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Re-evaluating the Role of Drylands in the Global Carbon Budget

Dr Alan Grainger (SoG), Dr Roel Brienen (SoG)

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In the conventional view of the role of drylands in the global carbon budget in the early 21st Century, drylands cover 45% of the Earth’s land surface but only contain 21% of terrestrial carbon stocks, of which 80% is in the soil (Watson et al., 2000). There has since been much progress in refining estimates of carbon stocks and fluxes for forests in humid areas (e.g. Pan et al., 2011; Baccini et al., 2017), but little progress in improving estimates for the drylands. This is due to lack of data on tree cover in dry areas, a gap filled only last year by the first global survey employing very high (≤ 1 m) resolution (VHR) satellite data. This found 1,327 million ha of drylands with at least 10% tree cover in 2015 (Bastin et al., 2017), increasing fivefold an earlier estimate of tropical dry forest area, based on lower resolution satellite data (Miles et al., 2006). This new survey offers a fantastic opportunity to re-evaluate the role of drylands in the global carbon budget.


This project aims to:

1. Produce a new global map of the distribution of carbon stocks and fluxes in vegetation and soil in the world's drylands.

2. Make a new estimate of the contribution of the degradation of dryland vegetation and soil (desertification) to global climate change.

3. Assess the implications of these new estimates for the overall global carbon budget.

Materials and Methods

A model will be devised, based on empirical data reported in the literature, that incorporates all combinations of grasses, shrubs and trees that constitute the full range of dryland ecosystems, from savanna grasslands to savanna woodlands and closed forests.

This model will then be combined with global empirical data on the distribution of dryland trees, shrubs and land use, collected in the First Global Drylands Assessment (GDA) of the UN Food and Agriculture Organization (FAO), based on VHR satellite data (Bastin et al., 2017), to predict the distribution of carbon in vegetation and soil in dryland ecosystems. These data, and FAO’s Collect Earth software that was used to analyse VHR satellite data, are openly accessible. Alan Grainger and other Leeds colleagues were trained to use Collect Earth.

Fieldwork for additional data collection and validation will be undertaken in sample sites across the drylands in cooperation with research institutes in China, Senegal, the USA and other countries with which Alan Grainger collaborates.

Potential for High Impact Outcomes

This project will advance previous research published in Science as its cover story (Bastin et al., 2017) and should lead to at least three papers in high-impact journals.


The student will be trained in global change monitoring and mapping by Dr Alan Grainger and Dr Roel Brienen, and benefit from the University of Leeds’ PGR skills training programme (, which takes advantage of the VITAE Research Development Framework ( The student’s specific training needs will be assessed at the start of the project and be carefully monitored as they meet regularly with their supervisors and every six months with their Research Support Group.

Student Profile

This project is ideal for a student who wishes to make a career in global change research, specializing in the neglected drylands component. A strong background in ecology, global biogeography and mathematical modelling is essential, and skills in remote sensing and geographical information systems are desirable.

Click here for a full project description.


Bastin J.-F. et al., 2017. The extent of forest in dryland biomes. Science 356: 635-638.

Baccini A et al., 2017. Tropical forests are a net carbon source based on aboveground measurements of gain and loss. Science 358: 230-234.

Miles L. et al., 2006. A global overview of the conservation status of tropical dry forests. Journal of Biogeography 33: 491–505.

Pan Y.D. et al., 2011. A large and persistent carbon sink in the world’s forests. Science 333: 988–993. 

Watson R. et al. (eds), 2000. Land Use, Land-Use Change and Forestry. Cambridge University Press, Cambridge.

Related undergraduate subjects:

  • Ecology
  • Environmental management
  • Geography
  • Physical geography
  • Plant science