Modelling rainfall and canopy controls on net-precipitation beneath selectively-logged tropical forest

Understanding spatio-temporal patterns in rainfall received beneath tropical forest is required for eco- hydrological modelling of soil-water status, river behaviour, soil erosion, nutrient loss and wet-canopy evaporation. As selective-logging of tropical forest leaves a very complex mosaic of canopy types, it is likely to add to the spatio-temporal complexity of this sub-canopy or net precipitation. As a precursor to addressing this problem, the analysis presented here will examine the two dominant biophysical controls on sub-canopy precipitation. These controls are: (a) the spatial and temporal patterns in above-canopy or gross rainfall, and (b) the rate of wet-canopy evaporation associated with each type of canopy structure created by selective-forestry. For this study, over 400 raingauges were installed within a 10 km2 area of lowland dipterocarp forest affected by selective-forestry some 9-years prior to this work. Gauges were located beneath various canopy types and within large openings. The spatial distribution of gross rainfall (monitored within the openings) was modelled using variography, while the effects of different canopy types on sub-canopy preciptation was analysed by comparing 6-month totals. The temporal distribution of gross rainfall over an 11-year record collected at the same site (Danum Valley Field Centre) was modelled with Data-Based-Mechanistic (DBM) approaches. These DBM approaches were also applied to the rainfall time-series of the two adjacent meteorological stations; all three gauges being contained within a 5000 km2 region of Eastern Sabah in Malaysian Borneo.