Spatial And Temporal Variation Of Meteorological Drought In Haihe Plain And Its Influence On Vegetation Coverage

Drought is caused by China's economic and social,one of the worst natural disaster loss of agricultural production,the study of regional drought can be for the local economic development and ecological environment construction to provide important decisions,the haihe river plain area is drought every year in our country the most times,is also a important grain production base in north China,so the study of haihe river plain drought is of great significance.Based on the daily precipitation data of 20 weather stations in Haihe Plain from 1955 to 2017,the standardized precipitation index(SPI)with different time scales was calculated to analyze the temporal and spatial variation rules of meteorological drought in haihe Plain 63 A.Then the spatial characteristics of the vegetation coverage of nearly 10 A in Haihe Plain were analyzed by using the enhanced vegetation index(EVI)data from 2007 to 2017.Finally,SPI and EVI are combined to reveal the influence rule of meteorological drought on VEGETATION coverage in Haihe Plain,and the response of vegetation coverage to drought and irrigation is discussed in typical regions.The main conclusions are as follows:(1)The drought frequency of Haihe Plain mainly concentrates in [0.28,0.31],showing the characteristics of high frequency of light drought and low frequency of heavy drought;The frequency of spring drought is the highest and winter drought is the lowest.In summer,the incidence of drought in wheat growth period was higher than that of maize,but there were significant inter-annual and inter-regional differences in maize growth period.(2)According to the Mann-Kendall mutation test and wavelet analysis,drought occurred for 7 times in Haihe Plain 63 A,and the last mutation was drought,which showed an increasing trend,and the inter-annual drought had obvious periodicity.In the four seasons,there were different Numbers of abrupt transitions,in which spring and autumn were abrupt transitions to wetness and drought presented a downward trend,while summer and winter were abrupt transitions to drought and drought presented an upward trend.Droughts in the four seasons also had obvious periodicity and would continue to be arid in a long time series.(3)The characteristic values of the SPI cloud model based on 63 A of 20 stations show that the uniformity and stability of the occurrence of drought in the study area are relatively strong in the dry years,but weak in the wet years.Moreover,the annual dispersion and instability of SPI index in Haihe Plain is greater than that of each station.(4)According to THE EVI from 2007 to 2017,the monthly scale EVI value of Haihe Plain is basically between [0.13,0.69].The seasonal scale EVI value has obvious seasonal difference,which is manifested as > in summer,> in spring,> in autumn,and > in winter.EVI in spring,autumn and winter has an obvious growth trend,while EVI in summer has an obvious decline trend.The annual EVI value of The Shanghai River plain showed an obvious upward trend,indicating that the vegetation of the Shanghai River plain as a whole was gradually getting better,mainly covering crops.(5)By the correlation of spatial distribution of the haihe river plain SPI and EVI,in four seasons,summer,autumn EVI and overall SPI were positively correlated,the smaller the drought degree of vegetation is lush,winter and spring,but most of the areas show the negative correlation relationship between,probably because the vegetation coverage is mainly determined by winter wheat,the drought occurs,the person of wheat crops irrigation can still keep the area coverage is higher.(6)Through the analysis of the cooperative interaction between EVI and SPI in haihe plain at different time scales,it can be seen that on a short time scale,SPI and EVI are positively correlated,but with the extension of time scale,the impact of drought on FVC also decreases.Therefore,SPI with a time scale of less than 3 months should be used to evaluate drought in Haihe Plain.(7)Through to the vegetation coverage in the typical regions in response to drought and irrigation degree impact study,can be found that a typical region during the spring and summer,vegetation coverage degree of response to drought and irrigation were not significant,and in the autumn,shijiazhuang vegetation coverage degree of response to irrigation was not significant,but the degree of response to drought,and with the occurrence of drought,vegetation coverage increase with the decrease of the first.