Climate change poses a significant threat to global biodiversity, but freshwater fishes have been largely ignored in climate change assessments. Here, we assess threats of future flow and water ...temperature extremes to ~11,500 riverine fish species. In a 3.2 °C warmer world (no further emission cuts after current governments' pledges for 2030), 36% of the species have over half of their present-day geographic range exposed to climatic extremes beyond current levels. Threats are largest in tropical and sub-arid regions and increases in maximum water temperature are more threatening than changes in flow extremes. In comparison, 9% of the species are projected to have more than half of their present-day geographic range threatened in a 2 °C warmer world, which further reduces to 4% of the species if warming is limited to 1.5 °C. Our results highlight the need to intensify (inter)national commitments to limit global warming if freshwater biodiversity is to be safeguarded.
Comparison between high-precipitation (HP) years and low-precipitation (LP) years led to our main findings which are as follows: Cyprus lows are instrumental in the cooling of surface and epilimnion ...water in subtropical Lake Kinneret and in the cooling of eastern Mediterranean surface water. Cyprus lows are responsible for cold weather, rainfall, and for an increase in cloudiness causing a decrease in solar radiation over the eastern Mediterranean and north Israel (including Lake Kinneret). In the daytime, comparison between HP and LP years of Kinneret surface water temperature (SWT) and epilimnion water temperature (WT) showed water cooling of up to 2 °C in HP years. This study was carried out using the 21-year period of satellite and in-situ data: (1) MODIS 1 km × 1 km resolution records of SWT, in (2) shipboard measurements of WT vertical profiles down to a depth of ~40 m (2000–2020). We found that a decrease in solar radiation caused by Cyprus lows (due to an increase in cloudiness) was the main factor contributing to Kinneret water cooling. In winter (December–January) when solar radiation (SR) was minimal, no water cooling was observed: the WT difference between HP and LP years was insignificant. However, in spring (March–April) when SR increased and became the main factor contributing to water heating, water cooling was observed: SWT and epilimnion WT, averaged over the HP years, was lower by ~2 °C and ~1.4 °C, respectively, than SWT and epilimnion WT, averaged over the LP years. Not only was water cooling observed in Lake Kinneret, but also in eastern Mediterranean surface water. Comparison of SWT over the eastern Mediterranean between the same HP and LP years in spring showed SWT cooling by ~1.2 °C. This is evidence of the regional character of the daytime water-cooling phenomenon caused by Cyprus lows.
•A geothermal based system is presented in order to produce hydrogen and distilled water.•A Dual fluid ORC is employed to harvest the thermal energy into power.•A PEM electrolyzer and an RO ...desalination unit are employed to produce hydrogen and water, respectively.•Exergy analysis is used to find the highest irreversibility source of the presented system.•Exergy based economic analysis is adopted to estimate the cost of produced hydrogen and water.
Exergy and Exergoeconomic analysis are carried out for a new hydrogen and distilled water producing system. The presented cogeneration system is the combination of geothermal driven dual fluid organic Rankine cycle (ORC), proton exchange membrane (PEM) electrolyzer and reverse osmosis (RO) desalination unit. In fact, hot geothermal water is the system input energy, which turns into power and runs the PEM electrolyzer and RO unit. Exergy analysis revealed that the ORC has the highest exergy destruction among the all main units and causes 59% of the total exergy destruction. Also, within the ORC, low pressure evaporator has the highest exergy destruction compared with other components. An increase in the geothermal water temperature resulted in a reduction in system overall exergy efficiency. Furthermore, exergoeconomic analysis showed that 56% of the total investment cost refers to the ORC. Based on the exergoeconomic analysis and considering the unit exergy cost of 1.3 $/GJ for geothermal hot water, produced hydrogen and distilled water have costs of 4.257 $/kg and 32.73 cent/m3, respectively. Moreover, the annual payback period of 5.6 years indicates that the presented system can be of interest from the viewpoint of initial investment.
•Fins shadow effect is significant and should not be ignored.•Incorporating fins alone do not improve the productivity.•Hourly variations of beam radiation falling on tilted surfaces should be ...calculated.•High productivity can be achieved if utilizing both internal reflectors and fins.
Effect of utilizing both internal reflectors and fins on the productivity of solar still for several months has been experimentally and numerically studied. Accurate theoretical describing single sloped solar still integrated with fins and internal reflectors is developed. The effect of fins shadow is considered. Accurate calculations of solar radiation absorbed by the basin water and basin liner are performed considering solar path diagram and hourly variation of beam radiation falling on tilted surfaces. The performance of solar still is estimated under the Jordan weather conditions. The developed model is validated experimentally and found in great agreement with experimental work. The simulation results of this study show that adding internal reflectors at three sides of solar still (south, east and west reflector) increases the efficiency about 13%, 20%, 28%, 33%, 37% and 46% in June, April, September, October, January, and December respectively. While the average monthly efficiency increase and the average monthly productivity increase are 29.1% and 3.014 L/day⋅m2 respectively. Furthermore, the results show that there is no significant effect on daily water output and basin water temperature when adding fins alone. Finally, adding internal reflectors with fins together, tremendous increase in both productivity and efficiency is achieved.
•Our spatial calibration of predicted stream temperatures is novel for DHSVM-RBM.•This model bridges statistical models and airborne thermal infrared remote sensing.•High-resolution spatiotemporal ...temperature predictions inform resource management.
Conservation planners and resource managers seek information about how the availability and locations of cold-water habitats will change in the future and how these predictions vary among models. We used a physical process-based model to demonstrate the implications of climate change for streamflow and water temperature in two watersheds with distinctive flow regimes: the Snoqualmie watershed (WA) and Siletz watershed (OR), USA. Our model incorporated a downscaled ensemble of global climate model outputs and was calibrated with in situ and remotely sensed water temperatures. We compared predictions from our processed-based model to those from a publicly available and widely used statistical model. The process-based model projected greater changes in summer maximum water temperatures for the mixed-rain-snow Snoqualmie watershed than for the rain-dominated Siletz watershed as a result of the near-complete loss of winter snowpack and significant reduction in summer flow in the Snoqualmie watershed expected by the 2080s. Both models projected generally similar future spatial patterns of maximum water temperature in the two rivers, with cool reaches distributed farther upstream and fewer in number. However, the process-based model projected higher spatial heterogeneity in water temperature due to our spatially explicit simulation of streamflow and because we calibrated the model with spatially continuous remotely sensed water temperature data. We used stream temperature projections to assess the vulnerability of Pacific salmon and trout to changes in the spatial distribution of cold-water habitats during August by the 2080 s. Results suggest that salmonids may have fewer summertime cold-water habitats in both watersheds. Projected stream warming may further limit particular species and life stages, especially in the Snoqualmie watershed. Our comparison of models highlights the importance of considering what might be gained by using a process-based model for evaluating and prioritizing management actions that mitigate climate impacts on cold-water habitats for stream fishes.
Climate change potentially threatens the sustainable production of highly valued cold-water fish species in flow-through systems, such as salmonids. By analysing the relationship of water temperature ...to hydrological characteristics, air temperature, solar exposure, and precipitation, this study predicted temperature dynamics of five temperate cold-water aquaculture facilities under four projected climate change scenarios. Air temperature was found to be directly associated with facility site water temperature, and based on rational assumptions, two of the five facilities were predicted to face critical warming by mid-century. Extreme precipitation events induced acute short-term increases in water temperature of up to 5 °C. Significantly lower warming, roughly equal to the projected climate change–induced increase, was seen with artificial shading lowering temperature by 1 °C. Complementary niche modelling revealed that 37–77 % of current cold-water facilities will likely incur suboptimal climate conditions by the end of the century. Shading of raceways, more efficient water use, and disease management are proposed as key actions to preserve cold-water aquaculture.
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•Temperature dynamics were predicted under four projected climate change scenarios.•Water temperature rises significantly less in shaded facilities.•Extreme rain events could induce increases in water temperature of up to 5 °C.•37–77 % of cold-water facilities face suboptimal climate conditions in the future.•Management options are proposed as key actions to preserve cold-water aquaculture.
•Density currents were a prominent feature of tributaries in Three Gorges Reservoir.•Both density currents and unusual thermal profiles were modeled successfully.•Taguchi method was used to analyze ...what causes these density currents.
The initial filling of the Three Gorges Reservoir (TGR), China, has caused serious phytoplankton blooms in its tributary bays. A two-dimensional, laterally averaged, hydrodynamic and water quality CE-QUAL-W2 model was used to simulate the hydrodynamics and water temperature of a typical tributary (Xiangxi Bay XXB) of the TGR to study the relationship between phytoplankton and density currents. The CE-QUAL-W2 model was calibrated to data collected in XXB (depth profiles of velocity and water temperature at three locations) from January 2008 through December 2008. The model performed well in simulating (1) flow velocity profiles, (2) unusual water temperature profiles, (3) the plunge point location of the intrusion layer, (4) propagation speed, and (5) the travel distance of the density currents. The model was then used to examine potential factors that affect the density currents, such as water level fluctuations in the mainstem of the TGR, water temperature differences between the mainstem and XXB, and inflow rates to XXB. Therefore, a better understanding of the hydrodynamics of tributaries in the TGR can be used to understand the aquatic ecosystem dynamics of these tributaries.
According to the investigation materials about water bodies of Jiaozhou Bay in May, August and October 1979, this paper studied the changing process of water temperature in the surface and bottom ...waters. Based on the definition and model of Yang Dongfang temporal water temperature variation angle, the results indicated that in the water bodies of inside, around and outside of bay mouth, Viewing the waters inside of bay mouth, around the bay mouth and outside of bay mouth as one water body, the length of variation range of Yang Dongfang temporal water temperature variation angle is 2.98°when heating the surface of this water body, and 0.14°when heating the bottom. The length of variation range of this angle is 6.87°when cooling the surface and 7.28°when cooling the bottom, which displays the changing process of water temperature under the heating or cooling condition.
A Drier Future? Sherwood, Steven; Fu, Qiang
Science (American Association for the Advancement of Science),
02/2014, Letnik:
343, Številka:
6172
Journal Article
Recenzirano
Global warming is likely to lead to overall drying of land surfaces.
Global temperature increases affect the water cycle over land, but the nature of these changes remains difficult to predict. A key ...conceptual problem is to distinguish between droughts, which are transient regional extreme phenomena typically defined as departures from a local climatological norm that is presumed known, and the normal or background dryness itself. This background dryness depends on precipitation, but also on how fast water would evaporate. As the planet warms, global average rainfall increases, but so does evaporation. What is the likely net impact on average aridity?
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