| In the context of global change,frequent droughts in northern China have not only caused major losses to people's lives,property and socio-economics,but also brought a series of crises to the agricultural production and ecological environment.Therefore,how to efficiently monitor and evaluate drought levels,distribution characteristics,and spatial-temporal evolution has important guiding significance for the formulation of comprehensive measures for local agricultural production and drought prevention.Starting from precipitation,soil moisture and the response of surface vegetation,the main drought-causing factors and their remote sensing monitoring mechanism were comprehensively sorted out and summarized.And parameters that can characterize precipitation deficit,soil moisture deficit and vegetation growth status were selected as the main input variables.Then on this basis,the time-series Temperature Condition Index(TCI),Vegetation Condition Index(VCI),and Precipitation Condition Index(PCI)were calculated using MODIS and TRMM data,the three-dimensional space of TCI-VCI-PCI was established,and the Spatial Distance Model(SDM)was used to construct the Temperature-VegetationPrecipitation drought index(TVPDI),so as to reconstruct the spatial-temporal drought information of the vegetation growth season(from March to October)from 2001 to 2018 in fifteen provinces of the northern China.At the same time,in order to ensure the reliability and effectiveness of TVPDI,TVPDI was comprehensively evaluated from various aspects.And using the monitoring results of this index,the drought distribution characteristics and spatial-temporal evolution in the northern China were monitored and evaluated through time-series analysis methods such as linear trend,coefficient of variation,and Hurst index and spatial statistical methods.This paper drew the following conclusions:(1)TVPDI was consistent with crop yield per unit area,drought affected area,soil relative moisture and NPP,which indicates that the TVPDI index constructed in this paper can well reflect the changes of crop yield per unit area,drought affected area,soil relative moisture and NPP,and proved that TVPDI has certain effectiveness and reliability in drought monitoring.(2)In terms of meteorological drought and agricultural drought monitoring ability,TVPDI was compared with six common remote sensing drought indices,including VCI,TCI,PCI,Scale Drought Condition Index(SDCI),Drought Stress Index(DSI),and Temperature Vegetation Dryness Index(TVDI).By comparison,it was found that the TVPDI index showed more obvious advantages than the other six indices,indicating that TVPDI can be used for drought monitoring in meteorology and agriculture.(3)Using this index to monitor the distribution characteristics and spatial-temporal evolution of drought in northern China from 2001 to 2018,it was found that,the drought in northern China eased from 2001 to 2018,but it was still controled by light and moderate drought;from the perspective of spatial distribution,with the boundary of 35°N and 110°E,the overall pattern of "Light drought in the southern and moderate drought in the northern,light drought in the eastern and moderate drought in the western" was presented;from the perspective of spatial-temporal evolution,the drought degree in most areas have fluctuated less over the past 18 years.(4)From the perspective of the spatial-temporal distribution of monthly drought,the drought in northern China showed a change characteristic of "mitigating first and then aggravating" from March to October,which was the worst in March and April,and the lightest in July and August.From the perspective of future changes trend,the regions where the drought future aggravation area occupied a larger area and had the widest distribution from March to October;while the distribution of the drought future mitigation area is relatively small,indicating there is a danger of aggravating the drought from March to October.The above changes should be noticed by the relevant departments. |
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