Trends in the air–sea freshwater and heat fluxes and hydrographic properties of the Mediterranean Sea are investigated to assess changes in dense water formation over 1979–2023 and 2004–2023. Results show a strong annual evaporation increase that has accelerated over the last two decades following the higher warming rate. Positive trends in winter latent heat flux (LHF) were obtained over 1979–2023 in most of the East Mediterranean, driving an increase in both the ocean heat loss and the haline component of the surface density flux, but there were no significant long-term trends over the western basin and the dense water formation sites. Results show much larger trends over 2004–2023 when a broadscale decrease in sensible heat flux (SHF) is obtained over the western basin as the air temperature is increasing much faster than SST. Decreasing (increasing) LHF and SHF resulted in largely reduced (enhanced) ocean heat loss during winter in the Gulf of Lions (Aegean Sea) over 2004–2023. Robust positive trends are obtained for both the salinity and temperature fields throughout the basin, with accelerated warming and salinification rates after the 2000s. Deep waters have become warmer but also much saltier and denser over recent decades. A water mass transformation method is also used to investigate changes in volumetric distribution in temperature/salinity/density and T/S space. Results suggest that salinification over the last 45 years may have strongly enhanced salt preconditioning in all major dense water formation sites, sustaining or even increasing deep water formation despite the increasingly warming climate.

The fast development of the offshore energy industry becomes an essential component of resilient economies in most of the countries around the North Sea, addressing an increasing demand for cost-efficient and environmentally safe energy sources. Offshore wind farms are planned to be installed further away from the coasts to ensure stronger and more stable wind resources in this region. Oil and gas extraction infrastructures are also planned to move into deeper areas of the continental shelf and continental shelf slopes to explore new fields. These deeper areas of the ocean are characterised by harsh environmental conditions: stronger winds, larger waves and strong shelf slope currents, inducing considerably larger loads on offshore structures. This study brings together operational physical oceanography and the mathematics of fluid-structure interactions to estimate the likelihood of extreme environmental loads on offshore structures in the North Sea. We use the state-of-the-art Met Office high resolution ocean forecasting system, which provides high-frequency data on ocean and tidal currents, wave heights and periods and winds at a ~7 km horizontal resolution grid, spanning the North–West European Shelf. The Morison equation framework is used to calculate environmental loads on various types of offshore structures that are typically employed by the offshore industries in the North Sea. We use hourly data for a 2-year period to analyse the spatio-temporal variability of mean and extreme hydrodynamic loads and derive the relative contributions of currents, waves and winds in the region. The results indicate that waves dominate extreme hydrodynamic forces on the shallow shelf, whereas the current contribution is important at the shelf break and in the English Channel.

North Indian Subcontinent (NIS) is prone to disastrous and life-threatening floods during the summer monsoon period primarily due to its close proximity with the Himalayan foothills. Indian Meteorological Department (IMD) reported that during June 13–19, 2013, the Uttarakhand state in North India experienced a cumulative total of 322 mm rainfall, a 847% weekly departure against the long-term average rainfall (1971–2020) of 34 mm. After a decade, another state in the same region, Himachal Pradesh, received an unprecedented 223 mm of rainfall in just 4 days, viz 7–11 July 2023, a 436% deviation from the cumulative climatological rainfall of 41.6 mm for 4 days (July 7–11). It is shown that the atmospheric water vapor is transported towards NIS by two monsoon low pressure systems during the June 2013 event. In contrast, during the July 2023 flood, the monsoon trough shifted southward, resulting in the moisture transport pathway predominantly over the northern Indian Ocean. In conjunction, it was shown through upper-level air tracing that southward movement of the subpolar jet stream creates a trough in the subtropical jet stream, which intrudes along the western boundary of NIS, leading to upper-level divergence. This pattern was observed in both flood events. By leveraging the mass-conserving nature and unique capability of a Lagrangian tracing model to track atmospheric water backward in time, our novel analysis of the 2023 flood reveals that two evaporative sources near Madagascar and the western Indian Ocean were key contributors, and inland evaporation played a comparatively lesser role as compared to the 2013 case. The Bay of Bengal served primarily as a vapor transport pathway rather than a direct moisture source for both events. This novel Lagrangian approach, which exposes separate drivers of extreme monsoon rainfall, upstream and at lead times of days-weeks, has the potential to be used more extensively and operationally.

Subpolar and high-latitude regions of the North Atlantic are subject to changing buoyancy and mechanical forcing, alongside changing heat and freshwater exchanges with subtropical and polar regions. Associated changes in water mass formation and circulation are accompanied by changes in upper ocean stratification, of consequence for the large-scale ocean circulation, air-sea interaction, and ocean biogeochemistry. Changes in water mass volumes, and the associated overturning circulation, have been extensively evaluated with the water mass transformation (WMT) framework. Changes in stratification may be quantified with the Potential Energy Anomaly (PEA) framework, which has been extensively applied to seasonally stratified shelf sea environments. The WMT and PEA frameworks in combination provide complementary and holistic insights, for understanding hydrographic changes in relation to selected drivers. These frameworks are used with high-resolution model ocean datasets, obtained from hindcast and coupled simulations, the latter in control mode and forced by rising greenhouse gas concentrations through the 20th and 21st centuries. For selected sub-regions of the subpolar North Atlantic, bound by OSNAP and neighbouring hydrographic sections, mapped stratification (PEA) anomalies are related to respective changes in surface heat and freshwater fluxes. Residual differences between buoyancy-forced and full PEA tendencies are attributed to vertical mixing and divergences of heat and freshwater transports. Changes in regional stratification are evaluated alongside corresponding rates of water mass transformation and associated volumetric variability, for selected water masses. Eulerian perspectives provided by the WMT and PEA frameworks further complement Lagrangian perspectives provided by particle tracking. In full combination, these diagnostics elucidate multiple drivers of change in the North Atlantic that have potentially far-reaching consequences for the wider Earth System.