Abstract

Understanding the intensity and duration of tropical rain-events is critical to modelling the rate and timing of wet-canopy evaporation, the suppression of transpiration, the generation of infiltration-excess overland flow and hence to erosion, and to river responsiveness. Despite this central role, few studies have addressed the characteristics of equatorial rainstorms. This study analyses rainfall data for a 5 km² region largely comprising of the 4 km² Sapat Kalisun Experimental Catchment in the interior of Northeastern Borneo at sampling frequencies from one minute to one day.

The work clearly shows that most rainfall within this inland, forested area is received during regular short duration events (< 15 minutes) that have a relatively low intensity (i.e., less than two 0.2 mm raingauge tips in almost all 5 minute periods). The rainfall appears localised, with significant losses in inter-gauge correlations being observable in minutes in the case of the typical mid-afternoon, convective events. This suggests that a dense raingauge network, sampled at a high temporal frequency, is required for accurate distributed rainfall-runoff modelling of such small catchments. Observed rain-event intensity is much less than the measured infiltration capacities and thus supports the tenant of the dominance of quick subsurface responses in controlling river behaviour in this small equatorial catchment.