| Heihe Oasis is a typical oasis agricultural area in arid areas of Northwest China. As the development of social economy, the land use pattern of oasis is changing obviously in arid areas. Especially the development of agriculture in the middle reaches of Heihe River Basin lead to water contradiction of the whole basin. Since 2000, when Chinese government put forward the strategy of "large-scale development in west China" and "new silk road economy belt", a golden period of development has come for the Heihe River Basin. At the same time, the strategy has also brought a huge environmental challenge to the Heihe River Basin. Zhangye oasis, which is a typical area of the Heihe River Basin, is chosen as the study region in this paper. This paper will discuss land use change and its impact on regional ET of the study area.Taking Zhangye oasis as an example, this paper will analyse the evolution trend of land use pattern from 2000 to 2011 via the land use maps in 2000 and 2011 of the study area. The paper studies the variation of crop structure based on their planting area and anlyzes the annual variation characteristics and trends of Evapotranspiration (ET) via the inversion data obtained by ETwatch model from 2000 to 2013. Furthermore, the paper analyzes the temporal and spatial variation characteristics of ET in different seasons in 2000,2004,2008 and 2012. With the help of land use maps and ET data in 2000 and 2011, the impact of LUCC on ET in Zhangye is analyzed. The paper calculates the ET of crop in different growth period based on crop samples at the scale of cities and countries 2012 and 2013. And then, the paper studies the change of regional ET caused by the evoluation of crop planting structure combining with the planting areas from 2000 to 2013. The results are as followsing:(1)According to the land use maps in 2000 and 2011, the farmland and uncultivated land have undergone greatest change in the past 11 years. The area of farmland has increased 402.51km2, while the area of unused land has reduced 565.51km2. In terms of the change rate of LUCC, the comprehensive annual gradient, namely 0.17%, is relatively low, while the highest single annual gradient is up to 2.52% which the urban and rural construction land witness. From the standpoint of LUCC variation, the areas change of uncultivated land converting into farmland and grassland is greastest. With regard to the patch conversion intensity, the two most common land converting ways are farm land to urban and rural land and unused land to grassland.(2) The results of anlyzing crop structures in 2000 and 2013, the area of corn planting increases sharply and gather to northern part of the study area. on the contrary, the area of wheat and rape contracts from north to south, and the overall planting area of vegetables also increases in this region. The consequence of analyzing the regional planting configuration via Herfindahl index shows that configuration of crop planting becomes more simplified in the central plain area, such as Zhangye and Linze County, while it becomes diversified in Shandan and Minle Counties which are close to Qilian Mountain.(3) The inverse results of the ETwatch model display the values of ET is fluctuating during the last 14 years. ET values decline in Gaotai and its bordering other counties, but increase in Zhangye city, Shandan and Minle counties located in the central and southern of the study area. Meanwhile, the fluctuation of ET values of farmland in the central and northern area is larger than that in Qilian mountain area. The values of ET display seasonal fluctuation trend, namely summer>spring>autumn>winter in the selected years. At last, the study reveals that ET values of farmland is highest distrubting in plain, and values of southern mountain come second and the area around farmland and unused land distributing in northern are lowest. In addition, ET values varie spatially in different land types as well:woodland>cultivated land>grassland>urban and rural construction land>unusedland.(4)The paper sets up background areas to try to check the impact of LUCC on ET. Finally, it demonstrates that ET valuse vary from spring to winter result from the change of LUCC. In detail, the contribution ratios of autumn and winter is higher than that of spring and summer. The accurate ratios of four seasons are respectivitely 80.45%, 83.38%,89.80% and 86.88%.(5)The comparative results of ET values of various crops extracting from sample plants in the different growth periods show that:corn>other crops>wheat cole>barley. The change trend of ET values can be analyzed based on the structures of crop from 2000 to 2013, which can be concluded like this:ET values decelines in Shandan and Minle counties, while increases in Zhangye city, Linze, Gaotai and Sunan counties.(6) Policy Implications:according to the situation that ET values increased when unusedland and grassland converted to cultivated land, the study area should reclaim land reasonably with a certain number of the total cultivated land that the government requires and avoid water shortages and land salinization due to irrational reclamation. Considering that ET values increasing caused in the counties (cities) by the structure evolution of crops, the study area should rationally layout the planting structure of crops, While improve irrigation technology to enhance water use efficiency and promote the sustainable development of regional water resources. |
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