Jumpei Kubota

Snow ablation in an open field and larch forest of the southern mountainous region of eastern Siberia

Abstract The southern mountainous taiga region of eastern Siberia is the runoff source area of the basins of the rivers Lena and Amur, where snowmelt discharge is an important hydrological process. To evaluate the effect of the sparse larch forest canopy on snow ablation and energy balance in the snow-pack, meteorological conditions and snow ablation were observed in a larch forest (LF) and an open field (OP). At the beginning of snowmelt, the snow water equivalent was 54.4 and 95.5 mm at OP and LF, respectively. The snow disappeared at LF three days later than at OP. Sublimation accounted for about 8% of snow ablation at both sites from 1 April to 5 May 2002, the snowmelt period. The energy balance of the snowpack at the two sites was dominated by the net all-wave radiation onto the snow surface. The difference in snowmelt between the sites was primarily caused by a difference in the net all-wave radiation. Snow surface albedo correlated with snow surface density for densities from 150 to 350 kg m−3 at both sites.

Effects of Riparian Denitrification on Stream Nitrate-Evidence from Isotope Analysis and Extreme Nitrate Leaching during Rainfall-

The effects of riparian denitrification on stream nitrate were investigated by detailed soil water observations and isotope analysis at a small headwater catchment in an urban area near Tokyo, central Japan. In the base flow period, stream nitrate concentration (<100 µM) was comparable with that of riparian ground water which had less nitrate than unsaturated soil water. Nitrogen isotope analysis showed that the consumption of nitrate by denitrification took place in riparian ground water, suggesting that denitrification is an important process to control nitrate leaching to streams. During rainfall, the concentration of stream nitrate increased up to 400 µM, which was comparable with that of pre-event soil water. The fact that soil water nitrate directly leached to streams indicated that the riparian denitrification process did not work during rainfall because of the rapid discharge of water. A decrease of denitrification effects is a possible reason for high stream nitrate concentration during rainfall.

Evaluation of the Tortuosity Parameter for Forest Soils to Predict Unsaturated Hydraulic Conductivity

In order to accurately predict the unsaturated hydraulic conductivity for forest soils, we evaluated the tortuosity parameter for forest soils and investigated the relationships between the tortuosity parameter and parent materials and soil sampling depths. Undisturbed forest soil samples were taken from three parent material types: the granite group, Mesozoic-Paleozoic, and Quaternary. Samples taken from layers corresponding to the A-horizon were categorized as topsoil and others as subsoil. After retention parameters were fitted, the tortuosity parameter was optimized using the Mualem-van Genuchten conductivity model. No significant differences were found in the average values of the tortuosity parameter among depths or among parent materials. Optimized values of the tortuosity parameter varied from 3.20 to −5.23 with a high frequency in the range of about 0 to −2. The average value was −0.94. This means that, for most forest soils, the predicted hydraulic conductivity tends to be underestimated when the most common value (0.5) of the tortuosity parameter is used. Modifying this parameter value to −0.77, as explained in this study, corrected the underestimation tendency and reduced prediction errors. When the unsaturated hydraulic conductivity for forest soils is predicted from water retention, the tortuosity parameter should thus be modified to an appropriate value for more accurate prediction.

Variations in discharge from the Qilian mountains, northwest China, and its effect on the agricultural communities of the Heihe basin, over the last two millennia

Over the last two millennia, agricultural land in the Hei river basin, northwest China, has been subjected to a series of significant droughts and flood events. These documented hydrological events were compared to estimates of fluvial and fluvioglacial discharge from the mountains. Areal extents of glaciers are important for validation as water mass remaining in mountain area, although glacier area occupied only about 1.5 % at present in this high mountain area. These glacier mass balance and discharge estimates, calculated using proxy data, appear reasonable, as the total maximum glacier area during the little ice age (LIA) was comparable to the maximum glacier area deduced from the positions of terminal moraines. The precise timing of the glacier area maximum during the LIA in the Qilian mountains is unknown. However, variations in the calculated glacier area suggest that glacier extent reached a maximum between 1520 and 1690 CE. A number of the historical drought events occurred during periods of reduced discharge from the mountains, and, conversely, flood events tended to coincide with an increase in discharge from glaciers. Historical documents record five multi-year droughts in the basin between 1200 and 2000 CE. The modelling of the fluctuating pattern of fluvial and fluvioglacial discharge implies that at least two drought events were anthropogenically driven. Furthermore the reasons for the presence or absence of drought events are considered based on continuous discharge fluctuation and water demands of each ages, that can be estimated from analysing intermittent historical documents.

Perspectives on Sustainability Assessment: An Integral Approach to Historical Changes in Social Systems and Water Environment in the Ili River Basin of Central Eurasia, 1900–2008

This article proposes an alternative approach in sustainability assessment. The conceptual framework was developed by modifying Ken Wilbers All Quadrants, All Levels (AQAL) approach, and focuses on the inter-relatedness/inter-connection of various perspectives inherent to the concept of sustainability. To look at how our framework can facilitate the practice of sustainability assessment, we apply the framework to examine the relationships between social systems and the environmental changes in the Ili River basin across the period 1900–2008. This approach enables us to investigate the environmental problems of the Ili River basin in a four-quadrant framework, and combine the empirics of quadrants obtained from traditional disciplinary methodologies. The four-quadrant framework adopted in this study illustrates the interlocking relationships among various perspectives of environmental issues in the Ili River basin, namely, physical perspective, personal perspective, cultural perspective, and social perspective. In particular, the protruding development (evolution) of the lower right dimension is the fundamental cause of the environmental degradation and its related social problems in the Ili River basin. Compared to other established approaches in literature that emphasize on the tradeoffs of various perspectives of sustainability, our findings indicate the potential contributions of four-quadrant framework to sustainability assessment through its focus on the inter-relatedness/inter-connection of different perspectives.

Energy Balance of Irrigated Intercropping Field in the Middle Reaches of Heihe River Basin

Based on the experiments conducted in an irrigated intercropping field in Zhangye Oasis in the middle reaches of Heihe River basin in 2004, the characteristics of radiation budget are analyzed. Furthermore, energy balance is calculated by using Bowen-Ratio Energy Balance (BREB) method. The results show that the ratio of the absorbed radiation to the incoming short radiation in intercropping crop canopy-soil system is increasing with growing stages, from 0.81 in the initial growing stage (IGS) to 0.86 in the late growing stage (LGS). The net radiation, which is smaller in IGS, increases rapidly in the first period of the middle growing stage (MGS) and reaches the maximum value in the second period of MGS. It then somewhat decreases in LGS. The ratio of net radiation to total radiation has a similar trend with the net radiation. In the whole growing stages, latent heat flux, which takes up 70% or so of the net radiation, is the dominant item in energy balance. Sensible heat flux shares 20% of the net radiation and soil heat flux has a percentage of 10%. The characteristics of heat balance vary distinctly in different growing stages. In IGS, the ratios of latent heat flux, sensible heat flux and soil heat flux to net radiation are 44.5%, 23.8% and 31.7% respectively. In MGS, with the increasing of latent heat flux and the decreasing of sensible heat flux and soil heat flux, the ratios turn into 84.4%, 6.3% and 9.3%. In LGS, the soil heat flux maintains 0W/m2 or so, and latent heat flux and sensible heat flux take up 61.4% and 38.6% respectively. The energy balance also shows an obvious daily variation characteristic.