Waves to the lee of a meso-scale elliptic orographic barrier

Summary ?The paper considers a meso-scale, adiabatic, inviscid and Boussisnesq flow of a stably stratified fluid over a three-dimensional (3-D) meso-scale orographic barrier with elliptic contour, with special reference to a part of the Western ghats mountain along west coast of India and on the Khasi-Jayantia hill in the northeast India. The airstream characteristics are simplified by assuming that the upstream wind velocity (U) and buoyancy frequency (N) are constant with height. Solutions for perturbation vertical velocity (w′) and streamline displacement (η′) are expressed in terms of double integrals. These integrals cannot be evaluated exactly, hence they have been approximated by asymptotic expansion method. Side by side solutions using numerical method have also been obtained. The results of the study indicate that the updraft regions in the asymptotic solution are crescent shaped, symmetrical about the axis y = 0, tilting upwind and spreading laterally with height. The study also shows that in both asymptotic solution and numerical solution w′ and η′ fall off down wind of the barrier in the central plane (y = 0), further more in the asymptotic solution w′ and η′ fall off as x ⁻¹. The study also indicates that the discrete updraft regions obtained in the numerical solution, when joined, take a crescent shape. Received November 26, 2001; accepted February 27, 2002     

Discrimination and classification of mangrove forests using EO-1 Hyperion data: a case study of Indian Sundarbans

In remote sensing the identification accuracy of mangroves is greatly influenced by terrestrial vegetation. This paper deals with the use of specific vegetation indices for extracting mangrove forests using Earth Observing-1 Hyperion image over a portion of Indian Sundarbans, followed by classification of mangroves into floristic composition classes. Five vegetation indices (three new and two published), namely Mangrove Probability Vegetation Index, Normalized Difference Wetland Vegetation Index, Shortwave Infrared Absorption Index, Normalized Difference Infrared Index and Atmospherically Corrected Vegetation Index were used in decision tree algorithm to develop the mangrove mask. Then, three full-pixel classifiers, namely Minimum Distance, Spectral Angle Mapper and Support Vector Machine (SVM) were evaluated on the data within the mask. SVM performed better than the other two classifiers with an overall precision of 99.08%. The methodology presented here may be applied in different mangrove areas for producing community zonation maps at finer levels.     

Estimating statistics of sky brightness using radio interferometric observations

Radio interferometers are used to construct high resolution images of the sky at radio frequencies and are the key instruments for accessing the statistical properties of the evolution of neutral hydrogen over cosmic time. Here we use simulated observations of the model sky to assess the efficacy of different estimators of the large-scale structure and power spectrum of the sky brightness distribution. We find that while the large-scale distribution can be reasonably estimated using the reconstructed image from interferometric data, estimates of the power spectrum of the intensity fluctuations calculated from the image are generally biased. This bias is found to be more pronounced for diffuse emission. The visibility based power spectrum estimator, however, gives an unbiased estimate of the true power spectrum. This work demonstrates that for an observation with diffuse emission the reconstructed image can be used to estimate the large-scale distribution of the intensity, while to estimate the power spectrum, visibility based methods should be preferred.With the upcoming experiments aimed at measuring the evolution of the power spectrum of the neutral hydrogen distribution, this is a very important result.     

Analysis of water resources in the Mahanadi River Basin,India under projected climate conditions

The paper presents the outcomes of a study conducted to analyse water resources availability and demand in the Mahanadi River Basin in India under climate change conditions. Climate change impact analysis was carried out for the years 2000, 2025, 2050, 2075 and 2100, for the months of September and April (representing wet and dry months), at a sub‐catchment level. A physically based distributed hydrologic model (DHM) was used for estimation of the present water availability. For future scenarios under climate change conditions, precipitation output of Canadian Centre for Climate Modelling and Analysis General Circulation Model (CGCM2) was used as the input data for the DHM. The model results show that the highest increase in peak runoff (38%) in the Mahanadi River outlet will occur during September, for the period 2075–2100 and the maximum decrease in average runoff (32·5%) will be in April, for the period 2050–2075. The outcomes indicate that the Mahanadi River Basin is expected to experience progressively increasing intensities of flood in September and drought in April over the considered years. The sectors of domestic, irrigation and industry were considered for water demand estimation. The outcomes of the analysis on present water use indicated a high water abstraction by the irrigation sector. Future water demand shows an increasing trend until 2050, beyond which the demand will decrease owing to the assumed regulation of population explosion. From the simulated future water availability and projected water demand, water stress was computed. Among the six sub‐catchments, the sub‐catchment six shows the peak water demand. This study hence emphasizes on the need for re‐defining water management policies, by incorporating hydrological response of the basin to the long‐term climate change, which will help in developing appropriate flood and drought mitigation measures at the basin level. Copyright © 2008 John Wiley & Sons, Ltd.     

A meso-scale three-dimensional dynamical model of orographic rainfall

Summary A mesoscale three-dimensional (3-D) dynamical model is presented to diagnose orographic rainfall, with particular reference to the Western Ghats (WG) in India. This model has two parts, namely, a dynamical part and a thermodynamical part. In the dynamical part the vertical velocity induced by a mesoscale elliptical orographic barrier has been computed using the perturbation technique. In the thermodynamical part rainfall intensity (RFI) has been computed using the computed vertical velocities, with the help of continuity of moisture and mass. The computed RFI has been compared with observed RFI as well as with that computed by 2-D model. The present study shows that during the southwest monsoon season (SWMS), orographic rainfall enhancement in the WG area appears to be solely due to the vertical shear of the basic flow and its variation with height. Stability appears to have very little influence on it. The spatial distribution of RFI across the barrier shows that there are four regions of maximum rainfall, one primary on the windward side behind the peak of the barrier and three secondary on the leeward side. The symmetry in the locations of these secondary rainfall maxima appears to be critically dependent on the component of basic flow parallel to the major ridge axis of the barrier.     

A GIS and remote sensing based approach for siting cold storage infrastructure for horticultural crops: A case study for potato crop in Bardhaman district, West Bengal, India

A pilot study was taken up to evolve an optimum plan to locate cold stores for potato in Bardhaman district of West Bengal, India, a leading potato growing area. Remote sensing data from IRS sensors was used to delineate the potato growing area. Road and village information was derived from high-resolution remote sensing data and 1:50,000 scale Survey of India topographic maps. The analysis showed that the present capacity of cold stores can cater to around 40 percent of production. A combination of buffering and location-allocation analysis was performed using Art/Info software. Total 57 cold storage sites with average capacity were identified. Further, analysis was carried out for phase wise development of sites according to priority.     

Erodibility of fine soil from the composite river bank of Brahmaputra in India

The erosion of a composite river bank critically depends on the erodibility of its fine soils, as the fine soil has higher resistance against erosion. Therefore, for the estimation of the bank erosion in the case of a composite river bank, it is important to determine the critical shear stress and erodibility coefficients of the bank soil and their spatial distribution. In the present study, erodibility parameters of the river bank of Brahmaputra in India have been estimated through 58 in situ submerged jet tests. The significance of spatial and layer‐wise distribution of the erodibility parameters was tested through analysis of variance (ANOVA). Results indicate that the spatial variation of erodibility parameters is highly significant, but layer‐wise variations of the erodibility parameters are not significant. Therefore, the erodibility of the riverbank depends on the particular location, whereas layer‐wise average erodibility parameters can be lumped for the estimation of the bank erosion for the specific site. Using the measured erodibility parameters, yearly river bank erosions at the study locations were computed and found to fall within the reported range of the bank erosion in the Brahmaputra River. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthetic impact response functions for flood vulnerability analysis and adaptation measures in coastal zones under changing climatic conditions: a case study in Gippsland coastal region,Australia

There is an increasing concern that the current management practices for many coastal regions are unsustainable. Very few countries have planned to deal with the exacerbation of environmental decline in the face of sea level rise. It is therefore necessary to assess socioeconomic and environmental impacts of sea level rises to better understand the vulnerability of coastal zones, as part of devising adaptive and integrated management principles. This paper presents a systematic approach by which relevant stakeholders can be actively engaged in prioritising flood impact issues and deriving information for quantification of impacts for adaptation measures and demonstrates the approach through implementation in the Gippsland coastal region. As outcomes of the project, we have identified key issues of concern for this region for flood impacts and constructed synthetic response functions for quantification of impacts of floods on some of the key issues in the region. The analysis also showed that stakeholders consider that some of the issues are not likely to be significantly affected by floods and thus may not require adaptation measures. The analysis did not provide high agreement on some issues. Different approaches are required to assess the importance of these issues and to establish impact response functions for them.