Analysis of El Niño–Southern Oscillation and its impact on precipitation distribution over Iran

Southern Oscillation plays a significant role in climate change as a teleconnection pattern. This study employed two databases. The first database is the daily data of precipitation in the APHRODITE’s Water Resources in the Middle East with the dimensions of gridded 0.25 × 0.25° of longitude and latitude in the period from January 1, 1951, to December 31, 2017, which is equal to 20,819 days in Iran with 2491 spatial pixels. The second database is the Southern Oscillation Index (SOI) values in the same period as APHRODITE’s Water Resources precipitation data. The monthly correlation between precipitation and the SOI was calculated using the Pearson correlation, and the significance level was 95%. Finally, the area of each zone was determined monthly and annually. The SOI and APHRODITE’s Water Resources precipitation data of Iran show that the significant correlation between these two parameters varies in time and place. However, there are relatively strong negative correlations in northern, northwestern, eastern, and southeastern parts of Iran, which cover 24% of the area. There is no direct correlation between precipitation and the SOI in 76% of the land area, mainly in the southern, central, and southeastern parts of Iran. Also, in months when the SOI values (the warm phase of El Niño–Southern Oscillation (ENSO), called El Niño) decrease, precipitation covers more areas of Iran. The warm phase of ENSO (El Niño) substantially influences rainfall in Iran, especially during autumn.