Estimation of canopy water storage capacity from sap flow measurements in a Bornean tropical rainforest

Canopy water storage capacity (Sc) is a key parameter for estimations of rainfall interception using a big-leaf model (BLM). This study proposes a simple method for estimating Sc. The crucial factor in this method is the canopy drying time (or wet canopy duration) after rainfall. The time can be estimated from sap flow measurements in accordance with an earlier study of ours in a Bornean tropical rainforest. By using the estimated canopy drying time to calibrate a BLM for rainfall interception, we derived Sc. This method could also provide aerodynamic resistance (Ra). To validate our estimations, the derived parameters Sc and Ra were compared to Sc and Ra determined independently by a method based on net rainfall measurements on an event basis and on wind profile measurements, respectively. The parameters in our method (Sc=0.7mm, Ra=14sm−1) were shown to correspond well to the values determined by independent methods. Furthermore, the method proposed in this study is applicable to tropical forests where short canopy drying times can be expected after rainfall; that is, if the cloudy weather after rainfall becomes sunny within 250min.