Model analysis of forest thinning impacts on the water resources during
hydrological drought periods
- Hiroki Momiyama,
- Tomo'omi Kumagai,
- Tomohiro Egusa
Abstract
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 generator output, 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 severer
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, resulting in well reproducing the observed
flow duration curves. On the basis of projected flow duration curves for
the 100-year, despite the large increase in an annual total runoff with
ordinary intensifying thinning, low flow rates, i.e., water resources
from the catchment in the drought period in the year, in both normal and
drought years were impacted by the forest thinning to a lesser extent.
Higher catchment water retention capacity appreciably enhanced the
forest thinning effect on increasing available water resources.