No Consistent Evidence for Advancing or Delaying Trends in Spring Phenology on the Tibetan Plateau

Vegetation phenology is a sensitive indicator of climate change and has significant effects on the exchange of carbon, water, and energy between the terrestrial biosphere and the atmosphere. The Tibetan Plateau, the Earth\u27s “third pole,” is a unique region for studying the long‐term trends in vegetation phenology in response to climate change because of the sensitivity of its alpine ecosystems to climate and its low‐level human disturbance. There has been a debate whether the trends in spring phenology over the Tibetan Plateau have been continuously advancing over the last two to three decades. In this study, we examine the trends in the start of growing season (SOS) for alpine meadow and steppe using the Global Inventory Modeling and Mapping Studies (GIMMS)3g normalized difference vegetation index (NDVI) data set (1982–2014), the GIMMS NDVI data set (1982–2006), the Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI data set (2001–2014), the Satellite Pour l\u27Observation de la Terre Vegetation (SPOT‐VEG) NDVI data set (1999–2013), and the Sea‐viewing Wide Field‐of‐View Sensor (SeaWiFS) NDVI data set (1998–2007). Both logistic and polynomial fitting methods are used to retrieve the SOS dates from the NDVI data sets. Our results show that the trends in spring phenology over the Tibetan Plateau depend on both the NDVI data set used and the method for retrieving the SOS date. There are large discrepancies in the SOS trends among the different NDVI data sets and between the two different retrieval methods. There is no consistent evidence that spring phenology (“green‐up” dates) has been advancing or delaying over the Tibetan Plateau during the last two to three decades. Ground‐based budburst data also indicate no consistent trends in spring phenology. The responses of SOS to environmental factors (air temperature, precipitation, soil temperature, and snow depth) also vary among NDVI data sets and phenology retrieval methods. The increases in winter and spring temperature had offsetting effects on spring phenology

Remote Sensing of Land Surface Phenology

Land surface phenology (LSP) uses remote sensing to monitor seasonal dynamics in vegetated land surfaces and retrieve phenological metrics (transition dates, rate of change, annual integrals, etc.). LSP has developed rapidly in the last few decades. Both regional and global LSP products have been routinely generated and play prominent roles in modeling crop yield, ecological surveillance, identifying invasive species, modeling the terrestrial biosphere, and assessing impacts on urban and natural ecosystems. Recent advances in field and spaceborne sensor technologies, as well as data fusion techniques, have enabled novel LSP retrieval algorithms that refine retrievals at even higher spatiotemporal resolutions, providing new insights into ecosystem dynamics. Meanwhile, rigorous assessment of the uncertainties in LSP retrievals is ongoing, and efforts to reduce these uncertainties represent an active research area. Open source software and hardware are in development, and have greatly facilitated the use of LSP metrics by scientists outside the remote sensing community. This reprint covers the latest developments in sensor technologies, LSP retrieval algorithms and validation strategies, and the use of LSP products in a variety of fields. It aims to summarize the ongoing diverse LSP developments and boost discussions on future research prospects

Response of Inland Lakes to Climate Change across the Tibetan Plateau Investigated Using Landsat and ICESat Data

The Tibetan Plateau experienced tremendous climate change during the past four decades. Due to the large size, widely distribution of cryosphere, and diverse landforms, different parts of the plateau may experience different climate and cryosphere changing patterns. The changes of inland lakes within the plateau are important indicators of climate change as these lakes are fed by precipitation, permafrost degradation, and glacier melting that are all sensitive to climate change. To examine the spatial and temporal differences of lake variations across the Tibetan Plateau, Landsat images and ICESat/GLAS altimetry data were used to extract the changes in surface areas of 26 lakes selected from six different sub-regions during the 1970s-2010 and the changes in lake elevations of these lakes during 2003-2009. An automated model to extract lake surface area and elevation from Landsat and ICESat data is developed to improve the efficiency of processing the large amount of satellite data. By applying this model, the spatial and temporal changing patterns of selected 26 inland lakes across the Tibetan Plateau during the past four decades are revealed. The lakes from different parts of the Tibetan Plateau show different changing patterns. The lake expansion firstly started from the Central Tibetan Plateau in the 1980s, then moving northward and northwestward; the Northeastern and Northwestern Tibetan Plateau experienced obvious expansion after the late 1990s, and this expansion is still continuing in the northern part, whereas the rapid lake expansion either slowed down or stopped in the central and southern parts of the plateau. The differences in lake changing pattern are caused by diverse climatic regimes and the pattern of the cryospheric distribution in the Tibetan Plateau. For the southern part of the plateau, the change in precipitation and evaporation seems to be the dominating factor to control the lake changes; however, the cryospheric change caused by temperature increase is the most important factor influencing the lake fluctuations in the northern part. These patterns can provide insight into the mechanism of lakes dynamics in response to climate and cryospheric changes; and be applied to assess the potential impacts of climate change on water resources in the Tibetan Plateau

Energy and Water Cycles in the Third Pole

As the most prominent and complicated terrain on the globe, the Tibetan Plateau (TP) is often called the “Roof of the World”, “Third Pole” or “Asian Water Tower”. The energy and water cycles in the Third Pole have great impacts on the atmospheric circulation, Asian monsoon system and global climate change. On the other hand, the TP and the surrounding higher elevation area are also experiencing evident and rapid environmental changes under the background of global warming. As the headwater area of major rivers in Asia, the TP’s environmental changes—such as glacial retreat, snow melting, lake expanding and permafrost degradation—pose potential long-term threats to water resources of the local and surrounding regions. To promote quantitative understanding of energy and water cycles of the TP, several field campaigns, including GAME/Tibet, CAMP/Tibet and TORP, have been carried out. A large amount of data have been collected to gain a better understanding of the atmospheric boundary layer structure, turbulent heat fluxes and their coupling with atmospheric circulation and hydrological processes. The focus of this reprint is to present recent advances in quantifying land–atmosphere interactions, the water cycle and its components, energy balance components, climate change and hydrological feedbacks by in situ measurements, remote sensing or numerical modelling approaches in the “Third Pole” region

Remote sensing of glacier change in the Central Qinghai-Tibet Plateau and the relationship with changing climate

2016-2017 > Academic research: refereed > Publication in refereed journal201804_a bcmaVersion of RecordPublishe