Regional climate variability is generally controlled by atmospheric water vapor (WV), which sources and transport pathways are primarily driven by different large-scale teleconnection processes, particularly the El Niño-Southern Oscillation (ENSO). Hence, this study investigated spatial, temporal, and vertical variations in atmospheric WV during cold months of December through March in Iran over the period 2002–2020 and their relationships with the ENSO. Accordingly, we analyzed the atmospheric WV and cloud type data sets provided by the Atmospheric Infrared Sounder (AIRS) and the CloudSat, respectively, over different three atmospheric WV regions of Iran: Mountainous region (R1), the interior region as well as the Caspian Sea (R2), and southern seas (R3). Moreover, two of the strongest El Niño and La Nina events were selected for synoptic analysis and cloudiness monitoring over all three regions of R1, R2, and R3 in Iran. The results showed that atmospheric WV ranged from less than 8 kg/m2 over the R1 to higher than 14 kg/m2 over the R3. The atmospheric WV showed statistically insignificant (p > 0.05) decreasing trends across all three regions of R1, R2, and R3. The ENSO positively correlated with the atmospheric WV during both December in the R3 and March in the R2. The vertical atmospheric WV showed the highest anomalies at pressure levels of below 850 and above 500 hPa during the El Niño and La Nina events, respectively. The atmospheric WV over the mountainous regions in different longitudes of Iran was strongly affected by the La Nina events. However, across the southern seas, interior region, and mountains in eastern, central, and western Iran, respectively, the El Niño events influence the atmospheric WV. The Sudanese and the Eastern Mediterranean troughs (the Siberia and Arabia high-pressure systems) were highly contributed to atmospheric WV variability over Iran during the strong El Niño (La Nina) events in December 2015 (2010) and March 2016 (2011). The precipitable stratocumulus and nimbostratus clouds were mostly dominant over Iran (particularly across the R3) during the El Niño events in December. In conclusion, the warm (cold) phases of ENSO or the El Niño (La Nina) events effectively increase (decrease) the atmospheric WV over Iran during cold months, particularly both December and March.

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