TEHRAN – Normal precipitations have been recorded in the current water year that started on September 23, 2023, reaching 232.5 millimeters so far, the Metrological Organization reported.

A significant amount of rainfall deficit was compensated through the precipitations in spring.

Despite the increase in rainfall, the accumulated deficit in precipitations still persists.

According to the report, the provinces of Semnan (33 percent), Qazvin (26.3 percent), and Tehran (24.9 percent) have received the lowest amount of precipitation.

Also, Bushehr, Chaharmahal-Bakhtiari, Fars, and Kohgiluyeh-Boyerahmad have experienced less-than-normal rainfall.

However, 27 provinces have received more rainfall compared to the previous water year which ended on September 22, 2023.

Low rainfall forecast for fall

According to numerical weather prediction modeling, the fall weather is forecast to be warmer than normal with low precipitation, Metrological Organization has reported.

“During the past 13 months, the average temperature in each month has been the highest on record which is caused by extreme temperature anomalies,” ISNA quoted Ahad Vazifeh, an official with Metrological Organization, as saying.

The warm and cold phases of the Pacific Ocean affect the weather, but this indicator cannot be relied on this year because the transition from El Niño (warm phase) to La Niña (cold phase) is going on slowly, he added.

Most models indicate weak La Niña conditions from November to February. In this condition, indicators that change in the short term such as the North Atlantic Oscillation (Nao), and Madden-Julian Oscillation (MJO) become more effective and impact, he further noted.

Transition into La Niña or neutral conditions?

According to recent forecasts, there is the possibility of either neutral conditions or a transition into La Niña.

Concerning the fact that the cycle is currently moving from El Niño to La Niña, Sadeq Ziaeian, an official with national center for forecasting  Iran metrological organization, said: “There is over 60 percent chance for neutral conditions and 38 percent chance for experiencing La Niña in the country by August 20,” ISNA reported.

El Niño Southern Oscillation (ENSO) is a climate phenomenon that has three parts  El Niño,  La Niña,  and neutral phases.

El Niño and La Niña are opposite extremes of the ENSO, which refers to cyclical environmental conditions that occur across the Equatorial Pacific Ocean.

La Niña is characterized by unusually cold ocean temperatures in the Equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific.

These changes are due to natural interactions between the ocean and the atmosphere. Sea surface temperature, rainfall, air pressure, and atmospheric and ocean circulation all influence each other.

Ziaeian pointed out that in addition to the ENSO, other cyclonic events such as Acetic Oscillation (AO), NAO, MJO, and the Indian Ocean bipolar affect Iran's atmospheric condition.

Under optimal conditions, when La Niña dominates, there is a 60 percent likelihood that the fall season in Iran begins later, and the probability of facing a dry year increases.

MT/MG