Abstracts for the 6th International GAME Conf.
3-5 December 2004
Kyoto Japan
Observational Study of Hydrological Land-surface Processes on Semi-arid Grassland Underlain by Warm Permafrost in Mongolia
M. Ishikawa (2), T. Kadota (2), E. Munkhtsetseg (4), D. Oyunbaatar (4), T. Ohata (2), Yinsheng Zhang (2)
(2) Institute of Observational Research for Global Change (IORGC), Yokohama 236-0001, Japan
(4) Institute of Meteorology and Hydrology, Ulan Bator, Mongolia
To improve our understanding of water cycle processes at the periphery of the Eurasian snow cover/frozen ground region, a series of observation sites were established on a semi-arid grassland. The observation terms include radiation and heat fluxes, meteorology, phenology of grassland and water condition of surface ground layer.
The observation site was established on grassland at Nalaikh, southeast of Ulan Bator. Meteorological and heat budget data were obtained using an automatic climate observation system (ACOS), in which air temperature, humidity and wind speed profile were measured at height of 0.5, 1.0, 2.0 and 4.0 m respectively; short-wave radiation, long-wave radiation and photosynthesis active radiation (PAR) were measured both in up- and downward respectively; the sensors of air pressure, inferred radiative thermometer for surface temperature and net radiation were installed at 1.5 m above ground surface as well.
Soil moisture was observed both automatically and manually. 7 TDR probes and 7 Pt thermometers, installed parity at depth of 0, 0.2, 0.4, 0.8, 12, 2.4 and 3.0 m respectively; moreover, 2 sets of heat flux meters were set at 0.02 and 0.2 m; of these sensors and the data-logger consist a soil monitoring system (SMS). In addition, the soil moisture profile was observed with manual samples from a 7-m-deep borehole every month. The soil moisture in the surface layer (0-60 cm) was measured using manual sampling.
Phenology observations, including the coverage and biomass of grass, were made from July to September at 10-day intervals. Plant coverage is sparse, generally it reaches about 38-42%.@Also, plant type and species over pastureland are poor. About 60 percent of them occupied Artemisia frigita. Others are occupied by Arenaria and Leymus chinensis. The maximum grass height in mid July was less than 20 cm.
From observation in the period from July 1, 2002 to June 30, 2004, air temperature, relative humidity and wind speed are averaged to be: -4.1 oC, 61% and 2.6 m/s respectively. Total precipitation (two years) was 272.5 mm.
The all-wave radiation albedo show clear seasonal variation. That was low and stable in snow-free period but high and variable in snow cover period.
The heat budget fluxes were predominantly effect by snow cover condition. In the snow cover period, all of the heat budget components show gentle variability. In the period of two years, net radiation was averaged to be 59.5 Wm-2; sensible heat to be 42.6 Wm-2; latent heat to be 15.9 Wm-2; ground heat flux to be 0.1 Wm-2 repectively.
Coupling to total precipitation (two years) of 272.5 mm, actual evapotanspiration was totaled to be 316 mm. Snow sublimation was totaled to be 7.5 mm and 13.2 mm in winter of 2002/2003 and 2003/2004 respectively. The ground surface condition to affect evapotranspiration from such dry ground surface condition lead not only soil moisture but also the phonological feature of the grass. The evaporation efficient varying well with water content in the grass leaves. Just after snow melting, high soil moisture lead evaporation intensive increase closing to potential level. And vegetation plays an important role in the local land surface hydrological process even if with lower biomass. Transpiration at observing site proportioned about half amount in evapotranspiration in snow-free period.
Having summarized land surface water budget at study site in annual basis (Jul 2002 to Jun 2003 and Jul 2003 to Jun 2004), The evapotranspiration (including snow sublimation) were a little be more than precipitation, which might implying the ground getting drier under global warming.
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