Models to predict changes in annual runoff with thinning and clearcutting of Japanese cedar and cypress plantations in Japan

Forest management (thinning and clearcutting) can reduce evapotranspiration and increase catchment runoff. By summarizing data on the increase in annual runoff (Delta Q) due to forest management at various sites and analysing data using linear regression, traditional studies have reported large unexplained variability among data for different sites. To improve the predictability of Delta Q, it might be useful to model Delta Q for specific species and regions while considering underlying processes. This study performed such modelling for Japanese cedar and cypress plantations in Japan. Model 1 predicts Delta Q assuming that Delta Q equals the decrease in canopy interception loss (Delta E-i), which was further modelled by stem density using 46 data for interception loss. Model 2 predicts the potential maximum of Delta Q (Delta Q(max)) assuming that Delta Q(max) equals the sum of Delta E-i and the decrease in canopy transpiration (Delta E-t). Here, Delta E-t was calculated using a model developed in our previous study. Delta Q predicted using Model 1 approximated Delta Q observed for seven catchments, and the errors in prediction were less than those derived from traditional linear-regression analysis. Delta Q(max) predicted using Model 2 was greater than the observed Delta Q for all catchments. Thus, Models 1 and 2 would be respectively useful in assessing the effectiveness and limitations of managing Japanese cedar and cypress plantations to secure water resources, which have been controversial in Japan. Furthermore, the concept of the models gives implications for studies on other species and regions, because the models have demonstrated how to improve predictability of Delta Q considering underlying processes with the input of commonly available data. (C) 2015 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.