The Change Of Typical Vegetation Evapotranspiration And Analysis Of Its Influence Factors In The High-cold Grassland Area

Evapotranspiration is one of the important control factors in water circulation system.As the birthplace of the Yangtze River,Yellow River and Lancang River in China,the three river sources are known as the"water tower of China".The ecological function value of water resources in the three river sources is immeasurable.In this paper,Xinghai County,the source of three rivers,is taken as the research area.Although it is located in the upper reaches of the Yellow River,the annual precipitation is only 240-600mm.There is a saying of"In three years,it will be dry in two years,in five years,it will be very dry in one year,and in ten years,it will be dry in nine years",which seriously restricts the development of local animal husbandry and agriculture.It is of great significance for local water cycle regulation and water allocation for agriculture and forestry to carry out basic research on ecological hydrology and clarify the law of regional vegetation evapotranspiration.In this paper,the actual evapotranspiration(ET_a)of Achnatherum splendens in different stages(turning green stage,jointing stage,heading stage and seed setting stage)was calculated by using the observation data of Lysimeter and meteorological data in 2020.The reference evapotranspiration(ET₀)of corresponding period was calculated by combining with penman Monteith formula.The water consumption coefficient and water consumption of each stage of Achnatherum splendens were obtained on the basis of ET_a and ET₀.Sensitivity analysis,contribution rate analysis and correlation analysis were used to analyze the leading meteorological factors affecting the change of vegetation vapor volume.In this paper,the experimental data are combined with the mathematical analysis model,and the following conclusions are obtained:(1)In the growth cycle of typical herbage Achnatherum splendens in Xinghai County in 2020,The ET_a values of three Achnatherum splendens communities at each stage were 0:0.96 mm/d at regreening stage,3.06 mm/d at jointing stage,2.34mm/d at heading stage and 1.31mm/d at fruiting stage.The water consumption coefficient of Achnatherum splendens in each stage was 0.53 at rejuvenation stage,1.03 at jointing stage,0.96 at heading stage and 0.61at seed setting stage.The water consumption of Achnatherum splendens community in Xinghai County ranged from 1.86×10⁷m³to8.27×10⁷m³.The water consumption of Achnatherum splendens community was the highest at jointing stage and the lowest at fruiting stage.The water consumption of Achnatherum splendens community during the whole growth period was 20.61×10⁷m³.(2)During the 30 years from 1990 to 2020,the annual variation trend of ET₀value presents a"single peak type",which gradually increases from May to July,and gradually decreases from July to the end of September,and reaches the maximum value on July 16,the maximum value is about 3.26mm/d,and the total ET₀value is about 365.28mm during the growth period;however,the interannual variation trend of total ET₀in the growth period is not obvious,and its variation range is332.15-414.65mm between.(3)The sensitivity coefficients of ET₀to climate factors were as follows:S temperature=0.293,S sunshine hours=0.298,S relative humidity=0.402,S wind speed=0.101.The sensitivity coefficient of the four main meteorological factors is as follows:S _relativehumidity>S sunshine hours>S temperature>S wind speed.(4)The contribution rate of temperature is 2.858%,sunshine hours is-1.655%,relative humidity is-2.099%,wind speed is-0.851%.Among them,the contribution rate of temperature is positive,and the contribution of the other three meteorological factors is negative.Therefore,the order of contribution rate of climate factors to ET₀value change is:C temperature>C relative humidity>C sunshine hours>C wind speed.From a long-term sequence angle(nearly 30 years),because the ET₀value has a highly fitted relationship with the ET_avalue,it can indirectly reflect that temperature is the dominant meteorological factor affecting the change of ET_avalue(consistent with the2020 short-term study results),the ET_avalue increases with the increase of temperature,decreases with the decrease of temperature,and the two are linearly related.(5)The water needed for the growth of Achnatherum splendens is relatively tight in the growth period of turning green period,early heading period and high temperature period.The relevant departments of agriculture and animal husbandry can provide sufficient water for the growth of Achnatherum splendens by means of irrigation and artificial rainfall in these periods.At the same time,the local herdsmen should be encouraged to grazing reasonably to ensure the canopy density of Achnatherum splendens community in these periods.