Simulation of temperature threshold heat waves during warm-spell in Iran based on scenarios RCP (2016-2045)

IntroductionHeat Waves as a climatic extreme phenomenon had more occurrence in recent years which this case is an evidence of earth climate change. The heat wave is generally defined as a period of consecutive days with the unusual high temperatures which has become as a common risk in the world due to the effects it has on the nature and human beings including health, hygiene, water resources and agriculture. The identification of these effects requires recognizing the heat wave and determining its thresholds, we have tried to determine the temperature threshold of the heat wave in different regions of the country during the warm period of the year.Materials and methodsTo fulfill this purpose, the statistics of daily maximum temperature of the 90 synoptic stations during the statistical period of 1986-2015 from April to September was received from the country's meteorological organization. Then after the primary processing of raw data, the temperature threshold of the heat wave during the warm period of the year wase determined based on three global indexes (Percentile 95, Baldy, World Meteorological Organization).Baldy indicator: Tmax daily ≥ Tmean max daily + 1.5sdmax dailyPercentile 95 index: when the daily maximum temperature of each station is equal and larger than percentile 95 of that daily data’s station and continue at least 2 day, named as a heat wave. Global meteorological organization index: define the heat wave based on which daily maximum temperature of a station is 5 degree centigrade more than a long term mean for 5 day consecutive. Then in ArcGIS environment and by using a hybrid method of IDW and regression the temperature threshold was interpolated for the whole country, considering the latitude and altitude (as the 2 important and effective factors in the amount of the temperature threshold of the heat wave). the research is about simulation of temperatures threshold that  leading to heat waves in different parts of the country.At first, the temperature maximum of 90 stations in the warm spell of the year for 30 years (2016-2045) by General Circulation models CanEsm2 under 3 scenarios RCP 2.6, RCP 4.5 and RCP 8.5 and statistical downscaling of SDSM simulated. Then base on 3 global indices determined temperature threshold heat wave in different country.Results and DiscussionThe results showed that the temperature thresholds in the country's different times and places are not the same in the warm period of the year, and they have different ranges. In April the temperature threshold ranged from 15 - 40 ,in May from 21-46 ,in June  between 25-50, in July between 29- 49 ,in August between 32- 52 , and in September between 27- 47 degrees Celsius . In the months of April, May and September, the temperature threshold is higher from the local differences and in the months of June and July and August it has almost the relative uniformity, which is because of the presence of Azores subtropical high pressure which dominates all parts of Iran from the south of Alborz Mountains. On the other hand, the presence of this phenomenon makes the role of local factors such as altitude, latitude in the value of temperature threshold in these months not that much tangible, and the temperature threshold has the relative integration.ConclusionAlso, the results show that the highest temperature threshold of the heat wave in the warm period of the year is related to Khozestan province and the lowest temperature threshold of the heat wave is related to the parts of the North and North West of the country. Based on different scenarios RCP 2.6, RCP 4.5 and RCP 8.5 in future, low-temperature threshold in the spring almost 5 degrees will be increased. In addition, the boundary of classification of temperature have a sensible change. Classification with high threshold movement toward high-latitude and middle- latitude. In summer high threshold and low threshold don’t change than present. It is remarkable that in current, large part of country have threshold 35-40 degree of Celsius, but in future will be 40-45c.In the other hand, almost, 70 percent of country experiment threshold more than 40c spatially in high-latitude and middle- latitude and in warm spell, temperature threshold have most changes and increase in future than past.  The results of this research indicate this scientific truth that in order to obtain accurate temperature threshold for different regions of the country, different indices should be used because these indicators complete each other, and we cannot achieve the accurate results in this field by using just one index.