Comparison of conventionally observed interception evaporation in a 100-m2 subplot with that estimated in a 4-ha area of the same Bornean lowland tropical forest

With the intention of determining mean annual interception evaporation (IE) or rainfall interception loss from a 4-ha area of lowland tropical forest in the Lambir Hills National Park, Sarawak, Malaysian Borneo, throughfall (TF) and stemflow (SF) were measured for 3-years within this area with both static SF and TF gauges located inside a 10 × 10 m subplot, called a fixed subplot, and relocation TF-gauges, i.e., TF-gauges that were moved periodically among 23 subplots (10 × 10 m) and in a transect line within the 4-ha plot area. The derived data showed that mean annual IE was 210 mm/year or 8.5% of the mean annual rainfall in the study period (2466.3 mm/year) in the 4-ha plot, and 295 mm/year or 12% in the fixed subplot. Both the 4-ha plot and the fixed subplot IE values were concluded to be reliable estimates and the 3.5% higher IE value observed in the fixed subplot likely due to a greater water holding capacity of the vegetation in the fixed subplot, where a large infrequent tree with thick bark but not projecting crown exists, than the mean condition in the 4-ha plot. Considering the derived data in the scale of 22 individual subplots where TF was measured for short periods with the relocation TF-gauges and in the fixed subplot, IE values from 3% to 25% in these subplots within the 4-ha area were thought sensible. This range of IE values within the 4-ha plot encompass the IE values claimed in most, if not all, previous rainfall interception case studies in natural lowland tropical forests.