A comparison analysis: the 2022 drought on the Rhone and the Po basins

Global warming significantly affects the frequency and intensity of droughts worldwide. In Europe, the regions such as the Rhone basin in southeastern France and the Po basin in northern Italy has experienced several droughts in the last years and the future climate scenarios do show increasing drying in those areas. These two basins, separated by the Alps mountains, are unique due to their diverse sources of water flow (mountains, plains, Mediterranean areas). This report focuses on comparing the hydrological intensity of droughts in these two basins and aims to determine how they were affected by the 2022 drought event. To achieve this goal, hydrological data from French and Italian archives were compared using various indices. A preliminary meteorological analysis was conducted using the Standardized Precipitation Index (SPI) calculated on gridded data. Over a span of 30 years, the data indicates a significant decrease in rainfall in the French basin, while the Italian side shows a slight increase in yearly SPI values. However, the SPI maps for 2022 highlight the extreme dryness in both basins, especially in the Po basin. The hydrological conditions of the basins were studied using multiple indices to assess various drought parameters such as duration, frequency, and intensity. The primary analysis utilizes the QMNA (minimum annual monthly flow) to assess the exceptional low flow conditions. By examining the return period of QMNA and its evolution over 30 years, insights were gained into the impact of global warming and the response of water bodies to drought. Three distinct areas were studied: the northern plain of the Rhone basin in France, the downstream Italian area, and the Alpine region at the border of the two basins. Alarming low flow values were concentrated in the plain area, while the Alpine region showed a less dramatic variation, likely due to glacier and snow melt in summer. Additionally, a daily threshold analysis of major river stations revealed divergent trends at the river mouths. The Po River experienced record minimum daily flows for 23% of the days for the years 2022 since 1968 at its downstream station, whereas the Rhone River recorded such conditions for 7% of the days. The 2022 drought set numerous hydrological and meteorological records in both basins. The Rhone basin has seen a progressive decrease in its water resource through the years, while the year 2022 has set unprecedented records for the Po basin. New policies has been established to reduce the consumption of water during this extremely dry period.