Yousef Alipour; Naser Bayat; Ali Osanlu
Abstract
Extended AbstractIntroductionTemperature is considered to be an important element of climate whose changes have important consequences for human life. The present study seeks to detect trends and significant changes in the temperature at the 1000 hPa level in Iran. Due to its geographical location, Iran ...
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Extended AbstractIntroductionTemperature is considered to be an important element of climate whose changes have important consequences for human life. The present study seeks to detect trends and significant changes in the temperature at the 1000 hPa level in Iran. Due to its geographical location, Iran climate is affected by various patterns of sea level pressure such as subtropical high-pressure, Siberian high-pressure, Monsoon low-pressure, the Mediterranean low pressure, Black Sea low pressure and Sudan low pressure during warm and cold seasons. These patterns have changed in different time series leaving adverse effects such as decreased precipitation and increased temperature, while probably changing Iran climate from semi-arid to arid and causing climate hazards. Having enough information on the temperature characteristics and its future trends, it is possible to decide on macro politics and a comprehensive method for the management of an area. Therefore, the present study aims to detect trends and significant changes in air temperature at the 1000 hPa level. Materials & Methods45 ° to 64 ° Eastern longitude and 45 ° to 64 ° latitude were selected to study temperature changes at the 1000 hPa level in Iran. In this study, temperature data of 1000 hPa level recorded in a 70-year statistical period (1950 to 2020) and data retrieved from NCEP/NCAR with a spatial resolution of 2.5 by 2.5 degrees have been used to prepare time series and necessary maps. The Kendall Man test was used to analyze the trend of time series. The 70-year statistical period (1950 - 2020) was divided into 10 decades and average seasonal temperature was used. Results & DiscussionThe average temperature of Iran at the 1000 hPa level is rising by 1.34° C per century and its standard deviation has reached its maximum value in recent decades. In the last two decades of the statistical period, 30 ° C contour line has approached Iran from southwest. Temperature trend at the 1000 hPa level is investigated in 4 different seasons of Iran.Summer: according to the Mann-Kendall test, average temperature in summer shows a significant trend and has increased by 0.2 ° C every decade.Autumn: time series of temperature data in autumn shows a significant trend and the slope of the regression line (temperature) has increased with a rate of 0.0451 ° C every decade.Winter: average temperature has decreased at the beginning of the study series and increased at the end of the series. 15.26 ° C and 8.18 ° C (in 1966 and 1972) were the highest and the lowest average temperature recorded in winter, respectively.Spring:The average temperature in Iran has increased by 0.197 ° C every decade. In this 70-year statistical period, average temperature of Iran in this season was 24.37 ° C with the highest annual average temperature recorded as 27.18 ° C in 2008 and the lowest annual average temperature recorded as 21.83 ° C in 1972 and 1992. ConclusionAverage temperature in Iran is raising with a rate much higher than the global average (0.74 ° C per hundred years), due to wide fluctuations in the general circulation patterns of the atmosphere and changes in sea level pressure pattern. Thus, it can be predicted that the temperature in southern Iran may reach over 60 ° C by the end of the century threatening southern riparian provinces with dangerously rising water level and the risk of drowning. Wildfires will still be common in Iranian forests, the number and intensity of floods will increase sharply, and water resources will reach a critically low status.
AhmadReza Ghasemi; Morteza Moogooei
Abstract
Introduction
Climate change will affect the availability of water resources and the sustainability of their management. The impact of climate change on water resources has caused concerns and serious challenges around the world. Global climate change has decreased water resources in many regions ...
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Introduction
Climate change will affect the availability of water resources and the sustainability of their management. The impact of climate change on water resources has caused concerns and serious challenges around the world. Global climate change has decreased water resources in many regions and especially in arid and semiarid regions such as Iran. Water shortages decrease both agricultural production and food security and can also limit the economic development and ecosystem health. There is also growing evidence that climate change is changing the hydrological cycle.
The province of Chaharmahal-o-Bakhtiariis the main supplier of water for Khuzestan and Isfahan provinces and inter-basin water transfer talks have always been going on for these two provinces. However, there has not been a comprehensive study on the discharge changes in the rivers of this province, nevertheless, we cannot judge the future of water transfer. In Iran, there have been several studies on the seasonal changes in precipitation and other climatic variables, but assessments of river flows are limited. Therefore, the purpose of this research is to document statistically significant trends in seasonal and annual changes in stream flow in the main rivers in Chaharmahal-o-Bakhtiari.
Materialsand Methods
The total monthly and seasonal streamflow time series for the period of 1358–1389 (32 years) corresponding to 12 hydrometric stations across the Chaharmahal-o- Bakhtiari province were obtained from the Chaharmahal-o-Bakhtiari Regional Water Organization. This study is done with the latest data (1389) published by Chaharmahal-o-Bakhtiari Regional Water Organization. At first, the linear trends are determined on annual and seasonal timescales using Mann–Kendall (MK) non-parametric trend tests.The non-parametric Mann-Kendall tests are based on the calculation of Kendall's tau between two samples which is itself based on the ranks with the samples. This test has been widely used to detect trends in series of environmental data, climatic data or hydrological data, because it is less sensitive to the non-normality of the distribution and less affected by extreme values or outliers in the series.Also, the magnitude of trend- if a linear trend is present in a time series- is estimated by using the non-parametric Sen’ estimator test. The Sen’ estimator method is commonly used for calculating the trend slope. Thus, in this study this method is also used to calculate the trend slopes to obtain the extent of trend changes.
A number of methods can be applied to determine change points of a time series. In this study, the change point in the stream flow time series in 12 studied hydrometric stations is identified by Pettitt’s test. This test is a non-parametric approach for detecting change points based on the mann-whitney test. It has been demonstrated that the Pettitt’s test is a useful technique for examining the occurrence of abrupt changes in climatic records.
Results andDiscussion
The results of the non-parametric Mann-Kendall tests (MK) for all studied rivers through the Chaharmahal-o-Bakhtiari province showed a decreasing trend in the stream flow in all 12 hydrometric stations for both seasonal and annual scale. The amount of reduction based on the Sen’ estimator method, varies at different stations and seasons, from 0.8 m3/s to 17 m3/s in Gordbisheh and Beheshtabad, respectively. On seasonal scale, the results indicate a significant reduction in stream flow of all stations in summer, while in winter-except at two stations (Deh- Cheshmh and Soulegan) significant trend was not observed. The results of Pettitt's test also suggest that, the abrupt downward change (statistically significant) in most studied stations occured in the early 1370s. On the other words, in two recent decades a significant decreasing trend in stream flow has occurred in Karoon and Zayandeh Rood Basin. The results also showed that, in addition to the mean of stream flow, the extreme values of stream flow in these rivers also experience a very sharp decrease during the studied period.
Conclusion
Decreasing trend in all studied hydrometric stations through the Chaharmahal-o-Bakhtiari province clearly shows the reduction of water resources in this province and also the reduction of the role of the province in water supply to the country. The abrupt downward change that occurred in the early 1370s in most studied hydrometric stations also shows that the reduction of water production in the province has started from about 20 years ago. Therefore, for any water transfer plan from this province to other regions, the practical principles should be considered. Another important issue that must be considered is that, the water resources in Chaharmahal-o- Bakhtiari province are sharply decreasing and the water plants should not be based on the old information.
Hossein Asakereh; Hasan Shadman
Abstract
Abstract
Hotdays are temperature extreme states and are considered to be one of the important climatic phenomena. Long term changes (trends) of thisphenomenon arethe consequences and evidences of thermal-climatic changes. Also, these days can affect the ecosystems and human life. Therefore, recognizing ...
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Abstract
Hotdays are temperature extreme states and are considered to be one of the important climatic phenomena. Long term changes (trends) of thisphenomenon arethe consequences and evidences of thermal-climatic changes. Also, these days can affect the ecosystems and human life. Therefore, recognizing the behavior of hot days can be the source of many topics. In this research, we tried to investigate the long-term trend of Iran's hot days using the network data of the country’s average maximum temperature from 1961 to 2007 and statistical methods. For this purpose, the hot day profile was studied based on the percentile of ninety for each pixel from the network and was estimated on each day of the year. Thus, a threshold of heat occurrence was obtained for each pixel every day. Then, the days whose temperatures equaled or exceeded this threshold, were considered hot days.The average number of hot days in the country is 39 days. The cold season months, as well as April, have the highest frequency of the average hot days.The frequency of hot days is increasing. The number of hot days has made a positive trend for about half of the country. Also, the average temperature of hot days has also been checked. The trend of the average temperature of hot daysin more than half of the countryhas been positive and in around one third of the country has been negative.The hot days’ temperature-related events of Iran have a 3 to 4 year cycle. Toanalyze the trend in data, linear regression was used with least squares error method and a spectral analysis method was used to investigate the existence of significant fluctuations in the data.
Madjid Montazeri; Leyla Dadkhah
Volume 22, SEPEHR , July 2013, , Pages 89-91
Abstract
Dust has always been one of the most important environmental hazards and it leaves adverse environmental consequences. The present article seeks to identify and analyze dusty days’ trend in Bushehr station during the last 55 years.
In this regard, monthly and annual statistical data of dusty days ...
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Dust has always been one of the most important environmental hazards and it leaves adverse environmental consequences. The present article seeks to identify and analyze dusty days’ trend in Bushehr station during the last 55 years.
In this regard, monthly and annual statistical data of dusty days in Bushehr station between 1951 and 2005 was applied. First, normality test was performed using Ncss and homogeneity test was performed using Runs Test. After proving data abnormality, nonparametric test of Mann-Kendall was chosen.
Findings indicate that except for June, other months show an increasing trend of dusty days even in annual scale. Noteworthy, the increasing trend in cold months is more obvious than warm months of the year so that March and November with respectively 3.71 and 4.4 show an increasing trend in 99.9 percent significant level.
Majid Montazeri
Volume 20, Issue 80 , February 2012, , Pages 23-28
Abstract
In order to assess the climatic drought trend in 23 sub-basins of the Caspian Sea, monthly precipitation data were converted to the zoned data by interpolation method. Then, based on the coordinates of the basins, the monthly precipitation of each basin was separated. The Standard Precipitation Index ...
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In order to assess the climatic drought trend in 23 sub-basins of the Caspian Sea, monthly precipitation data were converted to the zoned data by interpolation method. Then, based on the coordinates of the basins, the monthly precipitation of each basin was separated. The Standard Precipitation Index (SPI) method was used to assess climatic droughts and this index was calculated monthly for each basin. According to the parametric test, linear regression of 23 sub-basins of Caspian Sea in January, May and December do not show any significant trend at 95% confidence level. Five sub basins in the months of February and July have a positive trend and 11 sub basins show negative trend in March and September. By applying non-parametric Mann-Kendall test on the SPI matrix of the 23 Caspian sub basin, it was found that no baseline shows significant trend in May. The highest trend in six sub-basins have been in the months of July and August.
