Investigating the response of LAI to droughts in southern African vegetation using observations and model-simulations

Abstract. In many regions of the world, frequent and continual dry spells are exacerbating drought conditions, which have severe impacts on vegetation biomes. Vegetation in southern Africa is among the most affected by drought. Here, we assessed the spatiotemporal characteristics of meteorological drought in southern Africa using the Standardized Precipitation Evapotranspiration Index over a 30-year period (1982–2011). The severity and the effects of droughts on vegetation productiveness were examined at different drought time-scales (1- to 24-month time-scales). In this study, we characterized vegetation using the Leaf Area Index, after evaluating its relationship with the Normalized Difference Vegetation Index. We found that the LAI responds strongly (r = 0.6) to drought over the central and south eastern parts of the region, with weaker impacts (r  We also examined how well an ensemble of state of the art dynamic global vegetation models (DGVMs) simulate the LAI and its response to drought. The spatial and seasonal response of the LAI to drought is mostly overestimated in the DGVM multi-model ensemble compared to the observations. The correlation coefficient values for the multi-model ensemble are as high as 0.76 (annual) over South Africa, and 0.98 in MAM season over the temperate grassland biome. Furthermore, the DGVM model ensemble shows positive biases (3-month or longer) in the simulation of spatial distribution of drought timescales and overestimate the seasonal distribution timescales. The results of this study may highlight areas to target for further development of DGVMs in order to improve the models’ capability in simulating the drought–vegetation relationship.