# Sentinel-2 Reveals Record-Breaking Po River Shrinking Due to Severe Drought in 2022
## 2 Materials and Methods  
### Study Area  
The Po River, the longest river in Italy, flows for approximately 652 km from the Monviso mountain in the Cottian Alps, to its delta in the Adriatic Sea. The Po basin covers approximately 74,000 km\({}^{2}\), counting 141 main tributaries and 31,000 km of natural and artificial channels, crossing seven Italian regions and a diverse range of geomorphological features, including mountains, hills, and plains [34]. According to the hydrometer located in Pontelagoscuro, considered as a reference for the Po River watershed [35], during the period 1923-2006 the mean recorded annual discharge was 1500 m\({}^{3}\)/s, with a maximum observed peak flow of 10,300 m\({}^{3}\)/s in 1951 and a minimum observed flow of 168 m\({}^{3}\)/s in July 2006 [34; 36]. The Po River hydrology is characterized by a mixed regime: Alps mountain streams are dominated by snowmelt, with seasonal peak flows in spring and early summer; the Apennine streams are dominated by rainfall, showing a minimum seasonal flow during the summer. The hydrological behavior is influenced by various tributaries, such as the Dora Baltea, Ticino, and Adda rivers, which play crucial roles in sustaining its flow and impacting its overall water balance [35; 37]. Po River watershed represents one of the most densely populated, cultivated, and highly developed areas in Europe, which results in high water demand for many purposes including irrigation, hydro-power production, and civil and industrial uses [34; 35]. As a result of the intense human activity, the morphology and the hydrology of the River Po have been significantly modified over time. Historically, the river had irregular, meandering channels formed by natural processes, with discontinuous embankments and minimal bank protection. However, extensive land use changes have led to the artificial straightening of its channels [36]. Agriculture dominates land use in the Po basin, contributing to 46% of Italy's total agricultural production [35]. To support this, an extensive network of artificial canals has been developed for irrigation. Currently, 80% of the irrigation water is withdrawn from surface water sources, amounting to approximately 16.5 billion m\({}^{3}\) per year, while the remaining 20% is extracted from aquifers [38]. Additionally, nearly 5 billion m\({}^{3}\) per year are withdrawn for industrial and civil uses. These water extractions, combined with evapotranspiration, significantly reduce available water, resulting in only about 60% of the total annual inflow being converted into discharge [36]. Climate change has intensified these challenges. Rising temperatures and decreasing precipitation have led to increased dryness, reducing surface runoff and intensifying seasonal flow variability. The combined effects of long-term water resource exploitation and climate change have made this region particularly vulnerable to both floods and droughs, placing growing pressure on all economic activities [39]. Furthermore, from an ecological perspective, the delta of the Po River is one of the most significant in the Mediterranean Sea for its substantial biodiversity, with the presence of 460 vertebrates and more than 1000 plant species [34; 40]. However, increasing hydrological instability threatens this ecosystem, jeopardizing habitats and species dependent on the river's natural dynamics. As a result, a robust monitoring system and sustainable management strategies are urgently needed to protect the Po River ecosystem and prevent conflicts over water resource access, ultimately fostering long-term resilience and sustainability [39]. Figure 1 shows the study area, which encompasses the Po River from the city of Turin (about 535 km from the river mouth) to the delta on the Adriatic Sea. In 2022, Europe experienced a severe meteorological drought, characterized by record-low precipitations and high temperatures. This led to an intensified hydrological drought, endangering the security of water resources and the stability of riverine ecosystems.