Dianchi Lake watershed impervious surface area dynamics and their impact on lake water quality from 1988 to 2017.

The relationships between impervious surface area (ISA) patterns and characteristics have long been studied to examine the impacts of hydrological cycles, water management, surface energy balances, and biodiversity. This study assessed the Dianchi Lake watershed as a case study area to illustrate ISA change characteristics and their impacts on Dianchi Lake water quality. More than 200 Landsat images (from 1988 to 2017) were first downloaded through the US Geological Survey (USGS) online portal. Then, a series of ISA maps of the Dianchi Lake watershed at an annual resolution were built using a robust method we proposed. Then, the change characteristics of main water quality parameters were analyzed from spatial-temporal viewpoints. Finally, correlations between ISA and Lake water quality were made. The research results indicated that the ISA proportion of the Dianchi Lake watershed rapidly increased (from 1.84% in 1988 to 34.32% in 2017), the annual ISA total growth rate exceeded 21 km2/year, and the urban area encircled Dianchi Lake. The Dianchi Lake watershed has begun to adopt the "Rashly Advancing" and "Great Leap Forward" strategies of urbanization. Chlorophyll a (Chla), dissolved oxygen (DO), and transparency (Trans) showed significantly changing tendencies, whereas the values of pH, total nitrogen, and total phosphorus stayed relatively constant. The polynomial regression models and corresponding R2 values indicated strong correlations between ISA and three water quality parameters (Chla, DO, and Trans). The development of better strategies for the control and reduction of water pollution without optimizing ISA spatial distribution is essential for Kunming's continued urbanization.