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نهر النيل : مشاركة في مورد نادر : عرض تاريخي وفني لإدارة المياه ولقضايا اقتصادية وقانونية
هذا الكتاب \"نهر النيل\" مرجع وثائقي لنهر النيل بكل مشتملاته الجيولوجية والمطبوغرافية والطبيعية والمناخية والسياسية والاقتصادية والاجتماعية والبيئية والتنموية والقانونية وغيرها ويتميز عن غيره من الكتب التي صدرت عن نهر النيل بأنه يشتمل على عدة دراسات في الموضوعات السالف ذكرها وتعبر عن وجهات نظر نخبة من الباخثين والعلماء والخبراء العالميين والمصريين والإثيوبيين والأوغنديين والكينيين والبريطانيين والأمريكان والألمان.
Book
Amplified seasonal range in precipitation minus evaporation
Climate warming is intensifying the global water cycle, including the rate of fresh water flux between the atmosphere and the surface, determined by precipitation minus evaporation (P−E). Surpluses or deficits of fresh water impact societies and ecosystems, so it is important to monitor and understand how and why P−E patterns and their seasonal range are changing across the globe. Here, annual maximum and minimum P−E and their changes are diagnosed globally over land and ocean using observation-based datasets and CMIP6 climate model experiments covering 1950–2100. Seasonal minimum P−E is negative across much of the globe, apart from the Arctic, mid-latitude oceans and the tropical warm pool. In the global mean, P−E maximum increases and P−E minimum decreases by around 3%–4% per ∘ C of global warming from 1995–2014 to 2080–2100 in the ensemble mean of an intermediate greenhouse gas emission scenario. Over land, there is less coherence across the 1960–2020 datasets, but an increase in the seasonal range in P−E emerges in future projections. Patterns of future changes in annual maximum and minimum P−E are qualitatively similar to present day trends with increases in maximum P−E in the equatorial belt and high-latitude regions and decreases in the subtropical subsidence zones. This adds confidence to future projections of a more variable and extreme water cycle but also highlights uncertainties in this response over land.
Journal Article
The Diurnal Cycle of Precipitation according to Multiple Decades of Global Satellite Observations, Three CMIP6 Models, and the ECMWF Reanalysis
NASA Precipitation Measurement Mission observations are used to evaluate the diurnal cycle of precipitation from three CMIP6 models (NCAR-CESM2, CNRM-CM6.1, CNRM-ESM2.1) and the ERA5 reanalysis. NASA’s global-gridded IMERG product, which combines spaceborne microwave radiometer, infrared sensor, and ground-based gauge measurements, provides high-spatiotemporal-resolution (0.1° and half-hourly) estimates that are suitable for evaluating the diurnal cycle in models, as determined against the ground-based radar network over the conterminous United States. IMERG estimates are coarsened to the spatial and hourly resolution of the state-of-the-art CMIP6 and ERA5 products, and their diurnal cycles are compared across multiple decades of June–August in the 60°N–60°S domain (IMERG and ERA5: 2000–19; NCAR and CNRM: 1979–2008). Low-precipitation regions (and weak-amplitude regions when analyzing the diurnal phase) are excluded from analyses so as to assess only robust diurnal signals. Observations identify greater diurnal amplitudes over land (26%–134% of the precipitation mean; 5th–95th percentile) than over ocean (14%–66%). ERA5, NCAR, and CNRM underestimate amplitudes over ocean, and ERA5 overestimates over land. IMERG observes a distinct diurnal cycle only in certain regions, with precipitation peaking broadly between 1400 and 2100 LST over land (2100–0600 LST over mountainous and varying-terrain regions) and 0000 and 1200 LST over ocean. The simulated diurnal cycle is unrealistically early when compared with observations, particularly over land (NCAR-CESM2 AMIP:−1 h; ERA5: −2 h; CNRM-CM6.1 AMIP: −4 h on average) with nocturnal maxima not well represented over mountainous regions. Furthermore, ERA5’s representation of the diurnal cycle is too simplified, with less interannual variability in the time of maximum relative to observations over many regions.
Journal Article
Why are critical event checklists not always used in the perioperative setting?: A retrospective survey
During surgery and anesthesia, life-threatening critical events, including cardiac arrest, may occur. By facilitating recall of key management steps, suggesting diagnostic possibilities, and providing dose and drug information, cognitive aids may improve clinician performance during such events. In actual clinical practice, however, cognitive aids may be available but inconsistently used. One possibility explaining aid non-use during critical events is a lack of familiarity with how cognitive aids may be helpful. We hypothesized that introduction of critical event cognitive aids along with implementation of cognitive aid resources would change the quantitative incidence of cognitive aid use and qualitative reasons for aid non-use. We surveyed members of an academic anesthesia department before and after implementation of critical event cognitive aid resources.
All anesthesia clinicians at a single academic medical center were surveyed. Participants were surveyed both pre- and post-training with a focused program to introduce critical event cognitive aid resources. Incidences of and reasons for cognitive aid use and non-use were collected and analyzed. Survey responses were compared pre- and post-implementation.
The response rate was 64.5%. One-hundred eighty-five reasons for non-use were collected before the focused program and 149 after. Overall, 80% of clinicians had encountered at least one critical event during the study period and use of cognitive aids during all reported events was 7%. Six categories of reasons for non-use were identified: 'Not Available', 'Not Needed', 'No Time', 'Another Person In Charge', 'Used In Another Way', 'No Reason Given'. After implementation, a decrease in the number of respondents who cited availability and who cited 'another person running crisis,' as reasons for non-use was observed (p < 0.001).
Implementation of cognitive aids for critical events in an academic anesthesia environment improved the perception of cognitive aid availability and decreased the number of subjects who chose to not use the aid due to another person running the crisis response. Looking at the multiple reasons for cognitive aid non-use may guide implementation, training, and design.
Journal Article
Eisenhart lift of 2-dimensional mechanics
The Eisenhart lift is a variant of geometrization of classical mechanics with d degrees of freedom in which the equations of motion are embedded into the geodesic equations of a Brinkmann-type metric defined on \\[(d+2)\\]-dimensional spacetime of Lorentzian signature. In this work, the Eisenhart lift of 2-dimensional mechanics on curved background is studied. The corresponding 4-dimensional metric is governed by two scalar functions which are just the conformal factor and the potential of the original dynamical system. We derive a conformal symmetry and a corresponding quadratic integral, associated with the Eisenhart lift. The energy–momentum tensor is constructed which, along with the metric, provides a solution to the Einstein equations. Uplifts of 2-dimensional superintegrable models are discussed with a particular emphasis on the issue of hidden symmetries. It is shown that for the 2-dimensional Darboux–Koenigs metrics, only type I can result in Eisenhart lifts which satisfy the weak energy condition. However, some physically viable metrics with hidden symmetries are presented.
Journal Article
Significantly wetter or drier future conditions for one to two thirds of the world’s population
Future projections of precipitation are uncertain, hampering effective climate adaptation strategies globally. Our understanding of changes across multiple climate model simulations under a warmer climate is limited by this lack of coherence across models. Here, we address this challenge introducing an approach that detects agreement in drier and wetter conditions by evaluating continuous 120-year time-series with trends, across 146 Global Climate Model (GCM) runs and two elevated greenhouse gas (GHG) emissions scenarios. We show the hotspots of future drier and wetter conditions, including regions already experiencing water scarcity or excess. These patterns are projected to impact a significant portion of the global population, with approximately 3 billion people (38% of the world’s current population) affected under an intermediate emissions scenario and 5 billion people (66% of the world population) under a high emissions scenario by the century’s end (or 35-61% using projections of future population). We undertake a country- and state-level analysis quantifying the population exposed to significant changes in precipitation regimes, offering a robust framework for assessing multiple climate projections.
The authors disentangle uncertainty in rainfall projections, revealing regions where multiple global climate models agree on future drying and wetting patterns with implications for one to two thirds of the world’s population.
Journal Article
Changes in atmospheric shortwave absorption as important driver of dimming and brightening
The amount of solar (shortwave) radiation that reaches the Earth’s surface underwent substantial variations over recent decades. Since the 1950s, surface shortwave radiation gradually decreased at widespread locations. In Europe, this so-called surface dimming continued until the late 1980s, when surface brightening set in and surface shortwave radiation increased again. In China, the dimming levelled off in the 1980s, but did not turn into brightening until 2005. Changes in clouds and aerosol are the prime potential causes for the phenomenon, but the scientific community has not yet reached a consensus about the relative role of the different potential forcing agents. Here we bring together co-located long-term observational data from surface and space to study decadal changes of the shortwave energy balance in Europe and China from 1985 to 2015. Within this observation-based framework, we show that an increasing net shortwave radiation at the top of the atmosphere and a decreasing atmospheric shortwave absorption each contribute roughly half of the observed brightening trends in Europe. For China, we find that the continued dimming until 2005 and the subsequent brightening occurred despite opposing trends in the top-of-the-atmosphere net shortwave radiation. This shows that changes in atmospheric shortwave absorption are a major driver of European brightening and the dominant cause for the Chinese surface trends. Although the observed variations cannot be attributed unambiguously, we discuss potential causes for the observed changes.Changes in the atmospheric absorption of shortwave radiation, probably through cloud and aerosol effects, is the main reason for the dimming and brightening over China and Europe in past decades, according to co-located surface and space observations.
Journal Article
Atmospheric Warming and the Amplification of Precipitation Extremes
Climate models suggest that extreme precipitation events will become more common in an anthropogenically warmed climate. However, observational limitations have hindered a direct evaluation of model-projected changes in extreme precipitation. We used satellite observations and model simulations to examine the response of tropical precipitation events to naturally driven changes in surface temperature and atmospheric moisture content. These observations reveal a distinct link between rainfall extremes and temperature, with heavy rain events increasing during warm periods and decreasing during cold periods. Furthermore, the observed amplification of rainfall extremes is found to be larger than that predicted by models, implying that projections of future changes in rainfall extremes in response to anthropogenic global warming may be underestimated.
Journal Article
Observed and simulated precipitation responses in wet and dry regions 1850-2100
Global warming is expected to enhance fluxes of fresh water between the surface and atmosphere, causing wet regions to become wetter and dry regions drier, with serious implications for water resource management. Defining the wet and dry regions as the upper 30% and lower 70% of the precipitation totals across the tropics (30° S-30° N) each month we combine observations and climate model simulations to understand changes in the wet and dry regions over the period 1850-2100. Observed decreases in precipitation over dry tropical land (1950-2010) are also simulated by coupled atmosphere-ocean climate models (−0.3% decade) with trends projected to continue into the 21st century. Discrepancies between observations and simulations over wet land regions since 1950 exist, relating to decadal fluctuations in El Niño southern oscillation, the timing of which is not represented by the coupled simulations. When atmosphere-only simulations are instead driven by observed sea surface temperature they are able to adequately represent this variability over land. Global distributions of precipitation trends are dominated by spatial changes in atmospheric circulation. However, the tendency for already wet regions to become wetter (precipitation increases with warming by 3% K−1 over wet tropical oceans) and the driest regions drier (precipitation decreases of −2% K−1 over dry tropical land regions) emerges over the 21st century in response to the substantial surface warming.
Journal Article