• Energy Research

AbstractVarious transboundary river basins are facing increased pressure on water resources in near future. However, little is known ab out the future drivers globally, namely, changes in natural local runoff and natural inflows from upstream parts of a basin, as well as local and upstream water consumption. Here we use an ensemble of four global hydrological models forced by five global climate models and the latest greenhouse‐gas concentration (RCP) and socioeconomic pathway (SSP) scenarios to assess the impact of these drivers on transboundary water stress in the past and future. Our results show that population under water stress is expected to increase by 50% under a low population growth and emissions scenario (SSP1‐RCP2.6) and double under a high population growth and emission scenario (SSP3‐RCP6.0), compared to the year 2010. As changes in water availability have a smaller effect when water is not yet scarce, changes in water stress globally are dominated by local water consumption—managing local demand is thus necessary in order to avoid future stress. Focusing then on the role of upstream changes, we identified upstream availability (i.e., less natural runoff or increased water consumption) as the dominant driver of changes in net water availability in most downstream areas. Moreover, an increased number of people will be living in areas dependent on upstream originating water in 2050. International water treaties and management will therefore have an increasingly crucial role in these hot spot regions to ensure fair management of transboundary water resources.

Il y a actuellement une grande quantité d'énergie gaspillée sur les soupapes de réduction de pression à travers le monde. Cet article soutient que cette énergie pourrait être exploitée avec la dépressurisation isotherme en appliquant une turbine de réduction de pression isotherme hydraulique. La turbine de réduction de pression isotherme hydraulique se compose de deux réservoirs remplis d'eau ou d'un liquide organique. Le gaz sous pression pénètre dans le réservoir, déplaçant le liquide, qui s'écoule à travers une turbine, générant de l'électricité. Le système proposé a des rendements autour de 90 %, ce qui est plus élevé que les turbines de réduction de pression habituelles. Le coût estimé de la technologie proposée est de 1300 USD/kW. La technologie proposée pourrait être réalisable pour exploiter le potentiel de production d'électricité gaspillé dans les soupapes de réduction de pression. Le besoin de cette technologie augmentera considérablement dans une future économie basée sur l'hydrogène, compte tenu de la faible densité volumétrique de l'hydrogène et des pertes d'énergie importantes lors de la compression et de la décompression de l'hydrogène. Actualmente se está desperdiciando una gran cantidad de energía en válvulas de reducción de presión en todo el mundo. Este documento argumenta que esta energía podría aprovecharse con la despresurización isotérmica mediante la aplicación de una turbina de reducción de presión isotérmica hidráulica. La turbina de reducción de presión isotérmica hidráulica consta de dos tanques llenos de agua o un líquido orgánico. El gas presurizado entra en el tanque, desplazando el líquido, que fluye a través de una turbina, generando electricidad. El sistema propuesto tiene eficiencias que rodean el 90%, que es más alto que las turbinas de reducción de presión habituales. El coste estimado para la tecnología propuesta es de 1300 USD/kW. La tecnología propuesta podría ser factible para aprovechar el potencial de generación de electricidad desperdiciado en las válvulas de reducción de presión. La necesidad de esta tecnología aumentará significativamente en una futura economía basada en el hidrógeno, dada la baja densidad volumétrica del hidrógeno y las significativas pérdidas de energía al comprimir y descomprimir el hidrógeno. There is currently a large amount of energy being wasted on pressure reduction valves across the world. This paper argues that this energy could be harnessed with isothermal depressurization by applying a hydraulic isothermal pressure reduction turbine. The hydraulic isothermal pressure reduction turbine consists of two tanks filled with water or an organic liquid. The pressurized gas enters the tank, displacing the liquid, which flows through a turbine, generating electricity. The proposed system has efficiencies surrounding 90%, which is higher than usual pressure reduction turbines. The estimated cost for the proposed technology is 1300 USD/kW. The proposed technology could be feasible to harness the potential for electricity generation wasted in pressure reduction valves. The need for this technology will increase significantly in a future hydrogen-based economy, given the low volumetric density of hydrogen and the significant energy losses when compressing and decompressing hydrogen. يوجد حاليًا كمية كبيرة من الطاقة التي يتم إهدارها على صمامات تقليل الضغط في جميع أنحاء العالم. تجادل هذه الورقة بأنه يمكن تسخير هذه الطاقة مع إزالة الضغط متساوي الحرارة من خلال تطبيق توربين هيدروليكي لخفض الضغط متساوي الحرارة. يتكون التوربين الهيدروليكي لخفض الضغط متساوي الحرارة من خزانين مملوءين بالماء أو سائل عضوي. يدخل الغاز المضغوط إلى الخزان، مما يؤدي إلى إزاحة السائل، الذي يتدفق عبر التوربينات، مما يولد الكهرباء. يحتوي النظام المقترح على كفاءات محيطة بنسبة 90 ٪، وهي أعلى من توربينات تقليل الضغط المعتادة. التكلفة المقدرة للتكنولوجيا المقترحة هي 1300 دولار أمريكي/كيلو واط. يمكن أن تكون التكنولوجيا المقترحة مجدية لتسخير إمكانات توليد الكهرباء المهدرة في صمامات تقليل الضغط. ستزداد الحاجة إلى هذه التكنولوجيا بشكل كبير في الاقتصاد المستقبلي القائم على الهيدروجين، نظرًا لانخفاض الكثافة الحجمية للهيدروجين والخسائر الكبيرة في الطاقة عند ضغط الهيدروجين وفك ضغطه.

Groundwater in sub-Saharan Africa supports livelihoods and poverty alleviation1,2, maintains vital ecosystems, and strongly influences terrestrial water and energy budgets3. Yet the hydrological processes that govern groundwater recharge and sustainability-and their sensitivity to climatic variability-are poorly constrained4,5. Given the absence of firm observational constraints, it remains to be seen whether model-based projections of decreased water resources in dry parts of the region4 are justified. Here we show, through analysis of multidecadal groundwater hydrographs across sub-Saharan Africa, that levels of aridity dictate the predominant recharge processes, whereas local hydrogeology influences the type and sensitivity of precipitation-recharge relationships. Recharge in some humid locations varies by as little as five per cent (by coefficient of variation) across a wide range of annual precipitation values. Other regions, by contrast, show roughly linear precipitation-recharge relationships, with precipitation thresholds (of roughly ten millimetres or less per day) governing the initiation of recharge. These thresholds tend to rise as aridity increases, and recharge in drylands is more episodic and increasingly dominated by focused recharge through losses from ephemeral overland flows. Extreme annual recharge is commonly associated with intense rainfall and flooding events, themselves often driven by large-scale climate controls. Intense precipitation, even during years of lower overall precipitation, produces some of the largest years of recharge in some dry subtropical locations. Our results therefore challenge the 'high certainty' consensus regarding decreasing water resources4 in such regions of sub-Saharan Africa. The potential resilience of groundwater to climate variability in many areas that is revealed by these precipitation-recharge relationships is essential for informing reliable predictions of climate-change impacts and adaptation strategies.

AbstractHumans and ecosystems are deeply connected to, and through, the hydrological cycle. However, impacts of hydrological change on social and ecological systems are infrequently evaluated together at the global scale. Here, we focus on the potential for social and ecological impacts from freshwater stress and storage loss. We find basins with existing freshwater stress are drying (losing storage) disproportionately, exacerbating the challenges facing the water stressed versus non-stressed basins of the world. We map the global gradient in social-ecological vulnerability to freshwater stress and storage loss and identify hotspot basins for prioritization (n = 168). These most-vulnerable basins encompass over 1.5 billion people, 17% of global food crop production, 13% of global gross domestic product, and hundreds of significant wetlands. There are thus substantial social and ecological benefits to reducing vulnerability in hotspot basins, which can be achieved through hydro-diplomacy, social adaptive capacity building, and integrated water resources management practices.

Evaluating global mean sea level (GMSL) in terms of its components—mass and steric—is useful for both quantifying the accuracy of the measurements and understanding the processes that contribute to GMSL rise. In this paper, we review the GMSL budget over two periods—1993 to 2014 and 2005 to 2014—using multiple data sets of both total GMSL and the components (mass and steric). In addition to comparing linear trends, we also compare the level of agreement of the time series. For the longer period (1993–2014), we find closure in terms of the long-term trend but not for year-to-year variations, consistent with other studies. This is due to the lack of sufficient estimates of the amount of natural water mass cycling between the oceans and hydrosphere. For the more recent period (2005–2014), we find closure in both the long-term trend and for month-tomonth variations. This is also consistent with previous studies.

AbstractBioenergy with carbon capture and storage (BECCS) is considered an important negative emissions (NEs) technology, but might involve substantial irrigation on biomass plantations. Potential water stress resulting from the additional withdrawals warrants evaluation against the avoided climate change impact. Here we quantitatively assess potential side effects of BECCS with respect to water stress by disentangling the associated drivers (irrigated biomass plantations, climate, land use patterns) using comprehensive global model simulations. By considering a widespread use of irrigated biomass plantations, global warming by the end of the 21st century could be limited to 1.5 °C compared to a climate change scenario with 3 °C. However, our results suggest that both the global area and population living under severe water stress in the BECCS scenario would double compared to today and even exceed the impact of climate change. Such side effects of achieving substantial NEs would come as an extra pressure in an already water-stressed world and could only be avoided if sustainable water management were implemented globally.