Water storage and evaporation as constituents of rainfall interception

Abstract

Intercepted rainfall may be evaporated during or after the rain event. Intercepted rain is generally determined as the difference between rainfall measurements outside and inside the forest. Such measurements are often used to discriminate between water storage and evaporation during rain as well. Two well-accepted methods underestimate water storage by a factor two as compared to direct observations. The underestimation of storage is compensated by an overestimation of evaporation during rain by a factor of three. The direct observations of water storage and evaporation appear to agree with previous direct observations. Thus, it is concluded that these observations are representative. Also, our results based on methods using only rainfall measurements inside and outside the forest appear to agree with previous results. This would result in the conclusion that the common methods systematically underestimate water storage and overestimate evaporation during rain. Indeed, the systematic errors can be explained by the neglect of drainage before saturation. Water storage is better simulated assuming an exponential saturation of a larger storage capacity. A smaller evaporation can be simulated using an appropriate resistance to vapour transport. The observations in dense coniferous forest showed water storage to be the dominant process in rainfall interception, but this conclusion should not be generalized to other forests and climates. Direct observations of water storage and evaporation are recommended to build a realistic set of parameters for rainfall interception studies of the main vegetation types. ᭧

Modelling and measurement of two-layer-canopy interception losses in a subtropical evergreen forest of central-south China

“…The values fall within the typical range of 0.5 to 2.5 mm for deciduous canopies and 0.3 to 2.4 mm for coniferous canopies (Whitehead and Kelliher, 1991;Návar and Bryan, 1994;Klaassen et al, 1998;. The storage capacity is assumed to be constant during a single storm, but is probably variable between events (Robin, 2003;Keim, 2004).…”

Experimental analysis of drainage and water storage of litter layers

“…The parameters b 0 and b 1 results in estimates of the ratio of evaporation to rainfall and S, respectively (Klaassen et al, 1998). Drainage was predicted using the relation between D and C (Bussiere and Cellier, 1994): and because the experiment was conducted in a laboratory environment and wind speed was zero.…”

Evaporation From rain‐wetted forest in relation to canopy wetness, canopy cover, and net radiation

“…The present analysis still suggests to use the common correction (E/EpM ---C/S, equation (6)). A larger correction also results from a decrease in canopy wetness (C/S), which can result from a decrease in C or an increase in S. The maximum storage capacity S is commonly determined indirectly from throughfall measurement and results in an underestimation of S when drainage from the canopy occurs before the canopy is saturated [Klaassen et al, 1998]. Three processes cause drainage before saturation: raindrops splashing on wetted parts [Calder, 1986], slow saturation of barks and undersides of leaves [Herwitz, 1985], and upper leaves sheltering lower leaves.…”

“…For dense forest, maximum storage is larger and results in an increase of interception. The realistic simulation of interception of dense forest using the reference model is thus explained by compensation errors, resulting from an overestimation of the evaporation rate and an underestimation of storage [Klaassen et al, 1998]. …”