Southeast 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 areas, such as bare lands, would induce a reduction in precipitation because of reductions in evapotranspiration, convection, and horizontal atmospheric moisture inflow. On the other hand, a decrease in evapotranspiration efficiency without changing the surface albedo could increase precipitation due to an increase in convection and horizontal atmospheric moisture inflow in compensation for the decrease in evapotranspiration. In detail, on the Maritime Continent, through changes in the land surface heating process and land-sea breeze circulation, the LULCC would impact the amplitude of the diurnal precipitation cycle in each region as defined according to the distance from the coast, resulting in changes in the precipitation regimes over the island.

The advection-aridity approach to estimate actual evaporation from natural land surfaces is one of the better known implementations of Bouchet's 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.

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.

The aim of this study is to evaluate rainfall partitioning at the forest canopy and reveal the physical process of canopy interception loss. Observations were conducted for 19 months in neighboring stands of Chamaecyparis obtusa Sieb. et Zucc. (Hinoki) and Cryptomeria japonica D. Don (Sugi). Cumulative amounts for the period showed that portions of throughfall (TF), stemflow (SF) and interception (IC) to rainfall (RF) for Hinoki were 65.3%, 9.1%, and 25.5%, respectively. Corresponding values for Sugi were 67.9%, 6.6%, and 25.5%. The smaller TF and larger SF in Hinoki than those in Sugi were induced by greater mean funneling ratio of a tree and greater tree density in Hinoki. Similar IC/RF would result from similar leaf area index. In analyses for rainfall events, rainfall period (RP) was defined as the period excluding short no-rainfall periods within an event, and rainfall intensity (RFI) was as RF/RP. In events with canopy saturation (RF >= 10 mm), IC/RF was insensitive to RP and RFI. This was related to an increasing rate of IC with RFI Evaporation for IC estimated by the model, based on the Penman-Monteith equation, was approximately 40% of cumulative IC observed. Underestimation was great in events with long RP, but not with large RFI. We suggest that large amount of IC occurred during rainfall, which is induced by splash droplets transport (SDT) by canopy ventilation. (C) 2013 Elsevier B.V. All rights reserved.

This paper reviews recent research topics and methodologies on terrestrial evapotranspiration and atmospheric boundary layer (ABL) over land surfaces. The methodologies referred in this paper includes eddy correlation method, use of satellite remote sensing data, cloud resolving model, and atmospheric water budget using re-analysis data. Careful applications would be recommended for estimating terrestrial evapotranspiration in different spatial scales.

This paper reviews recent research topics and methodologies on terrestrial evapotranspiration and atmospheric boundary layer (ABL) over land surfaces. The methodologies referred in this paper includes eddy correlation method, use of satellite remote sensing data, cloud resolving model, and atmospheric water budget using re-analysis data. Careful applications would be recommended for estimating terrestrial evapotranspiration in different spatial scales.

We investigated the diurnal variation of water vapor mixing between the atmospheric boundary layer (ABL) and the free atmosphere over the Loess Plateau in China. Water vapor and wind velocity in the troposphere were observed using a ground-based microwave radiometer and a wind profiler radar in 2005 and 2006. On sunny days in early summer, a strong vertical wind was generated in the afternoon followed by ABL development. Strong convection was enhanced when active cumulus convection developed in the afternoon. In such cases, water vapor decreased in the lower atmosphere from the early morning until late afternoon, while water vapor increased in the upper atmosphere. This finding suggests that water vapor was exchanged diurnally between the ABL and the free atmosphere. The strong convection in the ABL, which was developed by sensible heat from the land surface, played critical roles with link to cumulus convection in such vertical mixing of water vapor. Influences of other processes such as a local circulation and advection of cloud systems were also discussed.

The most severe dry-up has occurred in the downstream of the Yellow River in 1997. After that, it was legislated for the conservation of water, and was improved on the order of water use in each irrigation area. Since 2000, incidents relevant to dry-up seem to have not happened. The river water of the Yellow River at the mouth, however, continues to let low volume flow as the same as 1997. Its reasons and effect were/are studied as follows. The Yellow River project in RIHN was started to clarifying why the dry-up has occurred and what kinds of effects are to be occurred in surrounding circumstances. Now, the reason of the dry-up are considered due to the complicated factors, these are the decrease of precipitation, over-use of river water in large irrigation districts and recovery of vegetation on Loess Plateau. Though sediment production on Loess Plateau seems to decrease, the river bed in downstream of the Yellow River continues to rise up. It will enhance the danger of flood disaster in the North China Plain. On the other-hand, the environment of Bo-Hai Sea has changed in both water and material inputs from the Yellow River. Its effects are now investigated.

Seasonal changes in the water and energy exchanges over a pine forest in eastern Siberia were investigated and compared with published data from a nearby larch forest. Continuous observations (April to August 2000) were made of the eddy‐correlation sensible heat flux and latent heat flux above the canopy. The energy balance was almost closed, although the sum of the turbulent fluxes sometimes exceeded the available energy flux (Rn − G) when the latent heat flux was large; this was related to the wind direction. We examined the seasonal variation in energy balance components at this site. The seasonal variation and magnitude of the sensible heat flux (H) was similar to that of the latent heat flux (λE), with maximum values occurring in mid‐June. Consequently, the Bowen ratio was around 1·0 on many days during the study period. On some clear days just after rainfall, λE was very large and the sum of H and λE exceeded Rn − G. The evapotranspiration rate above the dry canopy from May to August was 2·2 mm day−1. The contributions of understory evapotranspiration (Eu) and overstory transpiration (Eo) to the evapotranspiration of the entire ecosystem (Et) were both from 25 to 50% throughout the period analysed. These results suggest that Eu plays a very important role in the water cycle at this site. From snowmelt through the tree growth season (23 April to 19 August 2000), the total incoming water, comprised of the sum of precipitation and the water equivalent of the snow at the beginning of the melt season, was 228 mm. Total evapotranspiration from the forest, including interception loss and evaporation from the soil when the canopy was wet, was 208–254 mm. The difference between the incoming and outgoing amounts in the water balance was from +20 to −26 mm. The water and energy exchanges of the pine and larch forest differed in that λE and H increased slowly in the pine forest, whereas λE increased rapidly in the larch forest and H decreased sharply after the melting season. Consequently, the shape of the Bowen ratio curves at the two sites differed over the period analysed, as a result of the differences in the species in each forest and in soil thawing. Copyright © 2003 John Wiley & Sons, Ltd.

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 anemometer at 10 Hz in the field were used as model input; plausible results were obtained. The model can represent the overall characteristics of turbulence in the surface layer.

上層に落葉広葉樹, 中·下層に常緑広葉樹から構成される二次林の6樹種について, 気孔コンダクタンスの日変化と季節変化を観測した. 観測された気孔コンダクタンスは, Jarvis型の気孔コンダクタンスモデルで表現し, どの環境因子が気孔コンダクタンスに影響を及ぼしているのかについて調べた. 上層木のコナラに関しては, 直達光にさらされる葉 (陽葉) とさらされない葉 (陰葉) とに分けて計測した. 陽樹であるコナラは, 日変化·季節変化を通して, 気孔コンダクタンスの変動量が大きかった一方, 中·下層の常緑広葉樹 (陰樹) は微少な変動に止まった. 気孔コンダクタンスと光合成光量子束密度との関係を光飽和曲線 (light response curve) と定義した場合, 陽樹はその光飽和点 (light saturation point) が高かったのに対して, 陰樹は光合成光量子束密度が小さい領域において, 光飽和曲線の初期勾配 (quantum yield) が大きかった. Jarvis型の気孔コンダクタンスモデルにおいて, 影響度の低い環境因子をＦ検定により抽出した結果, この二次林では土壌水分ポテンシャルが当てはまった. 一方, 光合成光量子束密度, 気温, 飽差は気孔コンダクタンスに与える影響が大きい環境因子として重要であった. 落葉広葉樹のコナラでは, 新葉展開後の気孔コンダクタンスがそれ以外の時期とは異なる傾向にあり, 中·下層木のソヨゴ·ネズミモチ·アオキでは, 3月∼5月にかけて, 異年葉の気孔コンダクタンスの特性が異なる傾向にあった. 葉齢と気孔コンダクタンスとの関係については, 将来の研究課題と考えられた.

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.