Community elders showed the effects of forestry

Deforestation in Ethiopia is extensive. This is believed to affect the river flow regime, with more extreme floods and longer periods of low flow during the dry season. But whether there can be less water in the dry season with less forest cover remains a hotly debate topic.

A fifteen per cent forest cover loss
In the area studied by Solomon Gebreyohannis and Kevin Bishop, the forest cover has declined from sixteen to one per cent since the 1960´s. During this period, the Department of Hydrology in the Ministry of Water resources has been monitoring river levels twice a day. Using these data, together with aerial photos and satellite imagery, Solomon Gebreyohannis has been looking for relationship between deforestation and stream flow in this river and a dozen others like it.
”Despite the largest documented extent of deforestation in a major river catchment, we saw no changes in either the high or low flows of the Koga river. That was unexpected to say the least,” says Kevin Bishop.

Fortunately the researchers were also pursuing another type of investigation into the river’s regime using interviews of community elders to explore the past. One group of elders lived in the upstream area where the deforestation had been most extreme and the other group lived downstream at the river mouth where the water levels were recorded.
”The interviews showed that people living upstream experienced both decreased low flows and increased high flows after the deforestation. On the other hand, people living downstream hadn´t noticed any big differences in river flow during the same period,” says Solomon Gebreyohannis.

Wetland covers the difference
One possible explanation to the results is that there is a large wetland in the downstream region that might even out the differences in the flow regime caused by the deforestation.
”The interviews also gave us more knowledge about the timing of the deforestation. It wasn’t a matter of continuous cuttings, but rather a burst of harvest focused around 1974/1975 when there was a major land tenure reform,” says Solomon Gebreyohannis.