THE dizzying midday heat of India’s northern plains cracks the earth. Farmers slump on the charpoys on which they sleep outdoors. It should be raining, yet the sky is clear. Prithi Singh, lean and wrinkled, says his entire rice crop has withered, along with fields sown for fodder.

After two summers of erratic and delayed monsoons, this year the rains simply failed. Mr Singh cannot afford to pay for a borehole, generator and diesel to reach ever-diminishing groundwater. Farmers always grumble. But Mr Singh has lost half of his annual income of 50,000 rupees ($890) and now depends upon his crop of winter wheat. Another farmer nearby fears he must sell his land to pay accumulated debts to moneylenders.

The monsoon months, June to September, bring three-quarters of India’s annual rainfall. Official studies show it to be erratic in four out of every ten years. Yet farmers rarely get any useful warning of shortfalls. As recently as late June, India’s meteorologists were predicting a normal monsoon. Punjab and Haryana, two north-western agricultural states, now say rains are about 70% below average. Six western states have issued drought warnings. The government in Delhi says it may soon offer emergency help.

The country remains predominantly rural: over 600m out of 1.24 billion Indians rely directly on farming. Nearly two-thirds of Indian fields are fed only by rain. A one-off drought is tolerable. Rural job-creation schemes have lifted incomes for the poorest. Food prices have only started to creep up. Granaries are overflowing, thanks to recent bumper crops.

What is disturbing, though, are tentative signs of long-term change to the summer rains. A less stable monsoon pattern would be harder to predict. It would arrive late more often, yield less water, become more sporadic, or dump rain in shorter, more destructive bursts (which happened two years ago in Pakistan, where the Indus basin disastrously flooded). The concerns of experts about the monsoon long predate today’s dry spell.

Too little is known about summer weather systems on the subcontinent. India is short of observation stations, weather planes, satellites, climate scientists and modellers. The government and foreign donors are scrambling to make amends. But even with better data, monsoons are ill-understood once they leave the sea or low-lying land. At altitude, notably, for instance, approaching the Himalayas, it is far trickier to grasp just how factors such as wind direction, air pressure, latent heating and moisture levels interact to deliver monsoon rains.

One trend looks clear: India has grown warmer over the past six decades. Glaciers are melting in the Himalayas, and orchards in the range’s valleys are being planted on ever-higher slopes in search of a temperate climate. Crops in the northern grain belt, notably wheat, are near their maximum tolerance to heat, and so are vulnerable to short-term blasts of higher temperatures. North India’s cities are also growing hotter.

How more warmth affects the monsoon is not straightforward. A land mass heating faster than the oceans will, in theory, draw in more moisture to produce heavier monsoons. Yet the reverse appears to be happening. Specialists who met in February in Pune, in Maharashtra state, reported a 4.5% decline in monsoon rain in the three decades to 2009.

India’s leading climate modeller, R. Krishnan, of the Indian Institute of Tropical Meteorology in Pune, points to a study showing a “steady decline” in rainfall on the Western Ghats, which run down the west coast. A Japanese model that he has applied to southern India predicts that a still more rapid decline in rainfall is likely.

Such a fall may matter little for states such as Kerala in the south, which gets a monthly drenching of 50 centimetres (20 inches) during the wet season. But Mr Krishnan notes other changes, notably evidence that far fewer depressions have formed in the Bay of Bengal, off India’s east coast, in recent summers. Since these help drive rain to India’s arid northern plains, he concludes that “there is every reason to be concerned about the monsoon.”

Explanations exist for some of this. One theory is that a growing mass of particulates, such as coal dust and biomass (from the widespread use of cow dung as fuel, for instance) in the air above India, now hinders rainfall. Timothy Lenton, a climate scientist at the University of Exeter, argues that such pollution could trigger wider instability in the monsoon.

Yet a decline in average rainfall may not be the main worry. Experts who met in Delhi in May to discuss climate-induced “extreme events” in India suggest that likelier threats include more short and devastating downpours and storms, more frequent floods and droughts, longer consecutive dry days within monsoons, more rapid drying of the soil as the land heats, and a greater likelihood that plant and animal diseases might spread.

It does not bode well for farmers, or for crammed cities with poor sewerage and other rotten infrastructure. Slums and coastal cities look especially vulnerable. Mumbai was overwhelmed in 2005 when nearly a metre of rain was dumped on the city in 24 hours.

Such events will happen more often, the highest official in the country’s environment ministry warns. He wants urgently to bring about a big increase in insurance schemes that spread weather-related risks. Rajendra Pachauri, who leads the United Nations’ Intergovernmental Panel on Climate Change, worries that India is not yet even seriously debating the new threats. He says it is ill-prepared for floods and droughts “that are now considered once-in-every-20-years events, but will be happening once in two years”.

The data harvest

The most pressing need is to gather and analyse data. This month Indian scientists and foreign partners launched a five-year “monsoon mission” to develop climate models for the region. India’s government is beginning to act, by setting up new Doppler radar stations to track weather systems over mountains. It is launching a new plane to fly into cyclones to study their behaviour. Better still, India and its neighbours could start sharing weather data, comparing ground and satellite observations, for example.

More can be done elsewhere, too. Most obviously, even the poorest farmers could work together better to store rainwater, for instance in ponds and tanks, rather than praying for the skies to open. The share of India’s farmland that is irrigated could roughly double, officials say. Huge scope exists to reduce losses through evaporation and leakage from shoddy irrigation systems.

More sophisticated farmers are getting better informed. One Indian firm, Weather Risk, sells forecasts to some 75,000 subscribers, mostly farmers across 15 states. Each pays just 30 rupees a month for the information the firm supplies. It looks worthwhile. Sonu Agrawal of Weather Risk notes growing demand for detail on highly localised conditions and short-term rain and hail forecasts. Demand for crop insurance is also rising.

Mr Agrawal and others remain sanguine about today’s dry patch, calling it typical of the sort of droughts that often show up in historic data stored by insurance firms. But given great gaps in knowledge about the monsoon, and uncertainties over climate change, the need for more accurate and complete data seems pressing. Studying the late rains this year will not help Prithi Singh and his parched plot today. But clarifying which, if any, trend poses the greatest threats to farmers like him could turn out to be one of India’s most important tasks.