Climate and Vegetation Trends

Anomalies in vegetation conditions (deviation from 1981-2010 average), derived from satellite series of fraction of Absorbed Photosynthetically Active Radiation (fAPAR), were correlated with drought intensity (negative deviations from the 1901-2010 average Standardised Precipitation and Evaporation Index, SPEI, version 2.3) within the vegetation growing season. The main map represents the linear trends in annual plant productivity in areas where the aforementioned correlations were significantly positive, i.e. where the vegetation showed below-average conditions due to deficits in precipitation. Map colours represent loss or increase in vegetation cover in areas vulnerable to drought. Red areas indicate vegetation loss, pointing to the places most vulnerable to drought. Green areas indicate increasing vegetation cover, which might suggest resilience to drought, naturally or through land management. Insets highlight conditions and responses in representative Ecosystem Response Types in selected areas between 1981 and 2010: Graphs show precipitation and temperature anomalies (red bars), their trends (dashed lines) and the response of vegetation anomalies (blue lines) in the selected areas. Small maps show the strength of the linear trend in drought intensities over the 1981-2010 period (ranging from dark blue: strong positive trend to red: strong negative trend).
Source: WAD3-JRC, 2018; from Ivits, E., Horion, S. and Fensholt, R.

Vegetation response to climatic variability

Changes in vegetation biomass are critical in assessing land degradation. Climate variations alone, or in combination with human-induced land use and land change, can affect biomass productivity and may trigger changes in vegetation type and structure. When perturbed through natural pressures (e.g. climate; fire), or through human land use, ecosystems can transition from an “original” equilibrium state to a new state, which may result in lower levels of productivity. Depending on severity and duration, precipitation anomalies can trigger or aggravate existing land pressures in managed and cultivated areas and accelerate ecosystem state changes, prompting long-term degradation. However, the response of plant productivity to climate fluctuations is highly variable5 and there are many uncertainties in predicting how ecosystem composition responds to drought. In part, the degree of impact depends on the resilience of the ecosystem and the level of other stresses that are at play. Identification of the factors influencing the vulnerability of an ecosystem and an understanding of the response of the ecosystem to climate and other perturbations complicate decision-making. However, predicted shifts towards increasing temperatures, modified distribution and increased variability of rainfall that lead to more frequent extreme climatic events will probably enhance the vulnerability of ecosystems to change. Providing an accurate assessment of the stability and sensitivity of ecosystems in response to disturbances at continental or global scale is thus pivotal to better understand how to mitigate the external forcing (climatic as well as anthropogenic) that might lead to land degradation