Historical Changes of High Temperature, Heat Waves, and Drought in Ecological Fragile Zones in China

High temperatures (HT), heat waves (HW), and droughts are the most important extreme weather and climate events affecting terrestrial ecosystems. Previous research focused on their changes in the whole of China, regions based on geographical divisions, or a single region in China. The historical changes of the extreme events in ecologically fragile zones (EFZs) in China still remain under debate. This study analyzes the spatial−temporal changes in HT, HW, and drought in the EFZs in China between 1980 and 2014 using observational daily maximum surface air temperature and monthly standardized precipitation evapotranspiration index datasets. It has been revealed that the frequency of both HT and HW increased between 1980 and 2014 over nearly all EFZs in China, and the long-term trends of HT and HW exhibited similar spatial patterns, with a significant increase in the central and western EFZs of northern China and the eastern EFZs of southern China. The area fraction with a significant increase was the highest in the southwest karst rocky desertification EFZs and the lowest in the southern agriculture and pasture EFZs. All EFZs showed increasing HT and HW frequency except for the southern agriculture and pasture EFZs, and the trends were significant except for the northern agriculture, pasture, forest, and grassland EFZs. In addition, after the mid-1990s, the frequency and interannual variability of HT and HW in the northern EFZs increased rapidly. Moreover, the EFZs in eastern China had a trend of dryness and increased drought events, while the rest of the EFZs had a trend of wetness and decreased extreme drought events, where only the trend of drought events in the southwest karst rocky desertification EFZ is significant.