Research papersSpatial patterns of vegetation carbon sinks and sources under water constraint in Central Asia
Introduction
The ongoing increase in carbon dioxide (CO2) concentrations around the world is causing an unrelenting rise in global average temperature. This situation is leading to a wide array of environmental problems that seriously affect the survival and development of human beings. The terrestrial ecosystem carbon cycle is an important part of the overall global carbon cycle (David, 1995, Schimel et al., 2001, Mitchard, 2018). CO2 in the atmosphere is fixed as organic compounds through the photosynthesis of vegetation, which is particularly vulnerable to climate change and human activities (Lu et al., 2017). Most studies on vegetation carbon sequestration focus on the estimation of net primary production (NPP) of vegetation or net ecosystem productivity (NEP) of large-scale forest and grassland ecosystems (Yang et al., 2010), aiming to provide guidance for greenhouse gas emission mitigation policies.
The dramatic spike in global temperature that occurred at the turn of the present century has had a considerable impact on the global water cycle and vegetation dynamics. The temperature in Central Asia also experienced the same sudden sharp increase nearly 20 years ago, and since that time has been in a state of high volatility (Fig. 1c), making the last decade the warmest period on record (Li et al., 2015, Chen et al., 2016). How will regional droughts change as a consequence of ongoing global warming? Despite the smaller overall trend of Palmer Drought Severity Index (PDSI), there is a switch to a drying trend over the past decade (Fig. 1b). Drought and water scarcity are key words for regional management in water-stressed regions (Van Loon and Van Lanen, 2013, Li et al., 2017). Because most dryland soil is relatively infertile and the vegetation cover is sparse, dryland ecosystems are substantially more fragile. Given this volatility, what are the expectations for changes in ecosystems, and what are the changes and potential attributions of the ecosystem carbon cycle? The influence of climate change and land use/cover change on the terrestrial ecosystem carbon cycle has not yet been fully investigated in Central Asia. To date, very little observational evidence exists to demonstrate either the magnitude of the change or the transformation processes of NEP in relation to the various conditions of climate and land types.
Central Asia, which consists of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan, is located in a key area of the Silk Road Economic Belt (Fig. 1). Deserts, semi-deserts and grasslands account for most of the region, with the Karakum, Kizilkum and Taklimakan deserts exceeding 30 × 104 km2 in total land coverage. The increasing water crisis in this region poses a significant potential threat to the construction of the Silk Road Economic Belt (Li et al., 2016***). Because the arid region of Central Asia is characterized by low vegetation coverage, the rising temperatures and increased evaporation accelerate the soil water dissipation, causing the shallow roots of desert plants to weaken and die. In addition to damaging ecosystems, the disappearance of water resources can hinder economic development and social stability in the region, and even have a noticeable impact on neighboring countries.
It is worth noting that routine surveillance programs ceased to operate following the dissolution of the Soviet Union during the 1980s and 1990s. Though currently lacking, research on recent dynamic climate change impacts on regional ecological environments is highly important for maintaining both the ecological stability and economic sustainable development of the Silk Road Economic Belt.
Section snippets
Data
The monthly grid data of the temperature and precipitation series from 2000 to 2015, with a spatial resolution of 0.5°, were collected from the Climatic Research Unit (http://www.cru.uea.ac.uk/data/). To calculate the PET, we collected the daily data of air temperature, maximum temperature, minimum temperature, pressure, relative humidity, U-wind, V-wind, net shortwave radiation and net longwave radiation from the NCEP/NCAR Reanalysis 1 (http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.
Results
In previous studies, it was generally asserted that positive net ecosystem productivity values (NEP ≥ 0) indicate carbon sinks, while negative NEP values (NEP < 0) indicate carbon sources (White et al., 1999, Luyssaert et al., 2008). Forest land is the largest “carbon pool” in the terrestrial ecosystem, generally considered a high carbon sink area (Sorensen, 1993, Thompson et al., 1996, Luyssaert et al., 2008). When NEP ≥ 300 gC m−2 a−1, almost all the land types in this area are forest land,
Discussions
Numerous models based on remote sensing have been developed to investigate CO2 exchange between the biosphere and atmosphere at regional, continental, and global scales (Wylie et al., 2007, Phillips and Beeri, 2008, Turner et al., 2004). Some scholars integrated hydro-biogeochemical simulations by linking SWAT examined the impacts of climate change on water-carbon coupling cycles (Zhao et al., 2018, Zhao et al., 2020). However, the biogeochemical models are often complex because they require
Conclusions
In this paper, the spatial distribution patterns of carbon sources/sinks of vegetation in Central Asia was studied in detail. The preliminary conclusions are as follows:
- (1)
The distribution of carbon sources and sinks shows obvious vertical zonal characteristics. Most carbon sources areas are mainly distributed in south-central Kazakhstan as well as parts of Uzbekistan and Turkmenistan. Carbon sink areas are mainly distributed in northern Kazakhstan, Kyrghyzstan and Tajikistan. Due to the flatness
CRediT authorship contribution statement
Zhi Li: Formal analysis, Writing - original draft. Yaning Chen: Writing - review & editing. Qifei Zhang: Data curation. Yang Li: Data curation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The research is supported by the National Key Research and Development Program (2019YFA0606902) and the Key Research Program of the Chinese Academy of Sciences (ZDRW-ZS-2019-3). The authors gratefully acknowledge the Youth Innovation Promotion Association of the Chinese Academy of Sciences (No. 2018480).
Author contributions.
Dr. Zhi Li and Prof.Dr. Yaning Chen conceived and wrote the main manuscript text, Dr. Qifei Zhang and Yang Li unified the spatio-temporal resolution of some data from
References (37)
Indonesian peat swamp forests and their role as a carbon sink
Chemosphere
(1993)- et al.
Climate change impacts on ecosystems and the terrestrial carbon sink: a new assessment
Global Environ. Change
(1999) - et al.
Adaptive data-driven models for estimating carbon fluxes in the Northern Great Plains
Remote Sens. Environ.
(2007) - et al.
Predicting the climate change impacts on water-carbon coupling cycles for a loess hilly-gully watershed
J. Hydrol.
(2020) - et al.
Climatic and hydrologic controls on net primary production in a semiarid loess watershed
J. Hydrol.
(2019) - et al.
Spatiotemporal features of the hydro-biogeochemical cycles in a typical loess gully watershed
Ecol. Indic.
(2018) - et al.
Terrestrial gross carbon dioxide uptake: global distribution and covariation with climate
Science
(2010) - et al.
Drought in the Southern United States over the 20th century: variability and its impacts on terrestrial ecosystem productivity and carbon storage
Clim. Change
(2012) - et al.
Changes in central Asia’s water tower: past
Present Fut. Sci. Rep-UK
(2016) - et al.
Understanding the long-term spatial dynamics of a semi-arid grass-shrub steppe through inverse parameterization for simulation models
Oikos
(2012)
Terrestrial ecosystems and the carbon cycle
Global Change Biol.
Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis
Ecol. Let.
Inversion of net primary productivity in the arid region of Northwest China based on various regressions
Resour. Sci.
Carbon dioxide budget in a temperate grassland ecosystem
J. Geophys. Res.
Multivariate assessment and attribution of droughts in Central Asia
Sci. Rep.
Climate change in arid environments: revisiting the past to understand the future
Prog. Phys. Geog.
Is net ecosystem production equal to ecosystem carbon accumulation?
Ecosystems
Cited by (38)
Spatial characteristics and trade-offs of ecosystem services in arid central asia
2024, Ecological IndicatorsEvaluating surface soil moisture characteristics and the performance of remote sensing and analytical products in Central Asia
2023, Journal of HydrologyCitation Excerpt :Central Asia (CA) is the largest arid region in Eurasia, with vulnerable ecosystems that are sensitive to climate change (Chen et al., 2020; Deng et al., 2020a; Yuan et al., 2021), particularly to water cycle variability (Hu et al., 2019; Shi et al., 2021; Zheng et al., 2019). CA is becoming a hotspot for focusing on carbon and water cycles (Chen et al., 2019; Li et al., 2020) and extreme climate events such as droughts (Guo et al., 2018a; Guo et al., 2019) and floods (Zheng et al., 2021). Due to the lack of sufficient in situ observations, gridded SM data have more potential for application to ecological monitoring in CA.
Desertification process and its effects on vegetation carbon sources and sinks vary under different aridity stress in Central Asia during 1990–2020
2023, CatenaCitation Excerpt :Our modeling analysis suggests that carbon sink regions were mainly located in northern Central Asia and the edge of the Tianshan Mountains, while most parts of southwestern and eastern Central Asia acted as carbon sources during 1990–2020. This result was supported by Han et al. (2016) and Li et al. (2020) in their recent studies. Furthermore, results also showed that dry sub-humid and semi-arid areas were major carbon sink areas in Central Asia.