| In the northwest of China,the water resources problem has always been the primary factor restricting the regional social-economic development.Therefore,Aiming at the situation of regional water resources shortage,in order to realize the transformation from traditional animal husbandry to ecological animal husbandry,we need to balance the relationship between natural grassland and artificial grassland.Study on ecological water demand of natural grassland under climate change conditions,It can help to reveal the changes of ecological water demand in grassland communities,and clarify the situation of grassland ecosystem water cycle and water balance.It provides a reliable scientific basis for regional grassland irrigation,grassland ecosystem restoration and planning and construction.This study is under the background of climate change,combined evolution characteristics of climate elements in typical pastoral areas in western China.Taking SuNan County as an example,calculate the typical hydrological annual ecological water demand and ecological water shortage of different grassland types in different representative areas;The evolution trend of grassland vegetation phenology was clarified,and the change rule of grassland vegetation ecological water requirement under different climate change scenarios in SuNan County was analyzed combining with three control variables of temperature,precipitation and phenological period.The main conclusions are as follows:(1)The climatic factors in typical pastoral areas in Western China have obvious spatial variation characteristics.From southeast to northwest,the average temperature decreases while the sunshine hours increases.From south to north,the spatial distribution of precipitation and relative humidity has a basically consistent trend,showing a stepped pattern of decreasing distribution.The average annual temperature of the typical pastoral areas in Western China has been rising in the past 60 years,and the range of temperature rise is 0.31 ?/10a.Through a 95%significance level,a significant mutation year occurred in 1996;the annual average temperature change rate of each station is-0.14?0.82 ?/10a,the average maximum temperature and minimum temperature showed an upward trend on the whole,and the overall heating rates were 0.26 ?/10a and 0.39 ?/10a,respectively.The change of annual average precipitation tends to be slightly humidified with an increase of 2.12 mm/10a,and failed to pass the 95%significance level.The annual average precipitation rate of each site is-31.18-21.34 mm/10a,the annual sunshine hours showed a downward trend overall,and the tendency rate was 15.47 h/10a.The average relative humidity and the average wind speed also showed a downward trend,and the propensity rates were 0.37%/10a and 0.1 m/s 1Oa-l,respectively.The average temperature of the natural grassland increased in the past 60 days in the typical pastoral area of western China,and the temperature rise reached 0.24 ?/10a.The precipitation in the growing season is on the rise,with an increase of 1.54 mm/10a;The overall sunshine hours,average relative humidity and wind speed all showed a downward trend,and their propensity rates were-9.56 h/10a,0.39%/10a,and 0.1 m/s·(10a)-1,respectively.The analysis of temperature,precipitation and sunshine hours during the critical growth period of natural forage grass showed that:The temperature and precipitation required for the heading period to the flowering stage are higher than the greening period,and the difference in solar radiation required is not large.(2)The spatial distribution of potential evapotranspiration increased from south to north in the typical pastoral areas of western China,and decreased from northeast to southwest.The annual average reference crop evapotranspiration showed a slowly increasing trend at a rate of 0.95 mm/l0a.The average annual reference crop evapotranspiration rate of each site is between-3.7 and 3.18 mm/a;The sensitivity of each climatic element to potential evapotranspiration was:relative humidity>wind>sunshine hours>temperature;The relative changes in climatic factors were:temperature>sunshine hours>relative humidity>wind.Only relative humidity in each climatic factor contributes positively to ET0,the maximum contribution rate is sunshine hours,and the contribution rate of relative humidity to ET0(positive influence)is less than the contribution rate of sunshine hours and average temperature to ET0(negative effect).(3)The average ET0 linear tendency rate in the growing season of Sunan County was 6.7/10a.The Mann-Kendall trend test shows that:Only ET0 in the growing season of Gaotai Station showed a downward trend,while Yongchang,Zhangye and Tuile stations showed a significant growth trend.During 57 years,the average annual growth rate of ET0 in Sunan County increased gradually from south to north.From the plain of Hexi Corridor to the middle and high mountainous areas of Qilian North,the ET0 gradually decreased with the increase of altitude.The ecological water demand quotas of different grassland types in the same representative area are different,and the difference in effective rainfall is small;there are also some differences in the ecological water demand quotas of the same grassland types in different representative areas,but the effective rainfall varies greatly.Except for Minghua Township,the ecological water demand of temperate grassland and alpine meadow grassland in other regions occupies a large proportion of the total regional ecological water demand,and the grassland ecological water shortage in each region is mainly represented by warm grassland.(4)The length of grassland vegetation growing season in Sunan County showed an increasing trend.Only the length of the grassland vegetation growing season in Yongchang Station was shortened,and the average climate tendency rate in the whole area was about 10 d/10a.The effects of elevated temperature and precipitation on ecological water shortage of different grassland types in different representative areas are different.Take Sunan County as an example,the ecological water shortage of grassland vegetation increased by 191.328 million m3 when the temperature increased by 0.5 ?;the precipitation increased by 10%,and the ecological water shortage of grassland vegetation decreased by 86.8643 million m3.(5)In RCP 4.5 and RCP 8.5 scenarios,the regional grassland ecosystem has gradually stabilized,and the RCP4.5 scenario is more conducive to vegetation restoration.In terms of the amount of grassland vegetation ecological water shortage in various towns and villages in Sunan County,in addition to Minghua Township and Qifeng Tibetan Township,The ecological water shortage of grassland vegetation in other towns and villages has decreased compared with the historical period,grassland vegetation ecosystems tend to develop steadily.In the RCP8.5 scenario,the overall ecological deficit of grassland vegetation in Sunan County has increased significantly,only in the 2050s period,the grassland vegetation ecological water shortage in some townships decreased.The ecological water shortage in Minghua and Qifeng Tibetan townships will increase relative to the historical period under the two climate scenarios in the future,and the ecological environment may deteriorate. |
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