How does urban population density decline over time? An exponential model for Chinese cities with international comparisons

Abstract

It is widely observed urban land expands faster than population grows, which results in declining urban population densities over time. However, it is not known how densities decline. By taking 35 major Chinese cities as examples, we propose an exponential model to quantify the temporal decline in urban population densities from 2001 to 2015. The average adjusted R2 of the exponential model for 35 cities is 0.68, indicating a moderate but powerful correlation with temporal variations in densities. The exponential model implies that the temporal decline in densities in cities is occurring at a constant but differentiated rate. Apart from Beijing and Shanghai, the annual decline rates vary from 1% to 9%, with an average of 4.65%, which means urban population densities declined by 4.65% per annum from 2001 to 2015. The bivariate correlation analysis and multiple regression model reveal that the initial urban population density and the growth rates of urban land, population, and GDP in a city are significantly correlated with the decline rates and that these four factors can explain 72.3% of the variance in the decline rates among cities. We further verified the transferability and applicability of the exponential model by applying it to 20 U.S. cities. Using a global dataset, we found the temporal decline rate in densities in Chinese cities was greater than those in India and other countries or regions, which highlights the necessity of efficient urban development strategies to slow down the temporal decline in urban population densities in China.