water-heat exchange and inconsistent surface temperature changes on the Qinghai-Tibet Plateau

What is it about?

Increase of surface temperatures has long been recognized as an unequivocal response to radiative forcing and one of the most important implications for global warming. However, it remains unclear whether the variation of ground surface temperature (GST) and soil temperatures is consistent with simultaneous changes of the near-surface air and land (or skin) surface temperatures (Ta and LST). In this study, a seven-year continuous observation of GST, Ta, and surface water and heat exchange was carried out at an elevational permafrost site at Chalaping, northeastern Qinghai-Tibet Plateau. Results showed a distinct retarding of warming on the ground surface and subsurface under the presence of dense vegetation and moist peat substrates. Mean annual Ta and LST increased at noteworthy rates of 0.22 and 0.32 °C/a, respectively, while mean annual GST increased only at a rate of 0.057 °C/a. No obvious trends were detected for the four radiation budgets except the soil heat flux (G), which significantly increased at a rate of 0.29 W · m
2 · a
1, presumably inducing the melting of ground ice and resulted in much higher moisture content through the summers of 2015 and 2016 than preceding years and subsequent 2017 at the depths between 80 and 120 cm. However, no noticeable immediate variations of soil temperatures occurred owing to the large latent heat effect (thermal inertia) and the extending zero-curtain period. We suggest that a better protected eco-environment, particularly the surface vegetation, helps preserving the underlying permafrost, and thus to mitigates the potential degradation of elevational permafrost on the Qinghai-Tibet Plateau.

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Why is it important?

(1) We've found at an elevational permafrost site, near-surface air and land surface temperatures increased significantly, but ground surface and soil temperatures increased insignificantly. (2) We've found that seasonal thawing layer deepened evidently by increasing of soil moisture content, while it could not be directly found via the isotherm of 0 °C as the zero-curtain effect due to a large amount of ground ice residing around the bottom of the active layer. (3) We also found soil heat flux increased significantly as the trend of annual albedo decreased.

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