United Nations Environment Program: Global Desert Outlook

I have found a great website from the United Nations Environment Program that provides a great range of interesting information on desert environments. Many of the topics I have discussed are included such as climate, evolution and global tele-connective properties including dust and biogeochemical cycling. Furthermore, many more features of the drylands are introduced. Biological adaptation, sustainable development and desert research are all mentioned.

In particular, I would like to draw your attention to this section of the website which expands on what I have been discussing recently in terms of humans in deserts, their effects and future change. Chapter 6, 'Scenarios of Change', talks about driving forces or change and scenarios of change for water and land degradation.

Well worth a read!

What future for dryland populations?

I have introduced concepts and provided evidence for climate change in exacerbating desertification and that anthropogenic activities may further enhance the associated environmental changes. With all this in mind, what is the future for desert occupation? Overcultivation, overgrazing, land use changes, unsustainable practices all induce a host of feedbacks including nutrient depletion, reduction of moisture-holding capabilities of soil, mobilisation of sediments etc etc (Mouat, 2008). In turn cultural and societal routines may be impinged through, for example, the exhaustion of food and water resources leading to malnourishment, famine, disease and so on. The effects of environmental change are both varied and extremely serious and may develop on an exponential basis according to those such as Charney, and recovery policies may be difficult to implement.

Critical to the future of dryland populations is our openness to adaptation. Without adaptation humans must migrate or risk death. By adaptation I mean a willingness to develop and utilise coping mechanisms (new technologies, methods etc) and perhaps most importantly, a preparedness to adopt an alternative lifestyle that may not be complicit with previously apparent traditional heritage or cultures. Mouat and Lancaster (2008) highlight the inextricable linkages between environmental security and human security.

One of the main concerns, however, is that not everybody is able to adapt or migrate. Meze-Hausken (2000) provides a table that explains the factors that may influence migration during times of drought:

The tables give great insight in to strategies that may be employed to help societies out of trouble in drylands. Policies should focus on varied and appropriate crop planting, family size and planning issues, water availability, civil unrest and war, and the number of survival strategies they themselves are aware of. It is highly apparent that there is a distinct lack of focused and directed education in these areas. Is education the most appropriate and sustainable dryland population management solution? 

Desertification Risk

I came across two very interesting maps from the United States Department of Agriculture Natural Resources Conservation Service (USDA NRCS). The first map shows desertification vulnerability. The second shows the risk of human-induced desertification. I felt it was particularly striking, perhaps a little obvious, but still extremely important to recognise how many of the regions most under threat were those of the largest populations! Does this exacerbate perception that humans may be the largest threat to desertification phenomena? The social and cultural 'sub-cycle' to Charney's hypothesis perhaps becomes even more important!   

Connecting Humans, Vegetation and Desertification: Charney’s Hypothesis

 In 1975, Charney et al published an influential paper outlining a biogeophysical feedback mechanism that attempted to help explain the global advancement of deserts. This classic paper, not without its criticisms, speculated that an increase in albedo as a result of a decrease in plant cover (overgrazing, misuse of the environment etc) causes a decrease in rainfall because of the reduced temperature and hence convective potential in the atmosphere. Subsidence in the troposphere would initiate the feedback processes of reduced precipitaiton and reduced plant growth and hence develop a potenitaly devestating and never-ending cycle ending in continued desertification.

This cycle raises interesting questions. Yes, reduced vegetation can be a result of drought, but also as a direct consequence of human intervention and misuse of resources. The biogeophysical feedbacks (anthropogenically or naturally induced) leads to a host of other ‘societal’ feedbacks. Desertification leads to a decrease in the productivity of land, social marginalisation, population pressures, further overgrazing etc etc. So whatever your take on the causes of the biogeophysical cycle one thing is for sure, the consequences can be vast. The interaction of these processes is neatly depicted below. The next couple of posts will ask what can be done about the externalities associated with desertification as we move deeper into the anthropocene, and humans have an ever increasing power over the environment. 

Could the Desert Sun Power the World?!

I recently stumbled upon this article in the Guardian. In an environment of increasing resource stress and awareness of the various externalities associated with resource misuse, could the deserts of the world really be used generate mass 'clean' power.

"In just six hours, the world's deserts receive more energy from the sun than humans consume in a year. If even a tiny fraction of this energy could be harnessed – an area of Saharan desert the size of Wales could, in theory, power the whole of Europe".......

                                                   From Leverage Academy

So... What do you think? Can you identify any significant pitfalls in the argument?

The Normalised Difference Vegetation Index (NDVI) and the Microwave Polarisation Difference Index (MPDI) for vegetation

The effects of desertification on human societies, and also its potential to initiate a host of other environmental feedbacks, makes it an important process to monitor, learn about past episodes, and to predict the scale of spread or decline in the future under a number of inputs. A classic paper by Becker and Choudhury (1988) discusses how the Normalised Difference Vegetation Index (NDVI) and the Microwave Polarisation Difference Index (MPDI) for vegetation can help to analyse desertification processes.

As previously highlighted desertification is associated with the reduction of crop yields, reduction of biomass, river flow and groundwater depletion, encroachment of sand sheets over settlements or productive lands, and significant social disruption. Furthermore, existing species may be preferentially replaced by less desirable species leading to the depletion of livestock materials etc. Monitoring global vegetation can hence provide a sensitive indicator of environmental changes.

Becker and Choudhury state that ‘several research efforts have been undertaken in order to find relevant indices characterizing these processes and which are observable from satellites. Among them, albedo (a), surface temperature (T), and Normalized Difference Vegetation Index (NDVI) have received much attention’ and that more recently ‘another index could be of great value… namely the normalized difference of brightness temperatures in horizontal and vertical polarization measured at 37 GHz by SMMR on board Nimbus 7’ (MPDI).

So how do they work as a tool in monitoring desertification? NDVI is correlated to leaf area index (LAI), defined by The Global Climate Observing System as ‘one half the total green leaf area per unit ground surface area’, and the vegetation cover fraction. The key mechanism is the absorptivity and reflectivity of biomass due to chlorophyll absorption. Hence chlorophyll concentrations received from satellite technology plays an important part in the NDVI calculation and hence the quantity of biomass at a given location. The MPDI method incorporates brightness temperatures in horizontal and vertical polarisation and is sensitive to the water content of plants rather than chlorophyll absorption. NDVI is generally considered more appropriate for monitoring vegetation. 

                                                         Global NDVI

Further advancement of these techniques will equip us with the tools to build high resolution, high accuracy models that help us to predict regions most susceptible to the threat of desertification and hence implement policies and practices designed to mitigate the ill effects it can bring. Remote sensing will no doubt be a key feature of desertification management and monitoring. 

Desertification Success Stories

This link to the United Nations Environment Program  illustrates wide ranging success stories in the control of desertification and how humans are trying to overcome its effects. Very much worth a look!