Rainfall partitioning patterns by Pinus tabulaeformis forest in Taihang Mountains

The Taihang Mountain Region is the ecological barrier and water source of North China Plain. In recent decades, with the implementation of Taihang Mountains Greening Project and other projects, the vegetation coverage in Taihang Mountain Region is recovering continuously, but the runoff in the mountains is rapidly declining. The mechanism of how the vegetation restoration affects the water yield is not clear. The process of rainfall partitioning is an important part of hydrological cycle. It is of great significance for the formation process of regional water yield and water resources. Pinus tabulaeformis is the main afforestation tree species in Taihang Mountain Region, and it affects regional water resources. The rainfall partitioning of P. tabulaeformis forest in Taihang Mountain Region remains poorly understood. It is required to assess the applicability of the revised Gash model and revised Liu model. In this study, the rainfall partitioning in P. tabulaeformis forest is examined from July to November of 2022. The canopy interception was simulated by revised Gash model and revised Liu model. The results showed that 1) the rainfall amount was 450.8 mm during the study period, the average rainfall duration was 10.4 h, and the average rainfall intensity was 2.7 mm∙h⁻¹. Furthermore, we found that the rainfall during the study period was mainly light rain. The canopy interception, throughfall and stemflow of P. tabulaeformis forest were 105.5, 338.2 and 7.1 mm, respectively, accounting for 23.4%, 75.0% and 1.6% of the rainfall amount. 2) Throughfall and stemflow began to occur when the rainfall amount reached 1.7 and 5.5 mm, respectively. Significant linear relationships were found between the rainfall amount and throughfall amount. However, the relationship between rainfall amount and interception followed a power function. The throughfall percentage increased quickly with increasing rainfall amount, but when rainfall amount reached 11 mm, the throughfall percentage increased slowly. The interception percentage firstly decreased and then stabilized with increasing rainfall amount. 3) Based on the revised Gash model, the canopy interception, throughfall, and stemflow were calculated to be 105.3, 340.7, and 4.6 mm, respectively. The relative errors between the measured and simulated values were 0.2%, 0.8%, and 34.7%. According to the revised Gash model simulation results, we found that the interception amount was dominated by canopy evaporation during rainfall, accounting for 55.0% of the interception simulation, followed by evaporation after cessation of rainfall, accounting for 27.8% of the interception simulation. The revised Liu model calculated the interception as 96.0 mm, with a relative error of 9.0% between the measured and simulated values. The revised Gash model had lower relative errors in the simulation than the Liu model. 4) Sensitivity of the revised Gash model parameters were mean evapotranspiration rate > mean rainfall intensity > canopy storage capacity > canopy cover > trunk storage capacity > stemflow coefficient. These results indicate that typical P. tabulaeformis forests in the Taihang Mountains can intercept 23.4% of rainfall, with 75.0% throughfall and 1.6% stemflow. The revised Gash model can be used to predict canopy interception in P. tabulaeformis forests and provides a theoretical basis for water resource assessment and water conservation capacity improvement in mountainous areas.