Interaction Between Vegetation Cover And Regional Climate On The Loess Plateau

Since 1998, the Project of Forest Rehabilitation from Slope Agriculture has been implemented in the Loess Plateau of China to restore the ecological environment, control soil erosion. Therefore, evaluating the benefit of the project becomes a research hotspot. This paper selected Loess Plateau as the study area, using MODIS/NDVI from 2000 to 2013 and meteorological data in recent 60 years to analyze temporal and spatial variation characteristics of vegetation cover and meteorological factors and the relationship between the space-time evolution characteristic of vegetation cover changes and the climate factors in Loess Plateau with GIS, RS technology and statistical methods. The main results of this analysis are as follows:(1) The vegetation cover in Loess Plateau Region was increased from 2000 to 2013. From the perspective of season, the largest increase happened in summer, followed by autumn, spring and winter in turn. From the perspective of month, vegetation cover on the Loess Plateau increased most quickly in July. Distribution of vegetation coverage of space was decreasing gradually from southeast to northwest with the 3 banded:NDVI> 0.2,0.2< NDVI< 0.4, NDVI≥ 0.4, which roughly corresponded to the dry temperate zone, middle temperate zone and southern temperate climate zone ofChina’s agricultural climate division. Vegetation cover increased most quickly middle temperate zone, wih Northern Shaanxi is a typical region, followed by day temperate zone, while no significant increase in south temperate zone.(2) In the Loess Plateau, precipitation, average wind speed, average maximum wind speed, average relative humidity, average minimum relative humidity and sunshine hours were decreased since 1951, while average temperature, average maximum temperature, average minimum temperature have upward trends. By comparing of climate change in 1951-2013 and in 2000-2013, the trend of precipitation, average temperature, maximum temperature after returning farmland to forest is inconsistent with the long-term changes. Precipitation was increased by 4.08mm/year, while average temperature and maximum temperature was decreased by-0.0085℃/year and-0.0026 ℃/year. The regional distribution of average relative humidity and minimum relative humidity increasing and the highest temperature declining was consistent with that of vegetation obviously improve in summer.(3) The correlation coefficients of NDVI and the previous meteorological data or the same period meteorological data under different temporal and spatial scales indicate that moisture was the important factors affecting the vegetation in Loess Plateau. The vegetation dependends on precipitation most obviously in the mid temperate zone of Loess Plateau, and the vegetation was the most sensitive to the highest temperature and wind speed in the dry temperate zone of Loess Plateau. Influence of precipitation, air temperature, sunshine hours on vegetation lags behind. Precipitation influence lags obviously in the middle temperate zone and the south temperate zone, and influence of air temperature and sunshine hours on the vegetation lag obviously on the whole Loess Plateau. The positive effect of precipitation on the vegetation in Northern Shaanxi was significantly and lagged behind, and the negative effect of average temperature and high temperature on the vegetation lagsobviously. From the point of the season, precipitation in spring and average relative humidity in previous winter had a significant role in promoting spring vegetation, and wind speed in spring and sunshine hours in previous winter have significant negative effect on spring vegetation. Precipitation, wind speed and sunshine hours have significant effects on vegetation in summer and autumn and lagged obviously. The vegetation in Northern Shaanxi dependence on precipitation in previous winter was relatively large. From the month view, the positive effect of precipitation on the 2～8 month vegetation was significantlyand lags obviously in the growing season (5～8 months). Wind speed had significant negative effect on the 4～10 month vegetation and also lags obviously ged. Air temperature had significant effect on the 1～8 month vegetation, with a positive effect on the 1～4 month vegetation and a negative effect on the 5～8 month vegetation. Sunshine hours had significant negative effect on the 5～9 month vegetation.(4) The correlation coefficients of NDVI and diuretic meteorological data under different temporal and spatial scales indicated that vegetation cover reduced maximum wind speed (the south temperate zone obviously), increased minimum relative humidity (the mid temperate zone obviously) and inhibited maximum temperature (Northern Shaanxi Loess Plateau relatively obvious). Judging from the season, vegetation in summer and autumn of the middle temperate zone and the south temperate zone had significant effect on wind speed, minimum relative humidity and average relative humidity in autumn, winter and next spring. Vegetation in summer on the Loess Plateau of Northern Shaanxi inhibited maximum temperature. From the point of view month, the 2～8 month vegetation had a blocking effect on wind speeds, the 5～7 month vegetation regulated maximum temperature.