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Abstract Climate change is projected to have substantial economic, social, and environmental impacts worldwide. Currently, the leading solutions for hydrogen storage are in salt caverns, and depleted natural gas reservoirs. However, the required geological formations are limited to certain regions. To increase alternatives for hydrogen storage, this paper proposes storing hydrogen in pipes filled with gravel in lakes, hydropower, and pumped hydro storage reservoirs. Hydrogen is insoluble in water, non-toxic, and does not threaten aquatic life. Results show the levelized cost of hydrogen storage to be 0.17 USD kg−1 at 200 m depth, which is competitive with other large scale hydrogen storage options. Storing hydrogen in lakes, hydropower, and pumped hydro storage reservoirs increases the alternatives for storing hydrogen and might support the development of a hydrogen economy in the future. The global potential for hydrogen storage in reservoirs and lakes is 3 and 12 PWh, respectively. Hydrogen storage in lakes and reservoirs can support the development of a hydrogen economy in the future by providing abundant and cheap hydrogen storage.

Abstract Alleviating water scarcity is at the core of Sustainable Development Goal 6. Yet the timing of water scarcity in its onset and possible relief in different regions of the world due to climate change and changing human population dynamics remains poorly investigated. Here we assess the timing of the first emergence of water scarcity (FirstWS) and disappearance of water scarcity (EndWS), by using ensembles of simulations with six Global Hydrological Models under two representative concentration pathways (i.e., RCP2.6, RCP6.0) combined with two shared socioeconomic pathways (i.e., SSP2, SSP3) for 1901–2090. Historically (1901–2020), FirstWS occurred predominantly in Asia (e.g., China and India) and Africa (e.g., East Africa); the peak time of emerging water scarcity began around the 1980s. Under all the four future RCPs-SSPs scenarios (2021–2090), FirstWS will likely occur mainly in some regions of Africa, for which the newly added area is double that in Asia. On the other hand, EndWS will mostly occur in China after 2050, primarily due to the projected declining population. We, therefore, call for specific attention and effort to adapt to the looming water scarcity in Africa.

Abstract Groundwater in north India remains a vital food and water security resource for more than one billion people. Both summer monsoon drying, and winter warming pose considerable challenges for rapidly declining groundwater. However, their impacts on irrigation water demands and groundwater storage under the observed and projected future climate remain unexplored. Using in situ observations, satellite data, and a hydrological model that considers the role of irrigation and groundwater pumping, we show that summer monsoon drying and winter warming accelerate groundwater depletion in north India during the observed climate, which will continue in the projected future climate. Summer monsoon precipitation has significantly (P‐value = 0.04) declined (∼8%) while winters have become warmer in north India during 1951–2021. Both satellite (GRACE/GRACE‐FO) and hydrological model‐based estimates show a rapid groundwater depletion (∼1.5 cm/year) in north India with a net loss of 450 km3 of groundwater during 2002–2021. The summer monsoon drying followed by winter warming cause a substantial reduction in groundwater storage due to reduced groundwater recharge and enhanced pumping to meet irrigation demands. Summer monsoon drying and winter warming will continue to affect groundwater storage in north India in the future. For instance, summer monsoon drying (10%–15% deficit for near‐far periods) followed by substantial winter warming (1–4°C) in the future will further accelerate groundwater depletion by increasing (6%–20%) irrigation water demands and reducing groundwater recharge (6%–12%). Groundwater sustainability measures including reducing groundwater abstraction and enhancing the groundwater recharge during the summer monsoon seasons are needed to ensure future agricultural production.

Ensuring universal and equitable access to water and sanitation for all by 2030 (United Nations Agenda 2030, Sustainable Development Goal or SDG 6) is one of the most important goals for the world. 785 million people do not still have access to basic drinking water services. This burden disproportionately affects women, who are often responsible for collecting water from distant sources in regions with limited or no water supply systems. Understanding the spatial patterns of socio-demographic and hydrological factors is key to address the interlinked challenges of gender equality and water security under SDG 5 (‘Achieve gender equality’) and SDG 6. While the challenges women face in securing water are widely recognized, quantitative analysis of gender inequality in global water security has not previously been studied. Here, we present, to our knowledge the first global assessment of gender inequality in water security. We measured water security by examining both water access and water scarcity (hereafter, water stress), incorporating population data for working-age individuals and children. We integrated this hydrological and demographic information at a spatial resolution of approximately 10 km from 2000 to 2014 when the information is available. Our results showed that more working-age women than men experience poor water access, particularly in Africa. In addition, women in countries with high water insecurity, defined as high water stress and poor water access—such as Burkina Faso, Togo, and Somalia—primary conduct water collection. Our results indicate significant gender-based differences in water security, with women frequently remaining in rural areas characterized by poor water access. These inequalities could be further intensified by climate change and socio-economic factors.

‘Water circles’ are presented as flexible water cycle diagrams aggregating the flows through a system for a specific region and time period, categorized by flow type and organized by magnitude. Water circles for an entire system and separate storage components can be interpreted as water cycle speedometers and can help compare and communicate different climate and human impacts on different regions, time periods, and storage components. Water circles can facilitate comparisons between hydrological models and other methods for deriving water balances.