DRIVING FORCES FOR FORESEEN CHANGES

SCENARIOS OF CHANGE FOR WATER AND LAND DEGRADATION

The record of unanticipated events in recent decades testifies to the difficulties in foreseeing the future. Political events, such as the collapse of central planning, economic changes (for example, the spread of market economies and the increasing globalization of economies), technological breakthroughs (for example, the coming of the information age and the emergence of the Internet), and unpredictable epidemiological challenges (as with HIV/AIDS) help to explain profound gaps between the predicted and the observed. Particularly for desert ecosystems, whose most predictable feature seems to be unpredictability, forecasts are both hard to make and fallible.

Despite their inherent imperfections, scenarios of alternative futures have become an important tool for defining the range of possible futures for society and the environment. These "lessons from the future" have proved to be indispensable for identifying the needs for action and the possible consequences of alternative actions, and may thus prompt changes in policy. A prominent example is the prediction, made in the 1980s, of forest dieback as a consequence of acid rain in Europe and North America. The projected cataclysm brought about large reductions in SO2 emissions. Partly as a result, the prediction of dramatic forest dieback never materialized (UN/EC 2001).

Like other models, scenarios are based on assumptions about cause-and-effect relationships among different elements of a system. The outcomes of scenarios depend on the identification of the major driving forces of change and specifications of how they, directly or indirectly, might affect the system of interest. Unlike some modelled ecosystems, desert ecosystems are notable for a high degree of variability, patchiness and unpredictability (see Chapter 1). These characteristics make scenario-building and analysis particularly challenging. Moreover, many deserts are not well studied, largely because they are usually marginal to national economies: neither environmental nor economic data are typically as available at the same resolution, quality, or length-ofrecord as they are in more humid and more densely populated areas.

While this chapter focuses on environmental changes in deserts, many of their driving forces operate at a global scale. Likewise, some desert processes have global implications. Thus, a change in the albedo of a desert surface and dust emissions from deserts may affect global atmospheric dynamics; or out-migration from deserts increases pressures in non-desert biomes (see Chapter 3).