Drought risk assessment using remote sensing and GIS techniques   总被引：1，自引：0，他引：1  

Abdel-Aziz Belal  Hassan R. El-Ramady  Elsayed S. Mohamed  Ahmed M. Saleh 《Arabian Journal of Geosciences》2014,7(1):35-53

Beginning with a discussion of drought definitions, this review paper attempts to provide a review of fundamental concepts of drought, classification of droughts, drought indices, and the role of remote sensing and geographic information systems for drought evaluation. Owing to the rise in water demand and looming climate change, recent years have witnessed much focus on global drought scenarios. As a natural hazard, drought is best characterized by multiple climatological and hydrological parameters. An understanding of the relationships between these two sets of parameters is necessary to develop measures for mitigating the impacts of droughts. Droughts are recognized as an environmental disaster and have attracted the attention of environmentalists, ecologists, hydrologists, meteorologists, geologists, and agricultural scientists. Temperatures; high winds; low relative humidity; and timing and characteristics of rains, including distribution of rainy days during crop growing seasons, intensity, and duration of rain, and onset and termination, play a significant role in the occurrence of droughts. In contrast to aridity, which is a permanent feature of climate and is restricted to low rainfall areas, a drought is a temporary aberration. Often, there is confusion between a heat wave and a drought, and the distinction is emphasized between heat wave and drought, noting that a typical time scale associated with a heat wave is on the order of a week, while a drought may persist for months or even years. The combination of a heat wave and a drought has dire socio-economic consequences. Drought risk is a product of a region’s exposure to the natural hazard and its vulnerability to extended periods of water shortage. If nations and regions are to make progress in reducing the serious consequences of drought, they must improve their understanding of the hazard and the factors that influence vulnerability. It is critical for drought-prone regions to better understand their drought climatology (i.e., the probability of drought at different levels of intensity and duration) and establish comprehensive and integrated drought information system that incorporates climate, soil, and water supply factors such as precipitation, temperature, soil moisture, snow pack, reservoir and lake levels, ground water levels, and stream flow. All drought-prone nations should develop national drought policies and preparedness plans that place emphasis on risk management rather than following the traditional approach of crisis management, where the emphasis is on reactive, emergency response measures. Crisis management decreases self-reliance and increases dependence on government and donors.  相似文献   

Phytoplankton and bacterial community structures and their interaction during red-tide phenomena     

Mona Mohamed Ismail  Hassan Abd Allah Ibrahim 《Ocean Science Journal》2017,52(3):411-425

Phytoplankton and bacteria diversity were studied before, during and after red tide phenomena during spring season 2015 in the Eastern Harbour (E.H.) of Alexandria, Egypt. Fifty five species of phytoplankton were identified and represented different distinct classes “Bacillariophyceae; Dinophyceae, Chlorophyceae, Cyanophyceae and Eugelenophyceae”. Also, Diatom formed the most dominant group. The average number of the phytoplankton density varied from 4.8 × 10⁴ to 1.1 × 10⁶ cell l^-1 during the study period and Skeletonema costatum was the agent causing the red tide. The existence percentages of bacteria ranged from 2.6 to 17.9% on all media tested. The bacterial isolates on the nutrient agar medium represented the highest existence with a total percentage of 43.6%, followed by MSA medium (25.7%), while the lowest percentage was for the AA medium at 7.8%. However, twelve isolates were selected as representative for bacterial community during study interval. Based on the morphological, biochemical, physiological and enzymatic characteristics, the bacterial strains were described. Depending on the 16S rDNA gene sequence, three common antagonists were aligned as: Vibrio toranzoniae strain Vb 10.8, Ruegeria pelagia strain NBRC 102038 and Psychrobacter adeliensis strain DSM 15333. The interaction between these bacteria and S. costatum was studied. The growth of S. costatum was significantly lower whenever each bacterium was present as compared to axenic culture. More specifically, 30% (v/v) of the all tested bacteria showed the strongest algicidal activities, as all S. costatum cells were killed after two days. 10% of R. pelagia and P. adeliensis also showed significant algicidal activities within six days.  相似文献   

Modeling Ground Water Flow and Radioactive Transport in a Fractured Aquifer     

Greg Pohll  Ahmed E. Hassan  Jenny B. Chapman  Charalambos Papelis  Roko Andricevic 《Ground water》1999,37(5):770-784

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A method for matching response spectra of endurance time excitations via the Fourier transform     

Mashayekhi  Mohammadreza  Estekanchi  Homayoon E.  Vafai  Hassan 《地震工程与工程振动(英文版)》2020,19(3):637-648

The endurance time(ET) method is a dynamic analysis in which structures are subjected to intensifying excitations, also known as ET excitation functions(ETEF). The ET method is a tool for structural response prediction. The main advantage of the ET method over conventional approaches is its much lower demand for computational efforts. The concept of acceleration spectra is used in generating existing ETEFs. It is expected that ETEF acceleration spectra increase consistently with time and remain proportional to a target spectrum. Nonlinear unconstrained optimization is commonly used to generate ETEFs. Generating new ETEFs is a complicated time-consuming mathematical problem. If the target acceleration spectrum changes, new ETEFs must be generated. This study intends to modify existing ETEFs to be compatible with a desired acceleration spectrum. This process, called spectral matching, obviates the need for using the complicated generating procedure in simulating new ETEFs. ETEFs spectral matching is introduced in this paper for the first time. A Fourier-based method for ETEFs spectral matching is proposed. This algorithm is then applied in a case study. Results are presented to prove the efficiency of the algorithm.  相似文献   

Variable hillslope-channel coupling and channel characteristics of forested mountain streams in glaciated landscapes     

Marwan A. Hassan  Stephen Bird  David Reid  Carles Ferrer-Boix  Dan Hogan  Francesco Brardinoni  Shawn Chartrand 《地球表面变化过程与地形》2019,44(3):736-751

Channel morphology of forested, mountain streams in glaciated landscapes is regulated by a complex suite of processes, and remains difficult to predict. Here, we analyze models of channel geometry against a comprehensive field dataset collected in two previously glaciated basins in Haida Gwaii, B.C., to explore the influence of variable hillslope–channel coupling imposed by the glacial legacy on channel form. Our objective is to better understand the relation between hillslope–channel coupling and stream character within glaciated basins. We find that the glacial legacy on landscape structure is characterized by relatively large spatial variation in hillslope–channel coupling. Spatial differences in coupling influence the frequency and magnitude of coarse sediment and woody material delivery to the channel network. Analyses using a model for channel gradient and multiple models for width and depth show that hillslope–channel coupling and high wood loading induce deviations from standard downstream predictions for all three variables in the study basins. Examination of model residuals using Boosted Regression Trees and nine additional channel variables indicates that ~10 to ~40% of residual variance can be explained by logjam variables, ~15–40% by the degree of hillslope–channel coupling, and 10–20% by proximity to slope failures. These results indicate that channel classification systems incorporating hillslope–channel coupling, and, indirectly, the catchment glacial legacy, may present a more complete understanding of mountain channels. From these results, we propose a conceptual framework which describes the linkages between landscape history, hillslope–channel coupling, and channel form. © 2018 John Wiley & Sons, Ltd.  相似文献   

What controls the disequilibrium state of gravel-bed rivers?     

Shawn M. Chartrand  A. Mark Jellinek  Marwan A. Hassan  Carles Ferrer-Boix 《地球表面变化过程与地形》2019,44(15):3020-3041

A river at equilibrium is described by a statistically-stationary mean bed elevation profile that arises in response to steady supplies of relief, water and sediment. Outside of the profile shape, how is the equilibrium state of a river most reliably identified and rigorously defined? Motivated by a proposed link between equilibrium and physical processes, we use scaling theory to develop the dimensionless channel response number ξ=KU_b/U_p. ξ is a metric for the local disequilibrium state of gravel-bed mountain streams, which reflects a balance between the rate of topographic adjustment U_b, and the rate of bed sediment texture adjustment U_p. The coefficient K can take one of two forms depending on choice of length scale for topographic adjustment. We hypothesize that equilibrium occurs where and when ξ≈O(1), and consequently, disequilibrium is the more general state captured by conditions of ξ≉O(1). The rates U_b and U_p are controlled by the mechanics of sediment deposition and entrainment at the local scale of the channel width. The extent to which either process regulates disequilibrium depends on the bed strength, which is set by the time-varying grain size distribution and packing. We use flume experiments to understand ξ and find that in the limit ξ>>1, the time-varying response of an experimental channel depends sensitively on the spatially-averaged bed shear stress ratio τ/τ_ref. When τ/τ_ref≈1.5, U_b was the dominant control on disequilibrium. However, when τ/τ_ref≈2.0, U_p contributed more significantly to disequilibrium. These results suggest that after an upstream supply perturbation, the equilibrium timescale is governed by U_p, which we show is consistent with expectations from linear damping theory. Our experimental test of ξ is promising, but inconclusive with respect to our hypothesis. This uncertainty can be readily addressed with numerical or additional physical experiments. © 2019 John Wiley & Sons, Ltd.  相似文献   

Width variations control the development of grain structuring in steep step-pool dominated streams: insight from flume experiments     

Matteo Saletti  Marwan A. Hassan 《地球表面变化过程与地形》2020,45(6):1430-1440

We report results from flume experiments designed to study the effect of width variations on the formation and stability of steps in steep streams. To physically model channel width changes we inserted multiple trapezoidal elements in the flume. Two competing effects are in play: a fluidic effect, suggesting that steps are more likely to form in wide areas because of deposition enhanced by lower shear stress, and a granular effect, suggesting that steps are more likely to form in narrow areas because of particle jamming. Our experiments show that width variations enhance the formation of steps. Although steps can form in every location, those in narrow/narrowing areas are more common, more stable and they occupy a larger portion of the channel width. These results stress the importance of particle interactions in coarse-bedded streams and help river engineers by providing a new element to consider when designing step-pool sequences in river restoration projects. © 2020 John Wiley & Sons, Ltd.  相似文献   

Co-evolution of coarse grain structuring and bed roughness in response to episodic sediment supply in an experimental aggrading channel     

Marwan A. Hassan  Matteo Saletti  Chendi Zhang  Carles Ferrer-Boix  Joel P.L. Johnson  Tobias Müller  Claudia von Flotow 《地球表面变化过程与地形》2020,45(4):948-961

We use flume experiments to better understand how gravel-bed channels maintain bed surface stability in response to pulses of sediment supply. Bed elevations and surface imagery at high spatial resolutions were used to quantify the co-evolution of surface grain-size distribution (GSD), bed roughness statistics, and bed surface structures (clusters, cells and transverse features). Using a new semi-automated method, we identified individual stone structures over a 2 m × 1 m area throughout the experiments. After an initial coarsening, surface GSD and armouring ratio remained nearly stable as sediment pulses caused net bed aggradation. In contrast, individual grain structures continued to form, increase or decrease in size, and disappear throughout the experiments. The response of the bed to sediment pulses depended on the history of surface roughness evolution and bed surface structure development, as these factors changed much more in response to supply perturbations earlier in the experiments compared to later, even as the bed continued to aggrade. We interpret that the dynamic production and destruction of bed surface structures can act as a ‘buffer’ to sediment supply pulses, maintaining a stable bed surface during aggradation with minimal change in grain size or armouring. © 2019 John Wiley & Sons, Ltd.  相似文献   

海洋工程试验池中风场模拟     

彭涛  杨建民  李俊 《海洋工程》2009,27(2):8-13

在考虑海洋工程装备在极端海况和运行海况下的载荷与受力,风载荷也是一个不可忽视的因素.目前物理模型试验仍是研究海洋工程结构物载荷与运动性能的重要手段,而深海结构物在水平漂移运动较大,如何在较大范围内得到满足试验要求的风场,是提高试验能力的重要问题.应用数值计算方法对大范围的风场模拟进行了分析,并进行了相应的物理实验,在此基础上对海洋工程试验的风场模拟提出了若干建议.  相似文献   

Numerical Evaluation of Local Site Effects on Amplification of the 2017 Mw 7.3 Sarpol-e-Zahab,Iran, Earthquake Waves Using Near and Far-Field Records     

Sharafi  Hassan  Raeisi  Niloofar 《Geotechnical and Geological Engineering》2022,40(6):3007-3037

Geotechnical and Geological Engineering - This is the first study to quantitatively evaluate the local site effects in the most severely affected neighborhoods of Sarpol-e-Zahab city following the...  相似文献