Spatiotemporal Characteristics of NPP Changes in Frozen Ground Areas of the Three-River Headwaters Region, China: A Regional Modeling Perspective

Abstract

Permafrost degradation triggered by climate warming can disturb alpine ecosystem stability and further influence net primary productivity (NPP). Known as the “water tower of China”, the Three-River Headwaters Region (TRHR) on the eastern Qinghai-Tibet plateau (QTP), is characterized by a fragile alpine meadow ecosystem underlain by large areas of unstable permafrost and has been subject to rapid climate change in recent decades. Despite some site-specific studies, the spatial and temporal changes in NPP in the different frozen ground zones across the TRHR associated with climate change remain poorly understood. In this study, a physically explicit Noah land surface model with multi-parameterization options (Noah-MP) was employed to simulate NPP changes on the TRHR during 1989–2018. The simulation was performed with a spatial resolution of 0.1° and a temporal resolution of 3h, and validated at two sites with meteorological and flux observations. The results show that the average NPP was estimated to be 299.7 g C m−2 yr−1 in the seasonally frozen ground (SFG) zone and 198.5 g C m−2 yr−1 in the permafrost zone. NPP in the TRHR increased at a rate of 1.09 g C m−2 yr−2 during 1989–2018, increasing in 1989–2003 and then decreasing in subsequent years. The NPP in permafrost area increased at a rate of 1.43 g C m−2 yr−2 during 1989–2018, which is much higher than the rate of change in NPP in the SFG area (0.67 g C m−2 yr−2). Permafrost degradation has complicated ecosystem implications. In areas where permafrost degradation has occurred, both increasing and decreasing changes in NPP have been observed.

Dynamic response and adaptation of grassland ecosystems in the Three-River Headwaters Region under changing environment: a review

“…From 1982 to 2014, the growing season temperature in the TRHR region showed the most significant upward trend in the northwest and southeast (Chen et al, 2020). Precipitation has increased slightly in the TRHR region in recent decades (Jin et al, 2022, Li et al, 2013a, Hu et al, 2022, Bai et al, 2020). The regional differences in precipitation increase are obvious.…”

“…Over the past 60 years, the TRHR has experienced significant warming, and the rate is higher than that of the global and overall Qinghai-Tibet Plateau (Bai et al, 2020, Jin et al, 2022, Hu et al, 2022, Li et al, 2013a, Bardgett et al, 2013. Warming varies by season and region (Liang et al, 2013).…”

“…Climate warming has also caused serious environmental problems. For example, the TRHR region has reported a significant reduction in the area of permafrost in recent decades, and those areas where the permafrost disappears consistently show the highest temperature increases, resulting in a thinning of permafrost thickness and eventual disappearance (Hu et al, 2022).…”

“…Studies have shown that climate warming is beneficial to healthy alpine ecosystems, but in degraded meadows at TRHR, rising temperatures exacerbate degradation by exacerbating degradation-induced droughts (Xue et al, 2017), thereby inhibiting meadow plant growth. In addition, the degradation of permafrost, linked to rising temperatures, leads to a drop in the groundwater table, which in turn inhibits the growth of shallow-rooted plants, leading to the degradation of alpine meadows (Song et al, 2018, Hu et al, 2022. The long-term effect of the deepening of the ecological groundwater level will promote the change of vegetation species and the regional evolution of plants.…”

“…The increase in air temperature makes the soil temperature rise and the permafrost thaw. Soil moisture in the root zone infiltrates due to the thawing of the permafrost, which eventually leads to poor soil moisture status (Hu et al, 2022).…”