# Sentinel-2 Reveals Record-Breaking Po River Shrinking Due to Severe Drought in 2022
## 4 Discussion
### Lessons Learned and Future Perspectives
However, such data are distributed at a cost, which makes this solution often not practically or financially feasible [33], even if less expensive than other high-resolution satellite or airborne imagery [33; 60]. For detailed characterization of specific stretches, the use of unmanned aerial systems remains a valuable tool [15], also for calibration and validation purposes [59], although without the ability to revisit in time. Future developments of the proposed methodology will consider the synergic use of Copernicus Sentinel-2 and PlanetScope imagery. LiDAR acquisitions can be complemented with multispectral optical data analyses to provide additional quantitative information useful in characterizing hydomorphological changes. The different large-scale information obtained from the analysis of remote sensing data would be useful not only to monitor a specific watercourse but also to support the integrated management of river systems at the regional or national level [15]. While the CV and SDI metrics generated from in situ river discharge measurements effectively measure the magnitude and variability of a hydrological event and highlight the anomalies, they have inherent statistical limitations. SDI is useful for long-term drought monitoring, but its sensitivity to extremes makes it less effective under climate change. For example, a single extreme flood can skew the standard deviation, reducing the SDI values and underestimating the severity of the drought. Conversely, a distorted standard deviation can exaggerate the coefficient of variation, making stable conditions appear highly variable. The CV, which measures relative variability, does not take into account long-term trends, such as increasing drought frequency due to climate change, meaning that a gradual decline in flow may not be reflected in the CV and may not indicate worsening conditions. In addition, both indices focus on streamflow droughs, neglecting meteorological and groundwater droughs, which may misrepresent actual water availability. Therefore, for a more comprehensive hydrological assessment, these indices should be used in combination with other methods and trend analysis. A list of specific goals for future developments, in order of priority, is as follows: (i) demonstrate PWC reliability through the comparison with other methodological approaches to extract the percentage of water content in pixel, as well as cost-effectiveness analysis; (ii) tune fuzzy transform function on specific sites and a variety of sensors; (iii) demonstrate the improved monitoring capabilities using virtual satellite constellations, even providing datasets at higher spatial resolution; (iv) account for homogeneous geomorphic units. Future development of the proposed methodology could, in fact, account for the subdivision of river stretches according to homogeneous geomorphic units at different spatial scales. This should enable an evaluation of the ecological response to drought conditions, as geomorphic units represent the physical foundation for habitat units, provided that also vegetation and bare-ground features are mapped, according to the applications proposed in previous studies [59]. Moreover, it will yield insights into the existing range of habitats present within a given reach [11], opening the way for the characterization of river habitats and the assessment of river ecosystem state. The proposed mapping products can be even used to extend the existing hydromorphological indicators, thus providing further information that can support decision-makers and agencies involved in hydromorphological monitoring. The provided insights would be useful for the assessment of river dynamics, allowing the analysis of the variation in these features over time and with different water levels [61], as well as understanding the past and current river processes and forecasting future watercourse dynamics.