Measurement and modeling of canopy interception losses by two differently aged apple orchards in a subhumid region of the Yellow River Basin

Canopy interception (Ic) of rainwater is an important component of hydrological cycles, and its measurement and modeling are essential for understanding water balances and formulating scientific strategies of management in different ecosystems. Large areas of traditional agricultural crops have been replaced with apple orchards in the Yellow River Basin, while few studies were conducted to quantify and model canopy interception for apple orchards with different ages. In this work, we measured rainfall, stemflow and throughfall and calculated Ic for young and mature apple orchards from May to September 2013-2016 in Changwu County on the Loess Plateau in the Yellow River Basin. The revised Gash model was applied to the two orchards. The results revealed that annual Ic for the young (range 22.2-29.2 mm) and mature (range 26.8-39.7 mm) orchards varied between years. During the past four years, cumulative modeled Ic was 7.6 +/- 1.0 and 10.5 +/- 0.9% higher than cumulative measured Ic for the young and mature orchards, respectively. Evaluation parameters the mean root mean square error and bias values (0.1719 mm and 0.0372 mm, respectively) between the measured and modeled Ic implied that the revised model performed better for the young orchard. For both orchards, the revised model was most sensitive to the ratio of mean evaporation rate to mean rainfall intensity and canopy storage capacity each year. The good agreement between the measured and modeled Ic indicated that the revised model was suitable for predicting Ic for apple orchards with different ages under our climatic conditions or similar conditions.