3.2.2. Characteristics of Spatial Changes in China’s Dry-Wet Climate Regions
In order to study the characteristics of dry-wet climate changes in different regions of China, we calculated the proportions of different dry and wet climate zones in seven regions, including northwest China, north China, northeast China, east China, central China, south China, and southwest China to the whole area of the region (
Table 4) in the periods of from 1981 to 2010, and analyzed the areas’ linear trend in each dry and wet climate zones in the past 60 years (
Table 5). The following is an analysis of evolutionary characteristics for different dry and wet climate zones.
The extreme arid zones in China cover an area of about 1,222,100 square kilometers, accounting for about 12.88% of the country’s land area. It is mainly located in the center and west of northwest China, the west of North China (generally in the western part of Inner Mongolia), and the west of southwest China (generally in the western part of Tibet). Northwest China has the largest extreme arid zone, accounting for 34.51% of the region. In the past 60 years, the extreme arid zones in China have shown a significant decrease, with an average reduction of 147,800 square kilometers (about 1.56%) every 10 years. The area in northwest China has the largest decrease, with an average reduction of 107,000 square kilometers (about 3.56%) every 10 years. The extreme arid zones in southwest China have also decreased significantly, with an average decrease of 33,200 square kilometers (about 1.43%) every 10 years. The significance test shows that the changes of extreme arid zones in northwest and southwest China passed the 99% confidence level. The extreme arid zones in north China have also decreased but not past the significance test.
China’s arid climate zones cover an area of about 1,850,400 square kilometers, accounting for about 19.5% of the country’s land area. The zones are mainly located in the northwest, north and southwest China, accounting for 36.19%, 23.39%, and 17.42% of the region’s land area, respectively, and there are also arid climate zones in northeast China and other places, but relatively small in proportion. In the past 60 years, the area of arid climate zones in northwest and southwest China has shown an increasing trend, increasing by 1.84% and 0.64%, respectively. The significance test in northwest China has passed the 99% confidence level. The main reason is due to the transition from an extreme arid climate to an arid climate. The areas of arid climate zones in north, east and central China show a decreasing trend, but the changes are not significant.
China’s sub-arid climate zones cover an area of about 1,848,300 square kilometers, accounting for 19.48% of the country’s land area. It is mainly located in north, northeast, southwest, and northwest China, accounting for 51.05%, 18.19%, 16.56% and 15.15% of the region’s land area, respectively. Among them, the area of sub-arid zones in north China is the largest, accounting for more than half of the region’s land area. In the past 60 years, the area of sub-arid zones in northwest and southwest China has shown an increasing trend, increasing by 0.94% and 0.01%, respectively. That in northwest China has increased by 28,400 square kilometers every 10 years, passing the 99% confidence level. The area of sub-arid zones in northeast, north, east and central China has shown a linear decrease, with an average decrease of 2.5%, 0.66%, 0.95%, and 1.02%, respectively, every 10 years. Among them, northeast China has passed the 99% confidence level, and central China has passed the 95% confidence level, while other areas have failed the test.
China’s sub-humid climate zones cover an area of about 1,507,100 square kilometers, accounting for about 15.88% of the country’s land area. It is mainly located in the northeast, southwest, central, north, east and northwest China, accounting for 48.11%, 17.51%, 15.24%, 14.95%, 13.67% and 9.24% of the region’s land area, respectively, of which the sub-humid zones in northeast China are the largest in area. In the past 60 years, the area of sub-humid zones in northwest China has shown an increasing trend, with an average increase of 28,400 square kilometers (about 0.94%) every 10 years, passing the 99% confidence level. That in north China has also shown an increasing trend, with an average increase by 0.67% every 10 years, but failed the significance test. The area of sub-humid zones in northeast, east, central, south, and southwest China has shown a decreasing trend, with an average decrease of 2.33%, 0.64%, 0.47%, 0.38%, and 0.06%, respectively, every 10 years, of which the northeast China has the most significant decrease, passing the 99% confidence level, while other regions have failed the test.
Most areas of southeast China belong to the humid climate zone, covering an area of about 2,715,900 square kilometers. It has the largest proportion in the dry-wet climate zone, accounting for 28.63% of China’s total land area, mainly located in the south, central, east, southwest and northeast China. The area of humid zones in south China is the largest, exceeding 80% of the land area of this region. In the past 60 years, the area of humid climate zones has increased by an average of 39,400 square kilometers (about 0.42%) every 10 years, but is still not significant. That in the northeast, north, northwest and southwest China has shown an increasing trend, with an average increase of 4.67%, 0.59%, 0.35%, and 0.53%, respectively, every 10 years. The increase in northeast China is the most significant, passing the 99% confidence level. The area of humid climate zones in south, central and east China has shown a decreasing trend, with an average of 2.94%, 0.91%, and 1.62% every 10 years, of which south China has passed the 95% confidence level.
The area of China’s extreme humid climate zones is about 343,400 square kilometers, around 3.61% of China’s land area. It is mainly located in the east, south and central China, accounting for 22.77%, 16.25% and 9.93% of the area, respectively. Over the past 60 years, the area of extreme humid zones in the east, south and central China has increased significantly, with an average increase of 3.27%, 3.36%, and 2.47%, respectively, every 10 years. Among them, east China has passed the 99% confidence level, while south and central China have passed the 95% confidence level. Although the area of extreme humid climate zones in other regions of China is also increasing, but the increase is relatively small and has not passed the significance test.
The characteristics of dry-wet climate change in different regions of China are obvious (
Table 5). In northwest China, the area of extreme arid zones has decreased most significantly. In the 2010s, the area of extreme arid zones decreased by about 660,000 square kilometers compared to the 1960s. However, in northwest China, the areas of other climate zones have shown increasing trends with different ranges and the area increase of arid, sub-arid, and sub-humid zones has passed the 99% confidence level. In north China, the area of arid climate zones has shown a decreasing trend, and that of humid climate zones has shown an increasing trend, but the confidence level has not passed the significance test. In northeast China, the area of sub-arid and sub-humid climate zones has decreased significantly, and that of sub-humid zones has increased significantly, indicating that the climate humidification has become more significant in this area. The area of extreme humid climate zones in east, central and south China has increased significantly, indicating that the southeast part of China has also become more humid. In southwest China, the area of extreme arid zones has decreased significantly, mainly in west Tibet, and its area of sub-humid zones has decreased slightly, and the areas of other climate zones have increased, but not significantly. From the above analysis, the climate in China’s different regions all show a tendency to become more humid with different ranges.