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Large-scale afforestation programmes are generally presented as effective ways of increasing the terrestrial carbon sink while preserving water availability and biodiversity. Yet, a meta-analysis of both numerical and observational studies suggests that further research is needed to support this view. The use of inappropriate concepts (e.g., the biotic pump theory), the poor simulation of key processes (e.g., tree mortality, water use efficiency), and the limited model ability to capture recent observed trends (e.g., increasing water vapour deficit, terrestrial carbon uptake) should all draw our attention to the limitations of available theories and Earth System Models. Observations, either based on remote sensing or on early afforestation initiatives, also suggest potential trade-offs between terrestrial carbon uptake and water availability. There is thus a need to better monitor and physically understand the observed fluctuations of the terrestrial water and carbon cycles to promote suitable nature-based mitigation pathways depending on pre-existing vegetation, scale, as well as baseline and future climates., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2024. Published by Elsevier B.V. All rights reserved.)

Study region: Northern Ireland (NI), and sub-catchments in the Republic of Ireland that drain to NI rivers, Study focus: Information on the potential future impacts of climate change on river flows is necessary for adaptation planning. There have been many such studies for Great Britain, but fewer for NI. Here, a grid-based hydrological model is configured for NI, and used to investigate changes in seasonal mean, extreme high and extreme low flows. New Hydrological Insights: When driven by observed climate data, the model shows good performance for a wide range of catchments, particularly where artificial influences are limited. When driven by ensemble data from the UKCP18 Regional (12 km) projections, model performance for the baseline period (1981–2010) is similar to that using observed data, especially when using a simple precipitation bias-correction. Model projections for a future time-slice (2051–2080) generally suggest decreases in spring–autumn mean flows, especially in summer (median −44%), but possible increases in winter mean flows (median 9%), with some variation between ensemble members, particularly in winter when some show large increases to the west. Consistent with this are large projected reductions in 10-year return period low flows everywhere (median −45%), and large increases in 10-year return period high flows for some locations and ensemble members (median 16%). Future applications could include expanding the range of climate data applied.

Study region: Catchments: Wölzerbach, Raab; Styria; Austria. Study focus: The study was carried out to investigate the fitness for purpose of the high-resolution Austrian National Climate datasets (ÖKS15) in hydrological applications. Provided as a standard for climate impact studies in Austria in 2016, the potential of the ÖKS15 data for hydrological impact studies has not previously been assessed. To fill this research gap, we evaluated the ÖKS15 datasets for the recent climate period (1961–2005) to determine their suitability for hydrological analyses. Hydro-meteorological indicators of the ÖKS15 datasets, as well as of the data used to obtain them by bias correcting and downscaling the EURO-CORDEX models, were assessed at different spatio-temporal scales and compared to the raw EURO-CORDEX data. The hydrological model WaSiM was driven with the different datasets to generate the hydrological simulations used for validation against long-term observations. New hydrological insights for the region: Hydro-meteorological indicators obtained from ÖKS15 models are comparable to observations and associated with less uncertainty than the raw EURO-CORDEX data. We thus consider the ÖKS15 dataset basically appropriate for hydrological impact studies. However, despite bias correction, some biases in the ÖKS15 data remain and differences in timing, magnitude and spatial characteristics lead to deviations in hydrological indicators at different scales.

The river flow regime and water resources are highly important for economic growths, flood security, and ecosystem dynamics in the Mekong basin - an important transboundary river basin in South East Asia. The river flow, although remains relatively unregulated, is expected to be increasingly perturbed by climate change and rapidly accelerating socioeconomic developments. Current understanding about hydrological changes under the combined impacts of these drivers, however, remains limited. This study presents projected hydrological changes caused by multiple drivers, namely climate change, large-scale hydropower developments, and irrigated land expansions by 2050s. We found that the future flow regime is highly susceptible to all considered drivers, shown by substantial changes in both annual and seasonal flow distribution. While hydropower developments exhibit limited impacts on annual total flows, climate change and irrigation expansions cause changes of +15% and -3% in annual flows, respectively. However, hydropower developments show the largest seasonal impacts characterized by higher dry season flows (up to +70%) and lower wet season flows (-15%). These strong seasonal impacts tend to outplay those of the other drivers, resulting in the overall hydrological change pattern of strong increases of the dry season flow (up to +160%); flow reduction in the first half of the wet season (up to -25%); and slight flow increase in the second half of the wet season (up to 40%). Furthermore, the cumulative impacts of all drivers cause substantial flow reductions during the early wet season (up to -25% in July), posing challenges for crop production and saltwater intrusion in the downstream Mekong Delta. Substantial flow changes and their consequences require careful considerations of future development activities, as well as timely adaptation to future changes., (Copyright © 2018. Published by Elsevier B.V.)