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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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While few studies have investigated the impacts of drought on vegetation, their findings are limited by the choice of vegetation proxy and model. Here, we used the LAI as proxy, and DGVMs to simulate drought impacts because the models use observationally-derived climate. We found that the semi-desert biome respond strongly to drought in the summer season, while the tropical forest biome shows weak response. This study could help target areas to improve drought monitoring and simulation.
Preprints
https://doi.org/10.5194/hess-2020-528
https://doi.org/10.5194/hess-2020-528

  27 Nov 2020

27 Nov 2020

Review status: this preprint is currently under review for the journal HESS.

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

Shakirudeen Lawal1, Stephen Sitch2, Danica Lombardozzi3, Julia E. M. S. Nabel4, Hao-Wei Wey4, Pierre Friedlingstein5, Hanqin Tian6, and Bruce Hewitson1 Shakirudeen Lawal et al.
  • 1Climate System Analysis Group, Department of Environmental and Geographical Science, University of Cape Town, Cape Town, 7700, South Africa
  • 2College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QE, UK
  • 3National Center for Atmospheric Research, Climate and Global Dynamics, Terrestrial Sciences Section, Boulder, CO 80305, USA
  • 4Max Planck Institute for Meteorology, Hamburg, Germany
  • 5College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK
  • 6School of Forestry and Wildlife Sciences, Auburn University, 602 Ducan Drive, Auburn, AL 36849, USA

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 < 0.4) over parts of Madagascar, Angola and western parts of South Africa. Furthermore, the latitudinal distribution of LAI responses to drought indicates a similar temporal pattern but different magnitudes across timescales. The results of the study also showed that the seasonal response across different southern African biomes varies in magnitude and occurs mostly at shorter to intermediate timescales. The semi-desert biome strongly correlates (r = 0.95) to drought at 6-month timescale in the MAM (summer) season, while the tropical forest biome shows the weakest response (r = 0.35) at 6-month timescale in the DJF (hot and rainy) season. In addition, we found a stronger response (in the year 1983, r = 0.84 over Namibia and eastern parts of South African) of the LAI to drought during dry years as compared to wet years; and we found different temporal variability in global and regional responses across different biomes.

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.

Shakirudeen Lawal et al.

 
Status: open (until 22 Jan 2021)
Status: open (until 22 Jan 2021)
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Shakirudeen Lawal et al.

Shakirudeen Lawal et al.

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Short summary
While few studies have investigated the impacts of drought on vegetation, their findings are limited by the choice of vegetation proxy and model. Here, we used the LAI as proxy, and DGVMs to simulate drought impacts because the models use observationally-derived climate. We found that the semi-desert biome respond strongly to drought in the summer season, while the tropical forest biome shows weak response. This study could help target areas to improve drought monitoring and simulation.
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