ABSTRACT
A warmer world is likely to be one with more flooding than at present. There is general agreement among the various climate models that rainfall intensity will probably increase with increasing greenhouse gas concentrations (Watson et al., 1996:337). And intensity is the driving force behind floods regardless of changes in average annual rainfall (Fowler and Hennessy, 1995). Rainfall, and rainfall intensities, are expected to increase by between 10 and 20 per cent in mid-latitude areas during winter, to be greater throughout the year in high latitudes, and to increase in monsoonal regions (Weijers and Vellinga, 1995). In contrast, and probably of more significance, rainfall in arid and semi-arid areas is expected to decline or at best remain the same. Rivers depending on snowmelt are expected to experience a change in their seasonably high flow from spring/early summer to winter; warmer winters are likely to result in the snowpack melting periodically during winter rather than accumulating for a single spring thaw. A second reason for the change in seasonality is the increased likelihood of winter rain causing flooding. In addition, fewer snowmelt floods are expected in plain regions because of decreased snowfall-however, the predictions for alpine areas are considered to be highly uncertain (Watson et al., 1996:336-337).
