Assessment of Vegetation Dynamics and Ecosystem Resilience in the Context of Climate Change and Drought in the Horn of Africa

Huifang Zhang,Alphonse Kayiranga,Lifeng Guo,Diwen Cai,Baozhang Chen,Shaobo Sun,Mengyu Ge,Xiaohong Sun,Simon Measho,Petri Pellikka

doi:10.3390/rs13091668

Abstract

Understanding the response of vegetation and ecosystem resilience to climate variability and drought conditions is essential for ecosystem planning and management. In this study, we assessed the vegetation changes and ecosystem resilience in the Horn of Africa (HOA) since 2000 and detected their drivers based mainly on analysis of the Moderate Resolution Imaging Spectroradiometer (MODIS) products. We found that the annual and seasonal trends of NDVI (Normalized Difference Vegetation Index) generally increased during the last two decades over the Horn of Africa particularly in western parts of Ethiopia and Kenya. The weakest annual and seasonal NDVI trends were observed over the grassland cover and tropical arid agroecological zones. The NDVI variation negatively correlated with Land Surface Temperature (LST) and positively correlated with precipitation at a significant level (p < 0.05) account for 683,197 km2 and 533,385 km2 area, respectively. The ecosystem Water Use Efficiency (eWUE) showed overall increasing trends with larger values for the grassland biome. The precipitation had the most significant effect on eWUE variation compared to LST and annual SPEI (Standardized Evapotranspiration Index). There were about 54.9% of HOA resilient to drought disturbance, whereas 32.6% was completely not-resilient. The ecosystems in the humid agroecological zones, the cropland, and wetland were slightly not-resilient to severe drought conditions in the region. This study provides useful information for policy makers regarding ecosystem and dryland management in the context of climate change at both national and regional levels.

Highlights

The Horn of Africa has been affected by its location in the tropics under the influence of the Sahara and Arabian Desert, the Red Sea, and the Indian Ocean
The maximum positive normalized difference vegetation index (NDVI) trends were common in western parts of Ethiopia and Kenya, while negative NDVI trends were exhibited in large parts of Somalia, Djibouti, and Eritrea (Figure 3)
The forest and cropland land covers showed the largest increase in the annual mean NDVI trend (Figure 4a), while the smallest trend change was observed in grassland cover during the past two decades apart from the sparse vegetation and the barren land as most of the barren land covers are masked out in the analysis

Summary

Introduction

The Horn of Africa has been affected by its location in the tropics under the influence of the Sahara and Arabian Desert, the Red Sea, and the Indian Ocean. Climate variability in the region is certain [1], and there is a high rate of vulnerability to the impacts of climate change in the plant species and the people who depend on the rain-fed farming [2]. Climate variability across East Africa from historical records show that temperatures have increased by 1.5–2 ◦ C on average and there are large rainfall variations in the direction and magnitude of changes over the past 50 years [3]. The countries in the Horn of Africa have been exposed to series of drought, and the region at large is exposed to the effects of drought, and the causes are associated with climate change and climate variability [4]. The overall impact of climate variability and climate change on vegetation dynamics and pressure on ecosystem services has been immense especially during the last two decades

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