جستجوی مقالات مرتبط با کلیدواژه "extreme indices" در نشریات گروه "جغرافیا"

Extreme weather and climate events have received increased attention in the last few years, due to the often-large loss of human life and exponentially increasing costs associated with them. These events have profound impacts on economies and livelihoods of many regions of the world. In this regard, diagnosis of extreme events in terms of intensity, duration, and frequency is crucial in order to frame mitigation and adaptation strategies to counter the impacts due to climate. The purpose of this research is to analyze the trend of changes in precipitation extreme indices to reveal the occurrence of climate change in Najaf Abad using 20-year daily statistics of Najaf Abad synoptic station from 2003 to 2022. For this purpose, the extreme indices of precipitation and the non-parametric Mann-Kendall test were used to investigate the changes. The results showed that the precipitation extreme indices present different patterns of intensity, duration and frequency of precipitation. PRCPTOT, CDD, CWD, R10mm, R20mm, R95p, Rx5day and SDII indices are decreasing and Rnnmm, R99p and Rx1day indices are increasing. But in general, due to the high dispersion and low amount of rainfall, the regional rainfall pattern cannot be clearly identified. The results of the analysis of the threshold indices of precipitation showed that the precipitation does not follow a regular trend and is irregular. The results of this research can provide solutions to workers and managers in line with correct management and use of other capacities to deal with possible situations. In addition, the combination of the results with long-term meteorological data and the perception of local communities affected by climate change can be examined and become a model for managers to make more appropriate and relevant decisions and plans.

Statement of the Problem:Precipitation is one of the most important climate variables in the world, and its changes can have different environmental, economic, and social consequences.

The purpose of this study was to evaluate the changes in rainfall indices in Iran.

For this goal, the latest version of the daily data of the Global Precipitation Climatology Center (GPCC) for the period from 1982 to 2016 was selected in 1×1 degree spatial resolution of latitude and longitude. By programming in the MATLAB software package, a matrix was constructed on the Iranian framework at 12784 × 750, the rows of which represented the days from 1.1.1982 to 31.12.2016, and columns represented the pixels in the region. The indices used in this study were selected from the list of standard indices recommended by the Climate World Committee of the World Meteorological Organization and the Climate Change Variation and Research Program, which made it possible to compare all stations in different countries.

The calculation of the indices changes with the help of the slope of the regression line on each of the pixels shows that in many parts in Iran, the intensity of daily precipitation is increasing. Also, in many parts of Iran, especially in western parts, the index of wet succession is decreasing, that is, the persistence of rainy days in many areas of the country is declining.

Global observation in recent years has shown remarkable changes in the behavior and characteristics of extreme atmospheric phenomena. Geographic location, topography and variety in the occurrence of atmospheric systems causes a number of these phenomena in the Mazandaran province every year. In recent years, the number and severity of extreme events in the province has increased. Therefore, it is necessary to identify temporal and spatial distributions of the mentioned hazards in order to adapt to these hazards and reduce the effects of extreme phenomena.  

Daily temperature and precipitation data were used in the 15 stations of the Mazandaran province in order to identify the temporal and spatial distribution of the extreme parameters. To ensure the quality of them, homogeneity, adequacy of data and recovering and estimation of lost data implemented. Data homogeneity was investigated by Run-Test method. In this method, each of the series values is compared with the mean of the data. The parameter z is computed (relation 1). If its magnitude is greater than 1.96, the data is considered at 95% heterogeneous confidence level here r, m and n are the total number of sequences, the number of values smaller than the mean and   the number of values greater than the mean, respectively. In the study of sufficient number of years for stations, the Makus relationship (relation 2) was determined. (2)   where y, t and R are the minimum number of required years, the Student’s t test value at the 90% confidence level and the ratio of y value based on 100 year return interval to y value based on a 2 year return interval. The minimum statistical years are 10 years old and a 15-year statistical period (2017-2003) selected in the present study. To study the trend of changes in extreme indices, Spearman nonparametric test was used in the Babolsar and Ramsar stations with long-term data (1971-2017). This method uses data’s rank instead of the actual values. Data are arranged in increments and ranks from 1 to n. If the Spearman correlation coefficient () (Equation 3) was greater than 1.96, the assumption of the trend in the data series was accepted, otherwise, the data series would be considered without trend. Here, for a sample of size n, i and  are the historical rankings in order of occurrence and the ordered historical rankings are in incremental order. The temporal and spatial frequency of  twenty extreme indices from the expert team ETCCDM[1]  for temperature and precipitation were determined using Rclimdex software.  

Long-term trend of extreme indices The number of cold nights and cold days as well as the number of frost days in recent years were dropped significantly. CSDI index was decreased only in Babolsar, while the WSDI was increased significantly at both stations. The number of summer days and tropical nights has increased. The max Tmax have been increasing in Ramsar. The min Tmin was increased at both stations. DTR index was dropped significantly. Rainfall indices at either of these two coastal stations do not show a meaningful change in recent years.   Daily temperature extreme indices The maximum number of FD was in Baladeh and the maximum number of ID was in Siyahbisheh. The maximum number of SU was in Amol, Sari and Ramsar and the maximum number of TR20 was in Babolsar. The monthly max of Tmax was happened in Sari, Galougah in May, and the monthly min of Tmin was happened in Baladeh in the month January. Most of the cool days and nights and cold spell duration were in Alasht and most of the warm days and nights and warm spell duration were in Ramsar.   Precipitation indices The highest and lowest total annual precipitations were observed in Ramsar (1915.4 mm) and Kojur (449 mm), respectively. The most RX1day and RX5day were in Ramsar. The highest number of days with heavy rainfall greater than 25 mm per year was in Ramsar (21 days) and the highest number of dry periods was happened at Amir Abad station (108 courses).   Seasonal indices The max Tmax was in Sari, Galougah and Dasht-e-naz (42.6 ˚C) during spring, in Galougah (42.2 ˚C) during summer, in Galougah (42 ˚C) during autumn and in Gharakheil (34.6 ˚C) during winter. The min Tmin was in Baladeh every Season, it was 4.6 ˚C in spring, 12 ˚C in summer, 6.2 ˚C in autumn and -9.4 ˚C in winter.

In the study of trend, it was found that the warm duration index, number of summer days and tropical nights were increased significantly and the temperature difference between the daily maximum and minimum values was decreased significantly. No significant change was observed in rainfall indices at any of two stations in recent years. Investigating phenomena associated with extreme temperature indices showed that the frequency of frost days is higher in highlands, and ice days in the coastal-plain areas occur rarely. The minimum daily temperature, cold days and nights indices show a direct correlation with elevation in the province. The average of maximum temperatures and the number of warm days and nights in the east coastal zone of province are the highest and it goes down to the high and western regions of the province. Diurnal temperature range has the highest amount in the mountainous areas of the province. Therefore, the indices of maximum air temperature in the eastern parts of the province have higher values. the minimum temperature distribution is in a good agreement with topography of the region in Mazandaran province. The rainfall indices determine that the amount and severity of rainfall reduce from the west to the highlands and east of the province. So far, the largest number of days with a very heavy rainfall of more than 25 mm in the period 2003- 2017 belongs to Ramsar (351 millimeter).

The purpose of this study is to identify and detect changes in rainfall extremes as indicators of climate change in  Iran. To conduct this research daily rainfall data of 76 synoptic stations were used from 1986 to 2016. The results show that the trend of the number of days with heavy rainfall was about 7 percent of Iran's negative and 93 percent of it was not observed. The trend of successive dry days in 28% of Iran is a positive trend and 37% there is a negative trend. The wet succession days in most areas of Iran are not trendy. The trend of the total amount of rainy days is about 99% of Iran's negative range. The maximum  negative slope of Iran's annual precipitation was observed at Masjed-e-Soleiman Station with a slope of -8.26  and there is a positive trend in the Bandar-e- Anzali. The trend of very wet days is about 78 percent of Iran is negative and about 14 percent is positive and 8 percent of it is trendless. The trend of very wet days in about 70 percent of Iran is negative. The highest wet days are observed in Khorramabad with a gradient of 1.4 and the highest decreasing trend in Sarpol-e-Zahab with a gradient of 2.78. Also, in 22% of Iran's range, there is no particular trend. The trend of one-day' precipitation in about 47% of Iran's negative and in 47% is without trend and 6% of it is positive. The trend of the maximum amount of 5-day precipitation about 73% of Iran is negative and in 2% it is positive and 25% of it is without a trend. The slope of the decreasing trend in Fasa and Masjed Soleiman stations is -2.4 and -1.9 respectively

The UN Population Demographics in 2014 has shown that there is a reversal of the demographic trend of urban and rural areas, with the world's largest population (54%) living in urban areas, and this trend is increasing, while by the year 1990 A small population lived in cities. This undocumented development leads to major changes in the environment, including the reduction of natural surfaces and the replacement of these with artificial and human land covers. Urban areas are often identified with impenetrable and constructional surfaces that often have a negative impact on ecosystems. Urbanization changes the natural landscape into human-made with different physical characteristics. Changing and transformation in surface land covers has an important effect on energy balance and local climate. As a result, urban climate is formed from the climatic factors of the city that are changing with the impact of urban factors over time.In order to study the effect of urban expansion on climatic condition of the Tehran, daily precipitation, minimum and maximum temperature data were extracted from Mehrabad synoptic station during a period of 50 statistical periods (1966-2016). Different methods and tests have been used to analyze trends and changes in climatic conditions. The trend in the cluster data series was studied using the Mann-Kendall test. The Mann-Kendall test, is a base-rating nonparametric test for trend analysis which was first used by Mann for public applications in 1945 and revised by Kendall in 1948 and presented in a different way. Then, RClimDex software was used to extract the process of extreme weather indicators. This software has been developed by Zheng and Yang (2004&2005) at the Canadian Weather Service's Climate Research Branch. In the present study, 23 indicators of ETCCDI indicators were used using RClimDex. Indicators are divided into five groups of indicators based on percentiles, periodic indicators, absolute indices, threshold indicators and other indicators (such as temperature change overnight).Based on non-graphical Mann-Kendall Test, both temperature parameters (minimum and maximum temperatures) have an incremental trend during the 1966-2016 period, which is more evident at the minimum temperature. While precipitation in the same period of time has been a slight downward trend. Also, based on the Mann-Kendall graphical test, when there is a significant trend in data, the lines ui and u'i interrupt each other. The results of the Man-Kendall test show that the increase in minimum temperature is higher than the maximum temperature. Moreover, during 1976-1986, Tehran experienced rapid physical growth, and this period coincided with an increase in temperature, which continued until the end of the period. Based on the analysis of the temperature extremes index, the cold days indices (TX10p) is facing a downward slope. On the other hand, the Hot Days Index (TX90p) faces an upward slope in the period of 1966-2016. In fact, it can be concluded that during the study period, the percentage of hot days in the Mehrabad station is increasing and cold days are facing a decreasing trend. These results are consistent with the studies of Rahimzadeh et al. (2011), Niw et al. (2006) and Brown et al., 2010, on the trend of the temperature range of the nightly temperature range. Conclusion In recent years, the spread of cities and their growth has had a great impact on the environmental conditions in different parts of the world. In the meantime, some cities have been experiencing rapid and significant growth. Urban change has today had widespread effects on urban climatic conditions. One of these effects is the change in the temperature of the cities (formation of the UHI) and the increase in night temperatures. The present research was carried out to investigate the effects of the expansion of Tehran on the climatic conditions of the Mehrabad synoptic station. The study of the climate conditions of the Mehrabad station shows that during the study period, the air temperature of the Mehrabad station has undergone a change. So that the minimum and maximum temperature is facing an increasing trend, which is, of course, more severe at the minimum temperature. The average minimum temperature of the Mehrabad station during the 1996-75 period was about 10.9 ° C, reaching about 13.7 ° C in the period 2005-2015, and on the other hand, the average maximum temperature during the 1975-1996 period was about 5.5 ° C 22 ° C and in the period 2015-2005 reached about 23.6 ° C. In addition to temperature averages, temperature indices have also changed significantly at Mehrabad station so that cold and warm extreme events have decreasing and increasing trend, respectively.

Abstract Interest in climate changes has significantly increased in recent decades due to the important economic and social consequences connected with extreme atmospheric occurrences. Hence, analysis of extreme precipitations and related extreme occurrences is of great importance in management of variety of sectors including agriculture, water resources, urbanization and transportation. In the recent research, Aphrodite gridded precipitation data set for the time period from 1951 to 2007 were applied in spatial resolution of 0.25 longitudes by latitude to explore possible trends in extreme precipitation over Karoon basin. The initial matrix of the data in the dimension of 20819*21000 was constructed for whole of the Middle East region in Matlab software. Then the second matrix in the dimension of 20819*100 was extracted from the first matrix that covered the studied region. The rows of this matrix represent the days and the columns show pixels. The selected indices used in this paper including Maximum 1-day precipitation (Rx1), Simple precipitation intensity index(SDII), Number of days with precipitation equal to or greater than 10, 20, and 25 mm(R10mm, R20mm and R25mm), Maximum number of consecutive dry and wet days (CDD and CWD) and Total precipitation when daily amounts are greater than 95th and 99th percentile of wet days(R95p and R99p) have been chosen from the indices recommended by Expert Team on Climate Change Detection and then the trend was evaluated using Mann-Kendall nonparametric test. The results illustrate that extreme precipitation trend is positive in the eastern, northern and central regions; while over a small part of the west and south, it was found to be negative. Indices did not follow any specific trend in the west part of Karoon. Not only has frequency of extreme precipitation increased, but also the intensity has been risen during the study period. In other words, the precipitation was concentrated in some days of the year and the high value of precipitation occurred during days with extreme and super-extreme precipitation. The greatest trend was seen in the indices of the simple daily intensity index (SDII), very wet days (0.99p), days with super heavy precipitation (R25) and days with very heavy precipitation (R20. The least upward trend was associated with the consecutive dry days index (CDD).

Today, it is accepted that the occurrence of any change in the climatic system is important in water and soil resources management. Climate fluctuations have had irreparable effects on water and soil resources of Khorasan Razavi area, especially in Mashhad. Hence, the attitude towards the future is considered as one of the essential requirements for metropolitan and regional management. In order to provide an outlook from future changes of extreme events, especially precipitation, the output of models of atmosphere general circulation (HadCM3, CNCM3, NCCCSM) are used based on A1B, and A2 scenarios under the LARS-WG model for the two upcoming periods of 2011-2030 and 2046-2065. The studied rainfall indices in this research include PRCPTOT, R10mm, R20mm, R95p, R99p, RX1day, RX5day, and SDII. The prediction of changes in the extreme events caused by global warming and climate change is very important in assessing the potential impacts of climate change on different sectors, such as water, agriculture, and management of urban water collection systems. Since the city of Mashhad has a density of large urban population and is known as a semi-industrial region in which the effects of climate parameters on different parts of the urban and industrial community are important, economic development and sustainable living conditions in the future years depend on the ability to manage the risks associated with extreme events. In this study, the magnitude of extreme values change in the predicted rainfall of Mashhad station was investigated for the two periods of 2011-2030 and 2046-2065 using simulated data through three general circulation models (HadCM3, CNCM3, NCCCSM) under the two scenarios of A2 and A1B, and was downscaled in the station scale by LARS-WG Model (Baseline Statistical Period 2014-2016). It was obtained from the reduction of the uncertainty of the average of calculated indices for the three models. Finally, the percentage rate and the amount of index change were calculated. In this research, data quality control was performed using a software package called RClimDex. Also, the homogeneity of the data used was done by using RHtests_dlyPrcp software package under R programming language. To investigate the ability of HadCM3, NCCCSM, and CNCM3 models in the simulation of weather data, especially rainfall, correlation coefficient was used between the monthly rainfall data observed and simulation data of the three models during the base period of 1966-2014. The results showed that there was a relationship between the two series of data with 99% confidence. Despite the low amount of correlation coefficient between the observed and simulated data, the significance test of this coefficient showed that there is a relationship between the two series of data with 99 certainty. The mean values, variance and standard deviation of climate variables can be compared using T and F tests in surveying the ability of LARS-WG model in simulation of climatic data. The climatic parameters of precipitation were firstly calculated using 53 years of monitored data in Mashhad station (2014-2016) using the semi-experimental distribution in the LARS-WG model. Then, the model was performed to generate 80 years of data based on the obtained parameters based on the data series observed at the station. This operation was performed several times by changing the random number to obtain acceptable statistical results. The results of t-test for this station showed that there was no significant difference in the significance level of 0.05 between the mean of simulated rainfall and its actual value, and, correlation coefficients, bias, and mean of absolute error were also calculated for this station in the monthly series of observed and simulated data. Consequently, a comparison was made between the mean values, the standard deviation, and the maximum of monthly rainfall of the two observational and simulated series. This study aims to present an outlook of the events and investigate the effect of changes in greenhouse gas rates based on A1B and A2 scenarios on the mentioned indices in terms of percent and the amount of their change relative to the basic period. The results showed an average of five-day precipitation and rainfall intensity during the 2011-2030 period will probably increase under the A2 scenario. Also, a more share of the total annual precipitation will belong to the occurrence of torrential and floody rains, i.e., precipitations over the percentile of 95 and 99 basic period. According to the results, the increase of these indices means an increase in the frequency of flood occurrence and its severity, especially during the upcoming period of 2011-2030. However, the probability of decreasing precipitation intensity and indices of maximum five-day rainfall are predicted during the period from 2046 to 2065. Due to the importance of the subject, it is recommended that the authorities pave the way for further studies such as the use of other methods of downscaling under new scenarios in this field, since such results are necessary in long-term planning in the urban services sector.

In recent years, there is an increasing concern in weather and climate extremes, since they may cause serious disasters to human society and nature and seem to more sensitive to climate change than the mean value. The rise in greenhouse gas emissions arising from increased industrialization and urbanization has, in recent years, contributed significantly to global warming. This global warming leads to the change of climatic extreme index and increases the intensity and frequency of occurrence of extreme climate events. Extreme events are relatively rare, unpredictable and often brief but they are highly destructive. Many studies show that climate extremes cause significant damage to crop growth and final yields, and the various frequencies and intensities of extreme events result in differing degrees of soil erosion and flooding. Climate variability is largely influenced by temperature change, which is particularly important through its role in the global climate system and energy cycles. Analyses of observed temperature in many regions of the world have already shown some important changes in the extremes. To predict future change in extremes understanding the recent past is essential. The objective of this study was to investigate the spatial and temporal distribution of temperature extremes in Khorasan Razavi province during 1990–2015 based on 15 climate indices proposed by the Expert Team on Climate Change Detection and Indices and to detect the effect of climate change

Climate change caused some changes in the global climate in recent decades. One of the climate change impact is the disturbance of the hydro- climatic cycle and discipline in the world. The effects of climate change on the hydrological cycle are including changes in groundwater levels, lakes, as well as changes in the distribution of the amount and timing of rainfall and river flows.
Intensity and frequency of extreme precipitation events and the risk of floods and droughts are increasing due to the climate change in the large parts of the world.
The impact of climate change on spatial and temporal characteristics of precipitation and extreme events, affected people's life. Hence, study on trend and changes of precipitation extreme can reveal the occurrence every related hazard. Studies around the world have shown that global warming and climate change impact and the precipitation condition has changed in different regions. The main objective of this study is evaluating of daily precipitation indices trend over Iran.
In order to analysis of daily precipitation indices trend, 47 synoptic stations were used to investigate the precipitation extreme events over Iran during the 1982- 2012 (11323 consecutive days). The RClimDex software was applied to extract daily precipitation trend.
The list of precipitation indices include the following:• RX1day: Monthly maximum 1-day precipitation
• Rx5day: Monthly maximum consecutive 5-day precipitation
• R10: Annual count of days when PRCP>=10mm
• R20: Annual count of days when PRCP>=20mm
• CDD: Maximum number of consecutive days with RR=1mm
• R95p: Annual total PRCP when RR>95th percentile
• R99p: Annual total PRCP when RR>99th percentile
• PRCPTOT: Annual total PRCP in wet days (RR>=1mm)
On Average, the amount of precipitation in climatic stations such as Bam, Zabul, Yazd, Tabas, Jask and Zahedan was less than 80 mm whereas Bandar Anzali, Rasht, Ramsar and Noshahr stations have experienced above 1000 mm of precipitation during the period 1982- 2012. Among of all studied stations, Anzali and Zabol stations have had about 1763 and 52 mm of precipitation during the studied statistical period, respectively. Investigation of total index of annual precipitation in Iran represents that the slope of precipitation in most of the stations is negative during the 1982- 2012. Averagely, the annual precipitation of Iran has decreased about 2.5 mm during the 1982- 2012.
Generally, results illustrated that the trend of CWD index in some regions was negative, in some regions was positive and in some regions there wasn’t any trend during the 1982- 2012. Among all studied stations, the CWD index had positive trend for 11 stations including Kashan, Semnan, Ramsar, Mehr Abad, Dooshan Tapeh, Zahedan, Khorram Abad, eastern Isfahan, Anzali and Abadeh. There was no trend in Arak, Bandar Lengeh and Shahrood stations and negative trend was observed in other stations. According to the results, the CDD index was increasing in most studied stations during the period 1982- 2012. Approximately, in %72.5 of the stations the index was raising and in %27.5 of stations showed decreasing trend. The trends showed that the number of days without precipitation is increasing. The greatest changes have experienced on the coast of the Caspian Sea and the Persian Gulf. Results showed, indices R 10 mm, R 20mm, R 25 mm, at most of the stations has decreased and R 10 mm index had more negative trend.
The trends indicated that the number of days without precipitation is increasing. Among the studied stations, Ramsar station has experienced the highest downward slope of R95p index with 6.4 mm annually. From this point of view, Saghez, Rasht, Sanandaj and Bandar Abas stations had the highest downward slope in very wet days. moreover, Gorgan station with 2.7 mm have experienced the most increasing trend among all stations annually and Shiraz, Esfahan and Chabahar with higher than one mm are in the next rank, respectively.
The results illustrated that all Precipitation Extreme Indices has been changed over Iran during the 1982-2012. There were negative trends in more stations. In most of studied stations, annual rainfall has decreased and the number of dry days (CDD) has increased, only a few stations in the central regions and the foothills of the Zagros have had positive trend.