Spatial-temporal variations of lake ice phenology in the Hoh Xil region from 2000 to 2011

Lake ice phenology, i.e. the timing of freeze-up and break-up and the duration of the ice cover, is regarded as an important indicator of changes in regional climate. Based on the boundary data of lakes, some moderate-high resolution remote sensing datasets including MODIS and Landsat TM/ETM＋ images and the meteorological data, the spatial-temporal variations of lake ice phenology in the Hoh Xil region during the period 2000-2011 were analyzed by using RS and GIS technology. And the factors affecting the lake ice phenology were also identified. Some conclusions can be drawn as follows. （1） The time of freeze-up start （FUS） and freeze-up end （FUE） of lake ice appeared in the late October-early November mid-November - early December, respectively. The duration of lake ice freeze-up was about half a month. The time of break-up start （BUS） and break-up end （BUE） of lake ice were relatively dispersed, and appeared in the early February - early June, early May - early June, respectively. The average ice duration （ID） and the complete ice duration （CID） of lakes were 196 days and 181 days, respectively. （2） The phenology of lake ice in the Hoh Xil region changed dramatically in the last 10 years. Specifically, the FUS and FUE time of lake ice showed an increasingly delaying trend. In contrast, the BUS and BUE time of lake ice pre- sented an advance. This led to the reduction of the ID and CID of lake. The average rates of ID and CID were -2.21 d/a and -1.91 d/a, respectively. （3） The variations of phenology and evolution of lake ice were a result of local and climatic factors. The temperature, lake area, salinity and shape of the shoreline were the main factors affecting the phenology of lake ice. However, the other factors such as the thermal capacity and the geological structure of lake should not be ignored as well. （4） The spatial process of lake ice freeze-up was contrary to its break-up process. The type of lake ice extending from one side of lakeshore to the opposite side was the most in the Hoh Xil region.

A comparative analysis of changes in the phasing of temperature and satellite-derived greenness at northern latitudes

Plant growth at northern latitudes is highly responsive to the climatic changes that have occurred over recent decades. However, the sensitivity of the phasing of the seasonal cycle of terrestrial ecosystems to a changing environment remains less widely understood. We present an investigation and comparative study of large-scale changes in seasonal cy- cling of both land surface temperature and plant growth. Our results have shown trends in- dicating a marked increased towards overall plant productivity by -3% from 1982 to 2005, reduced trends in seasonal variation at low-mid latitudes by ~2%, increased trends in sea- sonal variations at mid-high latitudes by ~7%, and an earlier phase in northern terrestrial ecosystems （~1.1 days） in parallel with changes in the phasing of surface temperatures at northern latitudes over the 24 years in this study. These shifts in annual cycles of terrestrial vegetation appear to have a distinct geographical zonality and are dependent upon latitudinal changes in climatic variables. More conspicuous changes in overall vegetation productivity and the seasonal phase of ecosystems have been observed in Eurasia compared to North America, largely because of a more rapid rise in temperature. Our results state that changing climate boosts plant growth at northern latitudes, but also alters the phase and seasonal variations of the annual cycle of terrestrial ecosystems.