SCIENTIFIC BACKGROUND AND OBJECTIVES. As the highest plateau in the world, the Tibetan Plateau (TP) directly impacts its surrounding climate and environment through atmospheric and hydrological processes. Meanwhile, the TP climate changed significantly (such as rapid warming, moistening, solar dimming, and wind stilling) over the past 30 years , which further altered its environment (e.g., glacier retreat, lake expansion, and permafrost degradation, etc.) and brought environmental risks and disasters to the plateau's surrounding regions. The "third pole" was proposed as a geographic element to cover the TP and its adjacent mountains (Qiu 2008), and the "Third Pole Environment" (TPE) was then launched as an international program in 2009, with intension to pool international efforts to reveal and quantify the "water-ice-air-ecosystem-human" interactions in this region (Yao et al. 2012). Among the multisphere interactions on the TP, soil moisture (SM) plays a fundamental role in controlling land surface energy partition, adjusting surface runoff and soil drainage, regulating canopy transpiration and carbon AFFILIATIONS: yang, Qin, y. Chen, anD Tang-key laboratory of tibetan environment changes and land surface Processes, institute of tibetan Plateau research, chinese Academy of sciences, Beijing, china; Zhao, han, LaZhu, Ding, Wu, anD Lin-key laboratory of tibetan environment changes and land surface Processes, institute of tibetan Plateau research, chinese Academy of sciences, and university of chinese Academy of sciences, Beijing, china; Z. Chencollege of global change and earth system science, Beijing normal university, Beijing, china; Lv-state key laboratory of resources and environmental information system, institute of geographic sciences and natural resources research, chinese Academy of sciences, Beijing, china CORRESPONDING AUTHOR: kun Yang, institute of tibetan Plateau research, chinese Academy of sciences, Bldg. 3, courtyard 16, lincui rd., chaoyang district,

Inter-annual dynamics of grassland yield of the Three Rivers Headwaters Region of Qinghai-Tibet Plateau of China in 1988-2005 was analyzed using the GLO-PEM model, and the herbage supply function was evaluated. The results indicate that while grassland yield in the region showed marked inter-annual fluctuation there was a trend of increased yield over the 18 years of the study. This increase was especially marked for Alpine Desert and Alpine Steppe and in the west of the region. The inter-annual coefficient of variation of productivity increased from the east to the west of the region and from Marsh, Alpine Meadow, Alpine Steppe, Temperate Steppe to Alpine Desert grasslands. Climate change, particularly increased temperatures in the region during the study period, is suggested to be the main cause of increased grassland yield. However, reduced grazing pressure and changes to the seasonal pattern of grazing could also have influenced the grassland yield trend. These findings indicate the importance of understanding the function of the grassland ecosystems in the region and the effect of climate change on them especially in regard to their use to supply forage for animal production. Reduction of grazing pressure, especially during winter, is indicated to be critical for the restoration and sustainable use of grassland ecosystems in the region.

Increasing heatwave and drought events can potentially alter the carbon cycle. Few studies have investigated the impacts of hundred-year return heatwaves and droughts, as those events are rare. In the summer of 2013, southern China experienced its strongest drought and heatwave on record for the past 113 years. We show that the record-breaking heatwave and drought lasted two months (from July to August), significantly reduced the satellite-based vegetation index and gross primary production, substantially altered the regional carbon cycle, and produced the largest negative crop yield anomaly since 1960. The event resulted in a net reduction of 101.54 Tg C in carbon sequestration in the region during these two months, which was 39–53% of the annual net carbon sink of China’s terrestrial ecosystems (190–260 Tg C yr−1). Moreover, model experiments showed that heatwaves and droughts consistently decreased ecosystem vegetation primary production but had opposite impacts on ecosystem respiration (TER), with increased TER by 6.78 ± 2.15% and decreased TER by 15.34 ± 3.57% assuming only changed temperature and precipitation, respectively. In light of increasing frequency and severity of future heatwaves and droughts, our study highlights the importance of accounting for the impacts of heatwaves and droughts in assessing the carbon sequestration in terrestrial ecosystems.

Abstract:Benefiting from the high spatiotemporal resolution and near-global coverage, satellite-based precipitation products are applied in many research fields. However, the applications of these products may be limited due to lack of information on the uncertainties. To facilitate applications of these products, it is crucial to quantify and document their error characteristics. In this study, four satellite-based precipitation products (TRMM-3B42, TRMM-3B42RT, CMORPH, GSMaP) were evaluated using gauge-based rainfall analysis based on a high-density gauge network throughout the Chinese Mainland during [2003][2004][2005][2006]. To quantitatively evaluate satellite-based precipitation products, continuous (e.g., ME, RMSE, CC) and categorical (e.g., POD, FAR) verification statistics were used in this study. The results are as follows: (1) GSMaP and CMORPH underestimated precipitation (about −0.53 and −0.14 mm/day, respectively); TRMM-3B42RT overestimated precipitation (about 0.73 mm/day); TRMM-3B42, which is the only dataset corrected by gauges, had the best estimation of precipitation amongst all four products; (2) GSMaP, CMORPH and TRMM-3B42RT overestimated the frequency of low-intensity rainfall events; TRMM-3B42 underestimated the frequency of low-intensity rainfall events; GSMaP underestimated the frequency of high-intensity rainfall events; TRMM-3B42RT tended to overestimate the OPEN ACCESS Remote Sens. 2014, 6 11650 frequency of high-intensity rainfall events; TRMM-3B42 and CMORPH produced estimations of high-intensity rainfall frequency that best aligned with observations; (3) All four satellite-based precipitation products performed better in summer than in winter. They also had better performance over wet southern region than dry northern or high altitude regions. Overall, this study documented error characteristics of four satellite-based precipitation products over the Chinese Mainland. The results help to understand features of these datasets for users and improve algorithms for algorithm developers in the future.