The Change of Growing Season of the Vegetation in Huanghe-Huaihe-Haihe Region and Its Responses to Climate Changes

Using the each ten-day data of NOAA/AVHRR from 1981 to 2000 and adopting the Maximum-Slope method, Curve-Fitting method and stepwise regression, the beginning and ending of the growth season of the vegetations in the Huanghe-Huaihe-Haihe (HHH) region are analyzed. Meanwhile, the pixel by pixel I_NDV map is worked out with typical bands as the sample. Through analyzing the change of green wave and brown wave, the changing rules of vegetation activities and its responses to climate changes in the past 20 years are revealed. The growth season in HHH region starts at the last 10 days of March with I_NDV 0.19604 and ends at the first 10 days of November with I_NDV 0.22899 on average. The tendency is that the growing season has prolonged obviously by starting earlier and earlier, while ending later and later from 1982 to 2000. The average I_NDV for the vegetation in the researched area in the past 20 years is generally increasing, especially in spring. According to the I_NDV map of typical bands as the sample worked out with the pixel by pixel, the green wave changes from south to north during January—July on the band of 116°E, the maximum of I_NDV occurs in August and decreases gradually after September. On the band of 36°N, to the east and nearby 116°E, the I_NDV has two peaks because of two crops a year, which is obviously different from other regions. The two peaks occur in April and August and they become clearer and clearer from 1982 to 2000, especially in agriculture area. However, the two peaks are not obvious to the north of 38.5°N, in the area of Beijing, Tianjin and the mountain areas, and the peak value of early summer is lower than that of autumn. In agriculture area, the peak interval of green wave is broadening with the time passing by, and it's more obviously from south to north. With the time passing by, the green wave of the critical value of the growth season in the area changes from south to north, while the emergence of brown wave prolongs from north to south. According to the stepwise regression result of the every ten-day meteorological data and the I_NDV of the typical sampling areas in the HHH region, the I_NDV of vegetation is closely related to the temperature and precipitation, especially it's more sensitive to the temperature, and the significance of the correlation is 0.01. The prolonging of vegetation growth season is a main response to climate changes of vegetation activities in target areas.