Spatial-temporal changes in urbanization level and influencing factors on the Tibetan Plateau: perspectives from long-term time series nighttime light data

It is of great theoretical and practical significance to accurately quantify changes in urbanization on the Tibetan Plateau, to understand economic, social and ecological responses in the region．Due to imperfect social and economic statistical data of the Tibetan Plateau, relevant research has not been done on urbanization level dynamics．The recently released long-term nighttime light data provides an opportunity to study changes in urbanization level on the Tibetan Plateau．The dynamics of urbanization level on the Tibetan Plateau was quantified from such data from 1992-2018．Changes have been analyzed on multiple scales: provincial-level administrative regions, prefecture-level administrative regions, county-level administrative regions, as well as watersheds．Spatial agglomeration characteristics and influencing factors in different time periods were analyzed．The overall urbanization level on the Tibetan Plateau showed an accelerated growth trend from 1992-2018, significant spatial differences were found．From 1992-2018, CNLI increased from 1.03×10⁻⁴ to 4.46×10⁻³, with an average annual increase of 1.67×10⁻⁴．The area and number of high-level urbanization clusters increased significantly．Three areas with high level of urbanization have formed around Xining, Lhasa, and southeast edge of the region．The urbanization levels are mainly affected by traffic and topography, influence of traffic factors is constantly increasing．It is concluded that quantification of urbanization from long-term nighttime light data is effective and can be applied to other areas with imperfect statistical data．