Quantifying effects of different types of droughts on gross primary production in China

Abstract

The increasing impact of drought stress on ecosystems with regard to climate change has received considerable attention, which has been demonstrated to have a time-lag effect on ecosystems. However, the time-lag effect on different types of droughts and gross primary production (GPP) at large regional scales remains unclear. Thus, using the GOSIF GPP product data of solar-induced chlorophyll fluorescence, the meteorological drought index (standardized precipitation evapotranspiration index [SPEI]), and the agricultural drought index (soil moisture deficit index [SMDI]) based on the soil moisture data obtained from the Global Land Data Assimilation System, the time-lag effect of regional drought and GPP and the contribution of drought to GPP variation were analysed in China from 2000 to 2018. Results showed that (1) China's annual GPP increased at an average rate of 9.26 g C m À2 y À1 . With regard to the average rate for each climate zone, the largest increase of 30.44 g C m À2 y À1 was observed in the southern subtropical region, and the smallest increase (4.01 g C m À2 y À1 ) was observed in the Qinghai-Tibetan plateau, with about 53.11% of the regions showing a significant upward trend.In addition, the significantly declining regions were primarily concentrated in urban areas, accounting for about 2.26% of China. (2) SPEI and GPP had an average lag time of 6.28 months, whereas SMDI and GPP had an average lag time of 7.17 months. The comparison demonstrated that SMDI had a greater influence on GPP than SPEI. (3) The average contribution rate of meteorological drought and agricultural drought to the decrease of GPP was 79.37% and 87.06%, and their average contribution rate to the increase of GPP was 39.11% and 50.57%, respectively. This study will provide comprehensive understanding of the effects of drought on carbon and water cycles in terrestrial ecosystems with regard to climate change.