Visible, potential, and functional land degradation assessment in
southern Africa
Abstract
Land degradation in drylands threatens vulnerable ecosystems and
socioeconomic development. Currently, NDVI derived from remotely sensed
data is the main tool used for degradation detection. Three indicators
have usually been used to detect land degradation: (1) NDVI trends for
visible degradation, (2) residual for human-induced potential
degradation, and (3) sensitivity of vegetation to rainfall for
functional degradation. However, few studies have integrated and
compared these three indicators. In this study, we used Global Inventory
Monitoring and Modelling System Version (GIMMS 3.1) NDVI dataset and
Multiple Source Weighted-Ensemble Precipitation (MSWEP) rainfall dataset
(1982-2015) and applied linear regression, Time Series Segmented and
Residual Trend (TSS-RESTREND), and Sequential Regression (SeRGs) methods
to detect degradation in southern Africa. The results showed that
degradation was detected by these three respective indicators in 18.7%,
11.3%, and 7.1% of the study area. Degradation from any one type was
found to occupy 27.21% of the total area, whereas the co-occurrence of
two or more types only occupied 3.84%. These results indicate the
dominant discrepancies among these indicators and the independent
relationships among the degradation processes. Despite significantly
greening, potential degradation and functional degradation were still
observed. On the regional scale, spatial patterns of degradation were
affected by different levels of aridity. On the national scale, the
proportions of degradation were still influenced by increased
population, inadequate policies, and other factors. This study
highlights the need to detect degradation with multiple indicators and
improves our understanding of degradation types and intensity.