Just deserts

According to Richard Lederer’s unnamed student^[1], deserts are defined by a climate "such that the inhabitants have to live elsewhere" and have to be "cultivated by irritation". Say the word desert to most people in the industrialised west, and they will visualise somewhere hot, sandy, and utterly devoid of any life except, possibly, Peter O’Toole and Omar Sharif striding (with or without camels) across photogenic dunes.

In the days when I was trying the patience of successive O-level geography teachers, we were given a more seductively precise and objective definition: annual mean rainfall of 250mm or less. That figure is still around, although it has generally been supplanted by more sophisticated relative concepts like relative moisture economy deficit (more water lost through evaporation and transpiration than is received in precipitation).

Generally speaking, the most widely used climatological classification systems go by distribution of vegetation, which both serves as an indicator of available water and decides the viability of other life. This approach naturally appeals to statistical data analytic bean counters like myself, though they do complicate matters by including temperature considerations. A desert, for my purposes here, is a region whose available water economy provides marginal (or nonexistent) support for life. It will usually be arid, but we won’t be too picky about semiaridity distinctions as many of the problems to be studied involve transition. It will often be megathermal, but not necessarily so.

Oceans cover about two thirds of the earth’s surface. Deserts account for roughly two thirds of what is left (and current trends, despite significant efforts at reversal, are towards net increase) so they are no small matter – either in themselves or in the computational challenges which they can present. It is not much of an exaggeration to say that only since the explosion of generally accessible scientific computing resources can they be realistically confronted at all. [More]

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1. Lederer, R., Anguished English : an anthology of accidental assaults upon our language. 1987, Charleston: Wyrick. 0941711048 (pbk.).