## 3 Results
### Grand Ethiopian Renaissance Dam (GERD)
In particular, on 5 May 2021 (i.e., when the first ad hoc COSMO-SkyMed StripMap HIMAGE scene as part of the present monitoring was collected), it was already clear that, due to the first filling phase, at least 32 of the total sites that we were able to map based on archive satellite imagery were already submerged (see cyan polygons within the highly radar backscattering central part of the reservoir in the amplitude change detection map in Figure 9C). It should be noted though, that this impact on local heritage occurred when most of the prospective reservoir had not been flooded yet, as shown by comparing the extent of the waters vs. the red polygon in Figure 9C. This highlights the high level of risk facing the surviving archaeological and ethnographic heritage. This condition further justifies the value for an archaeological and ethnographic research to be undertaken, even if the dam is already in operation. If research studies [85; 86] are confirmed, it is reasonable to imagine that there are still about 4 to 5 years before the complete loss of the cultural landscape of this large portion of the Nile valley due to the progressive dam filling process. On this basis, new COSMO-SkyMed images were regularly collected in parallel to the predefined Sentinel-2 acquisitions until the end of year 2021 (see Table 2). Such satellite monitoring allowed us to capture the second filling phase that started in mid-June 2021. As it can be seen from the dark black pattern in Figure 9C, this second impoundment led to a significant expansion of the total extent of the reservoir waters. Although the full  
Figure 9: Multi-temporal monitoring of GERD dam construction and impoundment by means of amplitude change detection maps using (**A,B**) archive COSMO-SkyMed StripMap HIMAGE (7 July 2013 vs. 3 October 2016) images and (**C–E**) ad hoc images collected in the course of 2021 (5 May 2021 vs. 5 October 2021). COSMO-SkyMed® Products ©ASI, Italian Space Agency, 2013, 2016, 2021.  
planned extent is yet to be reached, at least 8 more of the mapped sites were submerged (see examples in Figure 9D,E). This evidence confirms the value of such dynamic monitoring for archaeologists to reconstruct the trend of the filling process after the dam becomes fully operational. Indeed, while we should bear in mind that each dam has its own filling process and timing, understanding filling times and areas potentially affected using satellite images allows to plan more efficiently archaeological activities useful for both the PCARA (in particular, archaeological survey) and PFRAP protocols (archaeological excavations). It will become easier to plan activities in the field until the last useful moment. Finally, with regard to site identification, the most recent Sentinel-2 images collected in the course of 2021 have also been useful for confirming the potential cultural heritage evidence in areas not yet submerged. Instead, the change of temporal and environmental variables in satellite data selection and tasking did not improve the identification capacity of COSMO-SkyMed imagery, which revealed to be less effective in this area, especially if compared to Halabiyeh dam, given the local vegetation coverage.