TEHRAN –During the first week of the current water year that started on September 22, rainfall indicates over 224 percent increase in comparison to the same period last year.

The total rainfall since the beginning of the current water year amounted to 1.1 millimeters, compared to 0.3 mm last year. It shows a 24-percent increase in comparison to 0.9 mm rain in the long-term period (55 years), IRNA reported.

The provinces of Gilan, Mazandaran, Golestan, Qom, Qazvin, Alborz, Tehran, Khorasan Razavi, South Khorasan, Isfahan, and Sistan-Baluchestan, as well as Kerman witnessed rainfall.

The precipitations are forecast to go on over the week in some other provinces.

However, the state of the largest dams in the country shows a 27 percent decline in their water input in the same period.

Moreover, no rain was reported in 28 provinces of the country.

Over 250mm rain in previous water year

The previous water year (September 22, 2023 – September 22, 2024) came to an end with receiving 252.7 mm of precipitation, showing a 19 percent increase compared to the year before.

The low precipitations at the beginning of the previous water year were worrisome, but the volume of precipitations improved with the passage of time.

Due to successive years of drought, the increase in rainfall amounts did not compensate water deficit in the country, some provinces are suffering from water shortage, IRNA reported.

A total of 10 provinces received less than normal rainfall.

According to the latest reports, the total amount of recorded rainfall in the previous water year (ended on September 23) amounted to 252.7 mm, which signifies a 19 percent increase compared to 212.9 mm rain received in the water year before (September 2022 –September 2023).

Compared to the long-term figure, 248.7, it shows a two percent increase.

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.

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