Stream loss in an urbanized and agricultural watershed in China

Abstract

Stream losses are extensively observed due to human activities in the world, and the patterns of stream loss vary in different land use types. However, relationship between stream loss pattern and land use covers is poorly understood. We select the lower Taihu watershed (LTWS) within Yangtze River Delta (YRD), which is dominated by agricultural and urban covers and a typical case of most urbanized watersheds in China. In this study, we measured the stream loss of LTWS from 1960s to 2010s and investigated its relation to different land use covers and impervious area percentage (IAP) in order to figure out the main factor of stream loss in this area. The results show that urban area has tripled with fractional contribution from 10.3% to 33.18% in the form of conversion from agriculture to urban area during 1990-2015. 12.5% of all the streams are lost and 1st-order streams contribute most (91.8%) to the total stream loss. Urban cover contribute most (76%) to total streams loss compared to other land use types. We find that 1st-order streams have highest stream loss intensity, which is mainly caused by urban expansion, but preferred protections are given to highest-order streams. The linear model of correlation of pixel-level streams loss and IAP shows that the streams loss is statistically significant positive with IAP of cells (R² = 0.91). Tradeoffs between city expansion and river network make small channels sacrifice for the urbanization. Urgent measures including legislation must be taken to protect small streams during urbanization nowadays and in future.

Keywords: Land use cover change; Megacities; Streams loss; Urbanization.