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.
Taghi Tavousi
Abstract
Extended Abstract
Introduction
Land degradation process that affects the arid, semi-arid and sub-humid zones of the globe has been interpreted as desertification that great many debates have grown up around the concept. A fundamental debate has been whether desertification actually exists? If ...
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Extended Abstract
Introduction
Land degradation process that affects the arid, semi-arid and sub-humid zones of the globe has been interpreted as desertification that great many debates have grown up around the concept. A fundamental debate has been whether desertification actually exists? If so, how it might be defined, measured and assessed (Herrmann and Hutchinson, 2005). In fact, the term "desertification" was used by Aubreville (1949) to describe the change of productive land into desert, which was the result of human activities in the tropical forest zone of Africa (Tavousi, 2010).However, the United Nations Conference on Desertification (UNCOD), held in Nairobi in 1977, launched the desertification issue into the global arena (Herrmann and Hutchinson, 2005). Desertification as defined in the United Nations Conference on Environment and Development (UNCED) and also in the United Nations Convection to Combat Desertification (UNCCD) is land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities (Cardy, 1993). Also, on the basis of this Convention, arid, semi-arid and sub-humid arid regions are regions in which the ratio of precipitation to potential evapotranspiration is in the range of 0.05 to 0.65 (Tavousi et al, 2010).
Determining the contribution of climatic variability to desertification is very complicated, and it is virtually impossible to separate the impacts of drought and desertification, because these processes often work together (Nicholson et al., 1998). Although now a more understanding of climatic variability has emerged, the understanding of the causes of this variability is still unfolding.
Two prevalent paradigms are expressed for climatic variability: One Internal feedback mechanisms such as Biophysical feedback mechanisms between land surface and precipitation due to modification of land cover characteristics in dry land regions and the other are External forcings, such as influence of the El-Nino Southern-Oscillation phenomenon and other major driving forces that promote changes in atmospheric circulations. Most probably, nor of these two prevalent paradigms (internal and external forcings) are mutually exclusive. Relative contributions of climate variability and human agency to desertification will likely depend on specific regional contexts (Herrmann and Hutchinson, 2005).
On the basis of UNEP index we observed that most areas of Iran have arid and semi-arid climates. With respect to the desertification intensity class, these two kinds of climates have classes of severe and very severe conditions. After those two kinds of climates, ultra arid, dry sub-humid, very humid and sub-humid climates cover most areas in Iran respectively (Alijani et al, 2015).
The purpose of this study was to investigate the trend of fluctuations in annual precipitation and the trend of UNEP aridity index of diverse climatic zones in the west and northwest of Iran.
Materials & Methods
In order to study the increase of aridity index in diverse climatic zones of the west and northwest of Iran, in the first step, the area was isolated by cutting 32 N latitude and 50 E longitude. Then, annual temperature average and total annual precipitation data was provided from 43 meteorological stations in the study area during the period of (1981-2010).
This period was divided into three decades: 1981-1990, 1991-2000 and 2001-2010. Then, for each decade, a zoning map was drawn.
In order to classify the climate, evaluate the Aridity Climatic Index and displacement of climatic zones in the northwest of Iran, the aridity index of UNEP (United Nation Environment Program) was used. Also, Kendall's nonparametric test was used to determine the significance of changes in annual precipitation.
Since the air temperature determines the potential evapotranspiration, the UNEP relationship is expressed based on the average total of annual precipitation relative to the average total of annual evapotranspiration.
Discussion and Results
In order to analyze the change in the Aridity Coefficient for each year, the UNEP index was calculated for 43 weather stations in the west and northwest of Iran. Based on the average UNEP index in each decade, the zoning map of the Aridity Index was drawn for three consecutive decades. Then, the UNEP Aridity index was subtracted in successive decades and the change occurred in the studied area was investigated. The spatial displacement of climatic zones over these three decades, represents the increase in the aridity coefficient and expansion of the territory of arid and semiarid climate in the area.
Conclusion
The results clearly indicate climate change from humid climate to semi-humid arid climate and semi-humid arid climate to arid climate. Based on Aridity Index of UNEP, in most parts of the northwest of Iran investigated in this study, the coefficient of Aridity has increased from the moderate risk class to severe and very severe Aridity. Although the results of Mann-Kendall test showed that 32 stations have a negative trend, this trend is significant for the 6 stations of Urmia, Tabriz, Khoy, Miandoab, Piranshahr and Sanandaj at = 0.05 .
Seyyed Keramat Hashemi-Ana; Mahmud Khosravi; Taghi Tavousi; Hamid Nazaripour
Abstract
Extended Abstract Introduction Precipitation is one of the vital climatic parameters that plays a major role in human life. Therefore, the impact of Precipitation in occurrence or non-occurrence of droughts and dry spells have been very effective. Identification and extraction length of dry spells ...
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Extended Abstract Introduction Precipitation is one of the vital climatic parameters that plays a major role in human life. Therefore, the impact of Precipitation in occurrence or non-occurrence of droughts and dry spells have been very effective. Identification and extraction length of dry spells in arid and semi-arid regions are very important. According to the most recent climate classification that has been done, about 90 percent of the areas of Iran are located in arid and semi-arid climate, and more than 40 percent are facing a severe water crisis. Therefore, understanding the behavioral mechanisms of dry spells have a great significance in arid and semi-arid areas like Iran, especially with the pose of the phenomenon of climate change that caused the worsening dryness and desertification in some of the regions. Many researches simulated dry spells with climate change approach and use of the output of AOGCM models. Researches in this category are in less numbers, but the most recent research has been done by the authors (hashmy titles et al., 2015), investigating and modeling the length of dry spells in the Southwestern area of Iran. The aim of this research is to examine the Validation of AOGCMs Capabilities for Simulation Length of Dry Spells under the Climate Change and Uncertainty in Iran Materials & Methods According to the aim of this research, we used two databases in this study. The first database involves collecting and analyzing all data base information (minimum temperature, maximum temperature, rainfall and sunshine) on a daily scale in 234 synoptic stations (with different statistical period). But the format for the data station and point during the period of statistical modeling was needed for more than 30 years, which has a large statistical defects were excluded, and finally 45 synoptic stations that have favorable conditions (the maximum area coverage and continuous and reliabledata) were selected for the final processing of the first data base. The period of 1981-2010 was used as the base period.The second database contains data provided by version 5 models (LARS-WG) and on emission scenarios (B1, A1B, A2) from AOGCM models for the 2050s to be downscaled. In fact, this data is the first data base (minimum temperature, maximum, precipitation and sunshine) prepared based on the format models for analysis and predicting climate change, after downscaling it. Because this research was based on study and extraction length of dry spells in the range of long-term with the approach to climate change, so the methodology is based on several stages. At first, verification (validation) of LARS-WG, to ensure efficiency in the process model simulation will be discussed. Then the performance and capabilities of 15 AOGCM models in the new version of Lars-wg will be assessed. At the end, the precipitation threshold is defined and extraction of the longest length of dry spells and comparing it with the maximum length of the dry spells will be simulated. Results & Discussion After calibrating the model of statistical properties (comparison tests T, F and P values (decision criteria), all stations were used to confirm the validity of the model. The results of this calibration indicate that in more than 96% of the stations, for the minimum and maximum temperature and sunshine model, show high accuracy (results of error in Dezful and Gorgan stations were greater). In all of these stations like Abadan station, variables significant (P-value) were at./05. It is acceptable that the data generated is random.Considering the bias error, at more than 95 percent of stations there were very good agreements between the observed and modeling data (for every 4 variables). Based on the principles of (1 to 3), and using statistical methods and indicators, the AOGCM models to simulate and extract during dry spells were examined and it was found that two models (Hadcm3 and GFDL-CM2.1) had maximum performance (correlation) and the lowest error in estimating for simulation data precipitation. The model (INM-CM3 and NCPCM) have least amount of correlation and efficiency. To estimate the maximum length of dry spells Hadcm3 results were used under scenario (A2 and B1) for the decade 2050 and the use of the results of other models was skipped in this research. Maximum dry spells in Iran comply with dryness condition in central and eastern areas. So that the country could be on the threshold of ./1 mm divided into 6 orbital regions of the northern circuit during the period of 37 days (in Rasht station) minimum and 351-day observation period in Southeastern Chabahar stations. The values show that the threshold of ./1 mm at more than 65 percent of the area’s dry spells over 7 months there was no rain on them yet. With a threshold of 5 mm needs maximum length of dry spells that lasted about a year with 364 days in Yazd station. That is roughly the size of 5 mm precipitation a year not registered at this station. Conclusion Modeling dry spells by computing scenarios of climate change and taking into consideration uncertain resources at the AOGCM models output, showed that based on the worst-case scenario (A2), and the most critical situation (2080), the average temperature of the country has increased 2.7 degrees (ºC) and Despite increased precipitation in some Stations, the average rainfall is facing a 33% reduction in the whole country. According to the most optimistic scenario (B1), the average temperature of the country is increasing by 1.4 (ºC) and the precipitation is decreasing by 14% in relation to the observation period. The results of the uncertainty examination for dry spells in Iran showed that in both 2050s and 2080s and based on all three scenarios (B1, A1B, A2), length of dry spells increases in all areas of Iran. Most of the changes in length of dry spells belong to the northwestern areas of Iran (Urmia, Khoy, Kermanshah, Hamedan and Lorestan).
Mohsen Abbasnia; Taqi Tavousi; Mahmood Khosravi; Toros Hossein
Abstract
Recognizing and evaluating the climate changes in the coming decades is absolutely necessary for the purpose of appropriate environmental planning in order to adapt and mitigate its effects. In this research, the SDSM model was successfully calibrated and validated (1981-2010) tocomparatively analyze ...
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Recognizing and evaluating the climate changes in the coming decades is absolutely necessary for the purpose of appropriate environmental planning in order to adapt and mitigate its effects. In this research, the SDSM model was successfully calibrated and validated (1981-2010) tocomparatively analyze and explore the future maximum daily temperature variations over Iran forthe two future periods of (2041-70 and 2071-99) and based on the output of two general circulation models of atmosphere, namely, Hadcm3 and CGCM3 under the existing emission scenarios (A1B, A2, B1, B2), relative to the baseline period of 1981-2010. In other words, with regard to the uncertainty for the maximum daily temperature of the future data, downscaling was performed in 7 synoptic stations as the climatic representatives of Iran. Analysis of the output uncertainty showed that CGCM3 model under the B1 scenario among all different models-scenarios has had the best performance in simulating the future temperature. Also, the findings of the research on the studied stations indicate that the temperature in Iran in the middle and final decades of the 21st century increases in averagebetween 1 to 2 degrees Celsius, which based on different scenarios of the Hadcm3 model, this temperature increase has been higher compared to the CGCM3 model. In terms of spatial dispersion of the changes in the GIS environment based on the output of all scenario-models, the lowest temperature increase was observed at Bandar Abbas station located on the south lowland coast of Iran, and on the contrary, the temperature rise reaches the maximumat the Tabriz station located onthe northern latitudes and highland and mountainous regions of Iran. In total, the important and effective factors in the future changes of Iran's temperature can be classified into three groups: factors of altitude, latitude and atmospheric humidity, because, based on all the outputs of model-scenarios, the stations located on the northern latitude elevations of Iran will experience the highest temperature rise compared to the stations located on low-altitude and adjacent to the southern coast of Iran.
Taghi Tavousi; Mahmood Hoseynzadeh Kermani
Volume 22, SEPEHR , July 2013, , Pages 92-95
Abstract
In recent years, fequency of dust storms has increased. Dust storms can influence and change the environment, result in huge damages for human societies. Correct monitoring of disasters is an essential need. The present article monitor dust storm processes in April, 2006. The dust storm zone was extracted ...
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In recent years, fequency of dust storms has increased. Dust storms can influence and change the environment, result in huge damages for human societies. Correct monitoring of disasters is an essential need. The present article monitor dust storm processes in April, 2006. The dust storm zone was extracted concisely based on reflection features and dust storm absorption. Their intensity levels were estimated. Then, their moving directions were monitored using multi temporal data. Results indicate high consistency with the monitoring performed by meteorological group. To sum up, dynamic monitoring of dust storm processes with multi temporal data will be very useful in future.
Taghi Tavoosi; Mohsen Armesh
Volume 21, SEPEHR , February 2013, , Pages 28-30
Abstract
From a meteorological point of view, frost occurs when minimum daily temperature decreases to 0 °C. This study seeks to predict and rout early autumn frosts in Khash city. To study early frosts, the first day of frost in the statistical period of 1986 to 2008 was investigated. Probabilities and return ...
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From a meteorological point of view, frost occurs when minimum daily temperature decreases to 0 °C. This study seeks to predict and rout early autumn frosts in Khash city. To study early frosts, the first day of frost in the statistical period of 1986 to 2008 was investigated. Probabilities and return periods of autumn frosts (early frosts) were estimated using normal distribution and Log Pearson type 3 distribution. In Log Pearson type 3 distribution, there is 99 percent probability that frost does not begin before 8 October, 95 percent probability that frost does not begin before 15 October. In normal distribution, there is 95 percent probability that frost does not begin before 12 October. Coefficient of data change is 21.2 which indicates relatively high frequency in the time of frost. A graph of the first day of frost and its 11 year average was prepared and frost occurring process was routed. Results indicate that during the last decades frost has retreated toward winter.
Taghi Tavousi
Volume 8, Issue 30 , August 1999, , Pages 18-25
Abstract
Coastal regions have been paid significant attention by humans due to their natural conditions for life such as fertile soil caused by alluvial composition, rivers, abundant water, air’s mildness and access to marine resources and commercial paths, and have increased in political, military and ...
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Coastal regions have been paid significant attention by humans due to their natural conditions for life such as fertile soil caused by alluvial composition, rivers, abundant water, air’s mildness and access to marine resources and commercial paths, and have increased in political, military and economic importance after the Industrial Revolution and the consequent expansion of global commercial activities and development of economic, political and cultural relationships as well as tourism industry. Existence of such favorable conditions has helped the growth of human concentration and increasing establishment of industries, offices and hotels in coastal cities.The results of some of assumptions show increase in number and severity of meteorological catastrophes and natural disasters such as river and sea flooding on vast scales at highly populated coastal regions ( like Bangladesh, Caribbean coasts, etc.) and intensification of tropical storms and expansion of their areas of influence toward western Europe and higher geographic latitudes. This upward trend has been caused by climate change and has been intensified by population density in large cities, especially coastal areas, such as concentration of hotels in coastal areas vulnerable to the hurricanes like Florida Coasts or establishment of industries at storm-prone Northern Sea. Incidents will be more catastrophic when such establishments and construction of transportation networks in above-mentioned areas are not accompanied by technology.
