Monday, April 27, 2009

A quarter of the world's land area is degrading, reveals study

The Times of India, 22 Mar 2009

A new study has determined that almost a quarter of the world's land area is degrading, often in very productive areas.

Land degradation, which is the decline in the quality of soil, water and vegetation, is of profound importance, but until now, there have been no consistent global data by which to assess its extent and severity.

Now, a new study published in the journal Soil Use and Management attempts for the first time to measure the extent and severity of land degradation across the globe and concludes that 24 percent of the land area is degrading - often in very productive areas.

It measures global land degradation based on a clearly defined and consistent method using remotely sensed imagery.

The results are startling.

The new assessment indicates that 24 per cent of the land has been degraded over the period 1981-2003, but there is hardly any overlap with the GLASOD area that recorded the cumulative effects of land degradation up to about 1990.

"Degradation is primarily driven by land management and catastrophic natural phenomena," said Dr David Dent of ISRIC - World Soil Information.

"Our study shows the extent and severity of land degradation measured in terms of loss of net primary productivity, making allowance for climatic variability," he added.

Overall, a quarter of the world's population depends directly on these degrading areas. The worst-hit areas are Africa south of the Equator, SE Asia and S China.

The worst-affected countries, with more than 50 per cent of territory degrading are, in Africa, the Congo, Zaire, Equatorial Guinea, Gabon, Sierra Leone, Zambia and the most affected (95 per cent degrading) Swaziland; in Asia, Myanmar, Malaysia, Thailand, Laos, Korea and Indonesia.

In terms of the rural population affected, the greatest numbers are in China, with nearly half a billion, India, Indonesia, Bangladesh and Brazil.

"The usual suspects, such as the African Sahel and around the Mediterranean are much less affected," said Dent.

Comparison with land use reveals that 19 percent of the degrading area is cropland and 43 percent forest.

Cropland occupies 12 percent of the land area and forest 28 percent, so both are affected disproportionately.

The study found only weak correlations between degrading land and rural population density and with biophysical factors such aridity.

The researchers conclude that more detailed analysis of land use history is needed to uncover the underlying social and economic drivers of land degradation.