Because of the positive net radiation received in the tropics, this energy is the driver of the hydrological cycle, as is reflected in the frequency of some of the highest rainfall intensities (by global standards) found across the duration spectrum. There remains, however, considerable spatial and temporal variability in rainfall across the humid tropics. Such variability is partly a consequence of the different synoptic-scale, rain-producing meteorological phenomena which occur in this climatic region. Moreover, the link between synoptic climatology/rainfall characteristics/storm runoff hydrology, for example, is insufficiently represented within the hydrological literature, especially that pertaining to tropical forest hydrology.
Consequently, it will be necessary to go into some detail both within this chapter as we introduce the main features of the tropical atmosphere circulation and also in the subsequent one, where the focus is on particular synoptic- and meso-scale rain-producing systems, in an attempt to highlight the important linkage between synoptic climatology and rainfall characteristics. Later, varying responses in the storm runoff hydrology of tropical forests will be cross-referenced with material presented here.
Within the meteorological and climatological literature, there is no consensus on the terminology used to describe the various meteorological systems affecting the tropics. Commonly, many such rain-producing systems are ‘lumped’ under the phenomenon, the intertropical convergence zone (ITCZ). As this chapter (and the one following) will outline, the term ITCZ incorporates several phenomena between the synoptic (say 10° latitude by 40° longitude, Davidson et al., 1983) and mesoscale (length scale, 2–2000 km; Orlanski, 1975).