Regional climate simulations over Vietnam using the WRF model     

S. V. Raghavan  M. T. Vu  S. Y. Liong 《Theoretical and Applied Climatology》2016,123(1-2):161-170

Time-irreversible symmetry is a fundamental property of nonlinear time series. Time-irreversible behaviors of mean temperature measured on 182 stations over China from 1960 to 2012 are analyzed by directed horizontal visibility graph (DHVG for short), and significance of results has been estimated by Monte Carlo simulations. It is found that dominated time irreversibility emerges in nearly all daily temperature anomaly variations over China. Further studies indicate that these time-irreversible behaviors result from asymmetric distributions of persistent daily temperature increments and decrements, and this kind of symmetry can be quantified by distributions of consecutive daily mean temperature increasing or decreasing steps. At the same time, the findings above have been confirmed by artificially generated time series with given value of multiscale asymmetry.  相似文献   

U–Pb Ages for Zircon Grains from Nsanaragati Alluvial Gem Placers: Its Correlation to the Source Rocks          下载免费PDF全文

Nguo Sylvestre Kanouo  Rose Fouateu Yongue  Emile Ekomane  Emmanuel Njonfang  Changqian Ma  David R. Lentz  Zhenbing She  Khin Zaw  Akella Satya Venkatesh 《Resource Geology》2015,65(2):103-121

The Mamfe Basin is located in the SW of Cameroon and is an extension of the much bigger Benue Trough in the SE of Nigeria. Along the Asenem River and its tributaries in the western part of the Mamfe Basin (close to the border with Nigeria) gem placers yielding big zircon grains were found in recent river sediments close to Nsanaragati. In order to determine the source area and to establish a possible correlation between the zircons found in the Nsanaragati placers and rocks surrounding the Mamfe Basin 56 detrital zircon grains were analysed regarding their U–Pb ages and selected trace element contents by LA‐ICP–MS techniques. Possible source areas are rocks from the Benue Trough in the West and from the Cameroon Volcanic Line (CVL) in the SE of the study area. Based on microscopic analyses it was possible to distinguish two groups of zircons: reddish and non‐reddish ones, where the latter group comprises color variations from brown to orange, yellow to even colorless. In general, the detrital zircons show high hafnium values (4576 to 12565 ppm) and very variable thorium (7.8 to 1565 ppm) and uranium values (13.4 to 687 ppm). The Th/U ratios vary from 0.4 to 2.3, allowing correlations for some zircon grains to kimberlitic, granitic or syenitic affinities. It was also possible to distinguish zircon grains crystallised in mafic mantle‐derived melts from those crystallised in felsic melts, e.g. from continental rift‐related magmatic systems. In general, the U–Pb zircon ages obtained range from 11.7 to 1949 Ma. All zircons of the reddish group yielded almost similar ages resulting in a Concordia age of 12.4 Ma (Serravallian), an age unknown from the Mamfe Basin so far. The group of non‐reddish zircons showed various ages ranging from Serravallian to Orosirian. It was possible to correlate the youngest ages with rocks known from intrusions along the CVL, dated with K/Ar or Ar/Ar methods. The most probable sources were Mount Bamenda and Mount Bambouto in the east of the Mamfe Basin. Cretaceous ages are interpreted as re‐recycled clastic sediments whose original source had been rocks in the south and the north of the Benue Trough and who had been eroded and deposited within the catchment area of the Asenem river system in the Mamfe Basin in post‐Cretaceous times. The oldest ages are assumed to represent the pan‐African and pre‐pan‐African basement of the Mamfe basin.  相似文献   

Bringing communities at the Centre of Impact Assessment of Road Projects: integrating AHP with qualitative research     

Priya  Preeti  Venkatesh  Anand 《GeoJournal》2021,86(4):1625-1637

GeoJournal - This paper proposes a framework for measuring impacts associated with road projects on rural communities situated on either side of the road alignment. The extant approaches for...  相似文献   

Possible Impacts of Global Warming on the Hydrology of the Ogallala Aquifer Region   总被引：11，自引：0，他引：11  

Norman J. Rosenberg  Daniel J. Epstein  David Wang  Lance Vail  Raghavan Srinivasan  Jeffrey G. Arnold 《Climatic change》1999,42(4):677-692

The Ogallala or High Plains aquifer provides water for about 20% of the irrigated land in the United States. About 20 km³ (16.6 million acre-feet) of water are withdrawn annually from this aquifer. In general, recharge has not compensated for withdrawals since major irrigation development began in this region in the 1940s. The mining of the Ogallala has been pictured as an analogue to climate change in that many GCMs predict a warmer and drier future for this region. In this paper we attempt to anticipate the possible impacts of climate change on the sustainability of the aquifer as a source of water for irrigation and other purposes in the region. We have applied HUMUS, the Hydrologic Unit Model of the U.S. to the Missouri and Arkansas-White-Red water resource regions that overlie the Ogallala. We have imposed three general circulation model (GISS, UKTR and BMRC) projections of future climate change on this region and simulated the changes that may be induced in water yields (runoff plus lateral flow) and ground water recharge. Each GCM was applied to HUMUS at three levels of global mean temperature (GMT) to represent increasing severity of climate change (a surrogate for time). HUMUS was also run at three levels of atmospheric CO₂ concentration (hereafter denoted by [CO₂]) in order to estimate the impacts of direct CO₂ effects on photosynthesis and evapotranspiration. Since the UKTR and GISS GCMs project increased precipitation in the Missouri basin, water yields increase there. The BMRC GCM predicts sharply decreased precipitation and, hence, reduced water yields. Precipitation reductions are even greater in the Arkansas basin under BMRC as are the consequent water yield losses. GISS and UKTR climates lead to only moderate yield losses in the Arkansas. CO₂-fertilization reverses these losses and yields increase slightly. CO₂ fertilization increases recharge in the base (no climate change) case in both basins. Recharge is reduced under all three GCMs and severities of climate change.  相似文献   

Evaluation of global optimization algorithms for parameter calibration of a computationally intensive hydrologic model   总被引：1，自引：0，他引：1  

Xuesong Zhang  Raghavan Srinivasan  Kaiguang Zhao  Mike Van Liew 《水文研究》2009,23(3):430-441

With the popularity of complex hydrologic models, the time taken to run these models is increasing substantially. Comparing and evaluating the efficacy of different optimization algorithms for calibrating computationally intensive hydrologic models is becoming a nontrivial issue. In this study, five global optimization algorithms (genetic algorithms, shuffled complex evolution, particle swarm optimization, differential evolution, and artificial immune system) were tested for automatic parameter calibration of a complex hydrologic model, Soil and Water Assessment Tool (SWAT), in four watersheds. The results show that genetic algorithms (GA) outperform the other four algorithms given model evaluation numbers larger than 2000, while particle swarm optimization (PSO) can obtain better parameter solutions than other algorithms given fewer number of model runs (less than 2000). Given limited computational time, the PSO algorithm is preferred, while GA should be chosen given plenty of computational resources. When applying GA and PSO for parameter optimization of SWAT, small population size should be chosen. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Simulation of Flow in a Complex Aquifer System Subjected to Long-Term Well Network Growth     

Hua-Sheng Liao  Zachary K Curtis  Prasanna Venkatesh Sampath  Shu-Guang Li 《Ground water》2020,58(2):301-322

In west-central Lower Peninsula of Michigan, population growth and expanded agricultural activities over recent decades have resulted in significant increases in distributed groundwater withdrawals. The growth of the extensive well network and anecdotes of water shortages (dry wells) have raised concerns over the region's groundwater sustainability. We developed an unsteady, three-dimensional (3D) groundwater flow model to describe system dynamics over the last 50 years and evaluate long-term impacts of groundwater use. Simulating this large aquifer system was challenging; the site is characterized by strong, spatially distributed, and statistically nonstationary heterogeneity, making it difficult to avoid over-parameterization using traditional approaches for conceptualizing and calibrating a flow model. Moreover, traditional pumping and water level data were lacking and prohibitively expensive to collect given the large-scale and long-term nature of this study. An integrated, stochastic-deterministic approach was developed to characterize the system and calibrate the flow model through innovative use of high-density water well datasets. This approached allowed (1) implementation of a “zone-based,” nonstationary stochastic approach to conceptualize complex spatial variability using a small set of geologic material types; (2) modeling the spatiotemporal evolution of many water well withdrawals across several decades using sector-based parameterization; and (3) critical analysis of long-term water level changes at different locations in the aquifer system for characterizing the system dynamics and calibrating the model. Results show the approach is reasonably successful in calibrating a complex model for a highly complex site in a way that honors complex distributed heterogeneity and stress configurations.  相似文献   

Glacier mass balance simulation using SWAT distributed snow algorithm   总被引：2，自引：1，他引：1  

Nina Omani  Raghavan Srinivasan  Patricia K. Smith  Raghupathy Karthikeyan 《水文科学杂志》2017,62(4):546-560

Application of a temperature-index melt model incorporated into the Soil and Water Assessment Tool (SWAT) is presented to simulate mass balance (MB) and equilibrium line altitude (ELA) of three glaciers. The snow accumulation/melt parameters were adjusted to glacierized and free glacier areas, respectively. The SWAT snow algorithm enabled us to consider spatial variation of snow parameters by elevation bands across the sub-basins, while in the previous studies using SWAT, the related parameters were constant for an entire basin. The results show slight improvement in runoff simulation and significant improvement in simulated MB when considering ELA in model calibration. The results showed that SWAT can be applied to simulate MB, vertical MB distribution and annual ELA, with light calibration efforts for data-scarce catchments. The accuracy of the results depends on the modelled area of ablation zone from which most of the meltwater is released.  相似文献   

Modelling the behaviour of oil spills in ice‐infested waters     

S. Venkatesh  H. El‐Tahan  G. Comfort  R. Abdelnour 《大气与海洋》2013,51(3):303-329

Abstract

This paper describes methodologies developed for predicting the drift and spread of oil spills in ice‐infested waters. Particular emphasis is placed on oil spills in medium and high ice concentrations. For ice concentrations greater than about 30%, the oil is found to drift with the ice. Empirical methods are used to determine the spread of oil in ice of different concentrations. The study showed that the equilibrium oil thickness in slush or brash (broken) ice is nearly 4 times that on cold water, which is itself very different from that on warm water. Comparisons with limited available data show good agreement.  相似文献   

Estimation of damage to agriculture biomass due to Hudhud cyclone and carbon stock assessment in cyclone affected areas using Landsat-8     

Venkatesh Reddy Chejarla  Gobinath Palanisamy  Mithun Choudhary 《国际地球制图》2017,32(6):589-602

Developing countries are vulnerable to tropical cyclones due to climatic variability and the frequency and magnitude of some extreme weather and disaster events is likely to increase. Cities and towns situated along the coastal belt of Visakhapatnam district experienced severe damage because of Hudhub cyclone (12 October 2014). The main objective of this research was to identify and quantify the damage to agriculture and vegetation caused by Hudhud cyclone. In this study, landsat-8 satellite data-sets acquired before and after the cyclone have been used; image processing techniques have been carried out to assess the changes of pre- and post-cyclone condition. Economic loss of agriculture crops has been assessed using crop production loss per hectare and total economic loss for agriculture crops in the study area was calculated. Classification results and land use land cover change analysis show that 13.25% of agriculture-Kharif and 31.1% of vegetation was damaged. Crop Biomass was estimated with aid of crop conversion factor for pre- and post-cyclone conditions. Total ‘Above ground biomass’ of the agriculture crop area was estimated at 31.57 t/ha and total loss of biomass was assessed to be 4.2 t/ha. Carbon stock was found to be varying from 0.3 to 8.3 t.C/ha in specific agriculture crops. From the results, it was concluded that Hudhud has done significant damage to the rural and urban areas of Visakhapatnam. The outcome of this study can be used by decision-makers for the release of post disaster relief fund to affected areas.  相似文献   

Statistical downscaling rainfall using artificial neural network: significantly wetter Bangkok?     

Minh Tue Vu  Thannob Aribarg  Siriporn Supratid  Srivatsan V Raghavan  Shie-Yui Liong 《Theoretical and Applied Climatology》2016,123(3-4):453-460

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