| Based on the temperature and precipitation data in 1960-2009 and MODIS/NDVI data set in 2000-2009 in Three Gorges Reservoir Area, combined with linear trend, R/S analysis and spatial interpolation method, the climate changes in the 50 years, vegetation coverage variety changes in nearly 10 years and correlation between them were analysised at regional and grid level. The research reveals vegetation's variation characteristics in the reservoir and its connection with climate factors, which could provide realistic meaning and reference value for protection and research on the vegetation and ecological environment. The main conclusions are as follows:(1) Temperature interpolation obtained by the spherical model of Kriging, based on DEM (Digital Elevation) data, was better than the one obtained by the index model, and IDW (Inverse Distance) interpolation was the worst. As to rainfall interpolation, the CK (Co-Kriging) considered elevation was the best and IDW worst. Judging from the statistical results, there were no significant differences between IDW and SPLNE (Spline Function), OK (Ordinary Kriging) and CK, while the geostatistics method was obviously superior to the conventional one.(2) Annual average temperature in this area showed a significant rising and the linear wanning rate was 0.13℃/10a, a little lower than the national one. There was a warming trend in the seasonal level except the temperature in 2006 summer; temperatures increase obviously in autumn and winter, which take the largest contribution to the annual warming. Average annual temperature change exsists obvious spatial difference: increasing from east to west, no obvious changed from south to north except for the increasing in the eastern region. The seasonal average temperature in the western area was much higher than the eastern and central ones. Chongqing city was hottest and the southern area of Badong County located in the eastern was the cool center.(3) Average annual precipitation declined overall and the average reduction was 2.24mm, which was mainly caused by the reduction in autumn, the reduction in spring was not significant and precipitations in summer and winter even increased a little. As to the spatial variation, average annual precipitation increased from west to east; the highest rainfall area was Badang County and lowest were southern Chongqing city and Jiangjin district. Though average annual precipitation declined in most of the reservoir, there was a rising in Fuling district, Changshou district and Yubei district of western region. Precipitation isoline of four seasons in the eastern region were all east-west and increasing from north to south. Southern Badong County was the area of maximum rainfall and Xingshan County minimum.(4) Annual average temperature jump occured in 1996 and spring, summer, autumn, winter's occured in 1996,1993,1997 and 1996, the jump point of annual mean air-temperature roughly was synchronous with that of each seasonal one. Annual and seasonal rainfall variations failed to reach the mutation level, which showed that the rainfall variation was just random fluctuation in the past 50 years. It could be predicted that future temperature will increase gradually referring to the warming trend in the past 50 years with R/S analysis:annual and spring temperature will increase obviously; autumn and winter will increase with moderate persistent; summer will increase little, which was stochastic volatility. Average annual and spring rainfalls showed moderate's sustainable reduce trend, summer and winter showed a steady growth trend, autumn showed a highest persistent reduce trend. There was a long-range correlation between temperature and precipitation in the future, which meant that the change trends will be consistent to the past fact and the trend was evident.(5) As to the overall vegetation variation, the linear trend of average annual NDVI was 0.02/10a. Spring, summer, autumn, winter's NDVI linear trend was 0.045/10a, 0.01/10a,0.02/10a,0.002/10a respectively. Rising trend of NDVI in spring was the most obvious; steady in summer and autumn except for the summer, autumn NDVI in 2006 which was minimum in the past ten years caused by the high temperature, few rain weather in the southwest area; Winter NDVI changed little. Overall growth trend showed that comprehensive forestry and natural forest protection project in the reservoir since 1990s had already obtained obvious effects. NDVI in woodland, cultivated land and shrubland existed a similar linear uptrend in volatility, respectively for 0.02/10a,0.03/10a, 0.02/10a. NDVI in the three types of land increased significantly while decline 0.001/10a in other types.(6) Research on vegetation spatial distribution showed that average annual NDVI in years enchases and crosses in plaques, grades zonally in the overall and diminishes from east to west. General variation of average seasonal vegetation cover in years, which was similar with the annual NDVI, diminishes from northeast to southwest in four seasons: NDVI value in four counties of Hubei province (Yiling, Xingshan, Zigui, Badang) was highest; value in Chongqing city and surrounding areas was lowest; NDVI value in the south coast of Yangtze river was higher than the north in central and western regions. As to vegetation NDVI changed at space level, pixel with positive slope value accouted for 82.4% of the total in years while the negative only for 17.6%. But result of F test showed that most of pixel's variation was not significant except for 5.07% significant increment and 0.79% reducation. The result showed that vegetation coverage change in most of the region in the 10 years was random fluctuation, not vegetation landscape change caused by human activities. Vegetation increasing area was far larger than decreasing one in seasons which showed a increase trend in space, but few regions, such as Shapingba, Fuling, etc, presented some degradations in seasons.(7) Research on oversall correlation of vegetation cover and climate showed that vegetation NDVI and annual temperature, precipitation were positively correlated, but only significantly related with precipitation, not significant with temperature. It could be concluded that annual precipitation was the main meteorological factor that affects interannual vegetation dynamic changes in the reservoir. As to seasonal vegetation, it was precipitation that mainly affects its distribution too, especially the precipitation in winter and summer, also temperature in winter. We could find that climatic conditions in summer and winter had a great impact on the average NDVI. Research on the relationship between annual NDVI and meteorological factors showed that there was a positive correlation between temperature, precipitation and NDVI of various vegetation types, while correlation with temperature was not significant, NDVI in cultivated land significantly relates with annual precipitation, which showed annual precipitation's direct effect on the vegetation growth in cultivated land. Correlation between forestland vegetation and temperature or rainfall in spring was not significant; correlation between cultivated land and summer climate was significant, especially the precipitation, exorbitant summer air temperature was not conductive to NDVI growth in woodland; increasing precipitation in spring and summer was benefit for NDVI in shrubland.(8) Spatial correlation research showed that area of positive correlation between average annual temperature, precipitation and NDVI was dominant, which accouts for above 60% of the total. The NDVI was related significantly with the temperature in the northeast, south and southwest and the correlation coefficient reachs to about 0.7, but region negatively related to the NDVI was little; And correlation coefficient between precipitation and north-central area, such as Kaixian, Wuxi and north Yunyang, reached to about 0.8. Area of positive correlation between seasonal temperature, precipitation and NDVI was dominant too:precipitation increasing in spring, summer and winter had a positive effect on NDVI in most of the area; Summer exorbitant temperature was negative; Spring and autumn temperature rising was positive. |
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