Trend analysis of climate change compound indices in Iran

The time-placement scheme of climate extreme changes is important. In this regard, a set of a compound indices derived using daily resolution climatic time series data is examined to assess climate change in Iran. The compound indices were examined for 47 synoptic meteorological stations during 1981-2015. The results show that most stations experienced a negative trend for the cool/dry (CD) and cool/wet (CW) index and a positive trend in CW was observed in some dispersed small areas. Both warm/dry (WD) and warm/wet (WW) indices have similar behavior, but the magnitude and spatial consistency of WW days were much less than WD days. The results show that more than 80% of stations experienced a decrease in the annual occurrence of the cold modes and an increase in the annual occurrence of the warm modes. On the other hand, universal thermal climate index (UTCI) change demonstrated a significant increase in the annual occurrence of strong heat stress (32-38 degrees C) and significant decrease in the annual occurrence of no thermal stress class (9-26 degrees C). Moreover, trends in tourism climate index (TCI), including TCI >= 60 and TCI >= 80, showed similar changes but with weak spatial coherence.