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Omosalameh Babai Fini, Elahe Ghasemi, Ebrahim Fattahi,
Volume 1, Issue 3 (10-2014)
Volume 1, Issue 3 (10-2014)
Abstract
Global changes in extremes of the climatic variables that have been observed in recent decades can only be accounted anthropogenic, as well as natural changes. Factors are considered, and under enhanced greenhouse gas forcing the frequency of some of these extreme events is likely to change (IPCC, 2007 Alexander et al., 2007). Folland et al. (2001) showed that in some regions both temperature and precipitation extremes have already shown amplified responses to changes in mean values. Extreme climatic events, such as heat waves, floods and droughts, can have strong impact on society and ecosystems and are thus important to study (Moberg and Jones, 2005). Climate change is characterized by variations of climatic variables both in mean and extremes values, as well as in the shape of their statistical distribution (Toreti and Desiato, 2008) and knowledge of climate extremes is important for everyday life and plays a critical role in the development and in the management of emergency situations. Studying climate change using climate extremes is rather complex, and can be tackled using a set of suitable indices describing the extremes of the climatic variables. The Expert Team on climate change detection, monitoring and indices, sponsored by WMO (World Meteorological Organization) Commission for Climatology (CCL) and the Climate Variability and Predictability project (CLIVAR), an international research program started in 1995 in the framework of the World Climate Research Programme, has developed a set of indices (Peterson et al., 2001) that represents a common guideline for regional analysis of climate. It is widely conceived that with the increase of temperature, the water cycling process will be accelerated, which will possibly result in the increase of precipitation amount and intensity. Wang et al. (2008), show that many outputs from Global Climate Models (GCMs) indicate the possibility of substantial increases in the frequency and magnitude of extreme daily precipitation. eneral circulation models (GCMs) are three-dimensional mathematical models based on principles of fluid dynamics, thermodynamics and radiative heat transfer. These are easily capable of simulating or forecasting present-future values of various climatic parameters. Output of GCMs can be used to analyze Extreme climate. For this study high quality time series data of key climate variables (daily rainfall totals and Maximum and minimum temperature) of 27 Synoptic stations were used across Iran from a network of meteorological stations in the country. In order to get a downscaled time series using a weather generator (LARS-WG), the daily precipitation output of HadCM3 GCM, SRES A2 and A1B scenario for 2011-2040 are estimated. The Nine selected precipitation indices of ETCCDMI[1] core climate indices are used to assess changes in precipitation extremes and monitor their trends in Iran in the standard-normal period 1961–1990 and future (2011-2030). Due to the purpose of this study, at first changes in extreme precipitation indices in the standard-normal period is evaluated and its results show annual maximum 1-day precipitation increased in many regions in the East of Iran. Simple measure of daily rainfall intensity (SDII), annual maximum consecutive 5-day precipitation, annual count of days with daily precipitation greater than 10mm (R10mm), annual count of days when rainfall is equal to or greater than 20 mm (R20mm) have increased in the central areas, regions in the north , north east and southern parts of Iran. Similar results are obtained for the R25mm index. The consecutive dry days (CDD) index has generally increased across the west areas, southwest, north, northwest and southeast of Iran and indices of consecutive wet days (CWD) decreased in these areas. Trends of extreme precipitation indices simulated by HadCM3 SRES A2 showing increases RX1Day in North West expect west Azerbaijan Province, central, southwest, north east and coasts of Caspian Sea. Similar results are obtained for the R5mm index expects northeast. There are mixed changes in R10mm across Iran, increasing in west, southwest, coasts of Caspian Sea, Hormozgan and Ardebil provinces, East Azerbaijan, Zanjan and Qazvin provinces. Similar results are obtained for the R20, 25 mm index in northeast, south of Caspian Sea, and some parts in western and central areas. Same as HadCM3 SRES A2 pattern there are mixed changes in R10mm across the region. Positive trends are seen in part of the Isfahan, Markazi, Kuhkilue , Lorestan, Ilam, Chaharmahaland Khozestan provinces and some part of Hormozgan and Kerman and some areas in north west. Similar results are obtained for the R20mm and R25mm index and in west of Yazd to north of Khozestan provinces have increased. Consecutive wet days (CWD) have increased over most of the west of Iran, Khorasn Razavi and Southern Khorasn provinces, In contrast consecutive dry days (CDD) index has generally increased in many parts of the region.
[1]. Expert Team on Climate Change Detection and Monitoring Indices
Zeinabe Sharifi, Mehdi Nooripour, Maryam Sharifzadeh,
Volume 4, Issue 2 (7-2017)
Volume 4, Issue 2 (7-2017)
Abstract
Sustainable livelihoods approach as one of the new sustainable rural development approaches is one way of thinking and attempting to achieve development which arose in the late 1980s with the aim of progress and poverty alleviation in rural communities (Sojasi Ghidari et al.,2016).
Five critical concepts to understand sustainable livelihoods framework include the concept of vulnerability, livelihood assets, transforming structures and processes, livelihood strategies and livelihood outcomes (Motiee Langroodi et al,2012). According to the sustainable livelihoods framework, vulnerability is one of the fundamental concepts based on the vulnerability context (Forouzani et al.,2017). The vulnerability context forms the people's external environment. It comprises shocks (such as human, livestock or crop health shocks; natural hazards, like floods or earthquakes; economic shocks; conflicts in form of national or international wars) trends (such as demographic trends; resource trends; trends in governance), and seasonality (such as seasonality of prices, products or employment opportunities) and represents the part of the framework that is outside stakeholder’s control (Kollmair and Gamper, .(2002
Various research explored the factors influencing vulnerability and its dimensions and less research investigated to assess the vulnerability of rural households. Therefore, the purpose of this study is to investigate rural households' vulnerability in the Central District of Dena County. Accordingly, this research is to answer the following questions:
Five critical concepts to understand sustainable livelihoods framework include the concept of vulnerability, livelihood assets, transforming structures and processes, livelihood strategies and livelihood outcomes (Motiee Langroodi et al,2012). According to the sustainable livelihoods framework, vulnerability is one of the fundamental concepts based on the vulnerability context (Forouzani et al.,2017). The vulnerability context forms the people's external environment. It comprises shocks (such as human, livestock or crop health shocks; natural hazards, like floods or earthquakes; economic shocks; conflicts in form of national or international wars) trends (such as demographic trends; resource trends; trends in governance), and seasonality (such as seasonality of prices, products or employment opportunities) and represents the part of the framework that is outside stakeholder’s control (Kollmair and Gamper, .(2002
Various research explored the factors influencing vulnerability and its dimensions and less research investigated to assess the vulnerability of rural households. Therefore, the purpose of this study is to investigate rural households' vulnerability in the Central District of Dena County. Accordingly, this research is to answer the following questions:
- What is the status of rural households' vulnerability to shocks?
- What is the status of rural households' vulnerability to trends?
- What is the status of rural households' vulnerability to seasonality?
The research method is applied in terms of purpose and non-experimental survey in terms of data collection. The statistical population of the study consisted of 2500 rural households in the Central District of Dena County, which according to Krejcie and Morgan table 300 households were selected using cluster random sampling.
The research tool for data collection was a structured and research-made questionnaire. Face validity was used in order to determine the validity of the questionnaire and the face validity of the research tool was confirmed by a panel of experts. A pre-test study was carried out in order to determine the reliability of the various sections of the questionnaire, Cronbach's alpha was calculated and reliability of the questionnaire was confirmed.
Vulnerability was measured using 20 questions and in three sections including shocks (8 items), trends (6 items) and seasonality (6 items) with a three-point Likert scale (low, medium and high) and SPSS software was used to analyze data.
The results of calculated vulnerability showed that the rural households had the most vulnerability to shocks including "causing damage to crops due to frost", "causing damage to crops due to drought" and "plant pests and diseases". In contrast, rural households had the lowest vulnerability to shocks including "family fights and ethnic conflict", "animal disease" and "illness of family members".
The respondents had the most vulnerability to the trends including "the rise in food prices and other life necessities" and "the rise in the price of energy carriers such as diesel, gasoline, etc.". In contrast, the respondents had the least vulnerability in trends including "gradual air pollution" and "increase in households' population".
The respondents had the most vulnerability to the seasonality including "lack of funds and capital in low working seasons" and "fluctuations in the prices of agricultural products". In contrast, the respondents had the least vulnerability to seasonality including "the impossibility of growing crops in different seasons" and "decrease and increase in the amount of agricultural production in different seasons".
The results showed that generally respondents’ vulnerability to shocks, trends and seasonality and the total vulnerability was at a medium level for the majority of the respondents (over 40%), at a high level for about 25 percent of the respondents, at a very high level for about 15 percent of the respondents and at a very low level for only about 10 percent of the respondents. Therefore, it could be concluded that more than half of the respondents' vulnerabilities was at a low and medium level.
Furthermore, in two groups with low and medium vulnerability, the average vulnerability to shocks, trends and seasonality are almost the same, whereas in two groups with high and very high vulnerability, the most vulnerability referred to seasonality, trends and shocks, respectively.
According to the research findings, the following suggestions are offered in order to reduce the vulnerability of rural households.
In order to reduce the vulnerability of rural households to shocks including "causing damage to crops due to frost", "causing damage to crops due to drought" and "plant pests and diseases", it is suggested that educational courses are held by the relevant organizations such as Agriculture Jihad in order to get familiar with ways to deal with damages caused by frost, drought and plant pests and disease. In addition, the use of heating system before the frost, the use of drought resistant varieties, the use of such techniques as land fallowing in order to reduce the need for water, the use of integrated pests management are offered as well in order to reduce the vulnerability of rural households.
Considering that the respondents had the most vulnerability to the trends including "the rise in food prices and other life necessities" and "the rise in the price of energy carriers such as diesel, gasoline, etc.", the rise in food prices as well as energy carriers in rural areas should be cautiously.
Founding loan fund in order to give loan and credit to households in low working seasons as well as determining a guaranteed price for agricultural products by the relevant authorities to reduce the volatility of agricultural prices are recommended.
The research tool for data collection was a structured and research-made questionnaire. Face validity was used in order to determine the validity of the questionnaire and the face validity of the research tool was confirmed by a panel of experts. A pre-test study was carried out in order to determine the reliability of the various sections of the questionnaire, Cronbach's alpha was calculated and reliability of the questionnaire was confirmed.
Vulnerability was measured using 20 questions and in three sections including shocks (8 items), trends (6 items) and seasonality (6 items) with a three-point Likert scale (low, medium and high) and SPSS software was used to analyze data.
The results of calculated vulnerability showed that the rural households had the most vulnerability to shocks including "causing damage to crops due to frost", "causing damage to crops due to drought" and "plant pests and diseases". In contrast, rural households had the lowest vulnerability to shocks including "family fights and ethnic conflict", "animal disease" and "illness of family members".
The respondents had the most vulnerability to the trends including "the rise in food prices and other life necessities" and "the rise in the price of energy carriers such as diesel, gasoline, etc.". In contrast, the respondents had the least vulnerability in trends including "gradual air pollution" and "increase in households' population".
The respondents had the most vulnerability to the seasonality including "lack of funds and capital in low working seasons" and "fluctuations in the prices of agricultural products". In contrast, the respondents had the least vulnerability to seasonality including "the impossibility of growing crops in different seasons" and "decrease and increase in the amount of agricultural production in different seasons".
The results showed that generally respondents’ vulnerability to shocks, trends and seasonality and the total vulnerability was at a medium level for the majority of the respondents (over 40%), at a high level for about 25 percent of the respondents, at a very high level for about 15 percent of the respondents and at a very low level for only about 10 percent of the respondents. Therefore, it could be concluded that more than half of the respondents' vulnerabilities was at a low and medium level.
Furthermore, in two groups with low and medium vulnerability, the average vulnerability to shocks, trends and seasonality are almost the same, whereas in two groups with high and very high vulnerability, the most vulnerability referred to seasonality, trends and shocks, respectively.
According to the research findings, the following suggestions are offered in order to reduce the vulnerability of rural households.
In order to reduce the vulnerability of rural households to shocks including "causing damage to crops due to frost", "causing damage to crops due to drought" and "plant pests and diseases", it is suggested that educational courses are held by the relevant organizations such as Agriculture Jihad in order to get familiar with ways to deal with damages caused by frost, drought and plant pests and disease. In addition, the use of heating system before the frost, the use of drought resistant varieties, the use of such techniques as land fallowing in order to reduce the need for water, the use of integrated pests management are offered as well in order to reduce the vulnerability of rural households.
Considering that the respondents had the most vulnerability to the trends including "the rise in food prices and other life necessities" and "the rise in the price of energy carriers such as diesel, gasoline, etc.", the rise in food prices as well as energy carriers in rural areas should be cautiously.
Founding loan fund in order to give loan and credit to households in low working seasons as well as determining a guaranteed price for agricultural products by the relevant authorities to reduce the volatility of agricultural prices are recommended.
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Volume 4, Issue 4 (1-2018)
Volume 4, Issue 4 (1-2018)
Abstract
Dust is one of the common processes of arid and semiarid regions that its occurrence frequencies has increased in recent years in Iran. The proper identification of sand and dust storms (SDS) is particular importance due to its impact on the environment and human health. So far, several methods for identifying these sources have been proposed such as methods based on field studies and geomorphologic studies, as well as methods on the basis of a numerical model of air flow simulation. Therefore, identifying the process of land cover changes and changes in suspended particles in the air can help to identify the correct sources of sand and dust. Also, to manage the reduction of dust, it will be very useful to analyze the trend of changes in sand and dust sources. This data can provide some useful information to the decision makers about the future occurrence of sand and dust storm and control it. Satellite-based remote sensing is an appropriate tool for examining changes in the surface conditions of the earth over time. Satellite sensors are well suited for this purpose because of the fact that constant measurements can be repeated on a fix spatial scale. Therefore, in this research, we have tried to test different remotely sensed data time series for validation of the identified SDS sources using the latest remote sensing techniques and their integration with other information.
The aim of this study is to validate the identified dust generation sources in Alborz province using time series of satellite data and meteorological stations data. In first step, OLI data of Landsat 8 during the years 2013 through 2015 were used to make maps of vegetation cover, soil moisture and land cover sensibility to wind erosion. These maps were combined with geology and roughness indices by multi-criteria evaluation method to obtain a map of sand & dust source potential areas. Also, based on the location of the intersection of the air flow with the surface of the earth and the application of masks of non-wind erodible areas on them, probable sand and dust sources were identified. These regions were integrated with the map of sand & dust source potential areas using the MCE method (WLC) and based on a stratified random sampling plan, susceptible sites of sand & dust sources were identified. Then in this research, the time series of satellite data and weather stations data were used and the trend of vegetation, soil moisture and surface temperature at the location of identified areas during a 15-year period were monitored. Product of LPRM_TMI_DY_SOILM3 from TMI sensor, data of 16-day vegetation, 8-day land surface temperature and data of aerosol optical depth from MODIS sensor were received. Also ground- based data of dust from synoptic and air pollution monitoring stations were received. Changes Trend analysis of soil moisture, temperature and vegetation cover was done during the period. Also aerosol optical depth in dust events with high concentration was evaluated for possible sources. In addition, the areas with higher dust optical depth than other areas were identified during the period. Finally, identified sources was validated using ground- based data of dust.
The result of trend analysis showed a significant decrease in vegetation, soil moisture and land surface temperature at the place of possible dust sources during the studied period. Decreasing temperature in the southern part of Alborz Province and west of Tehran province was associated with higher frequency of dust in the area that shows why dust events has high frequency. Study of time series of aerosol optical depth data showed that concentration of dust is at or near the detected sources and the high concentration in this area is indicating identified areas are accurate. Checking optical depth in the event of high concentration and checking concurrent of air direction showed the detected sources has been correctly identified. Also Integration of dust information of synoptic and air pollution monitoring stations with the wind direction confirmed the high accuracy of identified dust sources.
Overall, findings showed the ability time series of remote sensing data to validate dust storm sources. The results of the analysis of the time series of the satellite remote sensing data showed that the surface temperature as an important climatic parameter can be well used in the identification and validation of sand & dust sources. Based on the results of this analysis in areas where the frequency of sand & dust storm events is high, there is a significant decrease in the surface temperature. This is particularly evident in the annual maximum surface temperature in the southwestern part of Iran, an area that is considered to be the predominant trajectory of sand & dust storm.
The aim of this study is to validate the identified dust generation sources in Alborz province using time series of satellite data and meteorological stations data. In first step, OLI data of Landsat 8 during the years 2013 through 2015 were used to make maps of vegetation cover, soil moisture and land cover sensibility to wind erosion. These maps were combined with geology and roughness indices by multi-criteria evaluation method to obtain a map of sand & dust source potential areas. Also, based on the location of the intersection of the air flow with the surface of the earth and the application of masks of non-wind erodible areas on them, probable sand and dust sources were identified. These regions were integrated with the map of sand & dust source potential areas using the MCE method (WLC) and based on a stratified random sampling plan, susceptible sites of sand & dust sources were identified. Then in this research, the time series of satellite data and weather stations data were used and the trend of vegetation, soil moisture and surface temperature at the location of identified areas during a 15-year period were monitored. Product of LPRM_TMI_DY_SOILM3 from TMI sensor, data of 16-day vegetation, 8-day land surface temperature and data of aerosol optical depth from MODIS sensor were received. Also ground- based data of dust from synoptic and air pollution monitoring stations were received. Changes Trend analysis of soil moisture, temperature and vegetation cover was done during the period. Also aerosol optical depth in dust events with high concentration was evaluated for possible sources. In addition, the areas with higher dust optical depth than other areas were identified during the period. Finally, identified sources was validated using ground- based data of dust.
The result of trend analysis showed a significant decrease in vegetation, soil moisture and land surface temperature at the place of possible dust sources during the studied period. Decreasing temperature in the southern part of Alborz Province and west of Tehran province was associated with higher frequency of dust in the area that shows why dust events has high frequency. Study of time series of aerosol optical depth data showed that concentration of dust is at or near the detected sources and the high concentration in this area is indicating identified areas are accurate. Checking optical depth in the event of high concentration and checking concurrent of air direction showed the detected sources has been correctly identified. Also Integration of dust information of synoptic and air pollution monitoring stations with the wind direction confirmed the high accuracy of identified dust sources.
Overall, findings showed the ability time series of remote sensing data to validate dust storm sources. The results of the analysis of the time series of the satellite remote sensing data showed that the surface temperature as an important climatic parameter can be well used in the identification and validation of sand & dust sources. Based on the results of this analysis in areas where the frequency of sand & dust storm events is high, there is a significant decrease in the surface temperature. This is particularly evident in the annual maximum surface temperature in the southwestern part of Iran, an area that is considered to be the predominant trajectory of sand & dust storm.
Noorallah Nikpour, Hossein Negaresh, Samad Fotoohi, Seyed Zeynalabedin Hosseini, Shahram Bahrami,
Volume 5, Issue 4 (3-2019)
Volume 5, Issue 4 (3-2019)
Abstract
Deforestation or vegetation degradation is one of the main drivers of global earth changes, which has significant consequences in terms of ecosystem performance and biodiversity conservation. One of the ways for studying vegetation changes as the most important indicator of land degradation is remote sensing. In this study, in order to monitor the vegetation degradation trend in Ilam Province.After obtaining and preparing the required data (410 downloaded images) in the ArcGIS and Surfer software, the multiplication, mosaic and georeferencing operations are made. Converting format of images into ASCII is the next stage of the study. By converting this format, the total number of 953552 pixels is studied within the range; after removing the lost and negative values, 328042 pixels are analyzed. Besides, using parametric statistical method of the classical linear regression and programming in R software, the trend of slope variations and significance of slope variations of vegetations are obtained for the 17-year period (2000-2016). Results of this study show that the focus of the highest trend of declining slope variations (trend of negative slop variations) is in the NDVI index across the western half of the studied area and the focus of the highest trend of increasing slope variations (trend of positive slop variations) is in the NDVI index in the center and east. Significance of the trend of slope variations also approves this claim. Thus, the focus of the highest trend of slope variations (negative) in the west and southwest of the studied area along with the highest trend of slope variations (positive) in the center and east is significant at the probable level of 0.05
Dr Hamid Ghorbani, Dr Abbas Ali Vali, Mr Hadi Zarepour,
Volume 6, Issue 2 (9-2019)
Volume 6, Issue 2 (9-2019)
Abstract
Drought is one of the most complex and unknown natural phenomena that causes a periodic water crisis in the affected areas. Increasing water demand on the one hand and the experience of droughts in the province in recent years have led to the water crisis. Knowing the drought is one of the requirements for water crisis management. The purpose of this study was to analyze the trend of the SPI drought index in Isfahan province using nonparametric Sen’s slope test, Pettitt’s change point test and Man-Kendall test. From the monthly climatic data of 10 synoptic stations with a length of 27 years (1990-2017) for time series The results of applying Mann–Kendall and Sen’s slope tests based on SPI Index for 9, 12, 18, 24 and 48 month time periods, shows drought trend is significantly increasing for all stations out of Ardestan, Esfahan and Shahreza stations. In Ardestan station, the drought trend is significantly decreasing for 9, 12, 18, 24 and 48 month time periods and in Isahan station, the drought trend is significantly decreasing for only 48 month time period, and in Shahreza statition, the drought trend is significantly increasingonly for only 18 month time period.
Despite all stations, the drought trend for one month time period, is significantly increasing just for Naein station.
In addition, applying Mann–Kendall test on monthly rainfall for all station shows downward but not significant trend.
Finally, applying Pettitt’s change point test based on SPI Index for 9, 12, 18, 24 and 48 month time periods indicates the existence of a significant change point. For same periods we observe no change point for the monthly rainfall in all stations.
In summation, considering the SPI drought index, about 59% of all stations show significant downward trend bases on Mann-Kendall test and 60% of all stations show significant slope based on Sen's slope test and 75% of all stations show significant change point based on Pettitt's test. In general, for drought analysis using different time periods for the SPI index, in a short time period. (such as 6 months) drought is more frequent but shorter, and as the period increases the duration of drought also increases but frequency decreases. All together, we are facing a water crisis in Isfahan province and we must manage water demand very urgently.
Reza Reza Borna, Shahla Shahla Ghasemi, Farideh Farideh Asadian,
Volume 6, Issue 3 (9-2019)
Volume 6, Issue 3 (9-2019)
Abstract
Today, the impact of climate is considered on the life, health, comfort, activity and behavior in a form of the branch of science such as human biology. Due to difference of frequency people with each other, the sensibility of every one from weather can be different from the other one that's why the climate can’t be totally undesirable or the climate can be totally desirable for all the people, so we can say that all of climatic elements are affected on human comfort but the effect of some of them is quite cleared and the effect of the others is mild and sometimes invisible. The greatest effect on comfort and discomfort can be included temperature, humidity and solar radiation. The aim of this research is to investigate and determine the area risk of climatic comfort. For this purpose, the temperature, precipitation and humidity data have been extracted for Khuzestan province form Esfarazi database. In this approach, first different properties of the temperature, precipitation and humidity for the area with climatic discomfort have discussed based on the conditional probability distribution. This study has been identified the areas of climatic comfort in Khuestan province using multivariate analysis (Cluster analysis and Discriminant analysis) and spatial autocorrelation pattern (Hot Spot index and Moran index) with an emphasis on architecture. The results showed that the risk area of climate comfort is included mostly of the western parts of Khuzestan province namely the border areas with Iraq and some parts of southern of province .On the other hand ,trend analysis the range of this area to climatic discomfort indicated that it has increased significantly in recent periods .The results also showed that the local distribution of precipitation in all periods in the areas of climatic discomfort has been a high the coefficient of variations.
Saeid Jahanbakhsh Asl, Behruz Sari Sarraf, Hosein Asakereh, Soheila Shirmohamadi,
Volume 7, Issue 1 (5-2020)
Volume 7, Issue 1 (5-2020)
Abstract
The study of temporal - spatial changes of high extreme rainfalls in west of Iran (1965-2016)
Extended Abstract
Introduction
Rainfall is one of the appropriate weather parameters not only in describing weather condition in one specific area but also is in estimating potential impacts of climate change in the environment and in many economic and social systems. Some studies show that during half a century weather patterns by more and severe raining events and by changes in scheduling and rain status has been changed. From 1960s with its much slope, the abundance and severity of extreme rainfalls throughout the world has increased and it is expected to continue the increase until the end of the current century. So understanding the behavior of extreme events is one of the main aspects of climate change and the increase of information about heavy rains has utmost importance for society, especially for the population who lives in areas with increased flood risk.
According to above mentioned cases and abnormal behavior and irregular rainfalls in Iran and its high variability from one hand and Iran's west region ability to heaviness and extension of rainfalls on the other hand, the necessity of understanding and study of temporal and spatial dangerous rainfalls is recognized. Among extreme rainfall characteristics, the portion of such rainfalls in total rain production is studied less. Due to the experiments carried out, the increase of annual rainfall in Iran happens through heavy rainfalls. Therefore heavy rainfall portions out of total annual rainfalls can be defined as an index of crisis. The increase of this index implies the heavy floods in rainy years and severe drought and drought years.
Data and Method
Iran's west region including East and West Azerbaijan provinces, Zanjan, Kurdistan, Kermanshah, Hamadan, Lorestan, and Ilam consists of about 14 percent of Iran's total area. The height of this region includes a domain of 100 to about 4000 meters. Zagros mountain ranges are the most important characteristic of west of Iran, which are drawn from north-west to south-east.
In this research, we used network data from interpolation daily rainfall observation of 823 meteorology stations from January 1st up to December 31st, 2016 by using Kriging interpolation method and by separating 6×6 km spatial. The results formed matrix interpolation process by dimension of 18993×6410. This matrix has the rain status of 6410 points of west of Iran for every day rainfall (18993). Extreme rain falls are identified in terms of threshold of 95 percentile in each point and each day of year. The rainfall of each day and each pixel is compared to that related pixel and corresponding to that day and those days which their rainfalls rates were equal to or larger than threshold were identified for studying extreme rain fall portion in total yearly rainfall, the total of equal rainfalls and more than 95 percentile is calculated for each year and each of pixel and, it is divided to total of the same pixel rainfalls in that year.
We used the least squarely error for understanding temporal- spatial behavior of regression.
Results and Discussion
The average extreme rain falls in west of Iran is under the influence of their roughness and placement and also synoptic rainfall. The proof of this claim identifies through placement of average extreme rainfall over altitudes of region. By increasing geographical latitude in Iran's western provinces, it is decreased both of total extreme rainfalls and portion of such rainfall out of total yearly rainfall. Total extreme rainfall trend shows a frequency in a domain with 16 mm in each year. The negative trend of total rainfall with the area of 74.72 percent consists of three quarters of Iran's west.
The narrow strip of the west of Kurdistan and south-west of west Azerbaijan have the highest amount of positive trend which is meaningful in certainty level of 95 percent.
The study of process showed the ratio of extreme rainfalls portion to total yearly rainfall, which is increasing about 60.7 percent of west area of this country extreme rainfalls in total yearly rainfall and the greatest part of this area is located in southern half of the studied area.
The negative trend also is located in northern half and they have consisted of 39.29 percent of studied area of these, only in 29.81 percent of region, the trend ratio of extreme rainfalls to total yearly rainfalls are meaningful in certainty level of 95 percent.
Keywords: Extreme Rainfalls, Trend, 95 Percentile, Rainfall Portion, west of Iran.
Sharifeh Zarei, Bohloul Alijani, Zahra Hejazizadeh, Bakhtiar Mohammadi,
Volume 8, Issue 4 (1-2021)
Volume 8, Issue 4 (1-2021)
Abstract
In this research, the most important synoptic patterns of widespread snowfall in the western half of Iran have been investigated. For this purpose, the data of current weather code and snow depth of 36 synoptic stations during the statistical period of 1371-1400, for the months of October to March, were received from the Meteorological Organization of the country. In order to investigate wide snowfalls, the days when more than 70% of the studied area saw snowfall at the same time were extracted as a wide day. In order to perform synoptic-dynamic analysis of wide snowfalls in the western half of Iran, the classification method using cluster analysis was used and maps of representative days were drawn, including atmospheric temperature, moisture flux, geopotential height, tovai, front formation, jet stream, omega index, and orbital and meridian wind data. Trend analysis was also performed using the Mann-Kendall test. The results showed that 4 models justify the widespread snowfall in the studied area in the best way. According to the results in all the models, at sea level, the collision of cold and dry air of northern latitudes with warm and humid air of southern latitudes has caused the formation of frontal fields in the western half of Iran. At the level of 500 hectopascals, the intensification of the meridional currents in the western winds caused the creation of closed centers and as a result the flow changed in the direction of the westerly winds, and the location of the western half of Iran in the east of Naveh Al-Aghti and Sardchal has provided the necessary conditions for air to rise. Also, there was no trend in the number of snow days in the western half of Iran at the significant levels tested. But; The number of snow days has been decreasing over time. In general, it can be concluded that due to the warming of the earth and climate change, the number of snowy days has decreased and these changes have led to a significant shortening of the snow season.
Leyla Babaee, Nahideh Parchami, Raoof Mostafazadeh,
Volume 10, Issue 1 (5-2023)
Volume 10, Issue 1 (5-2023)
Abstract
Changes in the hydrological response due to climatic parameters and human induced activities can be derived from indicators based on the analysis of flow duration curves. The purpose of this research is to determine the flood and the low flow parameters using the flow duration curves. The trend detection technique can be used as a useful tool in deterimining the temporal changes of the different hydro-meteorological parameters. The river gauge stations of the Ardabil province were used for the analysis of high and low flow occurrence in this study. The spatial variations of the flood events can be used as a preliminary guideline for the prioritization of the watershed in the vulnerability assessment and management-oriented measures. Also, the assessment of low flow condition is a useful tool in the allocation of environmental flow allocation and utilization of river surface water resources.
Methodology:
In this research, temporal and spatial changes of Q10, Q50, Q90, Q90/50 and Lane indices in 31 hydrometric stations of Ardabil province during the period from 1993- 2014 were evaluated. The flow duration curve of each river gauge stations was derived. The flow duration curves also were plotted based on the dimensionless flow divided by the mean discharge and the upstream area of each river gauge station. Also, the temporal variations of the of Q10, Q50, Q90, Q90/50 and Lane indices were analysed using non-parametric Man Kendall trend test. Then the significant level of upward and downward trend directions were determined. In this study, the results of 5 river gauge stations were presented as example based on the the river flow ranges, which includes low, medium and high river flow discharge (Hajahmadkandi, Nanakaran, Shamsabad, Polesoltani, and Booran).
Results:
Based on the results, the trend of Q10 (Flood flow index) was significant at the stations located on the main trunk of the Qarehsou river. Meanwhile the Q50 (average flow index) has a significant decreasing trend in most of the studied river gauge stations. In addition, Q90 and Q90/50 indices have a significant decreasing trend in most stations. In addition, Q90 and Q90/50 indices had a significant decrease at (p<0.05) regarding the Lane index as a flood related indicator in the Arbabkandi and Dostbeglo stations, which are affected by the dam construction there is a significant decreasing trend.
Conclusion:
I summary, the values of flood flow index in the upstream rivers of the Ardabil province had a increasing trend.
Popak Dananiyani, Ehsan Soureh, Bakhtiyar Mohammamdi,
Volume 10, Issue 2 (9-2023)
Volume 10, Issue 2 (9-2023)
Abstract
Thunderstorms are one of the atmospheric phenomena; when they occur, strong winds are often reported along with heavy rains and lightning. In many cases, their occurrence is accompanied by a lot of financial and human losses. This research was carried out to investigate the Spatio-Temporal of thunderstorms and understand their trends in Iran. For this purpose, the monthly data of the number of days of thunderstorms in 201 Synoptic stations in Iran from the beginning of establishment to 2010 were used. First, the frequency of monthly and annual occurrence of thunderstorms at Synoptic stations in Iran was calculated. Also, the trend of thunderstorms was investigated based on the non-parametric Mann-Kendall test and the amount of decrease or increase of this phenomenon was determined with the help of the Sen’s slope estimator test. The results of this research showed that thunderstorms occur in all areas of Iran. However, the frequency of this phenomenon is more in the North-West, South-West, and South-East of Iran than in other parts. In terms of time, in every month of the year, part(s) of Iran is the center of the maximum occurrence of thunderstorms. For example, in the winter of southwest, south, and southeast of Iran, in the early spring of west and northwest of Iran, and the late spring of the southeast of the country, the main focus of this phenomenon has been. In the summer, northwest to the northeast of Iran and southeast and south of Fars province are the main centers of thunderstorm formation. At the beginning of the autumn season, the coasts of the Caspian Sea to the north of the Persian Gulf and towards the northwest of Iran, and in November and December, the southwest and west of Iran were the main places of occurrence of this weather phenomenon. Other results of this research showed that the trend of thunderstorms was not similar in Iran. This phenomenon showed a significant increasing trend (more than 1 day per year) at the 99% confidence level in the northwest, southwest, and southern half of Kerman province. Also, a significant decrease (0.7 days per year) was estimated in the southeast and a large part of central Iran. In other parts of Iran, a decrease or increase in thunderstorms has been observed in a scattered manner, although the amount was not significant at the 99%, 95%, and 90% confidence levels.
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