Different Climatic Conditions In Iran Research Articles

Assessing the viability of using ground-air heat exchangers during winter months in different climatic conditions of Iran

ABSTRACT Ground combined with subsurface tubes as heat exchangers, known as Ground-Air Heat Exchangers (GAHEs), have recently gained attention for heating and cooling. However, several simplifications were used to capture complex airflow characteristics in previous studies which potentiate inaccuracy in their results. This gap is addressed in this study by developing a 3D transient model incorporating realistic heat dynamics and turbulent airflow simulation using the k-epsilon model over a complete temperature cycle. The experimental result serves to corroborate the model’s accuracy. Further, the model is utilised to assess energy-conversion potential of GAHEs for heating a generic building during January in four Iranian cities with different climates. Findings show distinct differences between the GAHE’s energy-conservation capacity in these cities. The GAHE can conserve up to 714.6 kWh of energy monthly in the coldest climate and reduce peak heating loads by up to 36.0% in the hottest climate, with these averages observed across all soil types. GAHE energy saving is increased up to 27.7% when the soil around it is silt with a higher conductivity. Additionally, an adverse impact on building’s heating is created by the GAHE in some cases, highlighting the significance of hourly management of the system. Highlights A 3D transient numerical scheme was created based on fluid mechanics principles to simulate a multitube GAHE, and the solution was verified using empirical data. The effectiveness of the GAHE and its ability to reduce the maximum heating demand of a particular building for different climates within Iran in January were examined. The impact of soil characteristics on the energy-saving capability of the GAHE was found to be significant in the four cities under study, and a distinct difference in heat flux to the working fluid was discovered in different climates.

Building integrated photovoltaic with hydrogen storage as a sustainable solution in Iranian rural healthcare centers

The reliable and sustainable energy source for supplying energy demand of rural health clinic centers (RHCC) is very important especially in Coronavirus Disease 2019 (COVID-19) epidemic. However, diesel generator due to the fuel supply and environmental challenges can’t be a sustainable source. In this regard a standalone energy system based on solar with hydrogen storage/fuel cell system is proposed to solve this issue. In the present study, five regions with different climatic conditions in Iran are considered and the layout are evaluated for the first time in RHCC with a load demand of about 10 kWh/day. HOMER software is used to optimize the size of the equipment. The results showed the capacity factor (CF) of photovoltaic panels is about 17.4–20.4%, while the CF of electrolyzers is 17–25%. The CF of fuel cell remains similar at about 36–37%. The net present value of the systems ranges 22,000–27,000$ and the levelized cost of electricity ranges 0.28–0.34 $/kWh, with the lowest (highest) values in Kerman(Gylan). The proposed system reduced the consumption of approximately 1,830 L of diesel, resulting in significant environmental benefits. The hybrid renewable energy system combining solar and hydrogen storage can be considered as sustainable solution in RHCC in Iran.

Comparison of different drought monitoring indices in different climatic conditions in Iran

This study evaluates drought in different climate zones (Rasht, Shiraz, and Birjand) in Iran, using meteorological, agricultural, and remote sensing drought indices. For this purpose, NDVI, SAVI, and SR were extracted from Landsat images for 2002 and 2014-2020. Then, these indices were compared with the SPI, SPEI, and PDSI. The results indicate an increase in drought and a decrease in vegetation cover in the study area. In Rasht, where the vegetation cover is high, NDVI and SAVI were equal. In Shiraz and Birjand, where the soil effect is more significant, the distance between these two indices increased, which shows that SAVI performs better than NDVI for Shiraz and Birjand. The results also show that the drought severity could grow with decreasing rainfall and more water demand due to temperature increases, according to SPI, SPEI, and PDSI criteria. The comparison of drought indices showed that the highest correlations were between NDVI plus SAVI and SPI in Rasht, SR and SPEI in Shiraz, and NDVI and SPEI in Birjand. Based on the results of the Mann-Kendall test, the increasing trend of drought in the studied area is confirmed based on the SPI, SPEI, and PDSI. Therefore, it is suggested that remote sensing techniques combined with drought indices can be considered a suitable tool for optimal management of water resources, land use planning, and reduction of costs due to drought.

Evaluation of Seasonal, Drought, and Wet Condition Effects on Performance of Satellite-Based Precipitation Data over Different Climatic Conditions in Iran

The Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Mission (GPM) are the most important and widely used data sources in several applications—e.g., forecasting drought and flood, and managing water resources—especially in the areas with sparse or no other robust sources. This study explored the accuracy and precision of satellite data products over a span of 18 years (2000–2017) using synoptic ground station data for three regions in Iran with different climates, namely (a) humid and high rainfall, (b) semi-arid, and (c) arid. The results show that the monthly precipitation products of GPM and TRMM overestimate the rainfall. On average, they overestimated the precipitation amount by 11% in humid, by 50% in semi-arid, and by 43% in arid climate conditions compared to the ground-based data. This study also evaluated the satellite data accuracy in drought and wet conditions based on the standardized precipitation index (SPI) and different seasons. The results showed that the accuracy of satellite data varies significantly under drought, wet, and normal conditions and different timescales, being lowest under drought conditions, especially in arid regions. The highest accuracy was obtained on the 12-month timescale and the lowest on the 3-month timescale. Although the accuracy of the data is dependent on the season, the seasonal effects depend on climatic conditions.

Evaluation of stability in maize hybrids using univariate parametric methods

Genotype × environment interaction is one of the complex issues of breeding programs to produce high-yielding and compatible cultivars. Interaction of genotype × environment and make the more accurate selection, the performance and stability of hybrids need to be considered simultaneously. This study aimed to investigate stable genotypes with yield using 12 maize hybrids in different climatic conditions of Iran. The experimental design used was a randomized complete blocks design in three replications in two cropping years in Karaj, Birjand, Shiraz, and Arak stations. The simple analysis of variance performed on grain yield of genotypes indicated that all hybrids studied each year and station were significantly different in grain yield. Also, the combined analysis results showed a significant effect on the environment, the effects of genotype, and the interaction of genotype × environment and t in the studied hybrids different. Comparing Duncan's mean on the data obtained from the research, KSC705 genotypes with an average yield of 7.21 and KSC704 genotype with an average yield of 7.04 were identified as high yield cultivars. In order to identify stable cultivars, six stability parameters were used. KSC260 and KSC707 genotypes had stability Based on the environmental variance, also had stability based KSC705, KSC707 genotype on environmental the coefficient of variation, and KSC260 genotypes had stability based methods of genotype and environment interaction. As well as based on Eberhart and Russell regression coefficient had the stability to KSC400 and SC647 genotypes. Also, they were identified as the most stable genotypes based on the detection coefficient method, KSC707, and KSC703 genotypes.

Two Comprehensive and Practical Methods for Simulating Pan Evaporation under Different Climatic Conditions in Iran

Evaporation from surface water plays a crucial role in water accounting of basins, water resource management, and irrigation systems management. As such, the simulation of evaporation with high accuracy is very important. In this study, two methods for simulating pan evaporation under different climatic conditions in Iran were developed. In the first method, six experimental relationships (linear, quadratic, and cubic, with two input combinations) were determined for Iran’s six climate types, inspired by a multilayer perceptron neural network (MLP-NN) neuron and optimized with the genetic algorithm. The best relationship of the six was selected for each climate type, and the results were presented in a three-dimensional graph. The best overall relationship obtained in the first method was used as the basic relationship in the second method, and climatic correction coefficients were determined for other climate types using the genetic algorithm optimization model. Finally, the accuracy of the two methods was validated using data from 32 synoptic weather stations throughout Iran. For the first method, error tolerance diagrams and statistical coefficients showed that a quadratic experimental relationship performed best under all climatic conditions. To simplify the method, two graphs were created based on the quadratic relationship for the different climate types, with the axes of the graphs showing relative humidity and temperature, and with pan evaporation, were drawn as contours. For the second method, the quadratic relationship for semi-dry conditions was selected as the basic relationship. The estimated climatic correction coefficients for other climate types lay between 0.8 and 1 for dry, semi-dry, semi-humid, Mediterranean climates, and between 0.4 and 0.6 for humid and very humid climates, indicating that one single relationship cannot be used to simulate pan evaporation for all climatic conditions in Iran. The validation results confirmed the accuracy of the two methods in simulating pan evaporation under different climatic conditions in Iran.

Integrated long-term planning of conventional and renewable energy sources in Iran's off-grid networks

In this study, a combined power supply system consisting of renewable solar and wind energies with backup and storage equipment including a diesel generator and a Battery Energy Storage System (BESS) with Demand Response (DR) was integrated and optimized, and optimally enhanced the reliability of the sustainable supply of the load demand. This study aimed at investigating the optimization and evaluation of the cost and advantage of combined systems for off-grid power supply in four regions with different climatic conditions in Iran, including Zahedan, Kerman, Birjand, and Hamedan. The simulation results showed that for Zahedan, the cost per kilowatt-hour (kWh) of electricity with one day of autonomy and a maximum LPSP of 5% is $ 0.312 per kWh in the first year. By optimizing and altering LPSP and the optimal number of days of autonomy under various operating conditions, the capacity of the batteries was decreased from 3870 kWh (38%) to 1860 kWh (22%), which is almost half of the previous value. Furthermore, the cost per kWh of electricity in the first year decreased from $0.312 to $0.256. According to the results, such a hybrid system is cheaper than installing each of the solar, wind, or diesel generators separately. The conditions of the other three regions were then examined and analyzed and the results showed a direct correlation between the cost of electricity and the climatic conditions of each region. However, in general, considering the Levelized Cost of Energy (LCOE) with a RE hybrid energy system for many areas away from the grid in Iran and due to climatic conditions and the trend of reducing the final cost, the utilization of renewable energy sources is economically competitive with the main grid and technically feasible. It also can meaningfully diminish environmental pollutants in line with the objectives of the Paris Agreement.

Detection of genomic regions associated with tiller number in Iranian bread wheat under different water regimes using genome-wide association study

Two of the important traits for wheat yield are tiller and fertile tiller number, both of which have been thought to increase cereal yield in favorable and unfavorable environments. A total of 6,349 single nucleotide polymorphism (SNP) markers from the 15 K wheat Infinium array were employed for genome-wide association study (GWAS) of tillering number traits, generating a physical distance of 14,041.6 Mb based on the IWGSC wheat genome sequence. GWAS analysis using Fixed and random model Circulating Probability Unification (FarmCPU) identified a total of 47 significant marker-trait associations (MTAs) for total tiller number (TTN) and fertile tiller number (FTN) in Iranian bread wheat under different water regimes. After applying a 5% false discovery rate (FDR) threshold, a total of 13 and 11 MTAs distributed on 10 chromosomes were found to be significantly associated with TTN and FTN, respectively. Linked single nucleotide polymorphisms for IWB39005 (2A) and IWB44377 (7A) were highly significantly associated (FDR < 0.01) with TTN and FTN traits. Moreover, to validate GWAS results, meta-analysis was performed and 30 meta-QTL regions were identified on 11 chromosomes. The integration of GWAS and meta-QTLs revealed that tillering trait in wheat is a complex trait which is conditioned by the combined effects of minor changes in multiple genes. The information provided by this study can enrich the currently available candidate genes and genetic resources pools, offering evidence for subsequent analysis of genetic adaptation of wheat to different climatic conditions of Iran and other countries.

Techno-economic assessment of a hybrid system for energy supply in the affected areas by natural disasters: A case study

Natural disasters are considered as severe humankind’s challenges, which would make a large number of people homeless. Hence, it is vital to provide people with temporary shelters, energy, and freshwater. The purpose of this article is to find the most reliable and economical way to supply energy and water for the residential and health care containers in the different climatic conditions of Iran. Accordingly, a stand-alone hybrid energy system, including solar panels, small wind turbines, fuel generators, and battery banks is taken into consideration. The main objective of this research is to estimate the impact of various parameters such as the project lifetime, dispatch strategies for hybrid system control, and salvage on the optimum system. In addition, a sensitivity analysis regarding the economic and climatic parameters is performed to generalize the results for other areas. The results show that the cycle charging strategy is an appropriate controlling method for a hybrid system, especially for the short-term projects, in which the salvage value causes a high economic uncertainty. In addition, the study indicates that, due to the uniform power generation profile and the affordable cost of energy ranging from 0.130 $/kWh to 0.167 $/kWh, the hybrid system could be practically attainable. For the long-term project, the optimal renewable fraction is between 31.9% and 55.2%; while, for the short-term project, this value is between 12.5% and 21.4%. In the optimum dispatch strategy, for the project lifetime between 4 and 20 years, the impact of salvage on the final cost of the system would vary from 30% to 3%. These results highlight the importance of the salvage parameter in the economic viability of renewable systems.

Thermal Performance of Electrochromic Smart Window with Nanocomposite Structure under Different Climates in Iran

Objective: This study investigated the optimization of thermal energy consumption using electrochromic components with a new nanocomposite layer (WO3+Ag) in a larger size (window) for a room with an educational application for five cities with different climatic conditions in Iran (Yazd, Tehran, Bandar Abbas, Tabriz, and Sari). Materials &amp; Methods: For this simulation platform, the software was implemented in Energy Plus. This feasibility study was modeled by DesignBuilder software which reported reduced thermal energy consumption across all climates in Iran (hot and dry, warm and semi-humid, warm and wet, moderate and dry, and mild and humid.). Four strategies were considered for better comparison. The first strategy used for common double-glazed windows, while the second to fourth strategies involved the use of the electrochromic window in three different modes; bleached mode (Off), colored mode (On), and switchable mode (controlled below comfort conditions). Results: The third and fourth strategies indicated a reduction in thermal energy consumption in different climates from 25 to 45% relative to typical windows. The best result of cooling energy consumption was observed in Tehran. Conclusion: For this climate, the average energy consumption dropped to 34% for the warm months of the year and even 42% for the warmest month of the year (August).

An evaluation for spiral coil type earth-air heat exchanger at different climate conditions

ABSTRACT The experiments have proven that the temperature level of subsoils in the summer and winter is, respectively, lower and higher than the ambient air temperature. The buried tubes in the soil can use this potential to cool or heat the ambient air. The spiral tube heat exchanger is a good choice for earth-air heat exchangers as they are buried in a fixed buried depth, and they serve higher heat transfer coefficient due to the existence of secondary flow in the cross section of tube. In this research, the spiral tube, in an earth-air heat exchanger, has been analyzed, and the performance has been evaluated in different eras and areas of use. Cities have been selected under different climatic conditions in Iran and thus the system had been simulated in both heating and cooling modes. Furthermore, the effects of various factors, such as the depth level of buried heat exchanger in soil, the velocity and the temperature of inlet air on the exhaust air temperature, as well as the thermal load absorbed by the heat exchanger, are all being investigated. Higher buried depth of the heat exchanger increases the transferred heat, while the increase in the inlet air velocity reduces the heat exchange between the soil and the air. Tabriz which is a city located in a semi-arid climate in Iran, serves the best heating and cooling loads; whereas Babolsar another city in Iran which has a humid subtropical climate, indicates the poorest performance of all in comparison to other cities and climate levels in Iran.

Feasibility study of using solar energy as a renewable source in office buildings in different climatic regions

PurposePresent research focus on using solar energy as a renewable option for office buildings in different climatic conditions in Iran. To seeking a way to use clean solar energy and reduce current expense in buildings an investigation carried out. Nine office buildings in various climatic regions selected as case studies. Through a precise examination, buildings specifications, energy demand and climate information carried out. In the first step based on the buildings type and hot water demand, solar water heater systems designed for each case. In the second step, a cost-benefit analysis is done to detriment the economic aspects of implement aforementioned type of solar system. A cost-benefit analysis is done from saving energy and return time of investment point of view. Results indicate that solar water heater with low investment about US$500 and payback time between 2 and 5 years can be noticed as a desirable renewable option in case studies. Furthermore, analysis reveals that thermal load of building is more effective on fuel saving in building, while solar radiation intensity has more effective on the payback in solar water heater utilization.Design/methodology/approachIn this study based on thermal load of nine building office and radiation of different part of Kermnashah province, the possibility of solar water system is investigated.FindingsAnalyses reveal that the thermal load of building is more effective on fuel saving, while solar radiation intensity has more effective on the payback in solar water heater utilization. The main originality goes back to consideration of different meteorological conditions in solar water heater selection.

Comparison of reconnaissance drought index (RDI) and effective reconnaissance drought index (eRDI) to evaluate drought severity

Drought is one of the main natural causes of damages to the ecosystems, agricultural productions, water resources, etc. Many indices have been developed to assess drought severity. Reconnaissance Drought Index (RDI) and Effective Reconnaissance Drought Index (eRDI) are two of the newest indices in drought evaluation. These indices are based on ratio of precipitation and potential evapotranspiration. In this study meteorological data of 22 synoptic stations with different climatic conditions in Iran during 1967–2014 were used to calculate values of RDI and eRDI indices. According to the result of means comparison of RDI and eRDI values, in stations with humid condition such as Ramsar and Bandar Anzali difference of the means between RDI and eRDI indices were not significant at 5% level, but in stations with hyper arid and arid condition such as Chahbahar, Bandar Lengeh, Yazd and Zabol, difference of the means in RDI and eRDI was significant at 5% level. Therefore, it is suggested to replace RDI with eRDI in regions with hyper arid and arid conditions, but in regions with sub-humid and humid conditions because of the similarities between RDI and eRDI, RDI index (without need to calculate the effective rainfall) was used.

Evaluation of single crop coefficient curves derived from Landsat satellite images for major crops in Iran

Improving the accuracy of single crop coefficient (Kc) for major crops at regional scales would significantly result in optimizing the consumption of agriculture water. In this study, a new approach is applied to generate Kc curves from satellite images based on the Priestley-Taylor equation. The equation mainly consists of shortwave radiation and thermal terms. Therefore in order to meet the equation’s requirements, the Landsat optical data was considered as the essential satellite-based input of the approach, yet thermal data was obtained from the MODIS imagery which was primarily downscaled using the TsHARP algorithm to fit the 30 m spatial resolution of Landsat; therefore, in this study the method is referred to as the MultiSensor Data Fusion for potential EvapoTranspiration calculation (MSDF-ET). The Kc trends were first evaluated for annual crops (forage maize, sugar beet, wheat, and barley) in two different regions (the Qazvin and Tehran-Karaj plains) using field observation data of Leaf Area Index (LAI). The method was then applied to the major crops in 31 selected plains with three different climatic conditions in Iran. Climatic conditions were categorized into cold (North West region), arid (Central region), and warm and humid (South West region). Eventually, crop water requirements (CWR) in different regions were compared considering long-term air temperature, wind, and relative humidity (RH) variations. Evaluation of the method in the Qazvin and Tehran-Karaj plains showed promising results. The Kc trend varied according to the LAI and temperature variability. Crop growth duration and especially Kc curves were successfully extracted using remotely sensed data in the studied areas. CWR in the zone with higher values of air temperature, notably in warm seasons, was higher in comparison with other climatic zones. Also lengths of the growing seasons were shorter. In conclusion, surface and groundwater resources management would be improved as the result of taking satellite data into account for Kc and subsequently CWR calculations.

A financial comparative study of solar and regular irrigation pumps: Case studies in eastern and southern Iran

While pressurized irrigation systems can be effectively powered using renewable energy sources, no serious related study is found in Iran in this regard. In the present study, in two different climatic conditions in Iran, development of small-scale solar irrigation were evaluated financially and compared with that of systems powered by the fossil fuel and electricity grid. Financial analysis of systems was provided using life cycle cost (LCC) method. Results showed that in the case of 4.5 and 5.5 kW pumps (for citrus orchard and a vineyard, respectively), photovoltaic irrigation pumps with batteries for energy storage are comparable to the systems in which the electricity used to drive pumps is transmitted through 0.25 km and 1.8 km private lines. It was concluded that, generally, if the required power of irrigation pumps exceeds 3 kW, the electricity supplied by a private power transmission line is more affordable than in-situ generated photovoltaic electricity, if the length of transmission line is less than 2 km. It was also observed that for required power less than 4.5 kW, photovoltaic energy is somewhat comparable to fossil fuel. As Iran is dependent upon its highly subsidized fossil fuels, the financing of solar irrigation projects will not be possible without the help of new policies and laws.

Techno‐economic assessment of employing hybrid power system for residential, public, and commercial buildings in different climatic conditions of Iran

As the world population grows rapidly, and the limited amount of fossil fuels begins to diminish along with their impact on the environment, countries have been taking action to promote a greater use of renewable energy resources. In this article, the feasibility of providing electricity from a hybrid power system (HPS) comprising diesel/wind/photovoltaic (PV), and battery considering residential, public, and commercial buildings, consuming the largest portion of energy in Iran is investigated. Tehran, Kish Island, and Binalood are the chosen cities in Iran with distinctive geographic and climatic conditions. In order to determine the optimal design and operational planning of the HPS, the hourly electricity demand data is required to be over 8760 hs during a 1‐yr study. The required hourly data was calculated by employing Carrier (HAP4.5) software. The economic analysis is performed based on net present cost (NPC), cost of energy (COE), diesel consumption, and renewable fraction for all cases by applying HOMER software. Furthermore, sensitivity analyses are carried out to specify the impact of fuel cost on the system by considering two different diesel fuel systems. The results of the economic analysis indicate that Kish Island with warm and temperate climatic conditions would be the optimum zone to install HPS for supplying the energy demand of projected buildings. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 614–623, 2019

Integration of vertical ground-coupled heat pump into a conventional natural gas pressure drop station: Energy, economic and CO2 emission assessment

City gate stations receive high pressure natural gas and decrease the pressure by throttle valves. Concurrent with the natural gas pressure reduction, the temperature also drops. Thus, to prevent blocking of the downstream pipeline by the liquid and solid particles, natural gas must be preheated before pressure reduction. Heaters utilized for preheating task, have a low thermal efficiency and consume a large amount of fuel. In addition to the high fuel consumption, they release a huge amount of CO2 into the atmosphere. Therefore, the present study proposes a new system for in-situ fuel consumption elimination at these stations. It utilizes vertical ground-coupled heat pump system as a renewable source of energy to preheat natural gas stream. The system performance was studied at two different climatic conditions of Iran which have also two different natural gas compositions. Results show that the system is completely capable to eliminate in-situ fuel consumption of city gate stations; however, by considering indirect fuel consumption of electrical heat pumps, the system fuel consumption reduction potential was calculated over 65%. It is also able to reduce CO2 emission up to 79%. The discounted payback period is computed around two years, which proves the suitability of offered system.

Comparison of Empirical Copula-Based Joint Deficit Index (JDI) and Multivariate Standardized Precipitation Index (MSPI) for Drought Monitoring in Iran

Multi-index drought indices are based on a combination of single drought indices and able to monitor the overall status of drought in a certain location. The aim of the present paper is to compare two recently developed multi-index drought indices, i.e., Joint Deficit Index (JDI) and Multivariate Standardized Precipitation Index (MSPI) under different climatic conditions of Iran. Although these drought indices are calculated using different statistical methods, they need twelve modified Standardized Precipitation Index (SPImod) corresponding to 12 time windows from 1 to 12 months as the input variables. In this study, these indices were calculated using the monthly precipitation data of 42 weather stations representing diverse climates of Iran during the period of 1966–2010. JDI and MSPI were compared from different viewpoints including temporal behavior, the relationship between drought severity and duration and frequencies of drought classes. The results showed that both indices have a similar trend of drought severity at all stations. Unlike the MSPI, the JDI faced two substantial problems in all stations of interest: 1) The lowest value of the JDI time series was frequently repeated in different parts of its time series, 2) The JDI was not able to identify the peak of drought severity during the critical drought periods. While the JDI could not identify the extreme (at about all stations) and very severe (at one third of stations) drought classes, the observed frequencies of the MSPI’s drought classes successfully matched the corresponding expected frequencies. The obtained results clearly indicate the superiority of the MSPI for monitoring overall status of droughts in different climatic conditions of Iran in comparison to the JDI.

Comparability Analyses of the SPI and RDI Meteorological Drought Indices in Different Climatic Zones

Comparability analyses are performed to investigate similarities/differences of the standard precipitation index (SPI) and the reconnaissance drought index (RDI), respectively, utilizing precipitation and ratio of precipitation over potential evapotranspiration (ET0). Data are from stations with different climatic conditions in Iran. Drought characteristics of the 3-month, 6-month and annual SPI and RDI time series are developed and Markov chain order dependencies are investigated by the Log-likelihood, AIC and BIC tests. Steady state probabilities and Markov chain characteristics, i.e., expected residence time in different drought classes and time to reach “Near Normal” class are investigated. According to results, both indices exhibit an overall similar behaviour; particularly, they follow the first order Markov chain dependency. However, climatic variability may produce some differences. In several cases, the “Extremely Dry” class has received a more critical value by RDI. Furthermore, the expected residence time of “Near Normal” class and expected time to reach “Near Normal” class are quite different in a number of cases. The results show that the RDI by utilizing the ET0 can be very sensitive to climatic variability. This is rather important, since if the drought analyses are for agricultural applications, utilization of the RDI would seem to serve a better purpose.

A SYNOPTIC STUDY ON SEASONAL PATTERNS OF WET AND DRY SPELLS IN MIDWEST OF IRAN

The effective patterns and mechanisms of synoptic systems during the wet and dry spells in Midwest of Iran(MWI) analyzed and discussed on seasonal scales from 1974 to 2003. Synoptic Analysis is based on synoptic chartson Sea Level Pressure (SLP), 850 and 500 Hpa levels. The results of synoptic analysis show that dry spells in MWIare mostly corresponded to Azores High (AZH) intensifying and its central movement to east and northeast of normalposition. Furthermore the Siberian High (SH) ridge is extended from northeast to Iran. The linkage between SH andAZH ridges through Iran, Mesopotamia (Iraq) and Arabic Peninsula lead to drought occurrence in the Middle Eastespecially Iran. The Sudan Low (SL) and Mediterranean Trough (MT) have a limited extend during drought periods(dry spells). The most important occurrence index of droughts in upper charts is reinforcing and extending northwardof Arabia South High (ASH) to Iran and Mesopotamia. This event is marked by a strong ridge in 500 Hpa charts overstudy area. The Circumpolar Vortex (CPV) is contracted to polar area during dry spells and expanded equatorward inwet spells. In Summarized SH extends during wet spells but dose not reach to Iran. In addition Mediterranean EastTrough (MET) reinforced and extended from 25°E to 40°E and its meridional expands reaches to the Red Sea (RS)and Sudan Low. The other result is that during wet and dry spells, the orientation of Blocking Highs ridges in thenorth of Caspian Sea and over Ural Mountain (UM) causes different climatic conditions in Iran.