Water balance of tropical rainforest canopies in north Queensland, Australia

Abstract

AbstractThe water balance of four different rainforest types in the Wet Tropics region of north Queensland is inferred from measurements of canopy hydrological components undertaken for periods between 391 to 657 days. These measurements of rainfall, cloud interception, stem‐flow, throughfall, canopy interception and transpiration have revealed considerable differences in the canopy water balance of different locations as a result of forest structural differences, altitude, exposure and climate. Cloud interception is a significant extra input of water to forests at high altitude sites (>1000 m) and varies between 7 and 29% of the total water input. At coastal and lower montane rainforests annual total evaporation is consistently around 50% of the total water input, but in upper montane cloud forest this drops dramatically to only 13% of the water input. At all sites actual evaporation is greater than potential evaporation for most of the year and on an annual basis exceeds potential by between 2 and 53%. The source of this additional energy is uncertain, but is likely to come from advection. Annual interception at all the rainforest sites was greater than annual transpiration, with transpiration dominating in the dry season and interception dominating in the wet season. All of the rainforests have a large annual net water balance to sustain runoff and recharge. Towards the end of the dry season runoff and recharge can cease in coastal lowland and lower mountain forests and they may have to draw on soil moisture and/or ground water at this time. In contrast, upper montane cloud forests have a positive net water balance throughout the year and are therefore an important source of dry season river flows. Furthermore, their exceptionally large annual runoff (∼6500 mm year−1) is a major source of downstream water. Copyright © 2007 John Wiley & Sons, Ltd.