Conference Agenda

The objective of this project is to assess the feasibility of remotely sensed products of key cryospheric and hydrological elements (snow, evapotranspiration, soil moisture and precipitation) in representative regions across the Third Pole region and the Heihe River Basin of China and selected test sites in other regions, e.g. northern Finland. The in-situ measurements used to validate remotely sensed products have been collected from several ground-based observation networks including the Finnish Meteorological Institute (FMI), the TERrestrial ENvironmental Observatories (TERENO), the Agrosphere institute (IBG-3) and The Qilian Mountain Observatories (QMO). Essential remote sensing products e.g. the GlobSnow data sets covering northern hemisphere and the soil moisture data set from SMOS, were evaluated by referencing ground-based observations in representative regions. The upscaling methods were developed to improve the representativeness of ground-based observations to remote sensing pixels. The validated products were also inter-compared with other gridded products, and the spatiotemporal trends were diagnosed by statistical indexes, e.g., RMSE and correlation coefficient. The performance of each product will be further evaluated in different landscapes, topographic conditions in the representative regions selected in China and Europe. The research results have been submitted to or published in international journals such as IEEE TGARS, Remote Sensing, and the Cryosphere. In addition, young scientists on this project made considerable efforts to observe snow, evapotranspiration, soil moisture and precipitation. They also assist with the validation of remotely sensed products on preprocessing data, developing validation algorithms and writing validation reports.

Driven by climate change and large-scale forestry projects, the vegetation coverage has been significantly afforested in China. An increase in vegetation greenness improves ecosystem productivity and reduce the water supply, which leads to potential conflict of water demands between ecosystems and humans. This problem has been well-assessed in dry environments with significant evidence, but there are a few studies in humid areas. Therefore, this study will focus on the Poyang Lake Basin in the humid areas of southern China. This study analyzed the change in global vegetation greenness reflected by the satellite-derived growing season LAI (LAIgs). The causes of vegetation dynamic change are firstly analyzed in combination with climate and land use data. The impact of vegetation greenness change on watershed water yield is then investigated based on the modified Water Supply Stress Index (WaSSI) model.

Results show that the vegetation in Poyang Lake Basin grows well. During the study period, the NDVI of the basin increased significantly with a trend of 0.0031/a, in which 78% of the regional vegetation showed a greening trend, while 22% of the regional vegetation showed a browning trend. Temperature rise and afforestation promote regional vegetation greening, but urbanization is the main driving factor of vegetation browning. The partial correlation coefficient between temperature and NDVI was 0.959 (p<0.01), while the partial correlation coefficient between precipitation and NDVI was -0.647 (p<0.05). The correlation between climatic factors and NDVI showed obvious spatial heterogeneity, which indicated the vegetation in the central basin was more vulnerable to climate change than that in other regions. During the study period, frequent droughts occurred in the Poyang Lake basin. The increase of vegetation greenness by 20-80% under different drought intensities resulted in a decrease in water yield by 3-27%. At the scale of sub-basins, the increase of vegetation greenness had a negative effect on water yield. In addition, the decrease of water yield caused by increasing vegetation greenness under persistent high-intensity drought was 2-3 times that under short-term moderate drought. The effect of vegetation greenness increase on water yield under drought conditions is related to vegetation type, duration, and intensity of drought.

The rapid increase of forest greenness caused by massive afforestation may lead to new environmental problems under the condition of continuous high-intensity drought in humid areas such as the Poyang Lake basin. Therefore, given the increasing frequency of extreme climatic events, afforestation with a targeted approach should be implemented as it would provide the most benefits. In addition, selective harvesting in forested areas with high density could be an effective strategy to maintain water supply in humid regions.