Response of Vegetation to the 2003 European Drought Was Mitigated by Height. Bevan, S. L.; Los, S. O.; and North, P. R. J. 11(11):2897–2908.
Response of Vegetation to the 2003 European Drought Was Mitigated by Height [link]Paper  doi  abstract   bibtex   
The effects on climate of land-cover change, predominantly from the conversion of forests to crops or grassland, are reasonably well understood for low and high latitudes but are largely unknown for temperate latitudes. The main reason for this gap in our knowledge is that there are compensating effects on the energy and water balance that are related to changes in land-surface albedo, soil evaporation and plant transpiration. We analyse how vegetation height affected the response of vegetation during the 2003 European drought using precipitation data, temperature data, normalized difference vegetation index data and a new vegetation height data set obtained from the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat). At the height of the 2003 drought we find for tall vegetation a significantly smaller decrease in vegetation index and a smaller diurnal temperature (DTR) range, indicating less water stress and drought impacts on tall vegetation. Over Germany for example, 98\,% of significant correlations showed a smaller anomaly in vegetation index anomaly with greater height, and 95\,% of significant correlations showed a smaller DTR with greater vegetation height. Over France the equivalent percentages were 94 and 88\,%, respectively. Vegetation height is likely associated with greater rooting depth, canopy heat capacity or both. Our results suggest that land-surface models can be improved by better estimates of vegetation height and associated with this a more realistic response to drought. [Excerpt: Conclusions] The 2003 drought provides an opportunity to explore differences in the response of short and tall vegetation to an extended period of water stress. For tall vegetation we find less negative anomalies in NDVI and lower values for the DTR than for short vegetation. The associations shown here point towards the importance of soil water availability or a closed canopy. Both effects increase the availability of water vapour in the canopy air space and can explain the relatively modest reductions in NDVI and smaller DTR. [\n] Based on the results of our present analysis we would expect warmer conditions for the summer for a land-cover change simulation where tall vegetation is converted to short vegetation with an important caveat that the comparison of land-surface models by Pitman et al. (2009) did not pertain to a drought. A simulation of the 2003 drought with the investigated models would likely reveal whether the response of tall versus short vegetation is correctly represented within the models. It is also likely that for Europe, land-cover changes resulting in more short vegetation would amplify future summer heatwaves and droughts compared with increasing areas of tall vegetation. [\n] Our results suggest that land-surface models would benefit from the inclusion of maximum rooting depth as a parameter but that existing global data sets, which include root depths only down to 3 m, may be inadequate. We find that over Europe the geographic distribution of root depths within these global data sets does not accurately reflect the relationship between vegetation height and root depth.
@article{bevanResponseVegetation20032014,
  title = {Response of Vegetation to the 2003 {{European}} Drought Was Mitigated by Height},
  author = {Bevan, S. L. and Los, S. O. and North, P. R. J.},
  date = {2014-06},
  journaltitle = {Biogeosciences},
  volume = {11},
  pages = {2897--2908},
  issn = {1726-4189},
  doi = {10.5194/bg-11-2897-2014},
  url = {https://doi.org/10.5194/bg-11-2897-2014},
  abstract = {The effects on climate of land-cover change, predominantly from the conversion of forests to crops or grassland, are reasonably well understood for low and high latitudes but are largely unknown for temperate latitudes. The main reason for this gap in our knowledge is that there are compensating effects on the energy and water balance that are related to changes in land-surface albedo, soil evaporation and plant transpiration. We analyse how vegetation height affected the response of vegetation during the 2003 European drought using precipitation data, temperature data, normalized difference vegetation index data and a new vegetation height data set obtained from the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat). At the height of the 2003 drought we find for tall vegetation a significantly smaller decrease in vegetation index and a smaller diurnal temperature (DTR) range, indicating less water stress and drought impacts on tall vegetation. Over Germany for example, 98\,\% of significant correlations showed a smaller anomaly in vegetation index anomaly with greater height, and 95\,\% of significant correlations showed a smaller DTR with greater vegetation height. Over France the equivalent percentages were 94 and 88\,\%, respectively. Vegetation height is likely associated with greater rooting depth, canopy heat capacity or both. Our results suggest that land-surface models can be improved by better estimates of vegetation height and associated with this a more realistic response to drought.

[Excerpt: Conclusions] The 2003 drought provides an opportunity to explore differences in the response of short and tall vegetation to an extended period of water stress. For tall vegetation we find less negative anomalies in NDVI and lower values for the DTR than for short vegetation. The associations shown here point towards the importance of soil water availability or a closed canopy. Both effects increase the availability of water vapour in the canopy air space and can explain the relatively modest reductions in NDVI and smaller DTR.

[\textbackslash n] Based on the results of our present analysis we would expect warmer conditions for the summer for a land-cover change simulation where tall vegetation is converted to short vegetation with an important caveat that the comparison of land-surface models by Pitman et al. (2009) did not pertain to a drought. A simulation of the 2003 drought with the investigated models would likely reveal whether the response of tall versus short vegetation is correctly represented within the models. It is also likely that for Europe, land-cover changes resulting in more short vegetation would amplify future summer heatwaves and droughts compared with increasing areas of tall vegetation.

[\textbackslash n] Our results suggest that land-surface models would benefit from the inclusion of maximum rooting depth as a parameter but that existing global data sets, which include root depths only down to 3 m, may be inadequate. We find that over Europe the geographic distribution of root depths within these global data sets does not accurately reflect the relationship between vegetation height and root depth.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13209670,~to-add-doi-URL,drought-tolerance,droughts,ecosystem-resilience,europe,extreme-events,extreme-weather,forest-resources,mitigation,tree-height,vegetation},
  number = {11}
}
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