Canopy interception

{{Short description|Rainfall intercepted by the canopy of a tree}}

File:Stormwater Management with trees.webm

Canopy interception is the rainfall that is intercepted by the canopy of a tree and successively evaporates from the leaves. Precipitation that is not intercepted will fall as throughfall or stemflow on the forest floor.

Many methods exist to measure canopy interception. The most often used method is by measuring rainfall above the canopy and subtract throughfall and stem flowHelvey, J. D., Patric, J. H., 1965. Canopy and litter interception of rainfall by hardwoods of Eastern United States. Water Resources Research 1 (2), 193–206.). However, the problem with this method is that the canopy is not homogeneous, which causes difficulty in obtaining representative throughfall data.

A method employed to avoid this problem is covering forest floor with plastic sheets and collecting the throughfall.Shuttleworth, W. J., Gash, J. H. C., Lloyd, C. R., Moore, C. J., Roberts, J. M., et.al, 1984. Eddy correlation measurements of energy partition for Amazonian forest. Quarterly Journal of the Royal Meteorological Society 110, 1143–1162.Calder, I. R., 1986. A stochastic model of rainfall interception. Journal of Hydrology 89, 65–71.Calder, I. R., 1990. Evaporation in the uplands. John Wiley & Sons. The disadvantage of this method is that it is not suitable for long periods, because in the end the trees will dry from water shortage, and the method is also not applicable for snow events.

The method by Hancock and CrowtherHancock, N. H., Crowther, J. M., 1979. A technique for the direct measurement of water storage on a forest canopy. Journal of Hydrology 41, 105–122. avoided these problems by making use of the cantilever effect of branches. If leaves on a branch hold water, it becomes more heavy and will bend. By measuring the displacement, it is possible to determine the amount of intercepted water. this method was refined in 2005 by making use of strain gauges.Huang, Y. S., Chen, S. S., Lin, T. P., 2005. Continuous monitoring of water loading of trees and canopy rainfall interception using the strain gauge method. Journal of Hydrology 311, 1–7. However, the disadvantages of these methods are that only information about one single branch is obtained and it would be quite laborious to measure an entire tree or forest.