基于连通性指数(IC)的近30年鄱阳湖流域水系结构与水文连通演变评估

由于气候变化和人类活动等多重影响,流域河湖水系格局与连通程度发生了显著变化,进而引发洪涝灾害等一系列水资源问题。本文以鄱阳湖流域为研究区,基于Google Earth Engine(GEE)提取1989—2020年5期水系数据,采用图论方法构建水系评价体系,定量分析该地区近30年来水系格局和结构连通性的时空演变特征,并结合该时期地形、土地利用和归一化植被指数(NDVI)等数据,利用连通性指数(index of connectivity,IC)评估功能连通性的动态变化,进而探讨水文连通与径流量和输沙量的联系。结果表明,近30年来鄱阳湖流域水系结构趋于复杂化,主要体现在流域北部。除干流外,其他等级河流的数量和长度均有所增加,其中Ⅲ级河流最为明显。河网密度、水面率、河网复杂度和发育系数均呈增加趋势,2000年后的变化率约为2000年前的两倍。水系连通环度、节点连接率和水系连通度总体增加,结构连通性呈好转趋势且变化幅度较小。功能连通分析表明,近30年来大部分流域IC减少,流域下游靠近主河道的平坦地区IC较高,上游远离河道的植被密集区域IC较低。此外,IC与年径流量和输沙量表现为显著的正相关性(...

Assessment on the evolution of river structure characteristics and hydrological connectivity in Lake Poyang Basin based on index of connectivity (IC) during the past 30 years

Patterns of river systems and hydrological connectivity in different river basins are changing significantly, mainly due to the effects of climate change and human activities. This may lead to a series of water resource problems such as floods and droughts. In this paper, we took the whole Lake Poyang Basin as our study area, and used graph theory to construct the evaluation systems based on the extracted river data of five periods during 1989-2020 by using Google Earth Engine (GEE). Therefore, we aimed to quantitatively analyse the spatial and temporal evolution of the river system pattern and structural connectivity in the study area. According to the data of catchment topography, land use and normalised difference vegetation index (NDVI), we used the index of connectivity (IC) to evaluate the spatial and temporal changes of functional connectivity, and further discussed the relationships between hydrological connectivity and runoff-sediment discharge. The results showed that the rivers in the Lake Poyang Basin had changed significantly over the past 30 years and tended to be more complicated. The number and length of rivers showed an increasing trend (except for the main rivers of the basin), and the associated changes occured mainly in the northern regions of the basin, especially for third class rivers. The water surface ratio, river development coefficient, drainage density and complexity showed a clear increasing trend. Moreover, the rate of change after 2000 was about twice as high as before. In general, river network connectivity, node connectivity and river network connectivity in the catchment showed increasing trends, and structural connectivity was in good condition with little variation. Functional connectivity analysis showed that IC values were generally high in flat areas close to the main downstream river channel, while IC values were relatively low in densely vegetated areas far from upstream river channels. Over the last 30 years, IC had shown decreasing variation and marked spatial heterogeneity. Statistical results showed that IC had a significant positive correlation with annual runoff and sediment discharge (correlation coefficient is 0.6 and 0.7, respectively). In short, the river structure in the Lake Poyang Basin had changed significantly, and the structural connectivity showed an increasing trend, while the functional connectivity of the discharge and sediment transport process gradually decreased after 2000. From the perspective of basin structure and functional connectivity, the results of this paper can provide scientific reference and support for relevant studies on the development of river system connectivity and water-soil resource management in the Lake Poyang Basin.