Spatial assessment of NDVI as an indicator of desertification in Ethiopia using remote sensing and GIS

Abstract: Desertification is a serious environmental and socio-economic problem occurring at global, regional and local scale. According to Article 1(a) of the United Nations Convention to Combat Desertification (UNCCD), define the term “desertification” means “land degradation in arid, semi-arid and dry sub-humid (dry lands) areas resulting from various factors, including climatic variations and human activities”. If a trend of vegetation cover is negative, then it can be a sign of ongoing desertification processes. The Normalize Differences in Vegetation Index (NDVI) derived from the long term (1982-2006) NOAA AVHRR satellite’s sensor and observed rainfall data at climate stations are used and analyzed to monitor desertification processes through NDVI and rainfall trends over time in Ethiopia. Vegetation cover naturally depends on precipitation. The suggested methodology called linear regression has been validated using vegetation trends as a proxy for degradation processes. Results show that at climate stations level, more than 80% of the stations have strong correlation(r) between NDVI and rainfall. A majority of the stations have no trend of NDVI and rainfall over time. Sixteen percent of the stations have experienced an increase and four percent of the stations a decrease both in NDVI and rainfall. The NDVI trend map, which is derived from 8_km AVHRR GIMMS satellite’s sensors, shows that a majority of the study area has no significant NDVI trend (p<0.05). More than 40% of the area has experienced a positive trend in vegetation cover (“greening”) and less than 6% of the area has experienced a decrease in vegetation. This over all positive trends is not in line with the previous study acclaiming widespread and irreversible degradation in Ethiopia.