Did scientists miss the real reason behind Gujarat's record rain? Meet the Pacific Decadal Oscillation | WION Decodes

Gujarat's cloudburst has put El Niño back in the spotlight. But scientists are now looking at a far slower climate cycle that could have quietly amplified the monsoon. It is known as the Pacific Decadal Oscillation. What is it? WION Decodes.

Gujarat's most intense rain spell

The Western India state recently received more than 400 mm of rain in just a few hours. The immediate question everyone asked was: Is El Niño to blame?

However, as researchers piece together what fueled one of the state's most intense rainfall episodes, another climate phenomenon has entered the conversation. It is called the Pacific Decadal Oscillation (PDO), a long-term ocean cycle that can quietly shape weather patterns for decades.

Unlike El Niño or La Niña, which dominate headlines every few years, the PDO rarely makes the news. Yet scientists say its current negative phase may have created conditions that allowed the Indian monsoon to become unusually vigorous over western India. So what exactly is the PDO, and could it have played a role in Gujarat floods?

What is the Pacific Decadal Oscillation?

Think of the PDO as El Niño's slower, longer-lived version. It is a climate pattern driven by changes in sea surface temperatures and atmospheric circulation across the North Pacific Ocean. Instead of flipping every year or two, the PDO remains in one phase for 20 to 30 years, shaping the background climate over entire decades.

The PDO has two phases:

- Positive PDO: Warmer-than-normal waters develop along the eastern Pacific near North America, while the central North Pacific becomes cooler.
- Negative PDO: In this, the pattern reverses, with cooler eastern Pacific waters and warmer conditions farther west.

These shifts influence jet streams, storm tracks, wind circulation and moisture transport far beyond the Pacific.

Isn't this just El Niño by another name?

While it seems similar to El Niño, it's different. Both involve the Pacific Ocean, but they operate on different time scales and in different regions.

El Niño and La Niña are part of the El Niño-Southern Oscillation (ENSO) and develop in the equatorial Pacific, typically lasting 9 to 18 months.

The PDO, by contrast, occurs mainly in the North Pacific and can remain in one phase for two or even three decades. Rather than replacing El Niño or La Niña, the PDO can amplify or weaken their effects.

So how could the PDO have influenced Gujarat's rainfall?

Scientists caution that the PDO did not directly cause Gujarat's extreme rainfall. Instead, it may have acted like turning up the moisture supply before the storm began.

Research suggests that a negative PDO creates atmospheric conditions that can strengthen the Indian summer monsoon by influencing tropical wind circulation and the Walker circulation.

One consequence is stronger moisture transport from the Arabian Sea into western India. That means when active monsoon winds, low-pressure systems and favourable upper-level winds arrive, there is simply more moisture available to produce intense rainfall.

Studies have also linked negative PDO phases with above-normal monsoon rainfall across parts of west-central India, including Gujarat, although researchers stress this relationship emerges over long climate records rather than explaining individual storms.

If La Niña-like conditions are also present, the two can reinforce each other, making the monsoon even more active.

Why didn't forecasts focus on the PDO?

Because the PDO is not designed for short-term weather forecasting. Weather agencies such as the India Meteorological Department (IMD) and NOAA rely primarily on ENSO, the Indian Ocean Dipole (IOD), the Madden-Julian Oscillation (MJO), sea surface temperatures and evolving monsoon systems because these have a more immediate influence on seasonal rainfall.

The PDO behaves differently. Its influence is gradual, indirect and often intertwined with other climate drivers, making it difficult to isolate in operational forecasts.

That is why scientists often examine its role after an extreme weather event through attribution studies rather than using it as a primary forecasting tool.

Does Gujarat's flood mean forecasting models need to change?

Not necessarily; researchers have emphasised that no single climate pattern explains extreme rainfall. They say that Gujarat's heavy rains were likely produced by a combination of active southwest monsoon conditions, strong Arabian Sea moisture, low-pressure systems, local atmospheric instability, large-scale climate drivers such as ENSO, the IOD and the MJO, and a potentially favourable background created by the negative PDO.

Rather than replacing existing forecasting methods, many climate scientists argue that better ocean observations, higher-resolution models and improved representation of long-term oscillations such as the PDO, IOD and Atlantic Multidecadal Oscillation (AMO) could improve seasonal forecasting.