Is Climate Change on the Tibetan Plateau Driven by Land Use/Cover Change?
Objective: The goal of this proposal is to address the degree to which long-term temperature changes on the Tibetan Plateau (TP) are influenced by land use and land cover changes. If we are able to quantify this component of climate warming and find support for our hypothesis that temperature increases are primarily driven by surface processes related to changes in land cover, this will then enable us to pursue a full research proposal and a more comprehensive analysis of land surface processes on the TP.
Background and importance
Similar to high-latitude regions of the Northern Hemisphere, high-altitude areas seem to be especially susceptible to global climate change and have been shown to have warmed more, and perhaps sooner, than the rest of the globe. The TP in particular has been argued to be a harbinger of climate change due to its early and accelerated warming. Anthropogenic greenhouse gas forcing is generally considered to be the main cause of the observed warming in high-elevation areas. However, evaluating the degree to which greenhouse gas loading contributes to the warming is difficult because topography (especially on the TP, which has the most complex terrain on the globe) is too poorly resolved in general circulation models. Models overlook many of the climatological details of mountain regions, making it difficult to evaluate the consequences of climate change on the hydrology, glaciers, or ecosystems.
Like elsewhere on the globe, an equally important anthropogenic component to climate change may be land cover and land use changes on the TP. These local–regional surface effects related to agriculture and urbanization potentially outweigh greenhouse gas forcing. In fact, our recent research has shown that plateau-averaged station records, biased toward low-lying populated regions, show a warming trend of 0.16°C decade-1 over the last 50+ years. However, plateau-wide trends from an independent data source free of surface contamination indicate no trend. This has led us to hypothesize that, indeed, land use/cover change (LUCC) could largely account for the reported warming on the TP.
Why is this important?
The TP plays a prominent role in the Asian monsoon system by acting as an anomalous midtropospheric heat source. Additionally, seven of the world's largest rivers originate on the plateau, and changes in this region are thus crucial for the water resources of most of the Asian continent. Climate change on the TP is arguably of heightened importance, as it impacts the livelihood of more than half of the world's population.
LUCCs are especially relevant on the TP as over 62% of the plateau is used for agriculture: farmlands, forests, and a majority (80%) is used for livestock grazing. According to some studies, the carrying capacity of parts of the TP has been far exceeded, partly due to inappropriate land management practices implemented in the 1950s. Additionally, urbanization, which can result in 8–11°C higher temperatures than in surrounding rural areas, has occurred on the TP in cities such as Lhasa, Golmud, and Xining. However, as in high-latitude regions, even villages and small towns at high altitudes can exhibit a strong urban heat island effect, especially during the cold season. In cold regions like the TP, this is accompanied by earlier snowmelt and increased thickness of the thawed layer, resulting in permafrost degradation and thus a further altered land surface. The many civil engineering projects currently under way, such as the construction of the Qinghai-Xizang railroad, combined with a conscious effort by China to urbanize the TP, will lead to further and likely greatly accelerated population increases and land surface changes in the future.
We first plan to detect and quantify changes in vegetation using historical AVHRR Normalized Difference Vegetation Index (NDVI) data for the last ~25 years, as well as 2000–present vegetation indices from MODIS. While NDVI can obviously only tell us the degree of "greenness" of the surface, this data source can still be useful to identify regions that are characterized by a decrease in vegetation cover, as well as areas that have undergone desertification. Having identified areas of land cover change, we expect to find amplified local air temperature increases in those regions, and lower or no temperature increases in undisturbed regions, where NDVI indicates no change.
We are in a unique position to acquire data not generally available to the public since the National Snow and Ice Data Center (NSIDC) is also a World Data Center (WDC). As such, we have recently obtained daily temperature data (1950s–2000) for 161 stations on the TP from the China Meteorological Administration. In addition to NDVI we will thus employ these long-term daily station records, as well as reanalysis products such as the European Centre for Medium-Range Weather Forecasts' 40+ year reanalysis (ERA-40), which we recently verified to accurately represent temperature variability on the TP.
Furthermore, to establish the degree to which station temperature records are influenced by urbanization, we may be able to compare co-located stations in, and away from, urbanized regions. For some sites on the TP, extensively quality controlled, corrected, and adjusted station records are available from the National Climatic Data Center (NCDC). Comparisons between our in situ records and NCDC's could also allow us to quantify the contribution of urbanization to the observed temperature increases.
What makes this innovative?
The innovativeness of this project arises from the fact that never before have land cover changes in this part of the world been assessed in terms of their contribution to climate change. While that assessment warrants a much larger effort than is proposed here and includes important social sciences components, our LUCC hypothesis needs to be verified before we can pursue any larger effort in this regard. Elsewhere on the globe, LUCCs have been shown to be a major contributor to anthropogenic warming. The TP likely represents one of the most crucial areas of LUCC and climate change on the globe, yet surprisingly LUCCs have not been evaluated for this region. This is partly because, outside of Asia, relatively little interest exists in the TP and research efforts geared towards this part of the world are difficult to fund. Although some effort has gone to evaluating climate change, e.g., the role of the TP (in particular, its snow cover) on the Asian monsoon, these and other investigations have been limited by coarse-scale gridded data products, notoriously plagued by data sparseness in this part of the world. This CIRES proposal, if funded, would therefore represent a first step towards an unprecedented effort to quantify anthropogenic changes on the TP directly relevant to over half of the world's population.
Additionally, NSIDC is in a unique position for this research because of its link to WDCs around the globe, including those in China, as well as an existing relationship with the Institute for Plateau Meteorology in Chengdu, a division of the China Meteorological Administration.
Expected outcome and impact: We expect to find that areas characterized by surface changes, such as decreases in vegetation cover, are also characterized by an amplified warming signal. Similarly, the urbanized and moderately industrialized regions on the TP are expected to exhibit amplified warming. This initial outcome would lead to further research, including a comprehensive study of (1) the impacts and feedbacks of climate change on land-surface processes related to LUCC, including soil moisture, frozen ground, snow cover, and the hydrologic cycle, (2) an assessment of the social causes and effects of LUCC and climate change, including educational outreach components geared toward local Tibetans, and (3) the generation of a variety of publicly available data sets and time series, to be archived at NSIDC, describing LUCC as well as climate change on the TP. The scientific impact of this proposed (and potential future) research is that because of the TP's importance for the water resources for virtually the entire Asian continent, changes in this part of the world are of heightened significance. Furthermore, because of the accelerating population increases and analogous land surface alterations on the plateau, quantifying past and present changes will allow us to predict future impacts on climate as well as on the livelihood of the entire Asian population.