Evapotranspiration and deep percolation of a small catchment with a mature Japanese cypress plantation

Quantification of hydrological components was conducted in order to clarify the water budget, especially deep percolation (D) into underlying rock, of a small headwater catchment covered by an old Japanese cypress plantation. Precipitation (P), canopy interception (E (i)), soil evaporation (E (s)) transpiration (E (t)), and runoff (R) were observed for 1 year in a 0.41-ha catchment in southern Kyushu, Japan. E (i) was calculated from P, throughfall and stemflow measurements, and E (s) and E (t) were measured using evaporimeters and heat pulse sensors, respectively. From these observations, deep percolation (D) under steady state condition into underlying sedimentary rock was estimated. As for the annual water budget, almost half of P was R and one-third was evapotranspiration (E), which was the sum of the E (i), E (s) and E (t). E (i) was almost the same magnitude as predicted for an old conifer plantation modeled by Komatsu et al. (J Hydrol 336:361-375, 2007b), but E (t) was lower compared to the model. E was not comparable to water loss in the catchment (P minus R). Therefore, D was estimated as a quarter of P and was slightly higher compared to previously reported values for sedimentary rock catchments.