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The Contribution of Land-Surface Processes to Climate Change on the Tibetan Plateau


CIRES  This project is funded by a CIRES Innovative Research Grant

Objective

To quantify the degree to which land-atmosphere interactions play a major role in driving climate change on the Tibetan Plateau

Collaborators

Oliver Frauenfeld is the PI, and Tingjun Zhang is Co-Investigator.

Project Summary

The Tibetan Plateau (TP), with an average elevation greater than 4000 meters and approximately the size of Texas, is a semi-arid environment occupied by montane grasslands and shrublands. Over 62 percent of this temperature and moisture limited plateau is used for agriculture. Since the early to late 1950s, and accelerated since the 1980s, significant urban expansion and changes in agricultural and industrial practices have shaped this part of the world, resulting in a substantially altered landscape. Because of the plateau's role in the Asian Monsoon system, the water resources of most of the Asian continent and therefore the livelihoods of over 3.7 billion people, the extensive changes to the land surface in this part of the world are arguably of heightened importance to local-global resources and the climate system.

We use long-term in situ temperature observations for 161 locations, ERA-40 temperatures, a MODIS land cover classification, and Normalized Difference Vegetation Index (NDVI) data. These data are used to quantify the degree to which land-atmosphere interactions play a major role in driving climate change on the TP. As socioeconomic changes have caused a net reduction in vegetation, this has resulted in significantly reduced soil moisture which feeds back to further decrease vegetation, but also increase sensible (versus latent) heat fluxes, and hence increase temperatures.

Our previous work had also demonstrated that reported warming on the TP seems to be confined to low-lying populated regions, but is absent in temperature data free of surface biases. Indeed, we observe statistically significant vegetation decreases over the last 20 years in the central and eastern TP. Based on this geographic distribution of vegetation changes as well as the land cover type classification, we also observe different temperature trends based on disturbed versus undisturbed regions. The seasonality of these changes plays an important role; however, vegetation changes alone do not account for observed temperature increases. Surface temperature trends are likely also affected by the reported general warming of the atmosphere in recent decades. A further complicating factor on the TP is the presence of discontinuous permafrost in certain regions, and we hypothesize that the distribution of permafrost also factors into the complex changes in vegetation, soil moisture, heat fluxes, and surface temperatures.

Map showing NDVI trends for 1981 to 2003 over the Tibetan Plateau
This map shows the 1981 to 2003 twice-monthly 1-kilometer NDVI trends over the Tibetan Plateau in standard deviation units.

Bar graph showing temperature trends from 1981 to 2003 over the Tibetan Plateau
This graph shows the 1981 to 2003 temperature trends over the Tibetan Plateau in °C/decade by land cover type based on in situ station observations.

Related Resources

For more information, see the The Contribution of Land-Surface Processes to Climate Change on the Tibetan Plateau Web page.

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