城市化对流域生态水文过程的影响研究综述

Abstract

了解流域水文过程（水量和水质）是流域综合管理的基础。城市化引起的生态环境问题已成为目前和未来一段相当长的时期内人类社会面临的重大问题。然而，城市化（土地利用/覆被变化、新污染物产生）、水文（降水、入渗、蒸散、径流过程）和生态系统服务（产水服务、调节气候、土壤保持、初级生产力、维持生物多样性等）在不同时空尺度之间的相互作用还存在知识空白。从城市化对流域生态系统结构和功能的影响、城市化对地表能量平衡与水量平衡的影响、城市化对水质和水生生物的影响、以及城市土地利用/覆被变化的大气环境效应等多方面系统总结了城市化影响流域生态水文过程的研究进展。研究发现，城市"热岛"、"干岛"、暴雨径流引起的城市内涝、水污染等环境现象都与生态水文过程密切相关。强调现代城市规划需要遵循生态水文学规律，从全流域生态系统角度认识近年来新出现的不同尺度的城市环境效应。城市最佳管理措施应以流域为单元实施，以调节土地利用/覆被、保护湿地（包括自然与人工湿地）为手段，充分发挥自然生态系统调节功能（如植被蒸散和净化水质）。未来城市生态水文学应围绕"低影响开发"以及"基于自然的解决方案"等城市流域管理措施，在稳定城市小气候、缓解洪涝干旱等极端水文气象灾害风险以及减轻城市水污染等方面开展多尺度综合研究。;Ecohydrology is the most basic science for guiding integrated watershed management. Rapid urbanization permanently alters land cover and the structure and functions of terrestrial ecosystems in a short period of time. Consequently, urbanization affects hydrological processes such as surface evaporation, runoff, and local and regional climate, and ecosystem services (e.g., water supply, carbon sequestration, biodiversity). Urbanization directly affects the physical properties of the near-surface atmosphere, the energy exchange between land and atmosphere, and the water budget of the ecosystems. These changes bring or aggravate a series of water quantity, water quality, and climatic effects, e.g., heat island, dry island, wet island, rain island, and turbid island. This study systematically summarized the research progress in understanding the impacts of urbanization on watershed ecohydrological processes with a focus on the consequences of urbanization on surface energy balance, water balance, water quality and aquatic organisms, and the meteorological effects of urban land use/cover change. The most direct impact of urban land use/cover change on the environment is the alternation of the energy and water balance at multiple scales. The unique physical properties of the urban surface and associated energy balance distribution characteristics are different from natural ecosystems, resulting in unique microclimate and eco-hydrology in an urban environment. Urbanization-driven surface processes have direct or indirect impacts on hydrological processes such as runoff, infiltration, evapotranspiration, groundwater recharge, and river network confluence at different scales by increasing impervious surface and changing vegetation cover conditions. Large-scale urbanization aggravates the peak flow, rainstorm runoff, and annual total water yield as a result of evapotranspiration reduction caused by the significant reduction of vegetation and surface soil infiltration rate. The influence of urbanization on non-point source water pollution is mainly reflected in the change of ‘source’, ‘process’, and ‘sink’ of non-point source pollutants. Urbanization aggravates water quality problems by the increase in impervious surface that elevates pollutant concentration and load and alters physical and chemical processes in aquatic systems. Large-scale conversion of forest lands to urban uses leads to a significant reduction in evapotranspiration, which reduces its ‘biological drainage’ function, coupled with an increase in the impervious surface, and is likely to exacerbate the risk of flooding or the risk of ‘light rainstorms, heavy waterlogging’ phenomena in urban watersheds. The conversions of vegetated ecosystems reduce their ‘air conditioner’ functions and are likely to exacerbate the ‘urban heat island’ and ‘urban dry island’ effects. We summarized measures and strategies centered on ‘Low Impact Development’ to mitigate the urbanization risks through reducing extreme hydrological effects of impervious surface, enhancing the regulating function of natural ecosystems, and implementing the Urban Best Management Practices at a watershed scale. We concluded that future urban ecohydrological science should focus on the studying the mechanisms of ‘Low Impact Development’ and ‘Nature-based Solutions’ in mitigating environmental impacts from the perspectives of water and energy balances and biogeochemical cycling at multiple scales.