Author(s): Di Xie; Deyu Zhong; Yinglin Tian
Keywords: Net Ecosystem Production; Qinghai province; Random forest; Precipitation; Carbon neutrality
Abstract: Located in western China, Qinghai province plays an important role in ecological carbon sequestration due to its rich grassland resources. In this paper, the historical spatiotemporal characteristics and future potential of the ecological carbon sink in Qinghai are evaluated adopting Net Ecosystem Productivity (NEP) as the indicator. First, the spatial distribution and temporal variation of NEP in this region are analyzed using the historical data from Coupled Model Intercomparison Project Phase 6 (CMIP6) during 2000-2020. Second, to investigate the restriction of the climate factors on the ecological carbon sequestration, a correlation analysis is conducted between NEP and three hydrometeorological variables (precipitation, surface air temperature, and shortwave radiation) using the data in the SSP2-4.5 scenario from CMIP6 during 2021-2060. Finally, the random forest model trained by data in the Sanjiangyuan protected region is applied to assess the potential of carbon sink with minimal human activity under SSP2-4.5 scenario. The results are as follows: (1) In terms of the spatial distribution of NEP in Qinghai in the last 21 years, an overall decreasing trend from southeast to northwest was observed, with an average value of 6.300 gC per square meter per year; as for the temporal variation, the annual-mean NEP in Qinghai showed an upward trend, but the inter-annual fluctuations were large, with the maximum and minimum occurring in 2008 (12.670TgC) and 2006 (3.463 TgC), respectively. (2) NEP in the study region is positively correlated with all of the three climate factors in the next 40 years. Among them, temperature is the most influential factor, having a high correlation coefficient in almost the whole region. Precipitation plays an important role in the southeast part and the radiation only shows a high correlation in a small area in the north. (3) The results from random forest indicates that in the absence of human activity, the yearly cumulative NEP in Qaidam Basin under the SSP2-4.5 can increase from 1.768 TgC to 3.322 TgC, while that in the northeastern area of Qinghai will decreases from 2.785 TgC to 1.300 TgC. If the precipitation is further added on the basis of SSP2-4.5 scenario condition, the NEP in the Sanjiangyuan region and northeastern area will grow with it, but the opposite tendency would be observed in the Qaidam Basin. This study can contribute to understand the variation and impact factors of NEP and also lay a scientific foundation for the projection of the potential of carbon sink under different conditions in Qinghai province and the formulation of strategies to increase biological carbon sinks there.