Organic carbon storage in China's urban areas

Abstract

China has been experiencing rapid urbanization in parallel with its economic boom over the past three decades. To date, the organic carbon storage in China's urban areas has not been quantified. Here, using data compiled from literature review and statistical yearbooks, we estimated that total carbon storage in China's urban areas was 577 ± 60 Tg C (1 Tg = 10(12) g) in 2006. Soil was the largest contributor to total carbon storage (56%), followed by buildings (36%), and vegetation (7%), while carbon storage in humans was relatively small (1%). The carbon density in China's urban areas was 17.1 ± 1.8 kg C m(-2), about two times the national average of all lands. The most sensitive variable in estimating urban carbon storage was urban area. Examining urban carbon storages over a wide range of spatial extents in China and in the United States, we found a strong linear relationship between total urban carbon storage and total urban area, with a specific urban carbon storage of 16 Tg C for every 1,000 km(2) urban area. This value might be useful for estimating urban carbon storage at regional to global scales. Our results also showed that the fraction of carbon storage in urban green spaces was still much lower in China relative to western countries, suggesting a great potential to mitigate climate change through urban greening and green spaces management in China.

Figure 1. Carbon storage in four major pools in China's urban areas in 2006 at 95% confidence intervals (i.e., the mean±1.96× standard error).

Figure 2. Carbon storage (Tg) and density (kg C m⁻²) in the provinces (municipalities or autonomous regions) in China's urban areas in 2006 (except Taiwan, Hong Kong and Macao).

Carbon storage is the sum of four pools: vegetation, soils, humans and buildings. The confidence intervals are the same as shown in Figure 1.

Figure 3. Sensitivity of total urban carbon storage to a 10% increase in the each of the input variables.

Figure 4. Relationship between urban carbon storage and urban area (a) or urban carbon density (b) at the provincial level.

The confidence intervals are the same as shown in Figure 1.

Figure 5. Comparisons of the total urban carbon storage and urban areas (a), and the fractions of four major carbon pools (b) between China and the Conterminous United States.