Drought Dynamics and Vegetation Productivity in Different Land Management Systems of Eastern Cape, South Africa—A Remote Sensing Perspective

Valerie Graw,Ayman Abdel-Hamid,Yvonne Walz,Gohar Ghazaryan,Andries Jordaan,Ruben Piroska,Joachim Post,Karen Dall,Jörg Szarzynski,Andoni Delgado Gómez,Olena Dubovyk

doi:10.3390/su9101728

Abstract

Eastern Cape Province in South Africa has experienced extreme drought events during the last decade. In South Africa, different land management systems exist belonging to two different land tenure classes: commercial large scale farming and communal small-scale subsistence farming. Communal lands are often reported to be affected by land degradation and drought events among others considered as trigger for this process. Against this background, we analyzed vegetation response to drought in different land management and land tenure systems through assessing vegetation productivity trends and monitoring the intensity, frequency and distribution of the drought hazard in grasslands and communal and commercial croplands during drought and non-drought conditions. For the observation period 2000–2016, we used time series of 250 m Vegetation Condition Index (VCI) based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) and Climate Hazard Group InfraRed Precipitation with Station data (CHIRPS) precipitation data with 5 km resolution. For the assessment of vegetation dynamics, we: (1) analyzed vegetation productivity in Eastern Cape over the last 16 years with EVI; (2) analyzed the impact of drought events on vegetation productivity in grasslands as well as commercial and communal croplands; and (3) compared precipitation-vegetation dynamics between the drought season 2015/2016 and the non-drought season 2011/2012. Change in total annual vegetation productivity could detect drought years while drought dynamics during the season could be rather monitored by the VCI. Correlation of vegetation condition and precipitation indicated areas experiencing significant vegetation productivity trends showing low and even negative correlation coefficients indicating other drivers for productivity change and drought impact besides rainfall.

Highlights

Drought is one of the biggest disasters of the 21st century; threatens global food security causing environmental, societal, and economic problems; and ranks first in degree of severity, length of event, total area extend and social effect compared to other hazards [1,2]
The objectives of this study were: (i) to monitor vegetation productivity trends; (ii) to characterize and classify drought hazard occurrence in Eastern Cape during the last 16 years based on time series analysis of vegetation condition information (vegetation condition index (VCI)) and precipitation; and (iii) to compare drought characteristics in Eastern Cape, in different land management systems and particular communal and commercial croplands
Total vegetation productivity based on annual ∑Enhanced Vegetation Index (EVI) detected drought events after analysis of the full season

Summary

Introduction

Drought is one of the biggest disasters of the 21st century; threatens global food security causing environmental, societal, and economic problems; and ranks first in degree of severity, length of event, total area extend and social effect compared to other hazards [1,2]. Droughts are not clearly defined and rely rather on a conceptual definition describing a deficit of precipitation that results in damage of crops and yield loss [7]. The two relevant droughts, influencing vegetation, are meteorological drought, which is a consequence of reduction of precipitation, and agricultural drought, which refers to shortage of available water for plant growth [1,8,9]

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