Climate Change And Its Effect On Vegetation Phenology Over The Tibetan Plateau

Plant phenology is one of the best indicators of climate change which response to terrestrial ecosystem. Understanding and predicting the dynamic changes of the terrestrial ecosystem is of great importance. Based on average temperature, precipitation and other meteorological data as well as GIMMS(NDVI) and SPOT-VGT remote sensing data, climate change and phenological characteristics over the Qinghai-Tibet plateau were analyzed, and phenological responses to climate change were discussed. The conclusions were summarized below:(1) The annual and seasonal, as well as the coldest month and the hottest month mean temperature in most stations over the Tibetan Plateau and its vicinity displayed an increasing tendency passing the significance testing(p<0.05). However, the increasing ranges show a very different spatial pattern with strong warming distributed in the central, eastern and northeast and weak warming distributed in the southeast. In the study area, the temperature trend coefficients, besides spring season, appear increasing tendency with the elevation rise, especially in the Tibetan Plateau. However, it displayed diverse pattern in different elevation gradients. In terms of biological limits of temperature over the Qinghai-Tibet plateau and its surrounding area, ≥0℃、≥5℃、≥10℃ limit temperature starting date advanced, end date delayed, the growing season longer and effective accumulative temperature increased significantly, and the trends have obvious elevation-dependent.(2) The increasing trends of annual precipitation were displayed in most parts over the Qinghai-Tibet plateau during 1971-2012, especially on the South-Central region of the Qinghai-Tibet plateau. Statistical analysis showed that Potential evapotranspiration displayed a decreasing trend and humidity index showed an increasing trend in most parts on the Qinghai-Tibet plateau. With integrating temperature and humidity interannual variability, most of Qinghai-Tibet plateau tends to be warming and wetting.(3) From the multiple average of vegetation phenology on the Tibetan plateau vegetation, start of growth season(SGS), end of growth season(EGS), the length of growth season(LGS), showed a obvious delaying, advancing and shortening from southeast to northwest, respectively. Across the Tibetan plateau, start of growth season(SGS) has undergone a remarkable advance and no significant changes in two periods during the period from 1982 to 2012. End of growth season(EGS) showed no significant change in the overall period. Length of growth season(LGS) displayed the trends of longer, quickly shorten, and then longer. In terms of space change, opposite trends of phenological change were observed between the east and west of the plateau. Start of growth season(SGS) and length of growth season(LGS) on most of East and South-East displayed a significant advancing and longer trends, respectively.(4) In terms of altitude dependence, plant phenology on most of the ecological zones of vegetation showed significant elevation dependent, even though few ecological zones of vegetation displayed a marked fluctuation an altitude of about 3500 m over the sea. Change trend with altitude in end of growth season(EGS) and the length of growth season(LGS) on the eastern part of the Tibetan plateau declined with latitude. Alpine vegetation ahead of trends in start of growth season(SGS) and the length of growth season(LGS) showed a weakening trend as the altitude increase throughout the study area and the various ecological zones.(5) For the species and in site level, start of growth season(SGS) advance with the preseason average temperature raising, however, the relationship between start of growth season(SGS) and preseason rainfall is more complicate. End of growth season(EGS) delay with preseason mean temperature rising. Increasing spring temperature tended to advance the SGS in relatively moist areas.