Drought assessment in the United Kingdom: a comprehensive characterization through standardized hydrometeorological indices and influence on iron concentration

Droughts represent an increasingly concerning challenge for modern society: in the last decades, the natural variability of climate has been enhanced by anthropogenic effects, increasing the frequency, duration, and intensity of extreme hydrological and meteorological events. Projections show that, due to climate change and consequently warmer temperatures, droughts are predicted to further increase, challenging the well being of society. On these premises, in the present work, a first analysis regarding the identification of meteorological and hydrological droughts from 1985 to 2023 in the United Kingdom was carried out, with the employment of the Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI), statistical tools that fit individual measurements to long- term behavior in flow and precipitation time series, providing standardized results that quantify deficits and surpluses of the two variables. This led to a better understanding of the main drought years from the 80s: some of the major drought events identified were in 1985, 1996, 2006, 2011, 2019 and 2022, with high variability in intensity across different regions of the UK: Southern England results to be generally more prone to drought conditions than Northern UK (Scotland), ans similarly Eastern UK experiences more drought events than Western England, primarily due to differences in climate and the Atlantic’s influence, that leads to higher fluctuation in the rainfall amounts. The timing of the response of streamflow to precipitation inputs also plays an important role in the hydrological drought formation process: SPI and SSI are found to be slightly out of phase, indicating generally slower response times of freshwater bodies to an increase or decrease in precipitation. Analysis II aims instead to quantify the impact of low flows on iron concentration in England, through the calculation of Spearman’s Rank Correlation.