## 4 Discussion
### Implications of Vegetation Dynamics and Ecosystem Resilience to Drought  
The results of the pixel-based annual and seasonal trends of vegetation dynamics in the Horn of Africa showed areas of increasing and decreasing vegetation change, while there were weak NDVI trends for the grassland cover specifically in the arid lands. Similarly, the eWUE analysis based on the GPP and ET measurements revealed that there was an overall increasing trend of annual eWUE with the trend increased most in the grassland cover showing higher efficiency under water stress and drought conditions. The implications of the results indicate the climate variability and climate change have affected the different biomes of the ecosystems; the grassland and shrublands were the most vulnerable in the Horn of Africa. [PERSON] et al. [1] confirmed in the IPCC 2014 report that the impacts of climate change are more visible with occurrences of drought, water scarcity, and increasing threats in human health and biodiversity problems upon which Africa is the most vulnerable continent of the world. The drivers behind the NDVI change and eWUE variations showed that the key controlling factor was the intensity and fluctuation of precipitation in the region (Figures 6 and 9), however, the effect and resilience of the whole ecosystem could be caused by multiple factors. The drought was a secondary factor which affected the ecosystem and the response of each biome differs from place to place.  
The Horn of Africa has been exposed to recurrent drought conditions. The final map of ecosystem resilience (Figure 10) showed that 54.9% was resilient to drought disturbance, while 32.6% was completely non-resilient. This is mostly in agreement with the recent study on ecohydrological resilience to ecosystem shifts over the African continent [21]. However, our result showed that cropland and wetland were slightly non-resilient ecosystems to drought condition rather than the savannahs and barren lands. The ecosystem resilience to drought reveals that the warm-humid and cool-humid agroecological zones were slightly non-resilient to the most severe drought conditions; this indicates the vulnerability of these ecosystems to the warming trends and impacts of climate change in the region. The delimitation of non-resilient areas could be helpful to target local regions, and enhance their resilience to drought and minimize the environmental impacts from climate change; thereby can contribute to the ecosystem-centered drought protection, adaptation, and alleviation measures at a regional level. This action would further strengthen the management of water resources and terrestrial ecosystems in the region as the response of eWUE to drought conditions and the changing climate in each biome differs from place to place. The overall implication of the vegetation dynamics and productivity with variations in eWUE provides useful spatial and temporal information for policy and decision-makers. This can play a vital role in rangeland management, rarching decisions and strategies, vegetation degradation protection and management, drought and climate change mitigation measures at national and regional levels.