Rainfall redistribution in subtropical Chinese forests changes over 22 years

Abstract. Rainfall redistribution through the vegetation canopy plays a key role in the hydrological cycle. Although there have been studies on the heterogeneous patterns of rainfall redistribution in some ecosystems, the understanding of this process in different stages of forest succession remains insufficient. Therefore, this study investigated the change tendency of rainfall redistribution and rainwater chemistry in a subtropical succession forest area in South China, based on 22 years (2001–2022) of monitoring 740 valid rainfall events. Results showed that at the event scale throughfall ratio showed in order broadleaf forest (BF) < mixed forest (MF) < pine forest (PF), and stemflow ratio showed in order BF > MF > PF. At the interannual scale, annual gross rainfall considerably shifted over time, which directly induced the variable accumulation of annual throughfall and annual stemflow. In the last 22 years, annual variability of throughfall presented in order MF (CV, 9.7 %) < BF (15.6 %) < PF (16.1 %), and annual variability of stemflow presented in order MF (CV, 38.6 %) < PF (50.9) < BF (56.2 %). The spatial variability of stemflow was always greater than that of throughfall. Besides, the difference of rainwater chemistry fluxes (TN, TP and K+) among the three forest types were found and they changed over time. Throughfall was characterized with high chemistry fluxes compared to open rainfall followed by stemflow. On average, TN and TP fluxes of throughfall presented in order BF < MF < PF, while K+ flux of throughfall presented in order BF > MF > PF. The above results indicated that the patterns of rainfall redistribution often changed over time. The event-scale accumulation of throughfall and stemflow potentially induced the interannual-scale variability. Both water volume and chemistry of throughfall and stemflow depended on the effect of rainfall and forest factors. This study provided insight into the rainfall redistribution process by linking the long-term changing of rainfall pattern and subtropical forest succession sequence.