Response of gross primary productivity to compound dry-hot events in Xilingol Grassland, China.

We explored the impacts of compound dry-hot events on gross primary productivity (GPP) of the Xilingol Grassland. Based on MODIS GPP data and TerraClimate datasets, including potential evapotranspiration, maximum temperature, and precipitation, from 2000 to 2023 during the vegetation growing season (May to October), we constructed a standardized compound dry and hot index (SCDHI) by using the standardized temperature index (STI) and the standardized precipitation evapotranspiration index (SPEI). We then used Theil-Sen trend analysis and the Mann-Kendall non-parametric test to analyze the spatiotemporal variations of SCDHI and GPP, and used partial correlation analysis and ridge regression analysis methods to quantitatively assess the relationships between STI, SPEI, SCDHI, and GPP, as well as their relative contribution. The results showed that GPP of the study area during the growing season showed a non-significant upward trend (0.79 g C·m-2·a-1) from 2000 to 2023, while the SCDHI decreased at a non-significant rate of 0.005·a-1. In 84.3% of the study area, there was a positive correlation between SPEI and GPP, and the area with a significant negative correlation accounted for only 0.2%. In 69% of the study area, STI was negatively correlated with GPP, while in a few areas, it was positively correlated, with the area of significant positive correlation accounting for 1.8%. In most areas, SCDHI was negatively correlated with GPP, and the significant negative correlation areas were mainly distributed in the central and western parts, accounting for 47% of the area. In the study area, SPEI had the significant dominant regulatory effect on GPP in the northeastern and southern regions, STI had a relatively significant contribution to GPP in the northwestern part of Sunite Left Banner and Duolun County. Meanwhile, GPP in the western and southern regions was greatly affected by compound dry and hot events. This study is of importance for deepening the understanding of the formation mechanisms of compound dry-hot events and guiding the development of disaster prevention and mitigation strategies in the region.