Nonlinear dynamics and chaos in hydrologic systems: latest developments and a look forward   总被引：5，自引：3，他引：2  

Bellie Sivakumar 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(7):1027-1036

During the last two decades or so, studies on the applications of the concepts of nonlinear dynamics and chaos to hydrologic systems and processes have been on the rise. Earlier studies on this topic focused mainly on the investigation and prediction of chaos in rainfall and river flow, and further advances were made during the subsequent years through applications of the concepts to other problems (e.g. data disaggregation, missing data estimation, and reconstruction of system equations) and other processes (e.g. rainfall-runoff and sediment transport). The outcomes of these studies are certainly encouraging, especially considering the exploratory stage of the concepts in hydrologic sciences. This paper discusses some of the latest developments on the applications of these concepts to hydrologic systems and the challenges that lie ahead on the way to further progress. As for their applications, studies in the important areas of scaling, groundwater contamination, parameter estimation and optimization, and catchment classification are reviewed and the inroads made thus far are reported. In regards to the challenges that lie ahead, particular focus is given to improving our understanding of these largely less-understood concepts and also finding ways to integrate these concepts with the others. With the recognition that none of the existing one-sided ‘extreme-view’ modeling approaches is capable of solving the hydrologic problems that we are faced with, the need for finding a balanced ‘middle-ground’ approach that can integrate different methods is stressed. To this end, the viability of bringing together the stochastic concepts and the deterministic concepts as a starting point is also highlighted.  相似文献   

Encoding daily rainfall records via adaptations of the fractal multifractal method     

M. L. Maskey  C. E. Puente  B. Sivakumar  A. Cortis 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(7):1917-1931

A deterministic geometric approach, the fractal–multifractal (FM) method, already found useful in modeling storm events, is adapted here in order to encode, for the first time, highly intermittent daily rainfall records gathered over a water year and containing many days of zero rain. Through application to data sets gathered at Laikakota in Bolivia and Tinkham in Washington, USA, it is demonstrated that the modified FM approach can represent erratic rainfall records faithfully, while using only a few FM parameters. It is shown that the modified FM approach, by capturing the rain accumulated over the season, ends up preserving other statistical attributes as well as the overall “texture” of the records, leading to FM sets that are indistinguishable from observed sets and certainly within the limits of accuracy of measured rainfall. This fact is further corroborated comparing 20 consecutive years at Laikakota and a modified FM representation, via common statistical qualifiers, such as histogram, entropy function, and inter-arrival times.  相似文献   

Reducing Vulnerability of Agriculture and Forestry to Climate Variability and Change: Workshop Summary and Recommendations   总被引：1，自引：0，他引：1  

M. J. Salinger  M. V. K. Sivakumar  R. Motha 《Climatic change》2005,70(1-2):341-362

The International Workshop on Reducing Vulnerability of Agriculture and Forestry to Climate Variability and Climate Change held in Ljubljana, Solvenia, from 7 to 9 October 2002 addressed a range of important issues relating to climate variability, climate change, agriculture, and forestry including the state of agriculture and forestry and agrometeological information, and potential adaptation strategies for agriculture and forestry to changing climate conditions and other pressures. There is evidence that global warming over the last millennium has already resulted in increased global average annual temperature and changes in rainfall, with the 1990s being likely the warmest decade in the Northern Hemisphere at least. During the past century, changes in temperature patterns have, for example, had a direct impact on the number of frost days and the length of growing seasons with significant implications for agriculture and forestry. Land cover changes, changes in global ocean circulation and sea surface temperature patterns, and changes in the composition of the global atmosphere are leading to changes in rainfall. These changes may be more pronounced in the tropics. For example, crop varieties grown in the Sahel may not be able to withstand the projected warming trends and will certainly be at risk due to projected lower amounts of rainfall as well. Seasonal to interannual climate forecasts will definitely improve in the future with a better understanding of dynamic relationships. However, the main issue at present is how to make better use of the existing information and dispersion of knowledge to the farm level. Direct participation by the farming communities in pilot projects on agrometeorological services will be essential to determine the actual value of forecasts and to better identify the specific user needs. Old (visits, extension radio) and new (internet) communication techniques, when adapted to local applications, may assist in the dissemination of useful information to the farmers and decision makers. Some farming systems with an inherent resilience may adapt more readily to climate pressures, making long-term adjustments to varying and changing conditions. Other systems will need interventions for adaptation that should be more strongly supported by agrometeorological services for agricultural producers. This applies, among others, to systems where pests and diseases play an important role. Scientists have to guide policy makers in fostering an environment in which adaptation strategies can be effected. There is a clear need for integrating preparedness for climate variability and climate change. In developed countries, a trend of higher yields, but with greater annual fluctuations and changes in cropping patterns and crop calendars can be expected with changing climate scenarios. Shifts in projected cropping patterns can be disruptive to rural societies in general. However, developed countries have the technology to adapt more readily to the projected climate changes. In many developing countries, the present conditions of agriculture and forestry are already marginal, due to degradation of natural resources, the use of inappropriate technologies and other stresses. For these reasons, the ability to adapt will be more difficult in the tropics and subtropics and in countries in transition. Food security will remain a problem in many developing countries. Nevertheless, there are many examples of traditional knowledge, indigenous technologies and local innovations that can be used effectively as a foundation for improved farming systems. Before developing adaptation strategies, it is essential to learn from the actual difficulties faced by farmers to cope with risk management at the farm level. Agrometeorologists must play an important role in assisting farmers with the development of feasible strategies to adapt to climate variability and climate change. Agrometeorologists should also advise national policy makers on the urgent need to cope with the vulnerabilities of agriculture and forestry to climate variability and climate change. The workshop recommendations were largely limited to adaptation. Adaptation to the adverse effects of climate variability and climate change is of high priority for nearly all countries, but developing countries are particularly vulnerable. Effective measures to cope with vulnerability and adaptation need to be developed at all levels. Capacity building must be integrated into adaptation measures for sustainable agricultural development strategies. Consequently, nations must develop strategies that effectively focus on specific regional issues to promote sustainable development.  相似文献   

Simulation of biomass burning aerosols mass distributions and their direct and semi-direct effects over South Africa using a regional climate model     

M. Tesfaye  J. Botai  V. Sivakumar  G. Mengistu Tsidu 《Meteorology and Atmospheric Physics》2014,125(3-4):177-195

In this study, we examine the mass distributions, direct and semi-direct effects of different biomass burning aerosols (BBAs) over South Africa using the 12-year runs of the Regional Climate Model (RegCM4). The results were analyzed and presented for the main BB season (July–October). The results show that Mpumalanga, KwaZulu Natal and the eastern parts of Limpopo are the main local source areas of BBAs in South Africa. In comparison to carbonaceous aerosols, BB-induced sulfate aerosol mass loading and climatic effects were found to be negligible. All carbonaceous aerosols reduce solar radiation at the surface by enhancing local atmospheric radiative heating. The climatic feedback caused by BBAs, resulted in changes in background aerosol concentrations. Thus, on a regional scale, climatic effects of BBAs were also found in areas far away from the BBA loading zones. The feedback mechanisms of the climate system to the aerosol radiative effects resulted in both positive and negative changes to the low-level columnar averaged net atmospheric radiative heating rate (NAHR). Areas that experienced an NAHR reduction showed an increase in cloud cover (CC). During the NAHR enhancement, CC over arid areas decreased; whereas CC over the wet/semi-wet regions increased. The changes in surface temperature (ST) and surface sensible heat flux are more closely correlated with BBA semi-direct effects induced CC alteration than their direct radiative forcing. Furthermore, decreases (or increases) in ST, respectively, lead to the reductions (and enhancements) in boundary layer height and the vice versa on surface pressure. The direct and semi-direct effects of BBAs also jointly promoted a reduction and rise in surface wind speed that was spatially highly variable. Overall, the results suggest that the CC change induced by the presence of radiatively interactive BBAs is important to determine alterations in other climatic variables.  相似文献   

Biomarkers of selected heavy metal toxicity and histology of Chanos chanos from Kaattuppalli Island,Chennai, southeast coast of India     

Sivakumar Rajeshkumar  Samuvel Sukumar  Natesan Munuswamy 《Environmental Earth Sciences》2014,72(1):207-219

Bioaccumulation of heavy metals and its associated histological perturbations were studied in various tissues of Chanos chanos collected from Kaattuppalli Island, and they were compared with those of fish collected from the Kovalam coast. The concentration of four heavy metals: copper, lead, zinc and cadmium were determined in water, sediment and different tissues of fish (gills, liver and muscle). The result showed a marked difference between the two sites as well as significant variations within the water, sediment and biota samples. The decreasing trend of metals from both Kaattuppalli Island and Kovalam coast was in the order of Cd > Cu > Pb > Zn. Overall, the highest metal concentration was found in the sediment, water and biota collected from Kaattuppalli Island. The accumulation in the gills and liver of C. chanos was found to be quite high in comparison with that of muscle. These tissues were further investigated by light microscopy and the results were compared with the tissues from the reference site (Kovalam coast). The presence of large lipid droplets in the liver and increase of mucous cells in the gills were some of the most noticeable alterations observed that were related to heavy metal contaminants. It is concluded that histopathological biomarkers provide reliable and discriminatory data to augment heavy metal pollution in Kaattuppalli Island. Therefore, long-term monitoring is necessary to assess the eco-health of the Kaattuppalli Island environment by choosing a bio-indicator species like C. chanos, which provide accurate, reliable measurements of environmental quality.  相似文献   

Fluoride hydrogeochemistry and its occurrence in drinking water in Morappur region of Dharmapuri District,South India     

M. Panneer  R. Sivakumar  M. Senthilkumar 《International Journal of Environmental Science and Technology》2017,14(9):1931-1944

Groundwater is the major source of freshwater in region devoid of surface water resources. Once such region is the Morappur area, Dharmapuri district of Tamilnadu, wherein groundwater is major source of water for all purposes. The area is reported to be severely affected by fluorosis due to excessive Fluoride in groundwater. The area comprises of rocks of Archaean age, namely Charnockite, Epidote Hornblende Gneiss and ultramafic rocks. The area has experienced numerous tectonic disturbances in which numbers of vertical joints have developed and are filled with quartz/feldspathic veins, and highly mineralised. Two aquifer systems have been identified in the area, namely the weathered aquifer and fractured aquifer. In order to understand the factors controlling high Fluoride concentration in groundwater, 149 groundwater samples were collected during pre and post-monsoon period. Analytical results indicate that 35% groundwater samples show Fluoride concentration more than 1.5 ppm (permissible limit). Results indicate that both the aquifer units are affected by high Fluoride and deeper aquifers are more affected. Biotite and Hornblende minerals present in the area and interact with groundwater to release Calcium, Magnesium along with Fluoride. Further chloro-alkaline indices indicate that calcium ions are replaced by sodium due to reverse ion exchange, leading to high concentration of Fluoride along with high concentration of Sodium. Government has taken measures to provide Fluoride-free drinking water from distant surface water sources. However, it is important to follow certain water management methods to improve the groundwater quality.  相似文献   

Determination of suspended sediments particle size distribution using image capturing method     

Sivakumar Ramalingam 《Marine Georesources & Geotechnology》2018,36(8):867-874

Suspended sediments deposition at estuary affects marine life in coastal ecosystem. Particle size distribution (PSD) is used to find settling velocity of suspended sediments. In this study, a new image capturing system for size analysis (ICS4S) method using digital camera-based image capturing technique for determining PSD is proposed and validated. Image of suspended sediments is acquired using a low-cost setup developed, and ImageJ software is used for image processing. The PSD results obtained using ICS4S method is well correlated with hydrometer test and the Shen method. The proposed ICS4S method is easy to understand and implement both in laboratory and field.  相似文献