北洛河流域生态环境变迁及对水资源和水沙关系的影响

Ecological environmental changes and its impact on water resources and water-sediments relationship in Beiluo River Basin

黄土高原地区水土流失严重,水资源短缺,生态系统脆弱,限制了该区域的社会和经济发展。针对人类活动将如何影响黄土高原水沙变化以及如何配置退耕还林还草面积的问题,目前尚缺乏定量分析和研究。以黄土高原渭河子流域北洛河流域为研究区,分析了北洛河流域近20 a降雨、径流、水资源量、产沙量和归一化植被指数的时空变化,建立了流域分布式水文模型,定量评价了退耕还林还草对水资源和水沙关系的影响,探索了不同决策条件下的最优退耕方案。结果表明:流域水资源总量、径流量、地下水资源量和产沙量呈现递减趋势,年均减少量分别为0.07×10^(8)m^(3)、0.01×10^(8)m^(3)、0.012×10^(8)m^(3)、163×10^(4)t;归一化植被指数和降水呈现递增趋势,年均增加量分别为0.006 4,0.65×10^(8)m^(3);生态环境变化导致径流量和产沙量减少,流域分布式水文模型模拟显示退耕还林还草或植被覆盖率增加会导致流域径流量和产沙量共同减少,但产沙量的响应更为敏感;综合考虑径流与产沙的影响,基于多目标优化提出了退耕还林还草面积的优化配置建议,最优退耕面积约为全部耕地面积的28.1%。本研究可为黄土高原地区生态环境建设、水土保持、水沙资源的合理利用提供决策支持。

The Loess Plateau region is seriously affected by soil erosion,water scarcity,and fragile ecosystems,which severely hinder social and economic development in the region.There is currently a lack of quantitative analysis and research on how human activities will affect the changes in water and sediment on the Loess Plateau and how to allocate the areas for reforestation and grassland restoration.This study focuses on the Beiluo River Basin in the Loess Plateau,analyzing the spatiotemporal variations of precipitation,runoff,water resources,sediment yield and normalized difference vegetation index(NDVI)over the past 20 years.The study establishes a distributed hydrological model for the basin,quantitatively evaluates the impact of returning farmland to forests and grassland on water resources and sediment transport,and explores the optimal land retirement plan under different decision-making conditions.The results show that the total water resources,runoff,groundwater resources and sediment yield in the basin are decreasing,and the annual reductions are 7×10^(8)m^(3),1×10^(8)m^(3),1.2×10^(8)m^(3),and 1.6×10^(4) tons respectively.While NDVI and precipitation is increasing,and the annual increases are 0.0064 and 65×10^(8)m^(3) respectively.The continuous increase in NDVI has resulted in a reduction in runoff volume and sediment transport.Returning farmland to forests and grassland or increasing vegetation density can reduce the amount of runoff and sediment transport,with sediment transport being more sensitive.Considering both the impact on runoff and sediment transport,based on multi-objective optimization,an optimal allocation proposal for the area of returning farmland to forest and grass is proposed.The optimal land retirement area is 28.1%.This study provides decision-making support for ecological environment construction,soil and water conservation,and rational utilization of water and sediment resources in the Loess Plateau region.