Recent scientific achievements and advancements have indicated that at any given place on earth, complex human-environment interactions are at play, which include differing rates and magnitudes of drivers (e.g. overgrazing, climate change, agricultural practices) and consequences (e.g. soil erosion, changes in land productivity, loss of biodiversity). Hence, land degradation is not a phenomenon that can be modeled at global scale. The new World Atlas on Desertification (WAD) relies on a ‘converging of evidence’ in global datasets. In support of this, the WAD pragmatically illustrates the interacting components and their dynamics, such as soil, plant cover and how the land is used and managed. A number of combined processes at global scale that indicate potential pathways to land degradation are illustrated and explained with local examples.
Land productivity dynamics is an essential concept for monitoring land degradation. The dynamics of the earth’s covering biomass is a generally accepted reflection of land system productivity. Various approaches provide consistent and repeatable views regarding what areas of concern or improvement in productivity to highlight.
The map shown here, as processed at the JRC, is based on the global 1999-2013 1km resolution SPOT-VGT time series of remotely sensed vegetation index as provided through the Copernicus Global Land Component of the Land Service. This time series was decomposed into phenological and productivity related variables. The total seasonal biomass productivity is used to determine the long term, 15 years, dynamics. For each km2, or image pixel, this is then combined with the current (as per average of the last five years of the time series) level of performance of seasonal biomass production for that pixel as compared to its expected normal. The latter is derived using a stratification of ecosystem functional units obtained from an iterative clustering of a selection of phenological and productivity related variables. The combination of the long term dynamics and current performance provides classes of negative or positive change or stability of the land system productivity. This classification indicates a level of permanency of the land’s apparent capacity for sustaining a dynamic equilibrium of primary productivity for the given 15 years observation period. Whilst not an absolute measure of land productivity, this approach does provide a consistent, uniform and repeatable index with which to flag areas of concern, as well as identifying areas of improvement.
Such map alone cannot be a land degradation map and needs therefore to be integrated, together with maps on societal trends and other biophysical dynamics, in the ‘convergence of evidence’ scheme that the WAD promotes as approach to deal with land degradation mapping.