The Plains states where the production of corn and soybeans is key are being hit harder by excessive drought conditions in the wake of the hottest month on record in the continental U.S., contributing to a surge in global food prices.

The weekly U.S. Drought Monitor map released Thursday showed that the amount of the contiguous U.S. mired in drought conditions dropped a little more than 1 percentage point, to 78.14 per cent as of Tuesday. But the expanse still gripped by extreme or exceptional drought — the two worst classifications — rose to 24.14 per cent, up nearly 2 percentage points from the previous week.

That's because key farm states didn't get as much benefit from rains as elsewhere on the heels of temperatures in July that federal scientists said were so high they broke a record set during the Dust Bowl of the 1930s.

Growers in Iowa — the nation's biggest corn and soybean producer — saw their conditions further deteriorate, with the amount of that state in extreme or exceptional drought more than doubling from 30.74 per cent last week to 69.14 per cent now. In neighboring Nebraska, the expanse of land considered in the two worst drought categories rose to 91.2 per cent, up 8 percentage points. The amount of Kansas in exceptional drought also more than doubled, up to 38.58 per cent from 17.45 per cent, while extreme or exceptional drought in Illinois spiked roughly 10 percentage points, to 81.18 per cent.

"Same song, tenth verse last week as much of the Plains saw the pattern of excessive heat and dryness persist, leading to more expansion across Nebraska, Kansas, Oklahoma and parts of Texas," Mark Svoboda, a climatologist with the National Drought Mitigation Center, wrote in Thursday's report.

Those dry conditions have factored into a sharp rise in global food prices after three months of decline, the U.N.'s Rome-based Food and Agriculture Organization said in its monthly price report Thursday.

Severe drought punishing the U.S.'s midsection has sent corn prices soaring by almost 23 per cent, and expectations of worsened crop prospects in Russia because of dry weather sent world wheat prices up 19 per cent, according to the FAO, which keeps close tabs on volatile global prices. Spikes in the prices of staple foods have led to riots in some countries in recent years.

The U.S. leads the world in exporting corn, soybeans and wheat, and the surging prices are expected to be felt across the international marketplace, hurting poor food-importing countries, said a study by British charity Oxfam issued on the eve of the U.N. report.

The FAO said its overall food price index climbed 6 percentage points in July, although it was well below the peak reached in February 2011. The FAO's index, considered a global benchmark used to track market volatility and price trends, measures the monthly price changes for a basket of food items including cereals, oils and fats, meat, dairy products and sugar.

Corn, wheat, soybean and sugar prices rose. But on a brighter note, the July report said the price of rice and dairy products remained constant and the agency's meat price index fell.

Nonetheless, Oxfam cautioned that "millions of the world's poorest will face devastation" because of the rising prices.

"This is not some gentle monthly wake-up call — it's the same global alarm that's been screaming at us since 2008," Oxfam spokesman Colin Roche said after the latest figures were released. "These new figures prove that the world's food system cannot cope on crumbling foundations. The combination of rising prices and expected low reserves means the world is facing a double danger."

The U.S. Agriculture Department reported this week that as of Sunday exactly half of the nation's corn crop was rated poor to very poor, up 2 percentage points from the previous week and creeping closer to the peak of 53 per cent of 24 years ago. Some 39 per cent of soybeans now fall under those two categories, rising 2 percentage points for the second straight week and eclipsing the 1988 benchmark of 37 per cent.

The nation's rangeland and pastures are faring even worse, with roughly three-fifths rated to be in poor to very poor shape -- the largest area thus affected in 18 years.

"Indeed, recovery from this summer's extraordinarily hot, dry weather will be a lengthy process, requiring the change of seasons and multiple soaking rainfall events — not just occasional showers," wrote Brad Rippey, a USDA meteorologist.

That's perhaps because July was so brutal for growers. The National Oceanic and Atmospheric Administration reported Wednesday that the average temperature last month was 77.6 degrees, eclipsing the old record from July 1936 by 0.2 degrees. Records go back to 1895.

"It's a pretty significant increase over the last record," said climate scientist Jake Crouch of NOAA's National Climatic Data Center in Asheville, N.C. In the past, skeptics of global warming have pointed to the Dust Bowl to argue that recent heat isn't unprecedented. But Crouch said this shows that the current year "is out and beyond those Dust Bowl years. We're rivaling and beating them consistently from month to month."

Thirty-two states had months that were among their 10 warmest Julys, which Crouch said shows the breadth of the heat and associated drought.

The first seven months of 2012 were the warmest on record for the nation. And August 2011 through July this year was the warmest 12-month period on record, just beating out the July 2011-June 2012 time period.