Abstract
The factors controlling seasonal rainfall interception loss are investigated by using a double-mass curve analysis, based on direct measurements of high-temporal resolution gross rainfall, throughfall and stemflow from 43 rainfall events that occurred in central Taiwan from April 2008 to April 2009. The canopy water storage capacity for the wet season was estimated to be 1.86 mm, about twice that for the dry season (0.91 mm), likely due to the large reduction in the leaf area index (LAI) from 4.63 to 2.23 (m2·m−2). Changes in seasonal canopy structure and micro-meteorological conditions resulted in temporal variations in the amount of interception components, and rainfall partitioning into stemflow and throughfall. Wet canopy evaporation after rainfall contributed 41.8% of the wet season interception loss, but only 17.1% of the dry season interception loss. Wet canopy evaporation during rainfall accounted for 82.9% of the dry season interception loss, but only 58.2% of the wet season interception loss. Throughfall accounted for over 79.7% of the dry season precipitation and 76.1% of the wet season precipitation, possibly due to the change in gap fraction from 64.2% in the dry season to 50.0% in the wet season. The reduced canopy cover in the dry season also produced less stemflow than that of the wet season. The rainfall stemflow ratio ( P s f / P g ) was reduced from 12.6% to 8.9%. Despite relatively large changes in canopy structure, seasonal variation of the ratio of rainfall partitioned to interception was quite small. Rainfall interception loss accounted for nearly 12% of gross precipitation for both dry and wet seasons.
Highlights
Quantifying the partitioning of gross rainfall (Pg ) into interception loss (I) is very important for studying the water balance in surface hydrology, especially in forest hydrology
I = Pg + (1 − p − pt − ) Pg where Pg is the amount of gross rainfall; Pg is the amount of gross rainfall necessary to saturate the canopy, which can be determined by a double-mass curve (DMC) analysis [22]; p is the gap fraction or the fraction of direct throughfall; pt is the fraction of rainfall intercepted by the trunks; E is the wet canopy evaporation rate; R is the rainfall rate; and the bar denotes the average rate for a single event
Cumulative stemflow for the wet season was estimated to be 86.6 mm, representing 12.5% of the wet season rainfall, while the dry season estimate only accounted for 8.8% of the dry season rainfall (32.8 mm)
Summary
Quantifying the partitioning of gross rainfall (Pg ) into interception loss (I) is very important for studying the water balance in surface hydrology, especially in forest hydrology. The amount of interception loss changes the partitioning of Pg into throughtfall (Pt f ) and stemflow (Ps f ) but influences the nutrient flux dynamics in a forest ecosystem. The rainfall interception ratio (I/Pg ) can be formulated as an exponential decay function of rainfall intensity, temperature and wet canopy evaporation rate [4,5,6]. This type of approach often overlooks the effect of seasonal changes in the canopy structure on interception
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