Background The redistribution of precipitation by forest has always been a hot spot and difficulty in hydrology research. Japanese cedar (Cryptomoria japonica) is the main afforestation tree species in Lushan Mountain, which plays an important role in ecological function such as soil and water conservation, atmospheric purification, and forest recreation. The purpose of this article is to explore the penetration rain process under different rainfall characteristics.

Methods We did a research on monitoring data of real-time rainfall process of C. japonica forest in Lushan Natural Protection Area from April 2017 to September 2017 based on Lushan Ecosystem Observation and Research Station. And then we selected part of typical rainfall events (three different rainfall levels), and analyzed time lag effects in different rainfall intensity. Through the 5-point method, the throughfall sample points were arranged on sample plot in forest, rainfall sample points were arranged on outside forest, and the data for both of them were collected through the auto rain gauge.

Results In the rainy season of 2017, the rainfall characteristics of the Lushan Mountain were low (≤5 mm), low rainfall intensity(≤2 mm/h) and short duration of rainfall(≤2 h). During initial lag time from the beginning of rainfall outside the forest to the beginning of rainfall inside the forest, the initial lag time y decreased rapidly with the increase of the rainfall intensity x outside the forest, showing a power function relationship (y=0.656x^-0.822, R²=0.823 4). The relationship between the initial lag time and the rainfall outside the forest was not obvious. The statistical results showed that the average rainfall intensity with positive canopy retention effect was smaller than that with the negative retention effect, and the most retention effect at ≤2 h and >8 h of rainfall duration was positive, and negative retention effect was evident at >4~8 h of rainfall reaching peak (mid rainfall duration).

Conclusions The characteristics of rainfall (rainfall intensity and duration) determine the process of throughfall, and then affect time lag effects of canopy. It can be found that in the process of rainfall, the effective time lag effects of canopy on rainfall mainly occur in the beginning and end of rainfall, while in the middle rainfall duration, the effect of canopy interception can almost be considered to be ignored, and the rainfall intensity inside the forest is greater than that outside the forest.