Vegetation gross primary productivity responds to extreme compound dry and hot events in protected areas of China

Standardized dry and hot index (SDHI) is used as an indicator of compound drought and hotness, to evaluate the spatiotemporal characteristics of gross primary productivity (GPP) and SDHI in China’s warm seasons from 2001-2019． The response relationship and response time scales of GPP to SDHI and extreme compound dry and hot events were analyzed, for forest lands and shrub grasslands inside and outside protected areas． The trend of warm season GPP change is characterized by rising in the north and south of China and decreasing in the middle, with most regions showing an upward trend． The trend of warm season SDHI change is characterized by rising in the north and decreasing in the south in China, with most regions showing a downward trend, indicating an intensification of drying and heating． The average response time of warm season GPP to drought and hotness changes was 1.50 months, the spatial heterogeneity of response time was not obvious． The vegetation growth of forest lands and shrub grasslands within the protected area was less susceptible to the limitations of compound drought and hotness． The average response time of warm season GPP to extreme compound dry and hot events was 0.88 months, the spatial distribution of response time was characterized by low in the north and high in the south． The role of protected areas in helping vegetation, especially shrub grasslands, to withstand extreme compound dry and hot events was not apparent．