Relationship between net primary productivity and soil water content in the Shule River Basin

Soil water content (SWC) is the basic condition for the survival of terrestrial vegetation. Net primary productivity (NPP) directly reflects the status of vegetation growth. Therefore, studying the coupling relationship between NPP and SWC in the arid region of Northwest China is of great significance for vegetation restoration and the protection of fragile ecosystems. Based on remote sensing and SWC measured data, the CASA model and statistical downscaling methods were used to calculate the NPP and SWC, analyze the spatial and temporal evolution of them, and to explore their coupling relationship in the Shule River Basin (SRB) in China. Our results indicate that (1) an upward trend in NPP and SWC during the summers of 2001–2015. (2)The NPP and SWC were mainly positively correlated. There was a lag effect in the response of vegetation NPP to SWC in most areas of the basin. However, NPP had a greater impact on SWC in desert areas than in other regions. (3) Based on changes to SWC, two scenarios analyses of NPP were conducted to reveal how NPP responded to SWC. In scenario 1 (the SWC change only), as SWC increases, NPP gradually increases. Scenario 2 (increase of 1 °C temperature and 2% precipitation), compared with scenario 1, as SWC increases, the increase in NPP decreases. Based on the results, in scenario 2, the beneficial effect of SWC on vegetation growth was weakened. Thus, under future climate change, only by timely supplementing SWC can we better promote the growth of NPP, improve vegetation productivity, and effectively restore and protect the ecological environment of SRB. This study deepens our understanding of the coupling relationship between the ecological environment and water resources of the SRB and provides a scientific basis for formulating rational allocation of water resources and ecological environment restoration and protection measures in the arid regions of China.