Remember the moment in those old British war movies as anxious troops await the enemy attack? “It’s the waiting I can’t stand,” someone invariably mutters. That’s how I feel about the dividends at embattled mining giants BHP Billiton (LSE: BLT) and Rio Tinto (LSE: RIO). Enemy forces are amassing, as China slows and commodity prices crash, and investors are just waiting, sweating, and trying to keep their nerve.

BHP Billiton

Surely management at BHP Billiton has to accept the inevitable sooner rather than later. For crying out loud, the stock is currently yielding 13.9% and the share price is down 53% in a year to hit a 10-year low. It trades at just over seven times earnings. Earnings per share are forecast to fall a whopping 60% in the year to June. Management expects to book a $7.2bn impairment charge on its US shale oil and gas assets, the second in six months. How long can the line hold?

BHP Billiton isn’t just exposed to metals misery, it’s a large player in the beleaguered oil market, where talk has turned crazy, with predictions of $10 barrels, and the IEA warning that the world could “drown in oversupply”. Yes, I know the writedowns are non-cash and shouldn’t directly hit the dividend payment, but that’s a detail. The yield is nearly 14% and when Anglo American recently hit that level, its defences were breached. 

BHP hasn’t cut its dividend since the merger with Billiton in 2001, so there’s pride at stake, as well as the credit rating. Management even held the line after profits mined 10-year lows in August. But now it has to face up to today’s painful reality, and retrench. We’ll know more next month.

Rio Tinto

The numbers aren’t quite so desperate at Rio, which offers a comparatively modest dividend yield of 9.2%. The stock is cheap as chips, trading at just 4.7 times earnings. Its share price is down 43% over one year and 63% over five, pointing to the long-term nature of the decline. The 51% decline in EPS last year, plus a forecast 15% drop in 2016, show that even the best-run company can’t escape the commodity rout. 

Both Rio and BHP enjoyed some relief on Tuesday after markets decided that 6.9% annual GDP growth in China was better than it could have been, but in today’s turbulent markets the next panic attack isn’t far away. China isn’t just slowing, it’s shifting its economy from infrastructure and exports, to consumption and services. That will inevitably reduce its thirst for raw materials even if it avoids the dreaded hard landing.

At least Rio is shielded from the oil price collapse (maybe diversification isn’t always so clever). Rio also boasts lower costs than BHP, and a stronger balance sheet. But with the price of iron ore (its main resource) expected to stay low for a couple of years, it has little hope of respite. Rio’s defences may last longer than BHP’s, but unless relief comes in the shape of a commodity price rebound, at some point they too will crack.

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Harvey Jones has no position in any shares mentioned. The Motley Fool UK has recommended Rio Tinto. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.