Atsuhiro Takahashi

Balance And Behavior Of Carbon Dioxide At An Urban Forest Inferred From The Isotopic And Meteorological Approaches

Diurnal variations in δ 14 C, δ 13 C and the concentration of atmospheric carbon dioxide in an urban forest were measured on 9 February 1999 to discriminate and quantify contributions from different CO 2 sources. The biogenic CO 2 concentration remained relatively constant throughout the day. However, anthropogenic CO 2 concentration fluctuated with the atmospheric CO 2 concentration, and seemed to be controlled by wind velocity and the amount of exhaust gases from fossil fuel burning. The vertical profiles of anthropogenic, biogenic, and total CO 2 showed a constant concentration within forest during daytime because of the large vertical CO 2 influx, strong winds, and neutral atmospheric condition. The biogenic contribution at night decreased from the forest floor upwards with a smooth gradient, while the anthropogenic contribution showed a direct mirror because of the location of respective CO 2 sources-the vertical gradient of wind velocity and the horizontal CO 2 supply.

Effects of different representations of stomatal conductance response to humidity across the African continent under warmer CO2‐enriched climate conditions

General circulation models (GCMs) forecast higher global vapor pressure deficit (VPD) but unchanged global relative humidity (RH) in future climates. A literature survey revealed that 50% of Earth system models and land surface models embedded within GCMs employ RH as an atmospheric aridity index when describing stomatal conductance (gs), whereas the remaining 50% employ VPD. The consequences of using RH or VPD in gs models for water cycling and vegetation productivity in future climates on large spatial and temporal scales remain to be explored. Process-based global dynamic vegetation model runs, changes in the hydrological cycle, and concomitant vegetation productivity for the 21st century projected climate were conducted by altering only gs responses to VPD or RH and not changing any other formulations. In the simulations of the African continent under a 21st century warming trend, both stomatal functions of VPD and RH resulted in similar geographic patterns in gross primary production (GPP). However, continental total GPP was larger for the VPD response than that for the RH response. Transpiration rates were lower, resulting in a 13% increase in water-use efficiency for the VPD response compared with its RH counterpart.

Nonlinear advection‐aridity method for landscape evaporation and its application during the growing season in the southern Loess Plateau of the Yellow River basin

The advection-aridity approach to estimate actual evaporation from natural land surfaces is one of the better known implementations of Bouchets complementary principle. Detailed measurements at 2, 12, and 32 m above the ground surface during the growing seasons of 2004–2007 allowed validation of a generalized nonlinear form of this approach above the highly variable terrain in Changwu County in the southern Loess Plateau of the Yellow River basin in China. The obtained values of the parameters were found to lie well within the ranges to be expected on physical grounds or from previous measurements by different experimental means; calibration on the basis of any one year of data allowed predictions within roughly 5% on average. Relative to the corresponding observed turbulent vapor fluxes, the evaporation rates calculated with measurements at the highest level of 32 m displayed the least scatter but only slightly less than those calculated with measurements at the lower level of 12 m; however, those based on measurements at the lowest level of 2 m displayed considerably more scatter than those derived at the two higher levels. This is consistent with the existence of a blending height at higher elevations above the ground, where the effects of surface variability tend to fade away.

A Momentum Exchange Model for the Surface Layer over Bare-Soil and Canopy-Covered Surfaces

Abstract A multilayered turbulent transport model for the surface layer based on collisions between atmospheric layers is developed. The model can represent the average and perturbed components of turbulence relatively well, for both bare-soil and canopy-covered surfaces. The number of collisions increases linearly with height for a bare-soil surface, and decreases as the leaf-area density increases within the canopy layer. The intermittent nature of turbulent motion is reproduced in the model, even though the model is one-dimensional. The number of collisions increasing with height may cause the intermittent nature of the turbulence and may also relate to the gust motions for canopy flow; such gusts transfer large momentum downward intermittently and cause a secondary maximum in wind velocity in the lower layer within the canopy. In other words, the model can include the large-eddy effect by considering the different number of collisions among layers. Turbulence data measured with an ultrasonic anemomete...

Impact of Tropical Deforestation and Forest Degradation on Precipitation over Borneo Island

AbstractSoutheast Asian tropical rain forests in the Maritime Continent are among the most important biomes in terms of global and regional water cycling. How land use and land cover change (LULCC) relating to deforestation and forest degradation alter the local hydroclimate over the island of Borneo is examined using the Weather Research and Forecasting (WRF) Model with an appropriate land surface model for describing the influence of changes in the vegetation status on the atmosphere. The model was validated against precipitation data from Tropical Rainfall Measuring Mission (TRMM) satellite 3B42 measurements. A main novelty in this analysis is that the diurnal cycle of precipitation over the island, which is a dominant climatic characteristic of the Maritime Continent, was successfully reproduced. To clarify the impact of the LULCC on the precipitation regimes over the island, numerical experiments were performed with the model that demonstrated the following. Deforestation that generates high albedo a...