Relationship between fractional vegetation cover and humidity index after returning farmland to forest in Shaanxi Province

Vegetation is an important part of a terrestrial ecosystem,and climate condition determines the growth and development of plants. At the same time,vegetation also has a regulatory role on climate. Since 1999,a project to return farmland to forest has been ongoing in Shaanxi Province,leading to the mitigation of the deterioration in the local ecological environment. Therefore,an analysis of the vegetation and climate conditions in Shaanxi Province,as well as a study of the changed relations between the two,may provide an important theoretical basis for response to global climate changes,and should improve the further development of ecological environment construction in Shaanxi Province. In this study,MODISNDVI data were used to calculate the fractional vegetation cover,and the humidity index was taken as the climate indicator in order to reflect the degree of regional dryness and wetness,and the hydrothermal balance status. In addition,GIS and remote sensing technology and mathematical statistics were used to analyze the spatiotemporal variation laws and the changed relations between fractional vegetation cover and humidity index after returning farmland to forest in Shaanxi Province( 2000-2012). The following observations were made: 1) The fractional vegetation cover in Shaanxi declined from south to north,and the fractional vegetation cover in southern Shaanxi was the highest,followed by those in the Guanzhong region,Huanglong Mountain and Ziwu Mountain,whereas in the north,the Yan'an region was the lowest. The fractional vegetation cover showed clear seasonal variations,reaching a peak in August. From 2000 to 2012,the fractional vegetation cover in Shaanxi Province showed an extremely significant increasing trend in volatility,and this was most significant in northernShaanxi. Vegetation degradation occurred within the vicinity of some cities,especially on the border between Xi' an and Xianyang. 2) The spatial distribution of the humidity index was similar to the fractional vegetation cover,which also decreased from south to north. The southern Shaanxi region is a wet area,the area from Guanzhong to Yan' an in northern Shannxi is a relatively arid region,and Yulin has the highest drought levels. The humidity index also showed clear seasonal changes,and was at its highest in late summer and early autumn. From 2000 to 2012,the humidity index for Shaanxi Province had larger inter-annual fluctuations. The index for southern Shaanxi showed a clear rising tren