The ENSO cycle has three phases called the neutral phase, El Niño and La Niña. It is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific (approximately between the International Date Line and 120 degrees West).
In the neutral state (neither El Niño nor La Niña) trade winds blow east to west across the surface of the tropical Pacific Ocean, bringing warm moist air and warmer surface waters towards the western Pacific and keeping the central Pacific Ocean relatively cool. The thermocline is deeper in the west than the east.
According to the forecasts, El Nino–Southern Oscillation (ENSO) can lead to more rain in Iran in the second half of winter and early spring. The term El Niño refers to the large-scale ocean-atmosphere climate interaction linked to periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific.
La Niña is mainly referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO. These deviations from normal surface temperatures can have large-scale impacts not only on ocean processes but also on global weather and climate.
Sadeq Ziaeian, head of the national center for forecasting and crisis management of weather hazards told ISNA that this year is the third year that the country is in the La Nina phase and we have not had adequate rains yet, but according to the forecasts, ENSO will enter the neutral phase and we expect that the rainfall situation will be in a better condition.
Ahad Vazifeh, head of the national center for drought and crisis management also said that during La Nina, Iran's rainfall is lower than the average. It cannot be said that drought conditions always existed during La Nina, but in many years, the country’s average rainfall was lower compared to the long term.
The La Nina phase will gradually turn into neutral conditions from the middle of winter and then into El Nino, which is expected to increase precipitation in the country compared to the past two years, he stated.
Changes in airflow and temperature on the surface of the Pacific Ocean cause a change in the transfer of moisture from southern latitudes or tropical regions to subtropical regions - which Iran is also one of them - so it changes the amount of rainfall, he explained.
These predictions are somewhat optimistic. Perhaps, due to the lack of rainfall in the current autumn season, it is expected that the country’s average rainfall will be lower than normal by the end of the current water year (September 22, 2023), he also noted.
Low rainfall conditions continue in provinces such as Alborz, Tehran, and neighboring provinces, and we cannot be optimistic that water scarcity will be completely resolved with winter rains, he added.
We should still consider the pessimistic scenario for keeping water in dams unless the change process significantly changes the amount of rainfall and partially compensates for the existing low precipitation, Vazifeh suggested.
El Nino and La Nina episodes typically last nine to 12 months, but some prolonged events may last for years. While their frequency can be quite irregular, El Nino and La Nina events occur on average every two to seven years. Typically, El Nino occurs more frequently than La Nina.
By TEHRAN TIMES
# Tags
