Analysis of Vegetation Behavior in a North African Semi-Arid Region, Using SPOT-VEGETATION NDVI Data

Rim Amri,Zohra Lili-Chabaane,Claire Gruhier,Mehrez Zribi,Benoit Duchemin,Abdelghani Chehbouni

doi:10.3390/rs3122568

Abstract

The analysis of vegetation dynamics is essential in semi-arid regions, in particular because of the frequent occurrence of long periods of drought. In this paper, multi-temporal series of the Normalized Difference of Vegetation Index (NDVI), derived from SPOT-VEGETATION satellite data between September 1998 and June 2010, were used to analyze the vegetation dynamics over the semi-arid central region of Tunisia. A study of the persistence of three types of vegetation (pastures, annual agriculture and olive trees) is proposed using fractal analysis, in order to gain insight into the stability/instability of vegetation dynamics. In order to estimate the state of vegetation cover stress, we propose evaluating the properties of an index referred to as the Vegetation Anomaly Index (VAI). A positive VAI indicates high vegetation dynamics, whereas a negative VAI indicates the presence of vegetation stress. The VAI is tested for the above three types of vegetation, during the study period from 1998 to 2010, and is compared with other drought indices. The VAI is found to be strongly correlated with precipitation.

Highlights

Vegetation cover, which affects different processes, in particular the water cycle, absorption and reemission of solar radiation, carbon cycling, and latent and sensible heat fluxes, plays a key role in land surface processes [1,2]
The power spectral density of each Normalized Difference of Vegetation Index (NDVI) series was computed in order to analyze the persistence behavior of the three corresponding types of vegetation cover
This paper proposes to analyze the behavior of vegetation as a consequence of drought, using

Summary

Introduction

Vegetation cover, which affects different processes, in particular the water cycle, absorption and reemission of solar radiation, carbon cycling, and latent and sensible heat fluxes, plays a key role in land surface processes [1,2]. Any change to the vegetation cover can have a strong influence on local, regional and even global scales. Large-scale intensive droughts, affecting large areas, have been observed on all continents, and the high associated economic and social costs have drawn increasing attention to the importance of droughts [3]. It is important to note that a drought corresponds to a period of temporary dryness, in contrast to the permanent dryness found in arid areas. Drought is associated with below-normal precipitation, which lasts for a period of months or even years

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Conclusion