China's LDN progress tracking and its contribution to global LDN（2020）
| Highlights |
| This is one of the first studies to monitor and assess LDN baselines and progress at the globally consistent and spatially comparable national scale, on the basis of the UNCCD framework system and Big Earth Data. A trend of continuous improvement in China's LDN has been observed. Compared to the 2015 baseline, the net restored land area increased by 60.30% by 2018 and accounted for approximately 1/5 of the world's total, making it the number one contributor to global LDN. |
Background
The vision of SDG Target 15.3, "to achieve a land degradation-neutral world", is one of the key targets of the SDGs (United Nations, 2015). However, the definition of land degradation was a matter of considerable debate at one point, primarily as a result of divergence of opinion over the processes, causes, characteristics and effects of degradation. The lack of consensus is responsible for the huge discrepancies in the results of different land degradation assessments (4%-74% globally) and has seriously undermined the international community's ability to understand, at the scientific level, and accurately assess the real state of global/regional land degradation, thus hampering practical actions against, and effective management of, such degradation.
To tackle those challenges, the UN Inter-agency and Expert Group on SDGs (IAEG-SDGs) has defined a framework of indicators for Indicator 15.3.1 monitoring, including changes in land cover, land productivity and soil organic carbon, on the basis of which the United Nations Convention to Combat Desertification (UNCCD) and Group on Earth Observations Land Degradation Neutrality (GEO-LDN) Program have reviewed the methodologies for data selection and analysis and developed a Good Practice Guidance SDG Indicator 15.3.1 (Neil et al., 2019). However, global-scale, spatially disaggregated baselines and progress data for SDG 15.3.1 remain absent as a direct consequence of the unavailability of relevant data, methodological uncertainties and political sensitivities. Nonetheless, globally comparable and spatially disaggregated SDG 15.3.1 baselines and assessment findings, consistent with the UN 15.3.1 monitoring indicator framework, remain important from the perspective of Science, Technology and Innovation (STI) for SDGs.
In 2019, the CASEarth Project conducted a global land degradation baseline assessment for the 2000-2015 timeframe and developed a national-scale LDN report. This assessment provides a reliable baseline for tracking the progress of SDG 15.3.1 and is an indispensable frame of reference for the assessment of the overall progress towards the realization of SDG 15.3. Taking advantage of these resources and guided by the UNCCD LDN monitoring framework, in 2020, CASEarth Project proceeded to monitor and assess global SDG 15.3.1 progress (against the 2015 baseline), focusing on China's LDN dynamics and its contribution to global LDN.
Data used
① Data from SDG 15.3.1 assessment for 2000-2015 (Guo et al., 2019).
② Global land cover in 2015 and 2018 at 300 m spatial resolution from European Space Agency.
③ 2000-2018 Enhanced Vegetation Index (EVI) data at 500 m spatial resolution.
④ Global soil organic carbon, International Soil Reference and Information Centre (ISRIC) SoilGrid 250, at 250 m spatial resolution.
⑤ RESOLVE Ecoregions 2017.
⑥ Bulletins of Status Quo of Desertification and Sandification in China (2005, 2011 & 2015).
Method
Based on the assessed baselines for 2000-2015, a dynamic assessment for 2015-2018 was conducted against the three sub-indicators of the UN's IAEG-SDGs indicator system, i.e. land cover, land productivity and soil organic carbon. The land cover conversion matrix for 2015 and 2018 was used for land degradation and improvement assessment. Dynamic assessment of land productivity was made by analyzing the 2004-2018 trends, with significant increase, significant decrease and other changes defined as restored, degraded and stable respectively. Regarding soil organic carbon, assessment was done by correlating land cover changes with soil carbon changes as proposed by the Intergovernmental Panel on Climate Change (IPCC), thus identifying three levels of soil carbon: degraded, restored and stable. The 2015-2018 dynamics were assessed by combining the three sub-indicators of land cover, land productivity and soil carbon, on the principle that degradation under any of the sub-indicators constitutes degradation. The findings so arrived are then combined with 2015 baseline to get the progress of global land degradation.
Results and analysis
The dynamics of global land degradation from 2015 to 2018 are shown in Figure 1. Statistical analysis indicates that the overall trend of SDG 15.3.1 between 2015 and 2018 was positive, but there were certain spatial variations. China saw a steady improvement in LDN from 2015 to 2018 and its net restored area of degraded land increased by 60.30%, accounting for 17.76% of the global total in 2018 (the highest in the world), which is very similar to 18.24% in the base year of 2015, making China the largest contributor to global LDN.
According to the data on land degradation dynamics in China from 2015 to 2018 (Fig. 2), 29.16% of the land was restored, 1.56% degraded and 69.28% stable. Of the land whose status of degradation changed, compared to the 2015 baseline, 41.96% enjoyed continuous improvement, 28.05% went from stable to restored, 1.21% suffered continuous degradation and 2.32% went from stable to degraded. It is worth noting for the degraded land in 2015, 4.62×104 km2 became more degraded, but 8.02×104 km2 of land was reversed in 2018, pointing to China's success in land degradation recovery. The status of degradation also varied among different types of land cover. Current degradation was mainly observed in cropland and grassland. Judging by the ratios of degradation versus improvement, China's woodland was the best performer in ensuring the LDN target, followed by cropland, which had a lower degradation-to-improvement ratio despite some degradation and was therefore under no great pressure in ensuring the LDN target. However, grassland and barren land were at risk, with their current degradation-to-improvement ratios at 24.04% and 39.73% respectively. In view of the adverse effects of climate change, grassland and barren land warrant focused attention in the future.
Outlook
Guided by the UNCCD Good Practice Guidance SDG Indicator 15.3.1 and using internationally shared datasets, this study established tracking and monitoring of Indicator 15.3.1, assessed China's LDN trend and identified the contribution of China's LDN to global LDN based on globally consistent and comparable data, thus providing important informational support for the attainment of Indicator 15.3.1.
The methodology used in the study is applicable on a global scale, emphasizing compliance with the IAEG-SDGs indicator system, and the findings are globally consistent and comparable. These findings, therefore, do not reflect country or region-specific SDG Target 15.3-related figures, as the degradation processes and indicator system considered at this scale are more complex. This does not mean, however, that the findings of this study have no significant referential value for understanding the progress toward Target 15.3 at national and regional levels. The state and trend of LDN in China examined through the lens of Big Earth Data are consistent with the conclusion of the National Forestry and Grassland Administration that "since 2004, the area of both desertification and sandification in China has declined for three consecutive monitoring periods and China has achieved zero growth in desertified land".
It is worth noting that the assessment of improvement and degradation strictly corresponds to the time periods under assessment (UNCCD-LDN scientific framework), so there are cases where the assessment findings indicate that improvement is under way but the land is actually in the status of degradation. Therefore, while we take note of the positive progress in LDN, we must be cognizant of the considerable challenges facing China in land degradation. In the future, science-informed conservation and management should be strengthened and the LDN monitoring methodology and capacity enhanced, with a view to achieving a higher level of LDN by 2030.