Hydrology of natural and anthropogenically altered tropical montane rainforests with special reference to rainfall interception

Abstract

The water budget of tropical montane rainforests under near-natural conditions is characterized by high rainfall, the possibility of additional water input from cloud interception, low transpiration rates, high streamflow and high rainfall interception losses. A montane forest in the Ecuadorian Andes received 2504 mm yr-1 rainfall, from which 41% went into stream flow, 40% into rainfall interception and 19% into transpiration. Forest use or disturbance by logging leads to changes in forest structure, including decrease in tree height. In Sulawesi, Indonesia, rainfall interception diminished significantly along a gradient of forest use intensity (from 30% on average in natural forest to 18–20% in used forest stands) and was strongly correlated with tree height (r2 = 0.63). By means of satellite image analyses and modelling it was possible to predict rainfall interception from canopy reflectance characteristics of these forest stands. Application of the model at the landscape level (784 ha) provided realistic results with high interception values being rare and restricted to natural forest stands distant to villages, whereas low interception characterized the intensively used sites close to settlements. I conclude that 1) rainfall interception is a major component of the water budget in montane tropical rainforests, 2) forest use can significantly reduce rainfall interception, and 3) satellite image analysis can successfully be applied for predicting interception at the regional scale.