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Occult precipitation and chemistry of a small mountainous catchment
Tesař, Miroslav ; Šír, Miloslav ; Fottová, D.
The present contribution deals with the importance of occult precipitation from the wind-driven low clouds and fogs onto the vegetation cover in the selected mountainous regions of the Czech Republic (Šumava Mts., Jizerské hory Mts. and Krkonoše – Giant Mts.). The experimental monitoring network and sample taking devices for the collecting of samples of water from fogs and low clouds are described in fully details. The attention is paid especially to the evaluation of water and pollutants amount incoming to the monitored regions via occult precipitation.
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Comparison of two models of forest transpiration
Šír, Miloslav ; Čermák, J. ; Naděždina, N. ; Naděždin, V. ; Tesař, Miroslav
Two transpiration models were tested in the paper, one is with plant control, and another without plant control. Principle of the (1) model with plant control was, that physical mechanism of transpiration is evaporation actively controlled by plants. The supposed mechanism is: part of the heat (heat equivalent of the energy absorbed from solar radiation), which would cause overheating the plant above 25 ºC is dissipated by evaporation. The model has five physical parameters, which are in principle measurable. (2) The model without plant control is based on the assumption, that transpiration dissipates a constant fraction of the heat from the heat equivalent of absorbed solar radiation (about 45 %). The model needs only one measurable physical parameter. Both models were tested by comparing their results with results actually measured daily totals of transpiration (via sap flow) in the floodplain forest Pohansko (near the town of Břeclav, southernmost Moravia), which was typical with almost non-limiting soil water supply over the period May 1 to Sept. 30, 1998. Results of both models were almost equal. We discussed their physical differences evaluating their goals and weak points and specified a program for further testing the physical mechanism of transpiration.
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Plant transpiration and self-organization of hydrologic cycle
Šír, Miloslav ; Lichner, Ľ. ; Tesař, Miroslav
We quantified the influence of plant transpiration on the entropy production associated with the degradation of solar energy on the Earth’s surface covered by plants. Two surfaces were studied: (1) biotic surface – plant transpiration taken as equal to the potential one, (2) abiotic surface – plant transpiration taken as if equal to zero. Two sources of entropy were taken into account – the entropy production associated with the conversion of solar radiation into (1) the sensible heat, and (2) latent heat. Surface processes in hydrologic cycle were examined in the experimental watershed Liz located in the Bohemian Forest (Czech Republic). We found that in the growing season 1992 the entropy production in humid hydrologic cycle (the Earth’s surface is biotic) was considerably higher than in the arid one (in 39 % of days the Earth’s surface behaved as biotic, in 61 % of days behaved as abiotic). Considering that the biotic effect on the Earth’s functioning can be assessed using the entropy production, we can assume that the hypothesis that biota – represented as a biotic surface – regulates Earth’s environment is proved in the watershed scale.
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Climate change and plant transpiration
Šír, Miloslav ; Tesař, Miroslav ; Lichner, Ľ. ; Syrovátka, O.
The article shows how the plant transpiration cools the boundary level of the atmosphere. In a summer day, when the heat input is 5 to 6 kWh/m2 per day, in the mountainous and submontane areas of the Czech Republic (600 to 1400 m a.s.l.) the plant transpiration decreases: (1) maximum temperature of plant cover from 47 to 25 degrees C, (2) maximum temperature of boundary level of the atmos-phere from 29 to 21 degrees C, (3) maximum temperature of the soil in the depth of 15 cm from 15 to 8 degrees C. The cooling caused by plant transpiration substantially af-fects the energy balance of the land surface. Insufficient transpiration caused an increment of thermal energy of about 23
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Modeling water regime in a small watershed
Vogel, T. ; Tesař, Miroslav ; Císlerová, M.
The paper is focused on the role of the soil water regime in formation of subsurface runoff. One-dimensional dual-permeability model is used to simulate variably saturated movement of water in the soil, in which preferential flow effects were reported. Simulated pressure head variations are compared with the available tensiometric observations. A possible conceptual model of prevailing water transfer mechanism in a hillslope segment is presented. The shallow subsurface flow is approximated by one-dimensional saturated flow along the inclined soil-bedrock interface. For a selected growing season, the model generated hillslope hydrograph is compared with the observed stream hydrograph. The simulated subsurface runoff peaks compare well with the measured stream discharge peaks.
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