Dynamic assessment of urban environment in the Beijing-Tianjin-Hebei urban agglomeration with multi-source remote sensing data

Multi-source remote sensing products and comprehensive environment index (CEI) were used to evaluate dynamics of urban environment in BTH from 2000 to 2020． Differences of environmental dynamics in different areas in BTH were compared with Kruskal-Wallis and Mann-Whitney U tests． The urban environment in BTH region was found to show an overall improving trend from 2000 to 2020, with moderate-improved and improved urban environment accounting for 38.1% and 28.4% of the total land area, respectively． Total area of environmental degradation and moderate degradation in 2000-2005, 2006-2010 and 2011-2015 was found to be more than 90%． From 2016 to 2020, CEI in 50.8% and 41.7% of the region had improved． In this process, reduction in PM_2.5 concentration played a major role．Significant differences were found in environmental dynamics among the old urban area, the new urban area and the urban-rural transition zone． The environmental dynamics in the old urban area was mainly improved (66.5%), but in the new urban areas and urban-rural transition zones was similar or with minor improvement (45.6% and 49.3%)． In the future, joint construction and management should be strengthened in BTH, with special emphasis on pollution control and ecological improvement in ecologically vulnerable areas and areas with persistent environmental degradation. In urban expansion, development and construction at the cost of environmental pollution should be avoided, green and blue infrastructures should be built．