The Loess Plateau Vegetation Cover Change And Its Response To Climate Of Multi-scale

Changes in vegetation NDVI and its relationship with temperature and precipitation has become one of the key issues of global changes research in recent years. Nowadays the study of the interactive relationship between vegetation NDVI changes and the climate factors needs to be futher deepened. Based on the data of NDVI data and meterological records from1999to2008, this paper explored the changes in vegetation cover and climate (air temperature and precipitation) on the Loess Plateau by using time-lag analysis, GIS spatial analysis, and other methods. Responses of vegetation changes to climate at multi spatial-temporal scale were also analyzed in the study. Main conclusions are as follows:1. The NDVI in the area of Loess Plateau increase by10.5%during the last decade. The highest increase of NDVI was found in autumn, followed by that in summer and spring. The NDVI in winter changed slightly. Consindering spatial difference, the increase of NDVI in Northern Shaanxi Region was significantly higher than those in other areas. The air temperature decreased slightly while precipitation increased during the last ten yearswhile.2. According to the muli-time-scale analysis on the response of NDVI to temperature and precipitation, at the ten-day scale, NDVI had a ten-day and thirty-day time lag in response to temperature and precipitation, respectively. The correlation coefficient of NDVI with temperature is higher than that with precipitation significantly. At the month scale, NDVI had a one-month lag in response to both temperature and precipitation, and the correlation coefficient of NDVI with temperature was higher than that with precipitation. At the season (three monthes) scale, no time lag was found for NDVI in response to temperature and precipitation, and NDVI correlated to precipitation more closely than to temperature.3. Three vegetation areas were classified as temperate broadleaf forest (I area), forest-grass (II area) and grass-desert area (III area) in the Loess Plateau to measure the multi spatial-temporal response of NDVI to temperature and precipitation. At the ten-day scale, the responses of NDVI in the temperate broadleaf forest were similar with those in the forest-grass area, while NDVI in the grass-desert area had a longer maximum time lagging period. At the month scale, the maximum timelagging period of NDVI in all the three areas was one month in response to both temperature and precipitation. At the season scale, NDVI in the grass-desert area had a one three-month time lag in response to both temperature and precipitation, and no time lag was found for other two areas. In addition, three special regions as Northern Shaanxi Loess Plateau (geographic division), the Ningxia Hui Autonomous Region (administrative division), and Yuzhong County of Gansu province (administrative division) were also selected for spatial analysis. Simlar results were found from the analysis on such three regions.4. The maximum correlation coefficient of NDVI in response to temperature is on the whole higher than that to precipitation. Such two maximum correlation coefficients share the certain conformity either at both the ten-day scale and month scale, but on the quarter scale, the corresponding correlation coefficients are determined in the quarter. NDVI showed a multi spatial-temporal response to both temperature and precipitation in the Loess Plateau.