福建省长汀县河田水土流失区植被覆盖度变化及其热环境效应

Analysis of fractional vegetation cover change and its impact on thermal environment in the Hetian basinal area of County Changting, Fujian Province,China

南方红壤典型水土流失区——福建省长汀县河田盆地区的大片山地曾由于植被稀少、山岭裸露、气候炎热,而被称之为"火焰山"。通过20多年的水土流失治理,该区的生态环境有了很大的改善。利用遥感技术,计算了长汀县河田盆地区在1988—2010年间的植被覆盖度变化及其伴随的地表温度变化。结果表明,通过近22a的水土流失治理,该区的平均植被覆盖度有了明显的升高,从1988年的48.83%上升到2010年的59.78%;而同期盆地内外的温度差异也随之下降,盆地裸露区和周边地区的温差降低了近1℃。定量研究表明,河田盆地区的植被覆盖度每增加10%,可降低地表温度0.6—1℃。

Soil erosion has caused severe ecological problems in China. Being a typical reddish soil erosion region in southtern China, the hilly areas of the Hetian Basin in County Changting, Fujian province, have been called flame mountainous area, due to lack of vegetation covers, extensively exposed bare soils, and hot weathers. After more than 20 years of soil-loss treatment, the local ecosystem and environment have been greatly improved. This study used remote sensing techniques and four scenes of Landsat Thematic Mapper （TM） images, enquired in 1988, 1998, 2004, and 2010, to study the fractional vegetation cover changes and accompanied land surface temperature variations in the Hetian basinal area during the period from 1988 to 2010. Two remote-sensing based models for estimating fractional vegetation cover have been compared in order to select a suitable model for the retrieval of the fractional vegetation cover in the study area. The two models compared are the Carlson-Ripley and Gutman-Ignatov models. The comparative analysis confirmed that the Carlson-Ripley model had a higher accuracy than the Gutman-Ignatov model as it has a lower systematic error value. Therefore, the Carlson-Ripley model was used to retrieve the fractional vegetation cover for the study area. While, the land surface temperature change during the study period was evaluated through the temperature difference between the areas inside and outside the basin in each study year. The results indicate that the 22-year effort for the treatment of the soil lossin the Hetian basinal area has resulted in the notably increase in fractional vegetation cover in the area, averagely from 48.83% in 1988 to 59.78% in 2010. Meanwhile, the difference in land surface temperature between the areas inside and outside the basin has also been reduced from 3.39℃ in 1988 to 2. d8℃ in 2010, almost ICE declined. This suggests a lowering of the temperature in the area inside the basin. Obviously, the increase in fractional vegetation cover was accompanied with the lowering of regional temperature. Spatial and temporal analysis indicates that the changes in both fractional vegetation cover and land surface temperature mainly took place in the areas inside the Hetian Basin, while the areas outside the basin were rather consistent either in fractional vegetation cover or in land surface temperature. Quantitatively analysis suggests that each i0% increment in fractional vegetation cover would result in the lowering of local land surface temperature approximately by 0.6 to 1℃ based on regression models of the four study years.