid at their respective production temperatures, yielding six types of activated carbon. These organic waste materials, biochar, and activated carbons were added to soil contaminated with lead, zinc and cadmium at four application rates (0, 2.5, 5, and 10% by weight) in triplicate, 4.5 Kg Pot-1. The pots were incubated for one month under controlled temperature and humidity to achieve a relative equilibrium. Following incubation, the concentration of available heavy metals in the treated and control soils was measured. Corn was then planted in the pots, and at the end of the growth period, plant growth parameters (dry weight of shoots and roots) and heavy metal concentrations in plant tissues were determined. The data were analyzed using a completely randomized factorial design, and treatment means were compared to each other and the control.
Results and Discussion
Increasing pyrolysis temperature resulted in increased biochar pH, electrical conductivity (EC), and ash content, while the percentage of organic carbon, C/N ratio, and cation exchange capacity (CEC) decreased. Activation with phosphoric acid lowered the pH, ash content, EC, and organic carbon content of the biochars, while increasing their CEC. Amending the soil with biochar significantly increased soil pH and EC, whereas activated carbon amendments decreased these parameters. All amendments (organic waste, biochar, and activated carbon) significantly reduced the concentration of available heavy metals in the soil. Activated carbon had the greatest effect on immobilization, while organic waste had the least. The lowest concentrations of lead, cadmium, and zinc extractable with DTPA were observed with the 500°C activated carbon derived from wheat straw at a 10% application rate, with values of 1.6, 4.5, and 464 mg kg-1 soil, respectively, representing reductions of 99.46%, 83.67%, and 63.96% compared to the control treatment. This treatment also resulted in the lowest heavy metal concentrations in both the aerial parts and roots of the corn plants. Specifically, the lowest concentrations of lead, zinc, and cadmium in the aerial parts were 71.67, 490.67, and 1.67 mg kg-1 dry weight, respectively, while in the roots, they were 206, 1095, and 20 mg kg-1 dry weight, respectively. The highest dry weights of the aerial parts and roots were also observed with this treatment and a 5% application rate, with values of 5.76 and 1.84 grams per pot, respectively. The lowest concentration of heavy metals in corn tissues was observed in treatments with activated carbon produced at 500 °C and applied at a rate of 10%.
Conclusion
This study demonstrates that activated carbon derived from organic waste materials can be an effective and sustainable method for remediating soil contaminated with heavy metals and promoting plant growth. However, the presence of detectable heavy metals in corn tissues following activated carbon application suggests that this approach may be best suited for soils with low to moderate contamination levels.
Research Article
Agricultural Meteorology
Kh. Javan; A. Movaghari
Abstract
Introduction
The most important effect of global warming is the increase in extreme weather events. According to AR5 reports, between 1951 and 2010, the number of warm days and nights increased and the number of cold days and nights has declined globally. In addition, the duration and frequency of hot ...
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Introduction
The most important effect of global warming is the increase in extreme weather events. According to AR5 reports, between 1951 and 2010, the number of warm days and nights increased and the number of cold days and nights has declined globally. In addition, the duration and frequency of hot periods, including thermal waves, have increased since the middle of the twentieth century. The trend analysis of temperature extreme indices is important in estimating the trend of global warming. Temperature Changes are affected by many complex factors. A significant part of these changes is due to the elements of the general circulation of the atmosphere and the sea surface temperature. Given that extreme weather events are one of the most devastating natural hazards and have harmful effects on different parts of society, therefore, many researchers have studied the changes in the past and future of extreme events and the mechanisms that trigger these changes. This research attempts to study the trend of changes in extreme temperature indices in North-West of Iran, and also their relation with general circulation of atmosphere.
Materials and Methods
At first, diurnal data of minimum and maximum temperature of 20 synoptic stations of the Northwest of Iran, which have long-term and reliable statistics, extracted for the period of 1986-2010 and quality control and data homogeneity of them were investigated. afterwards, 16 Extreme temperature indices introduced by ETCCDMI were applied. In general, these indices are categorized into five categories of absolute indices, based on percentiles, based on thresholds, periodic, and amplitudes that measure the frequency, severity and duration of the temperature. These indices are estimated by RClimDex software and the trend rate of the changes in indices was shown through maps. To measure the changes in the general circulation of atmosphere the annual mean circulation composites extracted for the periods of 1961-1985 and 1986 -2016 based on the reanalysis data of the NCEP / NCAR. Then the difference maps plotted using grads software.
Results
The regional trend of extreme indices and the percentage of stations with a positive and negative trend were identified and the spatial distribution of the gradient of each of the indices was mapped. The results show that all absolute temperature indices have an increasing trend. On average, the maximum temperature (TXx and TXn) has increased by about 0.04 degrees over the decade. The increase rate of TNx is about 0.03 degrees, while the TNn increased by about 0.1 degrees Celsius per decade during the study period. Therefore, in the north-west of Iran, temperature increase has mainly occurred at night. The values of cold days (TX10) and cold nights (TN10) decreased with a gradient of -0.46 and -0.42 days in the decade. The warm days (TX90) and warm nights (TN90) have an increasing trend in 95% of the stations in the area. Frost days (FD) and icing days (IDs) have a decreasing trend, whereas, summer days (SU25) and tropical nights (TR20) have an increasing trend. The number of frost days with a gradient of -0.95 and the number of icing days with a gradient of -0.63 days in decade are decreasing. While, the number of summer days with a gradient of 0.81 and the number of tropical nights with gradient of 0.31 days in decade are increasing. In the northwest of Iran, all stations have been experiencing the increasing trend in Warm Spell Duration Index (WSDI), but the Cold Spell Duration Index (CSDI) in 70% of the stations in the region has decreased. Growing season length, as an effective index especially in agriculture, is increasing by an average of 1.1 days per decade. Based on the results of research carried out globally and at Iran, the trend of Daily Temperature Range (DTR) is negative, while this index has a positive and increasing trend in 65% of North-West stations in Iran. Except TNx and TNn indices that have positive trend in most stations in the region, Comparison of warm and cold extreme indices indicates that warm indices have a positive and incremental trend, while cold indicators show a decreasing trend. The positive gradient of these indices also corresponds to the decreasing trend of cold day and night indices, which indicates an increase in temperature and a decrease in cold days and nights. The study of large-scale changes in atmospheric circulation shows that the study area has got warmer in the spring and summer and colder in autumn and winter.
Conclusion
In this study, the trend of temperature extreme indices in North-West of Iran and its relation with the large-scale general circulation of the atmosphere have been investigated. The results show that all absolute temperature indices (TXx, TXn, TNx and TNn) are incremental. The indices of cold days (TX10) and nights (TN10) decreased with a gradient of -0.46 and -0.42 days in the decade and the indices of warm days (TX90) and warm nights (TN90) are increasing in 95% of the stations in the area. Frost days and icing days (IDs) show declining trend and summer days (SU25) and tropical nights (TR20) have an increasing trend. In the north-west of Iran, all stations have experienced an increasing trend in warm spell duration index (WSDI), but the cold spell duration index (CSDI) has been decreasing in 70% of the stations in the area. Growing season length (GSL) is increasing by an average of 1.1 days in every decade. Daily temperature range (DTR) has a positive and increasing trend in 65% of stations in north-west Iran. Comparison of warm and cold extreme indices indicates that warming indices have a positive and incremental trend, while cold indices show a decreasing trend. Study of the general circulation of atmosphere of the region by drawing and analyzing difference maps indicates that the study area has been warmer in spring and summer and colder in autumn and winter.
Research Article
Agricultural Meteorology
H. Fahimi; A. Faraji; B. Alijani
Abstract
Introduction
A subtropical high system that significantly impacts the Iranian climate is the Arabia Anticyclone (Raziei, 2012). This high-pressure system is located southeast of the Red Sea, over the Arabian Peninsula and the Arabian Sea. It is one of the semi-permanent centers in the lower levels of ...
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Introduction
A subtropical high system that significantly impacts the Iranian climate is the Arabia Anticyclone (Raziei, 2012). This high-pressure system is located southeast of the Red Sea, over the Arabian Peninsula and the Arabian Sea. It is one of the semi-permanent centers in the lower levels of the atmosphere, and its influence leads to notable climate changes and characteristics in the region (Karimi, 2016). This system is a component of atmospheric circulation affecting cold-period precipitation in Iran (Karimi et al., 2021); due to its dynamic structure, it has a great ability to provide humid air, especially in the lower layers (Mohammadi & Lashkari, 2018). So far, some studies have been conducted on subtropic high's effect on the Iranian climate, but its impact on the occurrence of precipitation in Iran, especially during the cold period of the year, has received less attention. Therefore, in this study, we aimed to examine the role of the Arabia Anticyclone (AA) subtropical high in the pervasive extreme precipitation during the cold season in Iran. By analyzing its influence at different atmospheric levels, we sought to gain a clearer understanding of how this system affects precipitation patterns in Iran. The study also explores the changes in the AA at various atmospheric levels and its relationship with other atmospheric circulation systems, as well as how these factors contribute to the occurrence of extreme precipitation events in the region.
Materials and Methods
Daily precipitation data of Iranian synoptic stations from 1989 to the end of 2020 were extracted from the Meteorological Organization of Iran. Based on the relative index method, the 95th percentile index of extreme precipitation for all days and all the stations were calculated and extracted by MATLAB software. The criterion was as follows: If at least 20% of the synoptic stations in Iran have extreme precipitation (in case of spatial homogeneity), the days with pervasive/extreme precipitation were obtained, which amounted to 450 days in the entire period. The isohyetal map of 450 days of extreme/pervasive precipitation was drawn in Surfer software to identify the spatial homogeneity of days with extreme/pervasive precipitation because days with this kind of precipitation did not necessarily have spatial homogeneity. The 450 days with extreme/pervasive precipitation were arranged in ascending order, and 7 patterns with the highest extreme precipitation and the highest spatial homogeneity during the cold period of the year (October-March) were selected. Upper atmospheric data of the selected days were then specified to plot and analyze the synoptic maps. The required atmospheric data were geopotential altitude (meter), wind speed (m/s), wind direction, specific humidity (g/km), and average sea-level pressure. The data used were ERA5 data extracted from https://www.ecmwf.int. The data were extracted at three levels: lower, middle, and upper. To synoptically analyze the selected patterns using the selected upper atmosphere data, the following maps were plotted in Grads software:
A) Combined map of geopotential altitude and winds was plotted at the selected levels to determine the geographical location of the subtropical high, its displacement at different levels of the troposphere, its penetration, and its impact on Iran.
B) Combined maps of specific humidity, geopotential altitude, and wind were plotted in order to identify the role of the subtropical high in the transfer of humidity and its transfer to Iran at different levels.
Conclusion
In selected patterns, the AA with its anticyclonic current and passing through tropical warm waters, leads to the transfer of tropical humidity to subtropical and extratropical regions. At different atmospheric levels, the location and establishment of the Anticyclone central nucleus and its degree of expansion towards the north and west are determined by the tropical penetration of the cut off lows and the western trough. The AA has the most dominance over Iran in the lower level. In fact, in the lower level, Iran is dominated by two patterns of cut off low in the western and northern regions and the AA in the southern and eastern regions.
Due to the greater penetration of the southern branch of the westerlies and the orbitalization of the western currents in the middle level, the AA is displaced eastward and southward. The interaction and accompaniment of the AA and the mid-latitude cut off low form an atmospheric river with a tropical origin. The AA plays an important role in transferring the atmospheric river to Iran and its humidity feeding. On the maps, the southerly and easterly displacement of the AA Arabia is an important factor in the lack of formation of an atmospheric river in East Central Africa. By transferring tropical humidity to Iran, the humidity of the extreme pervasive precipitation is supplied. Another major role played by the AA is to strengthen the ITCZ humidity in East Central Africa, where tropical humidity ascends through the cut off low, West trough, and jet streams. The AA takes the Indian Ocean humidity to eastern Central Africa with its anticyclonic movement. At the ground level, the AA diverts humidity from the Arabian Sea and the Persian Gulf to the western and northwestern regions, preventing Turkey low from entering the western and southwestern regions of Iran. Furthermore, by entering the South Red sea, prevents the entry of the Sudan low into the Middle East and prevents the entry of precipitation systems into Iran. However, in supplying humidity to the extreme pervasive precipitation of Iran, it plays a very important role both by creating an atmospheric river in interaction with the mid-latitude cut off low and by transferring humidity through its anticyclonic flow.
