2000 Fiscal Year Final Research Report Summary
Relationships between vapor condensation, evaporation and salinization near ground surfaces in arid and semi-arid areas.
| Project/Area Number |
11650536
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
水工水理学
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| Research Institution | Daido Institute of Technology |
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Principal Investigator |
SHIMOJIMA Eiichi Daido Inst.of Technol., Fac.of Eng., Professor, 工学部, 教授 (80027276)
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| Co-Investigator(Kenkyū-buntansha) |
TAMAGAWA Ichiro Gifu University, Fac.of Eng., Associate Professor, 工学部, 助教授 (40273198)
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| Project Period (FY) |
1999 – 2000
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| Keywords | arid-and seim-arid areas / evaporation / vapor condensation / salinization / experiment / numerical simulation |
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| Research Abstract |
By paying attention to the condensation of atmospheric vapor, the relation between soil-surface evaporation and salinization in arid/semi-arid areas was explored through an evaporation experiment from a sand column and a numerical simulation to meteorological data observed in a desert area in West China (HEIFE).
Using air-dried dune sand for HEIFE (Case A) and a fine silica sand (Case B), sand columns were set up on the balance, where only in the latter case, a shallow water table of NaCl solution with a high concentration was set. The columns were exposed to ambient air controlled at 65% humidity (corresponding to nighttime) and at 20% (daytime) alternately, where the air temperature is kept constant (25℃) and 550 W/m^2 of heat radiation was applied on the sand surface only at the dry air stage. Locations and movements of the evaporation and condensation zone for both cases were analyzed using information on vapor in the sand columns measured by humid-cups. For Case B the condensation amount at the wet stage was almost equal to the evaporation one at the dry stage, while for Case A, the evaporation was about ten times larger than the condensation and source of its surplus evaporation was the underlying aquifer. Soil water ahead of the evaporation front for Case B was chemically saturated and its concentration behind the front decayed exponentially with depth, while salinization for Case A was much lower.
A numerical simulation using a model of heat-moisture-solute movement in the atmosphere-land system was successfully undertaken. And it was known that source of evaporation in that desert was almost rainfall and a spike of solute concentration profiles observed at 〜10 cm deep from the ground surface appeared through the interaction between rain-infiltration and soil-water evaporation.
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