Abstract

Changes in cyclones in a region may lead to variations in the precipitation conditions of that region. The current study aimed at examining changes in the frequency of cyclones affecting precipitation in the Rood Zard basin, Iran, during 1976 to 2014. To this end, 1000 hPa maps of NCEP/NCAR and the daily precipitation data of 16 stations located in the basin of the Rood Zard were adopted. The results showed that the frequency of cyclones, their consequent precipitation, and the overall amount of cyclonic precipitation experienced a declining trend over the abovementioned period. The findings of the present study are in line with those of previous ones conducted on other areas in the Northern Hemisphere. Following the examination of mean differences in the cyclone frequency during the understudy period, a significant jump was also observed which tends to delay cyclones’ activities compared with those accruing in the previous years. Further, it was discovered that the seasons of cyclonic precipitation became shorter over recent years. The investigation into these changes can be attributed to climate change discussed in a bulk of previous studies. The existing cycles in the frequency of cyclones and cyclonic precipitation showed the presence of similar (3 and 4.6 years) cycles in both factors. Experts in the field have attributed these short-term cycles to quasi-biennial oscillation (QBO) in the troposphere, ENSO, and similar phenomena taking place frequently in climate change context.