## 5 Discussion  
### Impact of 2016 Warm Conditions  
The displacement observations from 2016 reveal the impact of unusually warm conditions. The difference of subsidence progression with respect to DDT by landcover agrees with expectations for the associated soil types. Organic material decreases heat transfer. Such locations have in general much lower thaw depths than the ALT measurement sites in central Yamal in the order of 40 cm [21]. The extreme summer of 2016 did not show an impact for these areas. Simulations have shown that increasing temperatures with climate warming have a smaller impact in areas with such soils, (e.g., [63]). Our results demonstrate that this also applies to temperature extremes as encountered in 2016. Figure 11: Examples from northeastern part of COSMO-Skymed area (location in Figure 1) for land cover (**left**, source: [PERSON] et al. [28], contains modified Copernicus data), COSMO-Skymed 2013 displacement (**middle**) and 2016 displacement (**right**). Legend as in Figure 10. Further symbols: solid line circle—drained lake basin with high displacement in both years; dashed line circle—wet to waterlogged graminoid prostrate to low dwarf shrubundra with low subsidence in both years; rectangle—dry to moist prostrate to erect dwarf shrubundra with higher subsidence in 2016. Projection and grid UTM Zone 42N. Figure 12: Active-layer thickness differences between 2016 and 2017: **left**—comparison of in situ records, **right** in situ difference versus scaled displacement difference from Sentinel-1. Larger displacement than in normal years at certain locations corresponds to higher active-layer thickness (Figure 12). Higher general displacement does, however, not imply a larger active-layer thickness contrary to what has been observed in previous studies at sites with in general shallow active-layer thickness and colder permafrost [7; 12]. Largest ALT is measured over the CALM grid (Figure 12) but overall subsidence is lower than for the other sites (Figure 7). The presence of saline clay may play a role at the CALM grid. Probing may result in larger depths than at other sites, as unfrozen soils can occur at below zero degree Celsius. VD-2 also shows comparably large ALT and at the same time lower displacement compared to VD-3 which is the site with the deepest average ALT and highest displacement. There are also little differences in displacement between wet sites (where ALT is expected to be low) and dry to moist tundra (Figures 10 and 11). Long-term in situ observations do only represent ALT of at least approximately 60 cm. Additional measurements at locations with thicker organic layer and higher water content would be needed to clarify the relationship between ALT and observed displacements. The rate of additional displacement with respect to the active-layer deepening in 2016 indicates that the ALT measurement sites are characterized by ground ice at the base of the active-layer. The rate of displacement until the average ALT is met is much smaller compared to the rate afterwards. Whereas 3 cm are characteristic over the upper 100 cm, further 3.6 cm occur for the additional 15-20 cm. This can be in cases tabular ground ice, where it exists close to the base of the normal active layer. Thermodenudation cirques in the proximity reveal the existence of pure ice relatively close to the surface. An example is shown in Figure 13.  
Spatial patterns of soil properties can be only determined under anomalously warm conditions, as occurred in 2016, as no differences in thaw progression can be distinguished in normal years. Subsidence was not only lower for wet to waterlogged sites in 2016, the rate of displacement varied throughout the season (Figure 9). Temporal patterns observed with InSAR in extreme years may therefore support identification of areas with sufficient near surface organic horizon/wet soils to buffer the influence of temperature variations.