京津冀城市群土地利用变化对地表径流的影响

城市化的显著特征之一是地表景观格局被人为改变,大量硬化地表覆盖、取代了原本自然或半自然的土地覆盖类型,极大地干扰了区域水文循环过程。其中,最直接的体现是对地表径流过程的影响。城市群作为当前我国城市化的重要模式,其聚集连片的扩张模式,对区域地表径流过程的干扰尤为严重。以京津冀特大城市群为研究区域,应用长期水文影响评价模型(L-THIA),以1980、1990、2000、2010、2015年5期土地利用数据、土壤数据以及1950—2015年逐日降雨数据为输入,模拟计算了不同土地利用/覆被格局对多年平均地表径流量的影响。结果表明,(1)经过率定的L-THIA模型能够较为准确地模拟京津冀城市群地区的地表径流分布特征,模型模拟误差在±10%内;(2)1980—2015年,京津冀城市群地区不透水地表面积急剧增加,其净增长值为12690.14 km~2。北京与天津等超大城市不透水地表面积增加最明显;(3)随着土地利用格局的变化,京津冀地区地表径流量呈逐年增长趋势。1980—2015年,京津冀城市群地区地表径流量的绝对增长值为17.84亿m~3,增幅11.83%。其中,1990—2000年及2010—2015年期间地表径流年均增长率较大,分别为0.36%与0.46%。对地表径流贡献较大的土地利用类型为耕地和不透水地表,其5期土地利用情景下的平均产流占比分别为35.38%、22.71%;(4)城市尺度上,不同城市的标准化年均径流深(NAARD)存在较大差异。天津、石家庄的产流能力较强,承德、衡水等城市的产流能力较弱,北京市的标准化年均径流深处于中等水平。另一方面,不同城市标准化年均径流深增长规律也存在较大差异。1980—2015年,天津市的NAARD增长最多,承德市增长最少,北京市的NAARD增长处于中等水平。本文对于京津冀城市群水文过程的时空演变研究以及国土空间优化指导具有参考意义。

Effects of land use change on surface runoff in Beijing-Tianjin-Hebei urban agglomeration

One of the remarkable features of urbanization is the dramatic change in the landscape pattern. A large number of impervious surfaces replaced the natural or semi-natural land cover types, which greatly interfered with the hydrological cycle in the region. The most direct manifestation is the impact on the surface runoff process. As an important mode of urbanization in China, urban agglomerations have a spreading mode of expansion, which is more serious to the regional surface runoff. In this paper, the Long-Term Hydrologic Impact Assessment model (L-THIA) was used to simulate the average annual surface runoff under different land use/cover conditions in Beijing-Tianjin-Hebei urban agglomeration, by using five periods of land use data in 1980, 1990, 2000, 2010, and 2015, the soil data and daily rainfall data from 1950 to 2015 as input. The results show that (1) by calibration, the L-THIA model can accurately simulate the surface runoff of the Beijing-Tianjin-Hebei urban agglomeration, and the simulation error is between ±10%. (2) From 1980 to 2015, the impervious surface area of Beijing-Tianjin-Hebei urban agglomeration increased dramatically, with a net growth value of 12690.14 km². The impervious surface area of megacities such as Beijing and Tianjin increased the most significantly. (3) From 1980 to 2015, the surface runoff in the Beijing-Tianjin-Hebei urban agglomeration showed an obvious increasing trend. The surface runoff in the Beijing-Tianjin-Hebei urban agglomeration increased by 1.784 billion m³ and the relative growth value was 11.83%. The average annual growth rate of surface runoff was larger during 1990-2000 and 2010-2015, 0.36% and 0.46% respectively. The cultivated land and impervious surface contributed more to surface runoff in the study area. The average runoff contribution rates of these two land use types under five land use scenarios were 35.38% and 22.71% respectively. (4) From the perspective of urban scale, the Normalized average annual runoff depth values of different cities vary greatly. Tianjin and Shijiazhuang have strong runoff production capacity, Chengde and Hengshui have weak runoff production capacity, and Beijing''s Normalized average annual runoff depth(NAARD) is at the medium level. In addition, there are great differences in the growth patterns of NAARD in different cities. From 1980 to 2015, Tianjin had the largest runoff growth, Chengde had the least growth, and the growth value of NAARD in Beijing was at a moderate level. This study is of great reference significance for revealing the spatio-temporal evolution of hydrological processe in the Beijing-Tianjin-Hebei urban agglomeration and guiding the optimization of land space.