In this paper, we analyzed interannual variations of normalized difference vegetation index (NDVI) and their relationships with climatic variables (temperature and precipitation) and human activity in China between 1982 and 1999. Monthly and seasonal NDVI increased significantly at both the country and biome scales over the study period. NDVI shows the largest increase (14.4% during the 18 years and a trend of 0.0018 yr−1) over 85.9% of the total study area in spring and the smallest increase (5.2% with a trend of 0.0012 yr−1) over 72.2% of the area in summer. The NDVI trends show a marked heterogeneity corresponding to regional and seasonal variations in climates. There is about a 3‐month lag for the period between the maximum trend in temperature (February) and that in NDVI (April or May) at the country and biome scales. Human activity (urbanization and agricultural practices) also played an important role in influencing the NDVI trends over some regions. Rapid urbanization resulted in a sharp decrease in NDVI in the Yangtze River and Pearl River deltas, while irrigation and fertilization may have contributed to the increased NDVI in the North China plain.

[1] We examined the spatial and temporal variation in precipitation observed daily at 272 weather stations operated by the China Meteorological Administration from 1960 to 2000. We found that precipitation in China increased by 2% over that period, while the frequency of precipitation events decreased by 10%. Seasonally, precipitation increased in winter and summer but decreased in spring and fall. Regional differences also appeared: Precipitation decreased in the North China Plain and north central China, showed almost no change in southwest China, and increased in China's five other climatic regions. Only the increase in northwest China, however, was statistically significant ( p = 0.05). For China as a whole and its eight climatic regions these changes in precipitation can be attributed mostly to changes in the frequency and intensity of heavy precipitation events. Nationwide, the increased frequency of heavy precipitation events contributed 95% of the total increase of precipitation in that category. At the same time, there were fewer light precipitation events, accounting for 66% of the national reduction in precipitation frequency. In seven of the eight climatic regions, changes in frequency accounted for most of the changes in the amounts of precipitation from heavy precipitation events; changing intensity accounted for a larger share in the southwestern region. The frequency of precipitation has decreased in all seasons and all regions except northwest China. The increasing proportion of precipitation delivered by heavy rainfall events and the decreasing trend of light precipitation events have potentially serious ramifications for flood control and vegetation production, especially for the non-irrigated croplands in the arid and semiarid areas of China.

In analyzing daily climate data from 305 weather stations in China for the period from 1955 to 2000, the authors found that surface air temperatures are increasing with an accelerating trend after 1990. They also found that the daily maximum (Tmax) and minimum (Tmin) air temperature increased at a rate of 1.27° and 3.23°C (100 yr)−1 between 1955 and 2000. Both temperature trends were faster than those reported for the Northern Hemisphere, where Tmax and Tmin increased by 0.87° and 1.84°C (100 yr)−1 between 1950 and 1993. The daily temperature range (DTR) decreased rapidly by −2.5°C (100 yr)−1 from 1960 to 1990; during that time, minimum temperature increased while maximum temperature decreased slightly. Since 1990, the decline in DTR has halted because Tmax and Tmin increased at a similar pace during the 1990s. Increased minimum and maximum temperatures were most pronounced in northeast China and were lowest in the southwest. Cloud cover and precipitation correlated poorly with the decreasing temperature range. It is argued that a decline in solar irradiance better explains the decreasing range of daily temperatures through its influence on maximum temperature. With declining solar irradiance even on clear days, and with decreases in cloud cover, it is posited that atmospheric aerosols may be contributing to the changing solar irradiance and trends of daily temperatures observed in China.

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The timing, length, and thermal intensity of the climatic growing season in China show statistically significant changes over the period of 1955 to 2000. Nationally, the average start of the growing season has shifted 4.6-5.5 days earlier while the average end has moved 1.8-3.7 days later, increasing the length of the growing season by 6.9-8.7 days depending on the base temperature chosen. The thermal intensity of the growing season has increased by 74.9-196.8 growing degreedays, depending on the base temperature selected. The spatial characteristics of the change in the timing and length of the growing season differ from the geographical pattern of change in temperatures over this period; but the spatial characteristics of change in growing degree-days does resemble the pattern for temperatures, with higher rates in northern regions. Nationally, two distinct regimes are evident over time: an initial period where growing season indicators fluctuate near a base period average, and a second period of rapidly increasing growing season length and thermal intensity. Growing degree-days are highly correlated with March-to-November mean air temperatures in all climatic regions of China; the length of the growing season is likewise highly correlated with March-to-November mean air temperatures except in east, southeast and southwest China at base temperature of 0• C and southeast China at base temperature of 5• C. The growing season start date appears to have the greater influence on the length of the growing season. In China, warmer growing seasons are also likely to be longer growing seasons.

China has seen a decline in recorded precipitation events over 1960-2000. We find that this decline is mainly accounted for by the decrease of light precipitation events, those with intensities of 0.1-0.3 mm/day. The annual number of light precipitation events drops off remarkably around 1978 and decreases rapidly until 1985. Trace precipitation events (precipitation noted but measuring <0.1 mm/day) decrease abruptly from 1982 through the end of the period. Meanwhile, the annual frequency of precipitation events with intensities above 0.3 mm/day shows almost no change for the same period. The analysis uses daily data from 272 stations distributed across China. We note regional and seasonal differences in the rates of change of different intensities of precipitation events. With almost no change in the frequency of precipitation events of 0.4-0.6 and 0.7-0.9 mm/day during the same period, it is difficult to attribute the abrupt decreases to inhomogeneities of the precipitation data. The temporal pattern of light precipitation events is similar to those observed for solar irradiance and total cloud cover, suggesting that there may be some connections between these climatic variables. Declines in solar irradiance and total cloud cover along with increased aerosol loading may have contributed to the abrupt decrease of these light precipitation events. However, light and trace precipitation events display different spatial and temporal patterns of change, complicating this explanation.

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