Abstract
The terrestrial ecosystem productivity (hereafter, TEP) is a key index of global carbon cycles and a fundamental constraint of carbon sequestration capacity, and also an important measure of ecosystem services and food security. However, the TEP has been significantly affected by the long-lasting droughts. Identifying the spatial relationship between droughts and the TEP is crucial for enhancing ecosystem services in China. Here the net primary production (hereafter, NPP) derived from the Carnegie-Ames-Stanford Approach model (CASA-NPP) and two drought indices, namely the Standard Precipitation Index (hereafter, SPI) and the Standard Precipitation Evaporation Index (hereafter, SPEI), are used to examine the spatial relationship between droughts and the NPP in China for the period of 1982-2012. Our main results have shown that: (1) China’s annual NPP has increased slowly from 3.82 to 4.35 PgC per year (hereafter, PgC/yr), while droughts have become much severer from 1982 to 2012; (2) On the 3-month timescale, the NPP in arid and semi-arid ecosystems has decreased at a rate of 1.28 TgC per month with per “unit” decrease in the drought index (indicating drier conditions). (3) Overall, the NPP in China has increased 5.71 TgC per month with per “unit” increase in the drought index (indicating wetter conditions); The contribution of this NPP increase is mainly from forests and farmlands; (4) The SPEI is a relatively more effective and sensitive index in representing China’s droughts. In southern China, the lagging period for the NPP response to droughts is about 3-month, while a 6-month lagging period is found in the arid and semi-arid ecosystems in northern China.
Highlights
The terrestrial ecosystem productivity is the fundamental indicator for ecosystem services, and an integrated component of global carbon cycles, biodiversity, and regional food security (e.g., Piao et al, 2005; Zhu and Pan, 2007; Luo et al, 2019) and is generally controlled by many interplaying factors (Li et al, 2018; Liu et al, 2019)
Many studies have shown that long-lasting droughts can significantly constrain vegetation activity and reduce the net primary production (e.g., Zhao and Running, 2010; Mk et al, 2011; Pei et al, 2013; Hou et al, 2014; Lai et al, 2018; Anderegg et al, 2019; Li et al, 2019a)
Our NPPs using the CASA model are generally higher than those derived from the MODIS products (MOD17 A3), which are produced by the Numerical Terradynamic Simulation Group (NTSG) of University of Montana (UMT) using MOD17 algorithm (Asrar et al, 1992; Figure 2)
Summary
The terrestrial ecosystem productivity (hereafter, TEP) is the fundamental indicator for ecosystem services, and an integrated component of global carbon cycles, biodiversity, and regional food security (e.g., Piao et al, 2005; Zhu and Pan, 2007; Luo et al, 2019) and is generally controlled by many interplaying factors (Li et al, 2018; Liu et al, 2019). Under the threats of global warming, both the broadness and devastation of droughts and floods will continue to intensify, which will greatly affect the TEP, especially under long-lasting droughts (e.g., Yu et al, 2007; Doughty et al, 2015; Lei et al, 2015; Huang et al, 2016; Su et al, 2018; Gherardi and Sala, 2019; Xu et al, 2019). Droughts are Impacts of Drought on the TEP Changes a comprehensive and frequently occurred natural disaster, involving both precipitation and temperature changes, and they control the soil moisture and vapor pressure deficit that will greatly influence the plant growth (Eamus et al, 2013). According to the “China Flood and Drought Disaster Bulletin” (2016), on average, 2.17 × 105 km farmlands were influenced by droughts each year from 1950 to 2007, resulting in a loss of nearly 15.8 billion kilograms of grain, accounting for 60% of the total loss caused by all-natural disasters (MWRPRC, 2016)
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