The Study Of Vegetation Evapotranspiration Variention In Sandy-meadow Area Of Horqin Sandy Land

The Agula eco-hydrology experimental area located in the southern of Horqin sandy land-town of Agula of Horqin left Banner. Horqin sandy land, which is one of the biggest sandy land of the China four typical sandy lands, and is the seimi-arid area under the temperate continental monsoon climate. It has unique characteristics in particular aspect of climate/ecosystem and hydrology cycle, and with abundant groundwater to supply people living also the plant evapotranspiration. As the features above, it means significant to know and study the water and heat transfer in the study area. The Agula eco-hydrology study region is a9.7km2area, and started establishments in2007, with advanced observing equipments like:automated climate observing system, soil observing system, Bowen-ratio system, automated groundwater depth1. Based on the climate data in2008and2009, the Penman-Monteith equition was used to evaluated the potential evapotranspiration of the study area, while Bowen-ratio, Hargreaves,Christiansen—argreaves and pan evaporation methods were applied to compare with the computation of P-M potential evapotranspiration.2. Applying model ISAREG to simulate the soil water balance in the root zone of natural vegetation Artemisia halodendron community, parament grass community and rainfed maize. Also calibrated the crop coefficient based on the climate condition, compared the simulated soil water content with the observations. The crop coefficient in the initial and middle growth stage for permanent grass were Kcim=0.3,Kcmid=0.85, for rainfed maize they were Kcim=03, Kcmid=1.053. The dual crop coefficient model SIMDualKc was chosen to simulate the soil moisture during the growth period, compared the simulations with the observations of Artemisia halodendron community, the permanent grass and rainfed maize, the results showed that the model was appropriate to predict the soil moisture. The actual evapotranspiration for site C3in2008and2009were454mm and464mm, for rainfed maize without irrigation were453and367mm respectively, which were lower than maize with irrigation in other district, the reason probably is that the plant height, the plant density and the leaf area index(LAI) were lower than that of irrigated maize. The basal crop coefficient (kcb) were calibrated and validated for each plant. The calibrated basal crop coefficient in the initial and middle season for permanent grass community were0.3and 0.75, for Artemisia halodendron community were0.4and1.0, while the Kcbim=0.3, Kcbmid=0.85.4. The relationship between crop evapotranspiration and the climate factors were analyzed in the study area, the main factors which influenced the grass evpotranspiration in2008were:air temperature, actural vapor pressure, net radiation and average wind speed. The impact climate factors for Artemisia halodendron evaportranspiration listed from higher to lower were:air temperature, the soil surface temperature, net radiation, relative humidity, and mean air pressure. The evapotranspiration goes up significantly after rainfall, and the response of evpotranspiration for both vegetation to the wind speed were not obvious.5. The soil evaporation (E) and crop transpiration (T) were calculated with the model for each site during the growth period, and the ratio of soil evaporation to evapotranspiration (E/ETc) were analyzed in each development stage. The groundwater contribution (GWC) was the key supplement for vegetation growth in the study area, the GWC of grass was162mm, which accounted for36%of evapotranspiration, and GWC increased to270mm in the dry year2009, applied about60%of the water consumption for evapotranspiration. The GWC for maize in2008and2009were235and187mm, respectively, accounted51.8%and50.9%for the evapotranspiration in each year.