Spatial and temporal variation of vegetation and its response to meteorological drought in Hebei Province
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Abstract:
Vegetation as an important part of the terrestrial ecosystem,it links the atmosphere,hydrosphere,and soil circle,and is a reflection and indication of regional climate characteristics.With the construction advancement of the ThreeNorth Shelterbelt and the conversion of farmland to forest and grassland,vegetation growth is being affected by human activities.Hebei Province has a forest coverage rate of 34% by the end of 2018.At the same time,it has fully promoted the threeyear national land greening initiative.In 2019,684,000 hectares of afforestation were completed,accounting onetenth of the total number of afforestation in the country.The semihumid and semiarid continental monsoon climate in Hebei Province and the geographical location of the farmingpastoral zone determine its ecological environment selfregulation ability,and it is extremely vulnerable to meteorological disasters,especially drought.Therefore,in the context of global warming,the accelerated frequency of climate extremes,and the increase in the intensity of human activities,comprehensive exploration of vegetation growth characteristics and attribution analysis has an important practical significance. The research methods include SPEI (standardized precipitation evapotranspiration index) and correlation analysis.The SPEI index not only considers precipitation and evapotranspiration but also retains the sensitivity to temperature and precipitation such as SPI (standardized precipitation index) and PDSI (palmer drought index).Describing drought objectively,correlation analysis and the inverse distance weighted interpolation method is used in ArcGIS,SPEI raster map combined with NDVI image to calculate the spatial correlation distribution map of NDVI and SPEI,and conduct a significance test to analyze the spatial relationship between NDVI and drought index. Hebei Province′s multiyear average NDVI fluctuates and rises on the time scale,especially in 2003,and it display a rapid increase of 0.028/(10 a),showing the distribution characteristics of high and low in the middle on the spatial scale.The increase of temperature is significant,and the spatial distribution shows an increasing trend from northwest to southeast in Hebei Province.Precipitation presents a low-medium-high distribution pattern from northwestcentralnortheast.The area and frequency of droughts are the highest in spring,and the high frequency area of summer drought is located in Tangshan in Zhangjiakou,the frequency of drought is the lowest in autumn,and light drought is dominant in winter.The correlation between vegetation NDVI and SPEI is strongest in summer (0.529),followed by spring and autumn,and relatively weak in winter.The central area of Yuxian Station,Zhangbei Station and Chengde Station are mainly negatively correlated,and the positively correlated are mainly distributed in the central region. Conclusions (1) The multi-scale SPEI (1/3/12) value of Hebei Province has a large range of changes,and the seasonal drought has obvious changes with phase characteristics,which mostly occur in spring,summer and winter.The annual scale SPEI judgment shows that the drought is serious and has a large deviation "Hebei Meteorological Bulletin".The seasonal scale SPEI value shows the drought situation in Hebei Province is more reasonable,but there is a degree of deviation in some years.(2) The correlation between NDVI and SPEI on a seasonal scale,with the strongest correlation in summer,followed by spring and autumn,and the weakest in winter.On the annual scale,the correlation between vegetation NDVI and SPEI has obvious regional differences.
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