Study On Dynamic Characteristics Of Vegetation Cover,water Consumption And Drought Status In Pastoral Area Of Midwestern China

The changes in the ecological pattern caused by climate change and the impact of human disturbance on vegetation have always been the hot topic of attention of scien-tists at home and abroad.Vegetation changes cause changes in evapotranspiration,water consumption,and drought conditions.The pastoral areas of midwestern China locate in the arid and semi-arid region,and their ecological fragility is extremely sen-sitive to climate and ecological changes.In addition,shortage in water resources is a common issue in these areas with uneven distribution in various sites and times,re-sulting in prominent contradiction in demand and supply of water.Therefore,it is es-pecially necessary to study dynamic characteristics of vegetation cover,water con-sumption and drought status under the influence of global climate change and human activities.The specific objective of this study is to clarify water consumption charac-teristics of vegetation in these areas,and the mechanism how water distribution is regulated by change in vegetation cover.This study will provide theoretical basis for optimizing water resource utilization and management in these areas,promoting eco-logical restoration,and further enhancing the productivity of agriculture and animal husbandry.In this study we used GIMMS 3g NDVI products,MOD16 ET products and me-teorological data.Spatiotemporal distribution and impact factors of vegetation cover,evapotranspiration,water consumption and drought condition were analyzed in the study area,including Qinghai,Gansu,Ningxia and midwestern Inner Mongolia,using Theil-Sen median trend analysis,M-K test,Hurst index,Morlet wavelet analysis,re-gression analysis,etc.1)From 1981 to 2015,the vegetation coverage in the pastoral areas of midwest-ern China tended to increase,showing a rise-drop-rise pattern.In the past 35 years,the area where vegetation cover is improved accounted for 41.9%of the total area.The improvement is most obvious from 2006 to 2015,accounting for 63.7%.Among the11 types of planting,cultivated vegetation was improved the most obviously and more than 80%of the total area was improved.The grassland was the second one that the improved area is larger and more than 60%of total area was improved.The restora-tion area mainly distributed in central Inner Mongolia,most of Ningxia,eastern and southern Gansu and Hexi Corridor,northern and western Qinghai.In short,the vege-tation coverage in these areas is in a positive sustainable development trend,which may be affected by the national ecological engineering and planting structure adjust-ment measures.In the future,the vegetation coverage in these areas will mainly sus-tain to be improved.2)From 2001 to 2016,the actual evapotranspiration?ET?in these areas showed an increasing trend,while the potential evapotranspiration?PET?showed a decreasing trend.During the year,ET increased first and then decreased,and peaked from June to August.The ET changes of all planting types were divided into unimodal,undulatory and bimodal types.The unimodal type mainly occured in the forest;the undulatory type mainly happened in natural grassland,desert,cultivated vegetation and marsh;the bimodal type was generally found in alpine vegetation and shrub.The ET in the study area generally increased from northeast to southwest,and the PET did not change significantly.3)The average annual reference evapotranspiration?ET₀?and drought index?AI?tended to decrease from 2001 to 2016,drought has eased.However,the AI in the study area is greater than 0.6,which still belongs to arid and semi-arid regions,and the climate is dry throughout the year.During the year,AI decreased first and then increased,and was the smallest in July.Morlet wavelet analysis showed that the interannual variation of ET₀ and AI in the study area was obvious periodical,showing there is a 14-year main cycle,a sub-period of about 11 years.In general,the vegetation cover in the midwestern pastoral areas of China in-creased as a whole under global climate change and the future is positively sustainable.The improvement of vegetation caused an increase in water consumption and the ET increased.It indicates that the soil available for plant utilization has an increasing trend,the degree of vegetation water needs has been alleviated,and the PET is re-duced.The study found that the AI in the study area was reduced,the drought situa-tion was alleviated,and it has significantly cyclical.