Compound hot-dry and the dry-wet seesaw transition are extreme meteorological events driven by the interaction between rainfall, temperature and soil moisture. Using data covering New Zealand for the 1950-2021 period we model these interactions using both copulas and single variables. The copula approach detects more frequent and intense events, particularly across eastern regions of the country, while also better representing the event drivers and improving our understanding of their risk.

Heavy rainfall over short periods can cause floods and damage in cities, yet rainfall is often only measured daily. We developed a new method to generate realistic hourly rainfall data from daily values, using information from many weather stations in Spain and the United States. Our approach reproduces extreme rainfall more accurately than existing methods, helping to improve flood risk studies, infrastructure design, and climate impact assessments.

River flow (streamflow) behaviour varies across Europe and is shaped by climate and landscape. Using data from more than 7000 European catchments, we identified 10 hydrological response types based on flow magnitude, timing, and seasonality. At the continental scale, streamflow behaviour is mainly driven by climate, but landscape features are equally or more influential in several regions. These results show that streamflow behaviour emerges from the combined effects of climate and landscape.

Improving how rainfall-runoff models estimate evapotranspiration is key to better reproducing water partitioning under current conditions, and will increase model realism under future changing conditions. We tested how well different conceptual rainfall-runoff model equations simulate evapotranspiration using Australian catchment and flux tower data. We found one equation consistently worked better than the others. However, even this equation had flaws, pointing to missing vegetation processes.

Evapotranspiration is an integral element of the water availability estimation in tropical regions like West Africa. Climate change is projected to impact the water cycle. In this study, we evaluate the importance of AET (actual evapotranspiration) simulation for future climate impact assessments. We highlight differences if AET is or is not integrated in the model calibration. Our work contributes to the reduction of uncertainties in hydrological climate impact studies.

In the coming decades Mediterranean floods are expected to change due to increased urbanization and climate change. We simulate floods under different conditions and show that future rainfall will likely reduce flood magnitudes, but increased urbanization will make them higher. Flood intensification is more pronounced at upstream sections and when soil moisture is high. As future flood trends may change between different regions further research is needed to cope with upcoming challenges.

This study of three peat bogs in Maine, USA suggests surface pools receive groundwater from depth based on interactions with the underlying sediments. Geophysical surveys mapped sediments, while thermal imaging paired with point temperature and water conductivity measurements revealed local patterns pointing to groundwater sources. Such discrete inflows may accelerate peat decomposition and carbon loss.

This study examines temperature changes in Rappbode Reservoir, Germany’s largest drinking-water reservoir, over four decades. By analyzing detailed temperature data and weather records, the research shows how factors like sunlight and air temperature impact water temperature at different depths. It also finds that late-season warming in deep waters is mainly caused by water withdrawals. These findings help improve understanding of lake ecosystems and can guide better water resource management.

Dams significantly change river flows, yet they are difficult to represent in global hydrological models. We tested four different modeling methods using data from 164 reservoirs to find the most effective approach. We found that tracking water storage is better than tracking outflow for predicting reservoir behavior. This discovery enables the use of satellite information for better water management. These improvements are being implemented in the European and Global Flood Awareness Systems.

We investigated how glaciers helped sustain summer river flow during the severe snow shortages of 2022 and 2023 in the Italian Alps. Using high-resolution modeling and long-term data, we found that glacier melt contributed up to three times more than in average years. This enhanced melt partly compensated for low snow and precipitation, showing the critical role of glaciers in supporting water resources during droughts.

To assess climate impacts on streamflow, we need models that can predict streamflow under future conditions. This study compares three model types: data-driven (LSTM - long short-term memory), conceptual (HBV - Hydrologiska Byråns Vattenbalansavdelning), and hybrid (LSTM-HBV). LSTMs perform best overall, but HBV and hybrid models generalize better to warmer climates. Hybrid models are a promising tool for climate impact assessments, combining LSTMs accuracy with better generalizability of traditional models. In snowy regions, all models struggle to generalize.

In mountain karst regions, seasonal snow is a key component of groundwater recharge, making them highly vulnerable to climate change. Using a rainfall-snow-discharge model in the southern French Alps, we show that warming shifts high-flow periods and causes a strong summer flow decline. Rapid karst flow paths lead to quick spring responses, limiting storage above the base level and increasing sensitivity to future hydrological change.

The study first estimated the summertime evaporation over lakes located in coastal Antarctica with direct (eddy-covariance) measurements collected during two austral summers (December–January) in 2017–2018 and 2019–2020. The lake evaporation was on average 1.6 mm d^-1 in the ice break-up period, and it doubled in the ice free period. The bulk aerodynamic method with a site-specific transfer coefficient of moisture well reproduced the observed day-to-day variations in evaporation over lakes.

The link between rainfall extremes and temperature has been widely studied and a scale dependence of the rate of increase with temperature is commonly reported. Here we investigate, with high resolution data, how rainfall variability across scales, and the associated extremes, change with temperature. We confirm scaling behaviour and find that the scale invariant maximum observable singularity increases on average with greater temperature. Connection with previous results are discussed.

Water transport in forest soils occurs both vertically and horizontally. We added a stable isotope label to a small forest plot and monitored its passage vertically into the soil and horizontally into stems of surrounding trees. The labelled water was detected in the upper layers of the soil and in trees up to 6.7 m away, but was mostly taken up by one tree adjacent to the plot. These results affect how we think about summing over individual trees to describe the water economy of a whole forest.

We evaluate the limitations of Gravity Recovery and Climate Experiment (GRACE) satellite data for estimating groundwater storage changes (ΔGWS) in a small, data-scarce coastal basin in Indonesia, where ocean signal leakage and spatial-scale mismatch present major challenges. On average, only 42% of ΔGWS estimates can be plausibly derived from GRACE, indicating that, without expanded in situ monitoring, ΔGWS estimates in this setting will remain uncertain.

In mountainous regions the interactions between topography and prevailing winds generate orographic effects, which modulate rainfall occurrence and intensity depending on slope exposure, finally creating strong rainfall gradients. This study introduces a geostatistical model dedicated to rainfall mapping in mountainous areas, which explicitly account for possible orographic effects.

Enhancing frozen soil infiltration based on soil liquid water significantly improves streamflow simulation in the SVS land surface model. Tested at over 580 stations in the Great-Lakes and Saint-Lawrence region for five years, this approach can be easily transferred to other land surface models (LSM). Our results suggest that promoting frozen soil infiltration in LSM is key for realistic large-scale streamflow simulations and critical for operational hydrological prediction in cold regions.