DATA ANALYSIS: DESERTS Republic’[5] to assertions by their Spanish


national action programme representative[6] that ‘35 per cent de la superfi cie española presenta riesgo signifi cativo de desertifi cación’. Nevertheless, the message from a wide range


of research is that aridity is going to increase in many areas. As one research team[7]


put it last


year, ‘there are some subtropical locations on every inhabited continent where dry seasons are expected to become drier in the decadal average, by up to 10 per cent per degree of warming. Some of these grid points occur in desert regions that are already very dry, but many occur in currently more temperate and semi-arid locations.’ The impact of moisture economy degradation on vegetation is not only a matter of density. Species that are already operating marginally at a given isoline may well, as desertifi cation progresses, fall off the edge of their environmental niche and be lost. A good example of this is the effect of increasing population in the south- western USA on two exemplar species in an ingenious in situ analysis-based study[8] published last year. Lost species in transition zones may well, in turn, be permanent biodiversity casualties with knock-on effects on future environmental resilience.


‘Species that are already operating marginally at a given isoline may well, as desertifi cation progresses, fall off the edge of their environmental niche and be lost’


A likely exception to the rule of increasing


aridity with climatic warming are the cold deserts. Since their lack of available water is down to most of it being permanently frozen solid, rather than lack of precipitation, rising temperatures will tend to make more moisture available rather than less. That doesn’t mean that they will escape biodiversity loss: there are species that have evolved to fi t the cold survival margins too, which will have nowhere to go as their environment heats up and melts. Study of these cold desert areas has recently led to greater understanding of both their present and historical biotic natures. In the McMurdo Dry Valleys of the Transantarctic Mountains, for instance,


www.scientifi c-computing.com


Arlequin analyses of microbial populations has revealed[9]


that ‘biodiversity near the


cold-arid limit for life is more complex than previously appreciated’. Modern transport into and through desert regions, even where it produces no static tenancy, brings its own changes. Roads are corridors of dispersal, but also change the land upon which they run in ways that traditional nomadic travel on foot or animal carriers did not produce. A Statistica- mediated study a decade ago, for example, demonstrated[10]


that the effects of a road are


immediate, dependent on means of building, and irreversible. Even when an unmetalled


Watering the future


road created simply by traffi c driving over the same route becomes disused, the land affected does not revert to its previous state. Since artifi cial soil enhancement is increasingly expensive and unsustainable, responding to degradation increasingly involve traditional botanical engineering measures. Vietnam, faced (thanks to remote sensing and analysis methods[11] 900km2


) with almost has instituted a 50,000km2


of mobile sand dunes on the march[12] reforestation


programme. At the other end of the scale, introduction of hardy, aridity adapted plants that concentrate essential nutrients (such as the Australian Ptilotus[13],


which accumulates ➤


Abu Dhabi water demand @RISK charts. Background: mean demand forecast curve with percentile bands, 2010 to 2030. Foreground: resultant demand probability distribution for 2010


‘In Abu Dhabi, potable water is a scarce resource and we depend on seawater desalination for producing it,’ explains Mohammad Al-Hajjiri, head of water forecasting. ‘So we need to plan its production carefully.’ Abu Dhabi is a rapidly developing economy


positioned between salt water and desert. The desalination plants to which Al-Hajjiri refers must meet current needs and a development plan for the next 20 years, not to mention exports to neighbouring emirates. Responsibility for balancing expensive overproduction against the catastrophic human and economic consequences of underprovision lies with a legal monopoly supplier, the Abu Dhabi Water and Electricity Company (ADWEC), whose Planning and Studies Directorate contains Al- Hajjiri’s section.


Desalination on this scale presents considerable operational, cost and


environmental challenges, requiring the most accurate forecasts possible if effi cient and effective water production is to be maintained. On the demand side are categories such as domestic, agricultural and industrial, each with its own set of data, assumptions and uncertainties. Inherently uncertain supply factors include seasonal variation, unplanned plant down time, water losses, population growth rates, and so on.


ADWEC used to prepare triple demand scenarios (high, medium, low). Since 2006, however, it has shifted to a probabilistic risk- based approach to analysis of demand and capacity assessment variables over different timescales using Palisade’s @RISK software. As a result of this change, ADWEC has been able to closely and consistently match production to demand, contributing to Abu Dhabi’s record as one of the few countries to experience no water shortages in recent years.


SCIENTIFIC COMPUTING WORLD OCTOBER/NOVEMBER 2010


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