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Rising temperatures entail important changes in the soil hydrologic processes of the northern permafrost zone. Using the ICON-Earth System Model, we show that a large-scale thaw of essentially impervious frozen soil layers may cause a positive feedback by which permafrost degradation amplifies the causative warming. The thawing of the ground increases its hydraulic connectivity and raises drainage rates which facilitates a drying of the landscapes. This limits evapotranspiration and the formation of low-altitude clouds during the snow-free season. A decrease in summertime cloudiness, in turn, increases the shortwave radiation reaching the surface, hence, temperatures and advances the permafrost degradation. Our simulations further suggest that the consequences of a permafrost cloud feedback may not be limited to the regional scale. For a near-complete loss of the high-latitude permafrost, they show significant temperature impacts on all continents and northern-hemisphere ocean basins that raise the global mean temperature by 0.25 K. Landscapes in the Arctic and subarctic zone are often very wet with highly water saturated soils and an extensive lake- and wetland cover. To some extent, this is due to the perennially frozen soil layers that underlay large parts of these regions and inhibit the movement of water through the ground. Thus, a thawing of the frozen soils, caused by rising temperatures, may ultimately lead to a drying of the landscapes. Here, we use simulations with the ICON-Earth System Model to show that such a drying increases regional temperatures via an atmospheric feedback: During the warm season, dryer conditions at the surface reduce the moisture transport into the atmosphere. This decreases the relative humidity in the boundary layer and the low-altitude cloud cover. Since clouds reflect more sunlight than the snow-free land surface, the reduced cloudiness increases the available energy, hence, temperatures and advances the thawing of the ground. Higher temperatures in the Arctic and subarctic zone, in turn, have important consequences for the net energy exchange between equatorial and polar regions. Thus, the effects of a large-scale drying of high-latitude soils may not be limited to the regional scale but could notably increase global mean temperatures. Advanced degradation of permafrost may facilitate large-scale landscape drying Dependency of clouds on terrestrial hydrology allows for feedback between permafrost thaw, diminished cloudiness and rising temperatures This feedback could amplify global warming notably

来源平台：GEOPHYSICAL RESEARCH LETTERS