چکیده:
The purpose of this research is to analyze heat waves characteristics in the warm period of the year as a climatic hazard in Iran. In this study, the daily maximum temperature is taken at 44 synoptic stations during the period 1981-2010. These temperature values were used to extract the intensity, frequency and duration of heat waves using percentile thresholds of 90, 95, and 98. The results showed that the average heat waves intensity is added between 3 to 4°C during summer more than spring. During spring and summer seasons, the most intense of heat waves is occurred on the southern coasts of Iran, and the most frequency of heat waves is occurred in the Zagros Mountains and eastern scattered mountainous of Iran. On average, the heat waves frequency is increased about 4 more heat waves during summer than spring. Furthermore, the seasonal average of the most duration of heat waves about 10 to 16 consecutive days has occurred in the southeastern of Iran. Generally, in the higher percentile thresholds heat waves frequency is reduced, but the intensity and duration are increased.
خلاصه ماشینی:
Krautmann (2012) considered some characteristics include duration, daily maximum and minimum temperature, atmospheric conditions, human health and location of the stations to detect a heat wave as a part of climatic hazards.
In several studies, 10 relative based thresholds were applied to detect heat waves (Steadman, 1984; Meehl & Tebaldi, 2004; Anderson & Bell, 2010; Peng et al.
In another study, heat waves have been defined using a period more than two consecutive days and above percentile threshold of 90th in daily maximum temperature (Keellings & Waylen, 2014).
Thus, the percentile thresholds were applied on daily maximum temperature time series of the 44 synoptic stations in Iran to detect heat waves in the warm period of the year between 1981-2010, and ultimately to understand the spatial distribution of the changes in terms of characteristics of heat waves over Iran.
In this method if the daily maximum temperature of a station is higher than the percentile thresholds of 90, 95 and 98 for a period of at least three consecutive days, then the event is considered a heat wave.
After detecting heat waves in all study stations in Iran, its characteristics includes intensity, frequency and duration which were separately calculated for all percentile thresholds, study stations, and months during the warm period of year.
In the spring, the spatial distribution of most heat waves based on the 90th percentile threshold were observed in the middle half of the central latitudes, especially in the area of the western mountains of Iran.