Trend Analysis of Extreme Temperature Indices in the North West of Iran

Natural environment is regulated according to the climatic conditions. Human communities are forced to adjust themselves to these conditions. Identifying the intensity، frequency and timing of climatic events can help solve the environmental problems and ease the coherent planning to mitigate these events changing behavior. To achieve this objective in the Northwest of Iran، daily minimum and maximum temperature data from 13 stations were obtained from the Meteorological Organization of Iran in the quality control format for the existing data period. Sixteen Extreme indices were extracted by RClimDex package and their changing behavior was checked by Mann – Kendall method. The results showed that the frequency of cold indices decreased but the frequency of extreme warm indices increased during the study period. According to the results of wavelet analysis all the extreme cold indices showed a significant periodic fluctuations of 2 to 4 years. Among the warm indices only the warmest days index (TXx) showed 2 to 4 years fluctuation and the number of tropical nights (TR20) exhibited 4 to 8 years of significant fluctuation.