Temporal and spatial variability of annual and seasonal rainfall over Ethiopia     

Negash Wagesho  N.K. Goel  M.K. Jain 《水文科学杂志》2013,58(2):354-373

Abstract

Characterization of the seasonal and inter-annual spatial and temporal variability of rainfall in a changing climate is vital to assess climate-induced changes and suggest adequate future water resources management strategies. Trends in annual, seasonal and maximum 30-day extreme rainfall over Ethiopia are investigated using 0.5° latitude?×?0.5° longitude gridded monthly precipitation data. The spatial coherence of annual rainfall among contiguous rainfall grid points is also assessed for possible spatial similarity across the country. The correlation between temporally coinciding North Atlantic Multidecadal Oscillation (AMO) index and annual rainfall variability is examined to understand the underlying coherence. In total 381 precipitation grid points covering the whole of Ethiopia with five decades (1951–2000) of precipitation data are analysed using the Mann-Kendall test and Moran spatial autocorrelation method. Summer (July–September) seasonal and annual rainfall data exhibit significant decreasing trends in northern, northwestern and western parts of the country, whereas a few grid points in eastern areas show increasing annual rainfall trends. Most other parts of the country exhibit statistically insignificant trends. Regions with high annual and seasonal rainfall distribution exhibit high temporal and spatial correlation indices. Finally, the country is sub-divided into four zones based on annual rainfall similarity. The association of the AMO index with annual rainfall is modestly good for northern and northeastern parts of the country; however, it is weak over the southern region.

Editor Z.W. Kundzewicz; Associate editor S. Uhlenbrook

Citation Wagesho, N., Goel, N.K., and Jain, M.K. 2013. Temporal and spatial variability of annual and seasonal rainfall over Ethiopia. Hydrological Sciences Journal, 58 (2), 354–373.  相似文献   

Development of isopluvial map using L-moment approach for Tehri-Garhwal Himalaya     

S. Sarkar  N. K. Goel  B. S. Mathur 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(3):411-423

Estimation of design rainfall intensity is crucial for design and planning of water resources engineering projects. The intent of the present study is to develop regional IDF curves for Tehri-Garhwal Himalayan region in India, wherein numbers of hydropower projects are in planning and execution stage. Self Recording Rain Gauge (SRRG) stations are generally not so frequent in the project locations. Under this situation, the engineers are forced to use regional intensity duration frequency (IDF) curves. Under this study, four stations viz. Tehri M.T.Lab, Mukhim, Pilkhi and Dhuttu were available with SRRG data. These data are used to develop the regional IDF curve for entire Tehri-Garwal region. After selection of the most intensive storms, return periods has been determined using regionalized L-moment method. After developing IDF curves for above four raingauge stations, Thiessen Ploygon method is applied to find out average IDF curve. To show the spatial variability, Isopluvial maps have been generated using ArcGIS and a relation equation has been developed.  相似文献   

Effects of supplemental viscous damping on inelastic seismic response of asymmetric systems     

Rakesh K. Goel  Cecilia A. Booker 《地震工程与结构动力学》2001,30(3):411-430

This paper investigates the effects of supplemental viscous damping on the seismic response of one‐storey, asymmetric‐plan systems responding in the inelastic range of behaviour. It was found that addition of the supplemental damping reduces not only deformation demand but also ductility and hysteretic energy dissipation demands on lateral load resisting elements during earthquake loading. However, the level of reduction strongly depends on the plan‐wise distribution of supplemental damping. Nearly optimal reduction in demands on the outermost flexible‐side element, an element generally considered to be the most critical element, was realized when damping was distributed unevenly in the system plan such that the damping eccentricity was equal in magnitude but opposite in algebraic sign to the structural eccentricity of the system. These results are similar to those noted previously for linear elastic systems, indicating that supplemental damping is also effective for systems expected to respond in the inelastic range. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Biodegradation of Nonylphenol Ethoxylate Surfactants in Biofilm Reactors     

Anubha Goel  Margit B. Müller  Mukesh Sharma  Fritz H. Frimmel 《洁净——土壤、空气、水》2003,31(2):108-119

The primary degradation of a technical nonylphenol ethoxylate surfactant with an average chain length of 10 ethoxylate units (NPEO‐10) was studied in a flow‐through system by means of miniaturized biofilm reactors (mBFR) with bacteria from an activated sludge plant. 5 mg/L of the test compound (total EO concentration) were spiked in synthetic wastewater (SWW) and fed to the reactors continuously for 64 days. Compound removal and the formation of degradation products (DP) were monitored under both oxic and anoxic conditions. Solid‐phase extraction and RP‐HPLC with fluorescence detection were employed for sample preparation and analysis. Better removal of the parent compound was seen with the oxic reactors (50 to 70%) than with the anoxic reactors (30 to 50%). Compared to SWW organic matter, the test compound proved to be of refractory nature. The appearance of degradation products in the effluent was earlier with anoxic reactors despite their lower elimination efficiency. After extraction of biomass only minor amounts of NPEO‐10 and metabolites were found, indicating that small amounts were present in adsorbed or intracellular form. Ultimate biodegradation of NPEO‐10 and of octylphenol ethoxylates (OPEO‐9.5; average chain length of 9.5 EO units) was tested by means of manometric respirometry at a theoretical oxygen demand (ThOD) of 100 mg/L. Whereas NPEO‐10 was biodegraded by only 26%, at best, in 28 days, OPEO‐9.5 degradation amounted to (40 ± 5)%.  相似文献   

Seismic response of linear and non‐linear asymmetric systems with non‐linear fluid viscous dampers     

Rakesh K. Goel 《地震工程与结构动力学》2005,34(7):825-846

This investigation is concerned with the seismic response of one‐story, one‐way asymmetric linear and non‐linear systems with non‐linear fluid viscous dampers. The seismic responses are computed for a suite of 20 ground motions developed for the SAC studies and the median values examined. Reviewed first is the behaviour of single‐degree‐of‐freedom systems to harmonic and earthquake loading. The presented results for harmonic loading are used to explain a few peculiar trends—such as reduction in deformation and increase in damper force of short‐period systems with increasing damper non‐linearity—for earthquake loading. Subsequently, the seismic responses of linear and non‐linear asymmetric‐plan systems with non‐linear dampers are compared with those having equivalent linear dampers. The presented results are used to investigate the effects of damper non‐linearity and its influence on the effects of plan asymmetry. Finally, the design implications of the presented results are discussed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Variable190Os/184Os ratio in acid residues of iron meteorites     

P. S. Goel 《Journal of Earth System Science》1987,96(2):81-102

In residual materials obtained on dissolution of iron meteorites in 2M H₂SO₄, the ratio of¹⁹⁰Os/¹⁸⁴Os has been measured by radiochemical neutron activation analysis. Most residues have a normal isotopic ratio (to within ±2%). However, in some residues both positive and negative deviations in the isotopic ratio are seen. The most spectacular deviations are in the insoluble fragments (nuggets) from Sikhote Alin iron meteorite where the¹⁹⁰Os/¹⁸⁴Os ratio is about 50% of the normal value. The new results confirm our earlier observations that iron meteorites contain pre-solar grains.  相似文献   

以减少碳损失为目标的印度大城市可持续林业：以德里地区为例     

Abhineety Goel  Dr. R. B. Singh 《地球科学进展》2006,21(2):144-150

试图识别德里从大气中固碳的碳源行为以及进一步证明各种造林工程有利于控制碳损失。碳化气的释放来源于城市的各个环节，包括城市的居民生活、工业过程、电力生产和轮船及热源工厂的辐射。这里主要想证明德里的土地利用/覆盖变化通过砍伐森林来进行地铁、立交桥、建筑和其他非森林可持续的城市建设对森林和树木覆盖造成的压力。所有的这些都导致德里的微气候变化，尤其是气温的升高。造林工程可以提供大量的气候变化缓解效应。  相似文献   

Mass Balance Reconstruction Since 1963 and Mass Balance Model for East Rathong Glacier,Eastern Himalaya,Using Remote Sensing Methods          下载免费PDF全文

Anubha Agrawal  Shresth Tayal 《Geografiska Annaler: Series A, Physical Geography》2015,97(4):695-707

In this study mass balance, accumulation, ablation, runoff and temperature lapse rate for the East Rathong glacier are estimated for the time period 1963–2011 using remote sensing methods and climate data. A mass balance model is proposed for the glacier that computes mass balance as difference of volumes of consecutive years. Volume estimates of glacier are based on application of volume–area scaling law to glacier area computed from satellite images. It is observed that the glacier is summer‐accumulation type. Time series analysis is applied to the annual mass balance series. The annual mass balance of the glacier is showing a statistically significant negative trend. It is also showing a statistically significant shift in the year 1985. Change in the mean of mass balance before and after the shift year is 0.19 m w.e. Cumulative mass balance suggests that the glacier has lost ～11 m w.e. or 0.047 km³ during the last 48 years.  相似文献   

Prediction of load displacement response of single piles under uplift load     

Shubhra Goel  Nihar Ranjan Patra 《Geotechnical and Geological Engineering》2007,25(1):57-64

Load displacement response and ultimate resistance of piles in sand under uplift load are predicted by load transfer approach. The pile is divided into number of segments and assigned geometrical and material properties according to actual soil pile situation. The shaft resistance is obtained analytically in accordance with existing studies. The proposed method takes into account the length, diameter and relevant surface characteristics of pile and soil properties. The load displacement characteristics and the value of uplift capacity of vertical piles from field test have been predicted. Reasonable agreement has been found out between predicted and observed values of uplift capacity. Load transfer mechanism is capable of predicting the nonlinear variation of load-displacement response of piles.  相似文献   

Development of unbiased plotting position formula for General Extreme Value distributions     

N. K. Goel  M. De 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(1):1-13

Expressions for the expected values of GEV order statistics have been derived in simple summation form and in terms of probability weighted moments. Using exact plotting positions from GEV order statistics a new unbiased plotting position formula has been developed for the General Extreme Value distribution. The formula can, explicitly, take into account the coefficient of skewness, (or the shape parameter, k), of the underlying distribution.The developed formula better approximates the exact plotting positions as compared to other existing formulae and is quite easy to use.  相似文献