Rainfall derivatives: How Mumbai's monsoon actually got priced in

Six weeks into India's first rainfall derivative, the numbers have more to say than the launch-day press release did

Picture a Mumbai morning in June: The sky, the colour of wet concrete by 7 am, and every person who has a deadline actively checking the weather app instead of their inbox! 

Until this May, that morning had no price attached to it. On May 29, that changed. NCDEX, working with a team from IIT Bombay and drawing on the India Meteorological Department’s (IMD’s) own rain gauges, listed RAINMUMBAI — a futures contract whose value rises and falls with how much it actually rains in the city. 

The benchmark is 30 years of rainfall history from two stations most Mumbaikars may never have heard of, Colaba and Santacruz. The pitch was straightforward. Give the businesses that live and die by the monsoon — builders, insurers, hydropower operators and farmers’ lenders, a way to hedge that does not involve filing a claim and waiting. The contract settles in cash, off IMD data, with no adjuster ever visiting a flooded basement. 

Whether it rains 40 mm over the historical average or 40 mm under, the payout is automatic and arrives before the bills do! 

Six weeks in, that theory has been tested more thoroughly than anyone at the launch event probably expected. 

Look at where the July contract has actually traded and you can read Mumbai’s monsoon off the page without checking a weather bulletin. It opened at ₹2,120 on May 29 and drifted lower for three weeks, not dramatically, just a steady grind, bottoming at ₹1,921 on June 19. This is roughly 300 points shy of the 2,206.70 “long period average” (LPA), the whole contract is anchored to. That grind was the price mechanically tracking a monsoon that, according to the IMD’s own bulletins, had stalled well short of the city after reaching Kerala on June 4 and arriving only on June 23, a delay last seen in 2019 and 2023. 

Then it flipped … and how! From the June 22 close of ₹1,957, the contract rallied through almost every session for the rest of the month, and by early July it was in a different universe. Colaba logged 791 mm of rain in the first week of July alone, more than its entire monthly average, and Santacruz came within 40 mm of its full month’s average in the same seven days. 

The contract’s response fits in a single session. On July 7, it gapped open at ₹2,748, spiked to a series high of ₹2,765, then gave back nearly ₹180 intraday to close at ₹2,588. A blow-off top, in miniature, made entirely of rain. What’s genuinely interesting is what that price path did for three very different people who might have been watching it. 

A trader with no rainfall exposure at all, who had the discipline to wait for the June reversal before buying — entering on June 19 near the ₹1,921 low — was sitting on a roughly 33 per cent gain by the second week of July. 

Someone nimble enough to sell into the July 7 spike got closer to 44 per cent. Someone with no exit plan for that one violent session gave back the better part of ₹9,000 per lot in a few hours. The lesson isn’t “buy low, sell high,” everyone knows that already. Interestingly, this instrument moves fast enough to punish a trader without a plan for the top, not just the bottom. 

Let us look at a hedger in the same seat: A Mumbai construction firm that bought the contract on Day One because heavy rain means idle labour and blown deadlines. Their position sat modestly underwater through most of June, and that’s fine, because June was dry and there was nothing to hedge against yet. By the time the rain arrived and started causing the disruption they feared, their long position had swung to roughly ₹22,000 per lot in the black, cash landing in the same weeks their sites were plausibly losing money to weather. That is about as close to the product working exactly as designed as you will find. 

Flip the exposure entirely and the story gets more interesting. Picture a lender with an agricultural loan book across Maharashtra, worried about a weak monsoon due to El Niño triggering repayment defaults, who sold the contract on Day One for the opposite reason, betting on deficit rather than excess. For three weeks they were right, gaining value alongside the mounting drought fear. Then the monsoon reversed everything, and that same position is now down about ₹22,000 a lot, the exact mirror of the construction firm’s gain. 

Read as a standalone number, that looks like a bad trade. Read as insurance against a drought that does not appear to be materialising, it looks like a premium paid and, happily for everyone except the lender’s profit and loss (P&L) line, not needed. That distinction, between a hedge’s price and a hedge’s purpose, is the whole ballgame. Both hedges could have gone worse with a different hand on the tiller. A desk that kept adding to the drought short as the deficit “confirmed itself” through mid-June would be nursing a bigger loss today than the one that simply held its original position, an expensive lesson in not doubling down right before a trend breaks. A desk disciplined enough to exit once the price crossed back above the 2,206.7 anchor in late June would have capped its loss at a fraction of the cost. The contract hands you your own exit signal, if you’re willing to use it. 

Beyond these two, the more interesting question is who else this instrument fits. Tata Power’s hydro stations in the Western Ghats, feeding 450 Mw into Mumbai’s grid off nothing but monsoon inflow, are a near-perfect candidate for the short side. Airlines operating out of Santacruz, literally the same postcode as one of the contract’s two reference stations, may have the cleanest exposure-to-instrument match on the list. Insurers with concentrated Mumbai flood books could use it as a fast-settling complement to catastrophe reinsurance, cash first, claims paperwork later. And, Brihanmumbai Municipal Corporation’s (BMC’s) own water math this week, a supply cut still in place even as reservoirs climbed past a quarter of capacity, is a reminder that even a contract with “Mumbai” in its name has geography it doesn't quite reach. The catchments filling those reservoirs sit in Thane and Nashik, not under either gauge RAINMUMBAI watches. 

What is the most honest thing anyone can say about six weeks of trading a genuinely new asset class in India? The mechanism works. The price tells the truth faster than any weather bulletin does. What it can’t tell you is whether the person on the other side of your trade understood what they were buying. 

Mumbai has spent four centuries building folklore around its monsoon: The potholes, the delayed trains, the office debates about whether it will “break” this week or next. It turns out the rain was always a market. Nobody had built the exchange for it until now! 

 

The authors are Professors at IIT Bombay