Challenges for remote sensing of the Sustainable Development Goal SDG 15.3.1 productivity indicator

Progress towards combatting land degradation as intended by Sustainable Development Goal 15.3.1 will be monitored using three sub-indicators, of which productivity of vegetation is one. This indicator is to be measured using trends in a remotely-sensed vegetation index. The use of vegetation indices is well-established and remotely-sensed data are readily available. However, their uses for monitoring production that is relevant to sustainable livelihoods have received little attention. This review identifies four areas in the currently-proposed monitoring methodology that are in need of further development. The first is the derivation of primary production from vegetation indices, which requires attention to physiological processes such as light-use efficiency and plant respiration. The second concerns the subsequent steps, in which ecological processes transform the net production into production of goods and services, such as crop products. The third is the need for explicit baselines or reference conditions that specify the productivity in the absence of anthropogenic degradation. The fourth, and most difficult, is to distinguish anthropogenic causes of degradation from potentially similar effects of natural environmental processes. Some of these issues are difficult to tackle with remote sensing alone, although several improvements are available, and others are in development. However, the current use of vegetation indices alone to remotely-sense degradation of ecosystem services does not provide an adequate SDG 15.3.1 productivity indicator.