Mahmoud Ahmadi; Abbas Ali Dadashi Rodbari; Behnaz Nassiri Khuzani; Tayebeh Akbari Azirani
Abstract
Introduction
Cloud is a special phenomenon formed by dynamic and thermodynamic changes of the general atmospheric circulation. Through dispersion and reflection of solar radiation, cloudschange energy balance of the Earth and affect its hydrologic cycleby producing rainfall in various forms. Determining ...
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Introduction
Cloud is a special phenomenon formed by dynamic and thermodynamic changes of the general atmospheric circulation. Through dispersion and reflection of solar radiation, cloudschange energy balance of the Earth and affect its hydrologic cycleby producing rainfall in various forms. Determining the state of clouds (in terms of clouds being liquid or ice) is crucial, sinceitaffects the atmosphere feedback mechanism. Moreover, the state of clouds is related with itsheight, i.e., higher clouds tend to have an icy state. Therefore, determiningtheir statusis especially important for the accuracy of elevation estimation. The present study seeks toinvestigatetemporal and spatial variation of liquid clouds in the geographical range of Iran using information received from meteorological stations and remote sensing techniques. It aims to find the feedback of cloudsin liquid phase and theirdominant condition.
Research Methodology
Data received from MODIS Sensor of TERRA Satellite (2001-2015) and Cloud mask (CM) algorithm were used in the present study. Moreover, long-term data of 31 synoptic meteorological stations collected during the period of 1960–2015 were used to compare satellite data. Followingdata decoding and required calculations, maps of each season were produced using Kriging method.
Results and discussion
Results indicate that maximum number of liquid clouds occurs in winter, while their minimum number occurs in summer. In winter, Rasht, Ramsar, Babolsar and Gorgan stations (with cumulative frequency of 174.33 to 305.66 days) have maximum frequency of liquid clouds.This country almost lacks liquid clouds in summer. Only in the coastal zone of the Caspian Sea, Rasht, Ramsar, Babolsar and Gorganstations with 153, 93.33, 77.66 and 26 days, respectively,had the maximum frequency of liquid clouds. The average thickness of liquid clouds in Iran was calculated on a seasonal scale. In winter, spring, summer and autumn, it was 22.23, 17.13, 14.11 and 16.7 microns, respectively. Results indicate that the average thickness of liquid clouds decreases in warm seasons. Maximum thickness of liquid clouds in winter, spring, summer and autumn was 33.04, 24.56, 24.85, 22.84 and minimum thickness of liquid clouds was 13.98, 6.82, 6.27, 8.09, respectively. In winter,maximum frequency of liquid clouds occurred in western Iran and the Caspian coastline, while maximum thickness of liquid clouds occurredin northwestern and western Iran.Moving from north to south and west to east,the frequency of liquid and icy clouds decreases. In contrast, maximum frequency of liquid clouds occurs in summer.
Conclusion
Results indicated that maximum frequency of winter and autumn liquid clouds mainly occur in high latitudes of northern regions, southern hillside of Alborz(west to east direction), and northwestern and western regions of the country. Maximum frequency of summer liquid clouds occurs in the Caspian Coasts, while maximum frequency of spring liquid clouds occursin the northern half and southeast regions of the country. This is well-justified due toactivities of the expected systems and local factors in each season. Liquid clouds of Iran have a nonlinear and possibly complex relationship, and factors such as hillside orientation, precipitation systems, distance from sources ofmoisture, lack of ascending factor, lack of sufficient moisture and many other factors contribute to this relationship.Evaluation of liquid clouds thickness indicated that elevated regions of central and western Zagros have the highest amount of liquid clouds in cold seasons, since low-pressure systems, fronts and mid-latitudewaves of atmosphere play a decisive role in the growthof cloud numbers in these seasons. This is also in consistencywith Masoudian (2011) results. Northwestern Iran and the Alborz belt are almost always affected by the western winds. Western winds pass over the Mediterranean Sea and its sufficient moisture resource, which play a significant role in the cloudiness of this area. Results are consistent with Alijani’sstudy(2010) that reported 120 cloudy days in Alborz Mountains, Khorasan and northern Azerbaijan altitudes. Increased cloudiness of southern and southeastern Iran during warm seasons is related with the monsoon system in July-September,which is also confirmed by Ghasemifar et al. (2018) and its mechanism is discussed by Yadva (2016). Results are also in consistency with the results of Ahmadi et al. (2018), which examined the cloud optical thickness (COT) and the total cloud cover (TCC) of Iran. In other words, results of Ahmadi et al.(2018) also confirm our findings.
Fatemeh Firouzi; Taghi Tavosi; Peyman Mahmoudi
Abstract
Extended Abstract Introduction With recent advances in satellite remote sensing productions in past few decades, several indices have been provided for the study of vegetation dynamics, and especially for the assessment of drought impacts. Among these, two vegetation indices -Normalized Difference Vegetation ...
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Extended Abstract Introduction With recent advances in satellite remote sensing productions in past few decades, several indices have been provided for the study of vegetation dynamics, and especially for the assessment of drought impacts. Among these, two vegetation indices -Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) - have gained the attention of various researchers. Therefore, the present study aims to investigate the reaction of these two vegetation indices (i.e. NDVI and EVI) to dry and wet years in a dry plain in Iran (i.e. Sistan plain in eastern Iran). Materials & Methods To assess the sensitivity of these indices to dry and wet years, two different databases were required. First, NDVI and EVI image base received from Terra satellite (MODIS sensor) for April, May and June 2000-2014, and downloaded from EOS website. Second, daily data base of Zabol synoptic meteorological station (for a statistical period of 30-years 1985-2014) received from Iran Meteorological Organization. After data acquisition, separate vegetation dynamics maps (for April, May and June) were produced for the study area based on the information derived through processing of MODIS sensor images (Terra satellite) using NDVI and EVI. Effective drought index (EDI) was used to determine the frequency of dry and wet years in Sistan plain. Results & Discussion Mapping of vegetation dynamics based on images received from MODIS sensor (Terra satellite) for a 15-year statistical period (2000 to 2014: April, May, and June) indicated that NDVI and EVI had significant differences in exhibiting the dynamics of vegetation in the study area. These differences were obvious in areas with average amount of vegetation (0.4-0.5 in both NDVI and EVI) and also in areas with sparse dispersed vegetation (0.3-0.4 in both NDVI and EVI). In average levels of vegetation, total area of vegetation calculated by EVI is much higher than what is calculated by NDVI, while in sparse and dispersed vegetation, total area of vegetation calculated by NDVI is almost higher than EVI. Subsequently by selection of a dry (2010-2011) and a wet year (2005-2006), we compared changes in total area of vegetation (average and sparse) calculated by NDVI and EVI. Regarding the response of these two indices to dry and wet years, it was concluded that NDVI shows a better and more logical response during droughts, while EVI provides better results in wet years. However, it should be noted that the mean annual precipitation of Sistan plain is so low (59 mm per year) and its evapotranspiration is so high (4800 mm per year) that precipitation does not play a significant role in vegetation dynamics of this plain. Therefore, water flow in Helmand River, which is the lifeblood of this desert, is much more important than this limited precipitation in Sistan plain; hence, we can conclude that meteorological drought monitoring indices cannot reflect the relationship between drought and vegetation dynamics in Sistan plain, and this makes it difficult to compare NDVI and EVI in the region. Conclusion In general, it can be concluded that NDVI is a more suitable index for dynamics of vegetation in plains such as Sistan, whose life depends not on precipitation but on water running in the river. Because of the computational nature of EVI, it responds better in areas with dense vegetation. According to the vegetation type obtained from MODIS sensor images and field visits, NDVI is a better index for these types of plains.
Mahtab Safari Shad; Mahmoud Habibnejad Roshan; Alireza Ildoromi
Abstract
Abstract The issue of drought is very important in water resources studies. Meteorological drought indices are calculated directly from meteorological data such as rainfall, and in the absence of such data, they will not be useful in monitoring drought. Therefore, remote sensing techniques can be considered ...
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Abstract The issue of drought is very important in water resources studies. Meteorological drought indices are calculated directly from meteorological data such as rainfall, and in the absence of such data, they will not be useful in monitoring drought. Therefore, remote sensing techniques can be considered as a useful tool in monitoring drought. In this research, using MODIS remote sensing satellite images, the trend of vegetation normalized index changes in Isfahan province for the years 2000-2008 was investigated. In addition to vegetation, NDVI index can be effective in addition to natural vegetation for drought monitoring, especially for drought monitoring of dry farming type.Considering this index, the vegetation cover was classified into 4 groups and the area of each of the classes was calculated. Finally, two SPI and NDVI indices were compared. The result of calculating the SPI index show that the occurrence of severe drought is in 2008 and moderate droughts are in 2000 and 2001 in Isfahan province respectively. The calculation of the NDVI index in these three years also indicated that the poor vegetation cover has been significantly increased. High level Pearson correlation (+0.704) was observed between SPI and NDVI in significant level of 0.01. However, the results of the effect of rainfall on the NDVI index showed that there is no coincidence of the occurrence of meteorological drought and agriculture droughts in all years. For the year 2006, despite the fact that precipitation was higher than the years before and the years after and more than the average rainfall of the province, but based on the results of the NDVI index, agricultural drought has occurred this year (Devaluation of the NDVI index). On the contrary, in 2002 and 2004 that precipitation was lower than 2006, but dry farming and pasture conditions were better than 2006. And also, in 2003 with a difference of 2 mm in precipitation compared to 2002, the NDVI index value dropped significantly. The results of this research double the necessity of defining a profile that expresses all of these issues.
Mohammad Fallah Zazuli; Alireza Vafaeinezhad; Mir Masoud Kheirkhah Zarkesh; Fariborz Ahmadi Dehka
Abstract
Dusthazephenomenon in the recent decadeis one of the most important environmental challenges in Iran, West and Southwest Asia.This phenomenon is one of the processes of desertification occurring in arid and semi-arid regions of the world. Remote sensing is thescience and technique for the acquisition ...
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Dusthazephenomenon in the recent decadeis one of the most important environmental challenges in Iran, West and Southwest Asia.This phenomenon is one of the processes of desertification occurring in arid and semi-arid regions of the world. Remote sensing is thescience and technique for the acquisition of information from geographic phenomena without any contact with them.Todetectthephenomenonofdusthaze,large-scaleimagesare needed withwidecoverageandhighfrequency. Therefore,theimagesrelatedtoMODISsensoraresuitablefor thestudies on thephenomenon of dusthazeduetothe presence of highspectralbands. Detection of the generating origin or the source of dust haze particles and its quick monitoring with accuracy and low cost is of great importance. The main objectives of this research are to identify the generating source of dust haze entering the West and Southwest regions of Iran and to monitor the movement of dust haze as well. In this research, the occurrence origin of dust haze phenomenon is related to June 18, 2012 which occurred in the Western and Southwestern parts of the country, and was identified with the help of satellite images and by using visible and thermal bands of MODIS sensor and usingthe Ackerman index.It was found out that, its main origin was the point where Tigris and Euphrates rivers meet, which is within the northern and northeastern parts of Iraq and western Syria, and It was further found that the images of the MODIS sensor are suitable for dust haze monitoring due to its availability, low cost, and its repeatability in 2 periods of time within 24 hours. Also, its synoptic analysis to detect the movement of dust haze from the source into Iran was investigated using 500 hectopascal level synoptic data of geopotential height, sea level pressure and the wind current direction maps of 500 and 1000 hectopascals. The results of the synoptic analysis have optimized the origin detection and the way of dust haze transmission, and makes it more appropriate to predict the path of the dust haze motion. Finally, its movement demonstration from the source into Iran was trackedby the use of GIS and Spatial Analysis Tools. Dusthazephenomenon in the recent decadeis one of the most important environmental challenges in Iran, West and Southwest Asia.This phenomenon is one of the processes of desertification occurring in arid and semi-arid regions of the world. Remote sensing is thescience and technique for the acquisition of information from geographic phenomena without any contact with them.Todetectthephenomenonofdusthaze,large-scaleimagesare needed withwidecoverageandhighfrequency. Therefore,theimagesrelatedtoMODISsensoraresuitablefor thestudies on thephenomenon of dusthazeduetothe presence of highspectralbands. Detection of the generating origin or the source of dust haze particles and its quick monitoring with accuracy and low cost is of great importance. The main objectives of this research are to identify the generating source of dust haze entering the West and Southwest regions of Iran and to monitor the movement of dust haze as well. In this research, the occurrence origin of dust haze phenomenon is related to June 18, 2012 which occurred in the Western and Southwestern parts of the country, and was identified with the help of satellite images and by using visible and thermal bands of MODIS sensor and usingthe Ackerman index.It was found out that, its main origin was the point where Tigris and Euphrates rivers meet, which is within the northern and northeastern parts of Iraq and western Syria, and It was further found that the images of the MODIS sensor are suitable for dust haze monitoring due to its availability, low cost, and its repeatability in 2 periods of time within 24 hours. Also, its synoptic analysis to detect the movement of dust haze from the source into Iran was investigated using 500 hectopascal level synoptic data of geopotential height, sea level pressure and the wind current direction maps of 500 and 1000 hectopascals. The results of the synoptic analysis have optimized the origin detection and the way of dust haze transmission, and makes it more appropriate to predict the path of the dust haze motion. Finally, its movement demonstration from the source into Iran was trackedby the use of GIS and Spatial Analysis Tools.
