Changes in regional moisture patterns under the impact of climate change are an important focus for science. Based on the five global climate models (GCMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), this paper projects trends in the area of arid/humid climate regions of China over the next 100 years. It also identifies the regions of arid/humid patterns change and analyzes their temperature sensitivity of responses. Results show that future change will be characterized by a significant contraction in the humid region and an expansion of arid/humid transition zones. In particular, the sub-humid region will expand by 28.69% in the long term (2070-2099) relative to the baseline period (1981-2010). Under 2°C and 4°C warming, the area of the arid/humid transition zones is projected to increase from 10.17% to 13.72% of the total of China. The humid region south of the Huaihe River Basin, which is affected mainly by a future increase in evapotranspiration, will retreat southward and change to a sub-humid region. In general, the sensitivity of responses of arid/humid patterns to climate change in China will intensify with accelerating global warming.
Central Asia (CA) is a continental region that is sensitive to water conditions. Hence, drought has one of the primary effects on the vegetation activities in CA and could vary with climate change. However, it is still unclear how the drought vulnerability of vegetation differs among vegetation types and varies with drought scales in CA. Therefore, this paper studied the drought vulnerability of vegetation in CA from 1982–2015. Droughts were detected by using the standardized precipitation evapotranspiration index (SPEI), and the vegetation activities were represented by the Normalized Difference Vegetation Index (NDVI). Only the areas with no change in vegetation types were analyzed, in order to avoid interference with changes in land use. Results showed that both the duration and intensity of droughts were higher in the central, southwestern, and northeastern CA. The growing season (April–October) NDVI decreased by −0.0095 ± 0.0065 per decade in response to drying trends of 0.21 ± 0.22 unit aridity index per decade in these drought-concentrated regions. Forests and savannas/woody savannas were more vulnerable to drought from July–September, and their vulnerabilities were higher to droughts with longer time scales. Shrublands and grasslands were more vulnerable to drought from April–May and May–September, respectively, and the vulnerabilities during these months were higher for the droughts at 6–12 months scales. Twelve months was the optimal (most vulnerable) drought scale for the shrublands and grasslands and the secondary drought scale for the savannas/woody savannas. Further analysis of the vulnerability of vegetation to 12 months drought found that it generally increased with the increase of the drought magnitude (duration or intensity) to some peak values and then decreased. However, the vulnerability of forests and savannas/woody savannas increased with the drought intensity. Results would help for the drought risk assessment of vegetation in CA.
Changes in the thermal variables of growing degree-days (GDDs) and season have substantial effects on vegetation growth and distribution. The magnitude and spatial distribution of changes in GDDs and season in China during the past century are still uncertain, mainly due to limited daily observations before 1950. In this study, a site-specific multiple linear regression method is developed based on the homogenized daily temperature data of 536 meteorological stations in China for 1960-2010, in order to estimate the annual variables of GDDs and season with only monthly temperature. The method is robust for all stations and interannual variability. Since it could accurately simulate the observed values in 2011, with relative errors of −0.02 and 0.96% for GDDs and growing season (GS), respectively. We simulated the thermal variables based on this method using gridded monthly temperature data for 1901-2010. The interannual variations of simulated GDDs and GS matched well with that of observed values from 1960 to 2010, with high correlation coefficients of 0.99 and 0.92, respectively. Overall, the GDDs and season showed significant (p < 0.01) increasing trends of 11.88 ∘ C·day 10 years −1 and 0.69 day 10 years −1 , respectively, in China as a whole, with the trends increasing from 1991 to 2010. Moreover, all eco-geographical zones showed positive trends during 1901-2010. The GS was more prolonged in northern zones, and degree-days were more increased in north-subtropical, south-subtropical, and tropical zones. However, both the GDDs and season have decreased in the part of Southwest China in the mid-subtropical zone over the past century.
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