Land-use/land cover change (LUCC) is one of the fundamental causes of global environmental change. In recent years, understanding the regional climate impact of LUCC has become a hot-discussed topic worldwide. Some studies have explored LUCC impact on regional climate in specific cities, provinces, or farming areas. However, the quick-urbanized areas, which are highly influenced by human activities, have the most severe land-use changes in developing countries, and their climatic impact cannot be ignored. This study aims to identify the impact of land-use change coupled with urbanization on regional temperature and precipitation in the metropolitan areas of middle and lower reaches of the Yangtze River in China by means of spatial analysis and numeric methods. Based on the exploration of land-use change and climate change during 1988–2008, the impact of land-use transition from non-built-up area to built-up area on temperature and precipitation was analyzed. The results indicated that the land-use conversion has affected the regional temperature with an increasing effect in the study area, while the influence on precipitation was not so significant. The results can provide useful information for spatial planning policies in consideration of regional climate change.
It is widely recognized that land-use/cover change (LUCC) at local, regional, and global scales is one of the crucial driving factors of global climate change [
As an important source of considerable human activities, urbanization causes changes of the land-use/cover over the urban areas [
Although there have been considerable reports of current researches, there is still much unknown about the impact of regional land-use change and urbanization on climate change. As the surface physical, chemical, and biological characters vary greatly across regions, the climatic influences of urbanization and land-use change vary correspondingly [
Since the overall economic reforms in the mid-1980s, China has experienced unprecedented urbanization. Cities in China started to face increasing climate risks [
The metropolitan area in the middle and lower reaches of the Yangtze River is located in 110°15′
Location of the study area and the land cover, 2008.
Mainly located in the Yangtze Plain with part of South Yangtze hills at this latitude, this area belongs to subtropical monsoon climate and subtropical moist monsoon climate region. Owing to moderate rainfall and sunlight, and with abundant amount of water resources, it is a fertile region which is famous for rice cultivation and fishery. It is an important grain producing area in China that plays a key role in the national agricultural industry. In addition, with the obvious locational superiority and favorable industrial and commercial basis, it is also one of the most dynamic economic regions across the country. Demographically, the proportion of urban population to permanent population in the study area also increased at an unprecedented speed since it rose from 19.8% in 1990 to 38.9% in 2000,and then to 49.3% in 2008 in the seven provinces, according to the official statistical data launched by National Bureau of Statistics of China and the involved provinces. At the same time, the regional land-use has changed severely. According to the land-use data extracted from remote sensing images, the total area of cultivated land was 215913 km2 in the late 1980s, which decreased by 13292 km2 to 202621 km2 in the year of 2008. In contrast, the amount of built-up area grew significantly from 19135 km2 to 30008 km2 during this period, which was almost 56.8% more than that in the year of 1988. Except for the water bodies increasing from 36654 km2 to 38528 km2 during 1988–2008, the areas of forestry, grassland, and unused area all slightly decreased. Consequently, it is of great significance to explore the changes of built-up area and their influence on regional climate.
The data used in this paper was collected from the data center of Chinese Academy of Sciences (CAS). It mainly included land-use data and meteorological data of the study area.
Land-use data was extracted from the Chinese subset of the Global Land Cover Characteristics database. The dataset is on the basis of land-use maps at the scale of 1 : 100 000, using the classification system of 6 classes of first level and 25 classes of second level, which relied on interpretation of Landsat TM imagery and ground survey of 2000 with high level of accuracy (about 98.7% of the average degree of interpretation accuracy and 97.6% of comparing the changing patches of land-use between two periods) [
The meteorological data during 1988–2008 was collected from meteorological stations of China Meteorological Administration, including the annual near-surface temperature and annual average precipitation. Based on the observational data acquired from the 756 observation stations distributed across China’s mainland (Figure
Distribution of the meteorological stations used for interpolation within and around the study area.
In order to explore the climatic impact of land-use change during the fast urbanization process, the land-use conversion matrix was first applied to calculate the total amount of conversion from non-built-up area to built-up area in each period of time. It is a fundamental tool in analysis of land-use change [
Land-use conversion matrix for non-built-up area to built-up area.
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CU | FO | GR | WA | UN | ||
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BU |
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Note: CU, FO, GR, WA, UN, and BU refer to cultivated land, forestry, grassland, water bodies, unused land, and built-up area, respectively.
After the land-use conversions and the changes of temperature and precipitation during the study period were evaluated by gird on the ArcINFO platform, numerical analysis was applied to examine their relationship. The parameter of
The research diagram for data handling and analysis is shown in Figure
Research diagram for data handling and analysis.
According to the land cover data, the amount of built-up areas and the conversion from other land cover types could be calculated. The overall area of built-up areas in the metropolitans of the middle and lower reaches of the Yangtze River grew from 19135 km2 to 30008 km2. It can obviously be seen that the main conversion type to built-up area in the region was the conversion from cultivated land (Table
Land-use conversion from non-built-up to built-up area, 1988–2008 (area unit: ten thousand hectares).
Period/land-use conversion | CU2BU | FO2BU | GR2BU | WA2BU | UN2BU | |
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1988–1995 | Area |
147.62 |
16.12 |
1.65 |
12.08 |
0.30 |
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1995–2000 | Area |
134.27 |
12.53 |
0.85 |
7.70 |
0.13 |
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2000–2005 | Area |
161.13 |
18.62 |
1.81 |
11.40 |
0.18 |
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2005–2008 | Area |
170.91 |
26.71 |
2.48 |
19.09 |
0.37 |
Note: the data was calculated according to land-use conversion matrix introduced in Table
Temporally, despite the areas of land cover conversion fluctuating in 1995–2005, the annual conversions of each type in the four periods were speeding significantly except for the conversion of grassland, water bodies, and unused land in 1995–2000. The years of 2005–2008 were the most prominent time that built-up area expanded while occupying other five land covers. During these three years, about 8.28% of the cultivated land and 4.93% of the water bodies were lost and the proportion of built-up area increased from 5.64% in 2005 to 6.24% in 2008. In the year of 1988, however, the percentage of the built-up area was just 3.97% (Figure
Structures of land-use in the middle and lower reaches of the Yangtze River, 1988–2008.
Spatially, most of the built-up areas were distributed in a zigzag manner along with the Yangtze River, with Shanghai metropolitan as the center (Figure
Distribution of built-up area, 1988–2008.
Generally, there were distinct changes in annual average temperature and precipitation in the metropolitans of middle and lower reaches of the Yangtze River from 1988 to 2008. The temperature showed an increasing trend in fluctuations in the study area, with the average temperature rising from 13.3°C in 1988 to 14.1°C in 2008 (Figure
Temporal changes of temperature and precipitation in the study area, 1988–2008.
Changes in spatial distribution of annual average temperature (a) and precipitation (b) in the middle and lower reaches of the Yangtze River, 1988–2008.
At the same time, the annual precipitation in the study area did not show a significant rising or descending trend (Figure
We overlaid the built-up area growth maps with the climate change maps, and the variations of the climate responses to the land-use change showed significant differences in spatial distribution (Figure
Variations of the temperature and precipitation response to land-use conversion from non-built-up to built-up area in periods 1988–1995 (a, e), 1995–2000 (b, f), 2000–2005 (c, g), and 2005–2008 (d, h).
The precipitation in spatial distribution significance across the region was not very obvious compared to the match of temperature with land-use change. The amounts of rainfall increased around Shanghai but decreased in Nanjing and Hefei metropolitans in 1988–1995. Another typical fluctuation was found in Nanchang metropolitan, the north of Jiangxi. The precipitation in this region went up in 1988–1995 and 2000–2005 but sharply cut down in 1995–2000 and 2005–2008 (Figures
The calculation results of
Changes of temperature (a) and precipitation (b) upon land-use conversions from non-built-up to built-up area.
According to the numeric observations, the land-use conversion from non-built-up to built-up areas did not have particular significance on precipitation changes in the study area during 1988–2008 (Figure
In this paper, the impact of the land-use conversion from non-built-up areas to built-up areas on surface temperature and precipitation in the middle and lower reaches of the Yangtze River during 1988–2008 was examined by using spatial and numeric analysis. The results showed that conversion from cultivated land to built-up area was the most important type of land-use change in the region under the rapid urbanization process, which was recognized as “urbanization of land” and concentrated much of focuses from academia. The loss of water bodies was another important source that made the growth of built-ups.
The numeric results indicated that the transitions from non-built-up areas to built-up areas had positive relationship with the rising trend of regional temperature in the study area, but the effects of different conversion types in different periods were varied obviously. All the conversion types except the unused land transition have very similar impact on the changes of temperature. Within the 20-year time period, the upward and downward changing trend of regional temperature was quite in accordance with that where grassland and forestry were changed to built-up areas. These trends were increasing first and then went down significantly. The change of regional climate slightly went up from 0.28°C in 1988–1995 to 0.3°C in 1995–2000, but both the warming effects of conversion from cultivated land and from water bodies on temperature change decreased steadily in this period of time, which kept on going downwards significantly to the bottom of 0.05°C during 2005–2008. As to the regional precipitation, the results did not show much significant impact of land-use conversions from non-built-up areas to built-up areas, even though there were some researches that indicate it could result in either increasing or decreasing effect on precipitation [
Generally, we have only focused on the physical climatic impact of transition from non-built-up to built-up areas in the urbanized area of the middle and lower reaches of the Yangtze River in this paper. The land-use change of transition from non-built-up to built-up areas influences the regional temperature mainly by altering the land surface net radiation and latent heat flux. The results are of great value for the state governments to guide land resource distribution and urbanization policies that respond to the regional climate changes.
Although the precipitation effect was also under consideration in this research, either the positive or negative influence was observed, probably due to the limited annual statistical data or the numeric methods involved. However, trapped by the limitations and the uncertainties of full understanding of the procedure mechanisms, the regional climate change is a very complicated process and there are many other factors that may take effect. As a consequence, it is a rather challenging goal to assess and quantize the climatic effects of land-use change since various biogeophysical and biogeochemical processes interact or even offset each other on the climate change [
The authors declare that there is no conflict of interests regarding the publication of this paper.
This research was cosupported by National Natural Science Foundation of China (Grant no. 41101535), China Postdoctoral Science Foundation funded project (Grant no. 2012M521503), and Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (Grant no. CUG120861). The authors also wanted to thank China National Natural Science Funds for Distinguished Young Scholar (Grant no. 71225005) for data support.