黄河中游典型流域径流锐减模式比较研究

Rapid decrease of runoff has happened in many tributaries of the Yellow River in the Loess Plateau since the 1990s, some of them even dried up overnight. This phenomenon has caused heated discussions and in-depth researches. The Hekou-Longmen reach, together with local floods, is the main source area for coarse sedimenta- tions into the Yellow River. Our research choose several typical tributaries in the middle reaches of the Yellow River, and use integrated approaches, such as field survey, statistical mining and model inversion. With statistic analysis of the rainfall-runoff relation in typical tributaries since 1950s, and introduced an elastic coefficient method of basin scale coupled heat and water balance model, we make comprehensive and preliminary judgment of the fact and the cause of rapid runoff decrease at a macro level. Then, With satellite remote sensing data, aerial images and the combination of field survey, we identified the spatial and temporal distribution of major warping dams, small and medium-sized reservoirs, microtopography of soil and water conservation (warping dams, terraced fields, fish-scale pits and so on) and vegetation changes, and build a land use classification system based on microtopography. Based on these researches, we structured the Microtopography Enhanced Hydrological Model (MEHM), and simulate the changing environment and corresponding hydrological responses in typical river basin with this model. We also proposed an triangle analysis method of underlying surface parameter to identify quantitative causes of hydrological changes, and do quantitative evaluation of contribution rates of climate factors and human activities to rapid runoff decrease. To provide a scientific basis to adaptive management of water resources under changing environment, we propose developing methods and a hydrological model for water resources assessments under changing environment, and make system analysis and quantitative evaluation of the cause of rapid runoff decrease. This comparative reach could be significant for partially revealing the mechanism of the changing discharge, and make references for water resources management of the Yellow River basin.

从20世纪90年代末开始，黄河中游黄土高原的许多支流河川径流快速减少，一些河流甚至一夜干涸，引起了社会各界热烈的讨论和深入的研究。本文选取其中若干条径流锐减成因模式不同的典型支流，结合实地调查、文献调研、统计挖掘、卫星遥感数据、模型反演等综合方法，首先从宏观层面对径流锐减事实和成因进行了综合初判，其次从微观层面识别和反演了典型支流微地貌的空间分布及演化过程，建立了加强微地貌特性及变化影响的分布式水文模型，发展了变化环境下水文水资源研究的方法和模型，对不同径流锐减模型的河川径流锐减成因进行系统分析和定量评估，计算气候和人类活动影响因子对径流锐减的贡献率，丰富变化环境下水文水资源的理论与方法，为变化环境下的水资源适应性管理提供科学基础，为黄河流域水资源管理提供参考。

报告选取黄河中游皇甫川、孤山川、窟野河、秃尾河和佳芦河等典型支流为研究对象，并基于大量基础数据，结合实地调查、统计挖掘、卫星遥感数据、模型反演等综合方法开展黄河中游典型流域径流锐减模式比较研究。. 主要研究内容、重要结果如下：（1）径流锐减：典型支流50多年来的产流能力呈现明显的阶梯变化，其中第三个阶梯的径流减正发生在气候变化和人类活动影响最剧烈的时期。（2）气候变化：研究区域近十年汛期降雨量与1980~1999年相比增加了20mm，变幅7%；平均雨强在2000年有明显的阶梯下降，突变后减少了0.3mm/h，变幅达18%，无疑将影响了以超渗产流为主的黄土高原地区的降雨径流模式。（3）微地貌变化：90年代以来，梯田、造林、种草、淤地坝等四项基本的水土保持措施的数量进一步增加，本报告基于相关土地利用分类标准提出突出微地貌特征的适合描述黄土高原区水文下垫面的土地利用分类。（4）模型构建：从微观层面识别和反演了典型支流微地貌的空间分布及演化过程，提出并建立了加强微地貌特性及变化影响的分布式水文模型MEHM，模型是在清华大学GBHM（杨大文，1998）模型基础上改进而成的，进一步强调了在变化环境下水文下垫面的细节变化产生的水文效应，分阶段率定了模型参数并验证。（5）结果分析：基于识别水文变化成因量化的下垫面参数三角分析方法，采用标准降水系列 （1985~2006）分别模拟三个阶段下垫面条件下皇甫川的径流响应，计算气候和人类活动影响因子对径流锐减的贡献率。气候变化因素不足30%，人类活动因素超过70%，是影响皇甫川径流减少的主要因素。下垫面变化的影响包括土地利用变化、微地貌变化和植被变化，各微地貌间的贡献比例是：水体30.4%，淤地坝24.7%，林地18.4%，耕地14.5%，种草12.0%。. 研究面向基于分布式水文模型的水资源评价，阐明了高分辨率降水观测数据描述水文过程的重要意义，研究了土地利用微地貌特征对产流能力的影响，并进行了典型流域径流锐减成因贡献的解耦反演，为变化环境下的水资源适应性管理提供科学基础，为黄河流域水资源管理提供参考。