长江流域土地利用时空变化特征及其径流效应

土地利用变化的径流效应是水循环研究中的重点内容之一。长江流域是中国最大的流域,土地利用变化及其径流效应分析是研究该流域径流演变、水旱灾害的基础。本文利用1980、1990、1995、2000、2005年五期土地利用数据,采用土地利用转移矩阵计算土地利用动态度、交换变量等指标,评价了长江流域土地利用的时空变化特征,识别关键变化区域及其变化原因。在此基础上,利用SCS模型的降水—径流方程,分析了土地利用变化的径流效应。研究结果表明：1980-2005年时期,长江流域土地转移活跃程度在第一(1980-1990年)和第四(2001-2005年)时期内明显高于1991-1995年和1996-2000年,中上游四川及其北部地区的活跃程度最大。1980-2005年期间水田、旱地、林地和草地面积变化幅度都在8%以内。但受不同时期环境保护和经济发展因素影响,耕地(水田和旱地)和林地、草地呈现相反的变化,而水域、未利用地和城镇用地相对变化较大;其中快速的城镇化导致城镇用地增幅最高,可达196.58%。土地利用变化直接导致流域的平均径流系数变大,变幅从-0.67%到0.80%,平均增幅0.05%,变化最显著的地区在城市化水平较高的长三角一带。径流系数的增加导致洪水发生的可能性增大。

Spatial distribution of land use change in the Yangtze River Basin and the impact on runoff

The impact of land use change on runoff is one of the key concerns in water cycle research. The Yangtze River Basin is the largest river basin in China, and land use change and its impact on runoff are key research questions for runoff variation and flood and drought hazards analyses of the basin. This study used land use data of the Yangtze River Basin in 1980, 1990, 1995, 2000 and 2005 to calculate the dynamic degree, swapping variable values, and other indexes between the four periods by land use transition matrix, evaluated spatial and temporal variation characteristics of land use, and identified key regions of change and driving factors in the basin. Based on the widely-used precipitation-runoff relationship of the Soil Conservation Service (SCS) model, runoff impacts caused by land use change were assessed. The results show that from 1980 to 2005, land transfer activity was more intense in the first (1980-1990) and the fourth (2001-2005) periods compared to the two periods in between (1991-1995, 1996-2000). The middle and upper reaches around Sichuan Province and to its north were the most active regions. Paddy land, dry land, woodland, and grassland areas changed slightly, less than 8%. Influenced by different approaches of environmental protection and economic development in the four periods, cultivated lands (paddy land and dry land) showed inverse changes with grassland, and water body, unused land, and urban land changed to a much greater extent. In particular, due to rapid urbanization, urban land increased by 196.58%. Land use change directly resulted in the increase of average runoff coefficient, which ranged from -0.67%~0.80%, with the mean of 0.05%. The most obvious changes were in highly urbanized regions, particularly around the Yangtze River Delta region. Increase of runoff coefficient would raise the occurrence probability of flooding.