The urban hierarchy and agglomeration effects influence the response of NPP to climate change and human activities

Abstract

In recent years, global climate changes and human activities have significantly reshaped ecosystems, posing a challenging aspect for research—accurately understanding how climate and human activities affect vegetation. This study employs the Carnegie–Ames–Stanford Approach (CASA) model to analyze the spatiotemporal distribution of Net Primary Productivity (NPP) in the Central Yunnan Urban Agglomeration (CYUA) from 1982 to 2019. It measures human activity intensity using the Comprehensive Human Activity Intensity Index (CHAII), which is derived from human activity intensity of land surface, population density, economic conditions, and remote sensing data. Spatial autocorrelation analysis is used to assess human activity clustering. The study employs Ordinary Least Squares (OLS) and Geographically Weighted Regression (GWR) to quantify the impacts of climate change and human activities on NPP in CYUA across different spatiotemporal scales. The findings are as follows: (1) Human activities in CYUA exhibit a spatial distribution radiating from Kunming City and display distinct spatial autocorrelation characteristics. (2) Increasing human activity reduces NPP. In areas with higher and more concentrated human activity, it suppresses NPP, while positively affecting neighboring areas. The threshold of human activity intensity affecting NPP varies across space and time, with higher thresholds in cities with greater human activity intensity compared to those with lower intensity. (3) NPP and precipitation exhibit a closely positive correlation. Reduced precipitation weakens this correlation. Rising temperatures since 2000 have negatively impacted NPP, especially in regions with higher human activity intensity. (4) This study provides a new institutional perspective for the analysis and formulation of adaptive strategies in regions where ecosystems are jointly impacted by climate change and human activities. Future research can further refine the study of NPP responses to human activities in cities with varying development levels, diverse urban organizational structures, and different urban expansion patterns.