Canopy interception by a spruce forest in the upper reach of Heihe River basin,Northwestern China

The aim of this study is to understand the canopy interception of Qinghai spruce forest under conditions of different precipitation characteristics and canopy structures in the upper reach of Heihe River basin, northwestern China. On the basis of a continuous record covering our investigating period by an automatic throughfall‐collecting system, we analysed the relationships between the canopy interception and the precipitation characteristics. Our results support the well‐established exponential decay relationship between the gross precipitation and the interception percentage after the canopy is saturated. But our results sufficiently illustrate a notable point that the variations in the interception percentage are almost independent from the variations in the gross precipitation before the canopy is saturated. Our examination into the relationship between the interception and the 10‐min average intensity of precipitation demonstrates a divergent relationship, and the divergent relationship is bracketed by an upper ‘dry line’ indicating that 100% of gross precipitation was intercepted before saturation and by a lower ‘wet line’ suggesting that the actual canopy storage capacity reached the maximum and evaporation was the only component of the interception. To search for the relationship between canopy structures and interception, we grouped the canopy covers over the 90 throughfall‐collecting tanks into ten categories ranging from 0 (no cover) to 0.9 (nearly completely covered), and the corresponding canopy interception was calculated by subtracting the averaged throughfall of each canopy‐cover category from the gross precipitation. The results show that the interception percentage increases faster with increasing canopy cover under intermediate rainfall conditions than that under heavy rainfall conditions. Unexpectedly, under light rainfall conditions the increasing rate of interception percentage with increasing canopy cover and also with increasing plant area index is not faster than that under the intermediate rainfall conditions simply because the tank‐measured percentage of interception was extremely high at near‐zero canopy cover conditions. Copyright © 2013 John Wiley & Sons, Ltd.