عنوان مقاله [English]
The increase in the global mean temperature during the twentieth century, in particular over the last 30 years, has provided a strong incentive for investigations of climate change. Climatic and weather hazards are amongst the most deadly and destructive natural disasters worldwide, resulting in loss of life, severe damage and large economic and societal losses (Nutter 1999 Su et al. 2006). Those natural and human effects are mainly triggered by shifts of frequency and intensity of extreme weather conditions related to temperature, precipitation, or other aspects of climate, rather than changes of mean climate (Katz and Brown 1992 Plummer et al. 1999). Heat or cold waves are characterized by the occurrence of a sequence of days with high or low values of temperature. These waves have significant impacts in terms of their socioeconomic effects on health, agriculture, forest fires, and the production and consumption of energy (SIAM, 2002 GarcÃa-Herrera et al., 2005 Pereira et al., 2005 Trigo et al., 2005). The aim of this study is investigation and recognition of cold wave and spatiotemporal analysis over Iran.
In order to recognition of cold waves in Iran the interpolated minimum daily data of Asfezari Data base during 1/1/1962 to 31/12/2004. The data matrix with dimension15706 7187 has been created that located on the columns pixels and on the rows are days. In this study, by 6 indices that calculate the intensity, duration and frequency of cold waves, the characterizations of the cold waves in Iran has been investigated. The indices were based on the 10, 5 and 1 percentiles. The indices calculated for any pixels over Iran. Then the significant of trends of indices investigated by nonparametric Mann-Kendal method. The slope of trend on the pixels that have trend in 95% confidence level calculated by linear method. The programs of the calculation has been written in Matlab software environment and the maps has been drawn by Surfer software.
Table1. Cold wave indices summary. The T1 value is defined as the 10, 5, 1th percentile value of minimum temperature based on the entire data record(1/1/1962-31/12/2004)
No Index name Definition Unit
1 10,5 ,1P value The value of the 10, 5 and 1th percentile minimum temperature for each year Â°C
2 Number of runs The number of runs of consecutive days(1or more) over the T1 value per year Day
3 Average run length The average length of a run of consecutive days over the T1 value per year Day
4 Maximum run length The longest run of consecutive days over the T1value per year Day
5 Minimum temperature index The mean of the warmest three consecutive minimum temperatures per
6 Cold Spell Duration Index Annual count of days with at least 6 consecutive days when Minimum temperature