A Multi-sensor Remote Sensing Study of the Dynamic of the Nile Basin Vegetation Cover

Abstract:

Sensitivity of the Nile’s basin vegetation cover to climate was assessed using a simple diagnostic and correlation analysis approach. Over the last 30 years the basin experienced extreme climate events, in particular droughts (80’ies) and a noticeable and sustained recovery starting in the 90ies. We looked at the associated changes in the vegetation index signal over the same period using the newly generated seamless multi-sensor long-term data record about vegetation and phenology. The V4 VIP (vip.arizona.edu) 30+year record of vegetation index and growing season compiled from AVHRR and MODIS sensors was used. Additionally climate data for the corresponding 30-year period was acquired from the Global Precipitation Climatology Centre (GPCC) and temperature from the Global Historical Climatology Network-Monthly (GHCN-M). A single year (2002) MODIS based Land Cover data was also used to cluster and assess change based on the vegetation type.

The overall response was complex owing to the complex climate regime (dry - wet, while increasingly hot), to topography, and the complex land cover of the region. Vegetation response was negative corresponding to the decrease in precipitation, until a strong and widespread recovery starting in the late 90’ies. The greening trend continued but started to break down with elevation as temperature started to play a more prominent role. The combined drier and hotter climate started to negatively impact high elevation vegetation. These changes were mostly driven by changes in the precipitation regimes with initially little impact of the temperature. However, the temperature sustained increase started to have the stronger impact when associated with the slightly drier conditions.

These diagnostic results coupled with climate models projection point to major negative impacts on the basin’s vegetation cover, productivity, and eventually their associated ecosystem services. These results suggest that the earlier and major changes will be experienced by the higher elevation areas.