investigation of meteorological extreme events in the north-east of iran

introduction: over the past hundred years, human activity has significantly altered the atmosphere and increase of concentration of greenhouse gases lead to warm the earth's surface. this global warming leads to change of climatic extreme index and increases the intensity and frequency of occurrence of extreme climate events. investigation of extreme values for planning and policy for the agricultural sector and water resource management is important.in this study, a comprehensive review of extreme indices of temperature and precipitation are discussed. this paper aims to investigate extreme temperature and precipitation indices defined in accordance with ccl, and the study of other climatic parameters in the north east of iran. materials and methods: in this research, statistics and data of some stations in the north east of iran during the period 1992-2012 were used. to evaluate the extreme climate indices trend, 27 indices of rainfall and temperature, were defined by the etccdmi. they were calculated by rclimdex software. in this software, prior to the index calculation, data by quality control software became quantitative and incorrect data were controlled and outlier data were examined. the indices were calculated by daily data. 11 rainfall and 16 temperature indices were calculated by this software.the target of the etccdmi process is to delineate a standardized set of indices allowing for comparison across regions. these extreme indices were classified in five categories which included the percentile-based extreme indices, the absolute extreme indices, the threshold extreme indices, the periodic extreme indices, and the other indices. they were estimated at the 0.05 significant levels. the mann-kendall test was used to investigate the climatic parameters, maximum relative humidity, sunshine duration and maximum wind speed. results and discussion: thermal analysis results are consistent with warming patterns, and they have showed that hot extremes indices have increased. hot days index (su25), shows a significant positive trend in all studied stations. number of tropical nights has a positive trend in all stations. hot day frequency (tx90p) and hot night frequency (tn90p) in all stations show a positive trend, indicating an increase in the number of warm days and nights. cold extreme indices show a decreasing trend. (tx10p) and (tn10p) show significant negative trends in all stations and indicate a decrease in cold days and nights. number of frost day index shows a decreasing trend. overall, the results revealed a decrease in the severity and frequency of cold events, while warm events during the study period were significantly increased. these results are consistent with the results of the intergovernmental panel on climate change and global and regional studies. rising temperatures could lead to increase in the maximum wind speed in the area. in the study of the maximum wind speed process, this trend was observed in most stations, and incremental changes can be associated with a reduction in the maximum relative humidity (which was observed in the results). the sunshine hour parameter depicted a decreasing trend in the most station trend. in the study of all rainfall indices in all studied stations there were a decreasing and negative trend for rainfall, although few significant trends over time were observed. comparison of years with the highest rainfall and those with the lowest, showed that the amplitude of fluctuations in precipitation in different years is very high and the distribution of rainfall at distinct stations is different. in general, due to the high dispersion and low rainfall in most stations, providing a clear and uniform regional rainfall pattern is not possible. due to the effects of temperature and precipitation extreme indices in a wide range of human activities, such as agriculture, water management and building design, it is necessary to consider the effects of these extreme climatic events in the future planning and policies in different sectors. conclusion the results showed that hot extreme indices, such as summer day index, the number of tropical nights, warm days and nights have increased, while, in the period of study, cold extreme indices have decreasing trend, which shows a decrease in the severity and frequency of cold events.the trend of the maximum wind speed was increased in most stations. rainfall indices show decreasing and negative trends, although over the studied period few significant trends were observed.