Study on the impact of urbanization and urban heat island effect on net primary productivity in Kunming

Urbanization greatly affects the net primary productivity (NPP) of vegetation in urban areas, but the spatial and temporal mechanisms of urbanization that drive the NPP of urban vegetation are unclear. In this study, the effects of urbanization on NPP were separated into direct (NPP_dir) and indirect (NPP_ind) effects, and the effects of urbanization on NPP_dir and the associated mechanisms and the effect of urban heat islands on NPP_ind were analyzed using the Geodetector tool and geographically weighted regressions (GWR), respectively. The results showed that urbanization was the dominant factor in the spatial and temporal heterogeneity of NPP, and the explanatory power of the interaction between urbanization and the urban heat island effect on NPP was greater than the explanatory power of the influence of single factors on the NPP distribution. Impervious surface abundance had a strong negative effect on NPP in urbanized areas, while the urban heat island effect had a positive contribution to NPP in urban centers. The urban heat island effect compensates for the negative impact of urbanization on NPP to a certain extent. Compared with the ordinary least squares regression model, the geographically weighted regression model had a better fit in the correlation analysis of both urbanization and NPP_dir and the urban heat island effect and NPP_ind. This study has value as a reference for further studies on sustainable urban development and the effect of urbanization on NPP and the carbon cycle.