"During the first rainfalls in the fall there will be a huge quantity of soil which will be dragged as sediment into bodies of water," Francisco Ferreira, the vice president of Quercus, Portugal's largest green group, told private radio TSF.

The group estimates more than 12.5 million tonnes of nutrient-rich surface soil will be washed away over the next 12 months, hurting agriculture and putting water supplies at risk.

"If there are people who supply themselves with water from rivers and lakes, the quality of that water could be harmed if there is a strong rainfall which drags ash and sediment into it," Ferreira said.

Portugal's forest administration estimated on August 12 that some 215,000 hectares (531,000 acres) of woodland and bush -- an area almost as big as Luxembourg -- had been destroyed by fires across the country since the start of the year, most of it since the end of July.

If the estimate is confirmed, the area is well above the 182,486 hectares burned in 1991, the worst year for forest fire damage since 1980.

The estimate does not include damage done by three major fires which raged last week in the mountains of the southern Algarve tourist region, one of Europe's top holiday spots.

Local officials estimate those fires burned some 40,000 hectares of land before they were finally put out on Saturday.

Quercus predicts 50 tonnes of soil will erode for every hectare of burnt land. It estimates 250,000 hectares of woodland were destroyed since the wildfires began at the end of July.

The government declared the wildfires a national disaster and estimates they have caused caused nearly one billion euros (1.1 billion dollars) in damage.

TERRA.WIRE