We have an El Niño tracker in space but the rainfall reshapers we need to study most are closer home

India has satellite data to help track rainfall and inflation risks arising from global tilts in oceanic warmth. The country’s challenge is to study atmospheric aberrations closer home—such as the Indian Ocean dipole and winter rain distortions.

Ginger, garlic, onions and sugar had far higher prices in August than in the same month last year, going by inflation data released by India’s statistics ministry, while the usual suspects among kitchen staples like potatoes and tomatoes were cheaper. Given their varying crop cycles and rain-catchment zones, scarcities caused by patchy rainfall have played varied roles in these outcomes.

Broadly, however, food has gotten dearer, even as monsoon rains begin to peter out with the country staring at a rain deficit of about 15%. Oilseeds and edible oils have seen price uptrends, pulses look set for the same and rice may need buffer-stock releases to keep the market well supplied.

That a drier rainy season than usual would cause some crop shortfalls was foreseen as soon as ‘El Niño’ was forecast as a near certainty this year. The link is a gloomy one for a country that relies on rain for much of its farm output, but the gloom also has a silver lining: India has satellite data that lets us track El Niño ‘live’ as this oceanic seesaw develops.

On 10 September, Indian Space Research Organisation (Isro) flagged a sharp depletion of chlorophyll across the equatorial Pacific Ocean as a clear bio-indicator of El Niño. It was detected by an ocean-colour monitor aboard Oceansat-3, an orbiter launched by Isro in late 2022. America’s space agency Nasa has issued a similar alert.

El Niño is expected to get stronger, with surface-wind readings from Oceansat-3’s scatterometer offering corroborative evidence. As tropical trade winds that usually blow from east to west weaken (or reverse), warm surface water faces less resistance as it slops across from the Pacific’s Asian side to the American.

This is an El Niño tilt, part of a slow ‘oscillation’ that unsettles typical patterns of warmth and rain across much of the globe, and this year’s could turn out to be one of the strongest on record. But what does a pigment best known for its role in oxygen supply reveal?

In the neutral phase of the oceanic seesaw, an upwell of cold but nutrient-rich water emerges to keep surface phytoplankton well fed. Should warm water suppress that feed, vast patches of plankton lose their greenness—as visible from space. Cruel as it sounds, algae starvation helps estimate the angle of the Pacific’s thermal incline.

Isro data on marine chlorophyll could also help track a tilt in the Indian Ocean, the ‘dipole’ effect that might be able to counter an El Niño dry-out. While the latter tilts Pacific warmth away from Asia, thereby reducing cloud formation via air convection in our part of the world, a ‘positive dipole’ driven by strong tropical winds blowing Africa’s way could alter the Indian Ocean’s balance of warmth just enough to push the atmosphere above it back in favour of rainfall over the subcontinent.

Although this chain of cause-and-effect is even more chancy and complex, which makes its impact harder to gauge, a positive dipole was forecast this year and signs of it are under watch from 740km above the planet’s surface.

Our remote readings may be too sketchy at this stage, but what’s clear is this: India’s quest for space-age tools to study rainfall risk is all the more valuable in the face of climate change. Next, El Niño could distort the path of rain clouds that feed our winter crops, a risk compounded by frequent episodes of jet-stream chaos traceable to global warming.

As the risk historian and author Peter Bernstein noted, the modern economy owes much to the conquest of risk. We have made good progress, but a lot awaits deeper research.