Correlation between climatic factors and EVI based on MODIS time-series data in Guizhou

To study the response of the vegetation of rocky desertification area to drought climate, this paper was focused on serious rocky desertification of karst development which is typical in Guizhou Province as the experimental area. Guizhou is located in southwest China, with longitude ranging from 103°36’ E to 109°35’E and latitude from 24°37’N to 29°13’N. The area is located in the eastern Yunnan-Guizhou Plateau with topographic low in the east and high in the west. The selection of experimental points was based on 19 benchmark standard meteorological stations which have direct rainfall record in the province (Chinese meteorological data network http://data.cma.gov.cn/). Wherein the criteria used to adjust that if a site fall in rocky desertification area can be referred to the book of "Remote sensing typical karst rocky desertification-GIS study: A case of Guizhou Province". According to the records, the drought widely occurred in southwest China in the spring of 2010, while it started in the fall of 2009 in Guizhou Province. In order to maintain the consistency of time series experimental data, the drought period is identified as from the fall of 2009 to the spring of 2010, whereas the periods from the fall of 2008 to the spring of 2009 and the autumn of 2010 to the spring of 2011 are not the drought. Using the enhanced vegetation index (EVI) as an indicator of vegetation coverage degree with the data derived from the 2008-2011 moderate resolution imaging spectroradiometer (MODIS,a spatial resolution of 250 m) ,as well as the average temperature (T) and precipitation (P) of weather station as climate factors, this paper comparatively analyzed the correlation coefficient r and F test results of the vegetation and climate factors in both karst rocky desertification area and the non-rocky desertification one. The results showed that,(1) Whether or not the sites fall in rocky desertification or non-rocky desertification area and the EVI of drought period or non-drought period, the correlation coefficient rEVI-T between EVI and climatic factors-temperature (T) were greater than 0.5 (rF=0.235,α= 0.05), which showed significant correlation of the two; (2) In non-rocky desertification area, the correlation coefficient rEVI-P of EVI in both drought period and non-drought period with the climatic factors-precipitation(P), were 0.234 and 0.212,respectively, which showed non-significant correlation of the both, but the case is contrary in rocky desertification area; (3) In a year after the drought, the correlation of the EVI in rocky desertification and non-rocky desertification regions with precipitation(P) were both significant, with the correlation coefficients rEVI-P of 0.516 and 0.489, respectively.