The Land Use/Cover Change And Its Impact On Climate In Xishuangbanna, Southern China

The land use/cover change (LUCC) is an important driver of global change and one of the most anthropogenic influences on earth system. It is recognized that LUCC has important consequences for climate system such as changing the exchange of energy, water vapor, atmospheric dynamic force, and greenhouse gases between land surface and atmosphere. With the research on climate change deepening, climate effects of land use/cover change are becoming the focus of attention. In the past decades, LUCC in Xishuangbanna was very obvious, and rapid development of economy leads to the excessive deforestation in this region. So, aiming at Xishuangbanna area, which was the main distribution area of primary tropical forest in China, the main rubber plantation area in China, and the transitional zone from tropical Southeast Asia to subtropical East Asia, the study of LUCC and its impact on climate had been carried out. It had important scientific significances for understanding the LUCC and its impact on climate in tropical area of China.In this study, based on GIS techniques, six periods of Landsat MSS/TM/ETM images and 1:50000 digital elevation model (DEM) were used to analyze the spatial patterns of LUCC and transfer rates affected by the topography; Then, the temperature jumps and trends, the correlation of LUCC intensity and trends of temperature change were analyzed; Last, we retrieved the land surface temperature (LST) of Xishuangbanna, and analyzed the influence of LUCC on LST. The main conclusions included:(1)Characteristics of LUCC in Xishuangbanna from 1976 to 20071)Forest, shrubland, rubber plantation, dry land and tea garden are the main land use/cover types in Xishuangbanna. From 1976 to 2007, the LUCC of Xishuangbanna was very obvious. The most significant changes were a decrease of forest from 13 193 to 8 336 km2 and an expansion of rubber plantation from 249 to 2 256 km2 at low elevation area. Shrubland tended to increase gradually, while the change of dry land was not consistent.2)The forest cover continuously decreased below 1 600m, while the rubber plantation expanded from 1 000 to 1400m, even though it was still dominated between 400 and 1 000m. Farmland was dominant in areas below 600m and decreased rapidly with elevation ascending. Forest cover decreased gradually at all slope gradients, while rubber plantation increased. Rubber plantation and farmland were mainly distributed in gentle slope, while forest occupied the major part of steep slope. After 1988, no considerable change of rubber plantation cover was observed below slope 5°, but continuously expansion above slope 5°; Aspect had large influence on the distribution pattern of cash crop and agricultural land. The rubber plantation of south aspect had a rapid expansion in comparison with a general increase trend to the north. Forest had a maximum percentage but dry land was lowest in north. Besides the change of built up area at low elevation, small slope, flat was obvious; the most rapid change rate at other elevation, slope, and aspect grade was the decrease of forest and the increase of rubber plantation and shrubland.(2)Weather station LUCC dominate period and its correlation analysis with temperature change trends1)The LUCC dominate period of Menglun station was from 1999 to 2007, other stations'were from 1976 to 1988. The beginning increase time of temperature in all stations was about in 1970s', the jump time of temperature was all most in 1980s'.2)In the period of greatest LUCC, most of all stations that exhibited significant trends (mean and maximum temperature) displayed warming trends, but there were relatively few significant warming trends before and after period of greatest LUCC. During LUCC dominate period, the warming amplitudes of average temperature and average maximum temperature were obviously higher than pre- and post- period of greatest LUCC, but the warming amplitudes of average minimum temperature were less than post-period of greatest LUCC. It showed that monthly temperature range increased in the period of greatest LUCC. In LUCC dominate period in Xishuangbanna, the monthly mean temperature exhibited significant warming trend, but warming trend of monthly mean temperature of Yunnan province was not significant. After LUCC dominate period in Xishuangbanna, the yearly mean temperature didn't exhibit significant warming trend, but warming trends of yearly mean temperature of Yunnan province and global area were significant. It was indicated that global warming had little effect on the climate of Xishuangbanna.(3)Characteristics of land surface temperature evolution in Xishuangbanna1)Dry land, shrubland, forest, grassland, and rubber plantation took an important role in regional thermal contribution, while others made little impact. The thermal pixel proportion index of forest was decreasing, while the shrubland and dry land were increasing. The area above mean LST of forest, shrubland, and dry land took a large proportion, and forest was decreasing, shrubland and tea garden were increasing.2)Forest area in low and sub-low temperature region was much larger than other types. The proportion of area of shrubland, rubber plantation, grassland, and dry land was gradually increasing along the rising temperature grade. The proportion of area of dry land and shrubland increased with the rising temperature grade, and absolutely dominated at high temperature region, while forest dominated at low and sub-low temperature region. The proportion of area of tea garden and rubber plantation had the rising tendency in medium and sub-high temperature region.