Modelling the impact of land-cover change on potential soil loss in the Taita Hills, Kenya, between 1987 and 2003 using remote-sensing and geospatial data

Abstract

In sub-Saharan Africa, natural vegetation is being transformed into agricultural lands at a fast rate, endangering ecosystem services and increasing soil-loss potential, which may trigger land degradation. For the Taita Hills study area in Kenya, multi-temporal land-cover models of 1987, 1999 and 2003, derived from Satellite Pour l'Observation de la Terre (SPOT) imagery using a multi-scale segmentation/object relationship modelling (MSS/ORM) methodology and a rainfall layer, a digital elevation model (DEM) and a digital soil map were applied to model potential soil loss. Population growth in the area has led to a shortage of agricultural land and movement of people to the lowlands, evidenced by a 39% (9.3 km²) increase in croplands from 30% to 41% of the study area during the research time frame. Expansion took place mostly in surrounding foothills and lowlands, at the expense of natural shrubland and grassland, but also occurred in the hills. Universal soil-loss equation (USLE) model results showed a 60% (4 km²) increase in the area of very high potential soil loss, from 7% of the study area in 1987 to 12% in 2003, due mainly to very high soil-loss potential in croplands. Whilst the area of croplands as a whole increased, the relative proportion of very high soil-loss potential in croplands remained 20%, both in 1987 and in 2003, indicating that newly cleared agricultural lands with vulnerable soils are the most at-risk areas.

Acknowledgements

This study was funded by the Academy of Finland, Council for Development Studies (TAITATOO project (http://www.helsinki.fi/science/taita)) and the University of Helsinki. The SPOT satellite image data were acquired through the ISIS (Incitation à l'utilisation Scientifique des Images Spot) programme of the French National Space Agency. The funders and data providers are greatly appreciated.

Notes

*This paper came from a workshop entitled ‘Potentialities and Limitations in the Use of Remote Sensing for Detecting and Monitoring Environmental Change in the Horn of Africa’. The workshop was organized by Somalia Water and Land Information Management (SWALIM) between 13 and 14 June 2007 at the Holiday Inn in Nairobi, Kenya. SWALIM is a project of the UN-FAO in Somalia (www.faoswalim.org).