Relationship between precipitation and vegetation growth status of the northern slope of Tianshan Mountains based on GF-1 imagery: a case study of Hutubi County in Xinjiang, China

Precipitation is one of the important factors that influences vegetation growth and distributions. Using GF-1 remotely sensed images and observed precipitation data, this paper discusses the response relationship between the normalized difference vegetation index (NDVI) and the standardized precipitation index (SPI) in Hutubi County at different time scales from January to December, 2014. The results show that: (I) From a macro point of view, NDVI has obvious geographical characteristics, the Central Plains region has the highest NDVI values; whereas mountains and hills in the southern region and deserts in the northern region have relatively low NDVI values. (2) There is a clear changing trend in the area of vegetation cover. (3) The SPI randomness decreases but the SPI persistence increases with increment in time scales. The sensitivity of the SPI to precipitation is different at different time scales. (4) The SPI has a good correlation with NDVI at six-months time scale. (5) The overall distributions of both basically have the same shape and trendwithhigher SPI values in April and May, and higher NDVI are from June to August. This confirms the lag-time of precipitation influence on vegetation.