Assessing the impact of cold and warm ENSO on drought over Iran

Document Type: Original Article

Authors

1 Department of Geomatics Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran

2 Babol Noshirvani University of Technology, Civil Engineering Department, P.O.Box 484, Shariati Ave, Babol,Mazandaran 47148-71167, Iran

Abstract

The impacts of El Niño Southern Oscillation (ENSO) on climate change and in the global scale are well
known, and have attracted the attention of researchers since the twentieth century. The study of ENSO
impact on climate using precipitation and near surface temperature data from re-analysis products makes
global and long-term analyses of this phenomenon possible. The common method to analyze the ENSO
impact is to quantify the probability of extreme drought occurrences when the surface temperatures of
central-east equatorial Pacific sea are abnormal. Although the results are always uncertain due to the
complexity of atmospheric teleconnections, application of the recently available gridded datasets helps one
to conduct more precise modeling and predictions. Spatiotemporal patterns of ENSO impact from 1980 to
the end of 2013 for four ENSO indices (e.g. Nino 3.4, MEI, ONI, SOI) over Iran was investigated in this
study. Spatial maps of the Pearson correlation coefficients and a composite analysis were obtained between
the GPCC precipitation and temperature dataset with ENSO states. In addition, the frequency maps of
extreme drought conditions during ENSO states were acquired. The results show that the western (along the
range of Zagros Mountain) and northern (along the Alborz Mountain and the coastlines of the Caspian Sea
to Khorasan Province) regions are more affected by ENSO events. The Pearson correlation coefficient for
all four ENSO indices over the mentioned regions was determined to be about 0.70 for precipitation datasets
and -0.70 for temperature datasets. The frequency analysis of extreme drought based and CZI (Chinese Z
Index) and ENSO phases shows that the western and northeast parts of Iran are more affected by centraleast equatorial Pacific teleconnections. Composite analysis for all four ENSO indices shows the precipitation
(over the rainy months)/temperature (over the summer months) anomalies, for the El Niño states about +25
(mm)/ -0.5˚ (C) and for the La Niña states about -25 (mm)/+0.6˚ to 1˚ (C).

Keywords

Main Subjects


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