Hiroki Momiyama*, Tomo’omi Kumagai, and Tomohiro Egusa


In Japan, there has recently been an increasing call for forest thinning to conserve water resources from forested mountain catchments in terms of runoff during prolonged drought periods of the year. How their water balance and the resultant runoff are altered by forest thinning is examined using a combination of 8-year hydrological observations, 100-year meteorological data output that is generated using a stochastic model, and a semi-process-based rainfall-runoff model. The rainfall-runoff model is developed based on TOPMODEL assuming that forest thinning has an impact on runoff primarily through an alteration in canopy interception. The main novelty in this analysis is that the availability of the generated 100-year meteorological data allows the investigations of the forest thinning impacts on mountain catchment water resources under the most severe drought conditions. The model is validated against runoff observations conducted at a forested mountain catchment in the Kanto region of Japan for the period 2010–2017. It is demonstrated that the model reproduces temporal variations in runoff and evapotranspiration at inter- and intra-annual time scales, and the flow duration curves were well reproduced. On the basis of projected flow duration curves for the 100-year, despite the increase in an annual total runoff with thinning, low flow rates (the flows within the range of >70% time exceedance) in both dry and normal years (the years in which low flow are the lowest and 50th the lowest) were impacted by the forest thinning to a lesser extent. Simulations also showed that low flows would increase more with higher catchment water retention capacity, and higher catchment water retention capacity would enhance the forest thinning effect on increasing available water resources. This study would be helpful in planning for better forest management considering runoff from forested catchments.

Paper Information

: Forest Ecology and Management
: 10.1016/j.foreco.2021.119593