GPS-derived precipitable water vapour and its comparison with MODIS data for Almora, Central Himalaya, India

The present study is an attempt to analyse the precipitable water vapour (PWV) derived from Global Positioning System (GPS) and observed meteorological data over Almora, Central Himalayan Region. The PWV values derived using GPS study is compared with the corresponding moderate resolution imaging spectro-radiometer (MODIS) data. The statistical analysis reveals a positive correlation between both methods. Moderate resolution imaging spectroradiometer near-infrared (MODIS NIR) clear column water vapour product shows a higher correlation (R ² = 90–93 %) with GPS-derived precipitable water vapour on annual scale as compared to the seasonal scale (R ² = 62–87 %). MODIS is found to be overestimating in NIR clear column where the magnitude of bias and RMSE show systematic changes from season to season. Monsoon is an important phenomenon in the Indian weather context and holds significant importance in Central Himalayan ecosystem. The monthly and seasonal variation in precipitable water vapour is related with monsoon onset in the region. Diurnal variations in precipitable water vapour are studied with other meteorological data over Almora during dry and wet season. The precipitable water vapour had minimum value in the morning, increases in the afternoon to evening and again decreases to the midnight in both the dry and wet seasons. These results suggest that diurnal variation of water vapour is caused by the transport of water vapour by thermally induced local circulation.     

Hurricanes and tropical storms: A necessary evil to ensure water supply?

Several parts of the globe including Southeast North America, the Caribbean, Southeast Asia, Australia, and China are often hit by hurricanes and tropical storms (HTSs), which can deliver a large amount of rainfall within a period of a few days. Although HTSs are mostly studied as disaster agents, considering that they occur during the period when water supply systems are generally depleted, it is important to ascertain their potential contributions toward sustaining water supply. Using the Lake Michie–Little River reservoir system that supplies water to the city of Durham (North Carolina) as a representative test case, we implemented an integrated watershed and reservoir management model, supported by publicly available observations, to evaluate the extent to which HTSs impact water storages. Results indicate that HTSs can have a significant impact on reservoir water storage, with their effects being felt for more than a year for some storms. The impact on reservoir water storage is identified to be primarily controlled by 3 factors, namely, streamflow response size from HTSs, storage in the reservoir right before the event, and streamflow succeeding the event response to HTS (henceforth referred as postevent streamflow). Although the impact of streamflow response size on water storage is generally proportional to its magnitude, initial water storage in the reservoir and postevent streamflow have a nonmonotonic influence on water storage. As all the 3 identified controls are a function of antecedent hydrologic conditions and meteorological forcings, these 2 factors indirectly influence the impact of HTS on water storage in a reservoir. The identification of controlling factors and assessment of their influence on reservoir response will further facilitate implementation of more accurate estimation and prediction frameworks for within‐year reservoir operations.     

Longitudinal Distribution of Solar Flares and Their Association with Coronal Mass Ejections and Forbush Decreases

Major Hα solar-flare events of high optical importance have been employed to study their heliographic distribution in longitude around the Sun for the period of 2001 to 2006. A statistical analysis was performed to obtain their relationship with halo/partial-halo CMEs and Forbush decreases (Fds) of cosmic-ray intensity. Our analysis indicates that 63% of the solar flares associated with halo CMEs and Fds occur in the western hemisphere and of 37% of such flares occur in the eastern hemisphere. Similarly, we found that nearly 60% of the solar flares associated with partial- halo CMEs and Fds occur in the western hemisphere and the rest (40%) occur in the eastern hemisphere. Finally, we conclude that the flares in association with CMEs and located in the western hemisphere of the solar disk are more effective in producing Fds. The magnitudes of Fds are observed to be higher when in association of halo CMEs. A slight excess in the eastern hemisphere is found for both the halo and partial-halo CMEs.     

Mean Flow Near Edges and Within Cavities Situated Inside Dense Canopies

A streamfunction-vorticity formulation is used to explore the extent to which turbulent and turbulently inviscid solutions to the mean momentum balance explain the mean flow across forest edges and within cavities situated inside dense forested canopies. The turbulent solution is based on the mean momentum balance where first-order closure principles are used to model turbulent stresses. The turbulently inviscid solution retains all the key terms in the mean momentum balance but for the turbulent stress gradients. Both exit and entry versions of the forest edge problem are explored. The turbulent solution is found to describe sufficiently the bulk spatial patterns of the mean flow near the edge including signatures of different length scales reported in canopy transition studies. Next, the ‘clearing inside canopy’ or the so-called ‘cavity’ problem is solved for the inviscid and turbulent solutions and then compared against flume experiments. The inviscid solution describes the bulk flow dynamics in much of the zones within the cavity. In particular, the solution can capture the correct position of the bulk recirculation zone within the cavity, although with a weaker magnitude. The inviscid solution cannot capture the large vertical heterogeneity in the mean velocity above the canopy, as expected. These features are better captured via the first-order closure representation of the turbulent solution. Given the ability of this vorticity formulation to capture the mean pressure variations and the mean advective acceleration terms, it is ideal for exploring the distributions of scalars and roughness-induced flow adjustments on complex topography.     

Net primary productivity and species diversity of herbaceous vegetation in banj-oak (Quercus leucotrichophora A. Camus) forest in Kumaun Himalaya, India

Net primary productivity and species diversity of herbaceous vegetation of banj-oak (Quercus leucotrichophora A.Camus) forest in Kumaun Himalaya,India were analyzed.Across different growth forms (tall forbs,short forbs,cushion and spreading forbs,grasses),short forbs were most dominant component during rainy season (IVI=152) and winter season (IVI=167) and grasses during the winter season (IVI=148).Maximum above-ground production occurred during rainy season (132.5 g m-2) and minimum during winter season (2.8 g m-2).Below-ground production was maximum (85.9 g m-2) during winter season and minimum (14.9 g m-2) during summer season.Annual net shoot production was 150 g m-2 and below-ground production was 138 g m-2.Of the total input 61 % was channeled to above-ground parts and 39% to below-ground parts.     

Evaluation of hydrogeochemical processes and groundwater quality in the Jhansi district of Bundelkhand region, India

A base line study involving analysis of groundwater samples from the Jhansi district were carried out to determine the major and trace element chemistry and to assess the hydrogeochemical processes and water quality for domestic and irrigation uses. Study results show that groundwater is mildly acidic to alkaline in nature and HCO₃ ^?, Cl^?, Ca²⁺, Na⁺ and Mg²⁺ are the major contributing ions for the dissolved loads. The data plotted on the Gibbs and Piper diagrams reveal that the groundwater chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources. In a majority of the groundwater samples, alkaline earth metals exceed alkalies and weak acid dominate over strong acids. Ca–Mg–HCO₃ is the dominant hydrogeochemical facies in the majority of the groundwater samples. The computed saturation indices demonstrate that groundwater is oversaturated with respect to dolomite and calcite. Kaolinite is the possible mineral that is in equilibrium with the water, implying that the groundwater chemistry favors kaolinite formation. A comparison of groundwater quality parameters in relation to specified limits for drinking water shows that the concentrations of TDS, F^?, NO₃ ^?, total hardness and Fe are exceeding the desirable limits in many water samples. Quality assessment for irrigation uses reveal that the groundwater is of good to suitable category. Higher salinity and residual sodium carbonate values at some sites restrict the suitability of groundwater and need an adequate drainage and water management plan for the area.     

Spatial and temporal variations in the groundwater contributing areas of inland wetlands

Water quality and groundwater dynamics in wetlands are strongly influenced by the spatiotemporal distribution of contaminant application, and variations and changes in climate, vegetation, and anthropogenic interventions in its neighborhood. For groundwater-fed wetlands, this relevant neighborhood at least extends to the groundwater contributing area (GCA) boundary. In spite of its importance, understanding of the nature of GCA dynamics vis-à-vis meteorological variations remains largely understudied. This work attempts to map GCA of inland forested wetlands. Following that, two specific questions are answered: (a) Is GCA extent and its variation different than that of the topographic contributing area (TCA)? and (b) Is the temporal dynamics of GCA for different wetlands, all of which are experiencing very similar climatological forcing, similar? Our results show that GCAs for wetlands vary temporally, are much different in extent and shape than the TCA, and on an average are larger than the TCA. Although wetlands in the studied watershed experienced similar meteorological forcings, their covariation with forcings varied markedly. Majority of the wetlands registered an increase in GCA during dry period, but for a few the GCA decreased. This highlights the role of additional physical controls, other than meteorological forcings, on temporal dynamics of GCA. Notably, wetlands with larger TCA are found to generally have larger average GCA as well, thus indicating the dominant role of topography in determining the relative size of average GCA over the landscape. Our results provide a refined picture of the spatiotemporal patterns of GCA dynamics and the controls on it. The information will help improve the prediction of wet period dynamics, recharge, and contamination risk of groundwater-fed wetlands.     

Metal contamination of agricultural soils in the copper mining areas of Singhbhum shear zone in India

The study was intended to investigate the heavy metal contamination in the agricultural soils of the copper mining areas in Singhbhum shear zone, India. The total concentrations of the metals were determined by inductively coupled plasma-mass spectrometer (ICPMS). Pollution levels were assessed by calculating enrichment factor (EF), geo-accumulation index (\(I_\mathrm{geo}\)), contamination factors (CF), pollution load index (PLI), Nemerow index and ecological risk index (\(R_{I}\)). The metal concentrations in the soil samples exceeded the average shale values for almost all the metals. Principal component analysis resulted in extraction of three factors explaining 82.6% of the data variability and indicated anthropogenic contribution of Cu, Ni, Co, Cr, Mn and Pb. The EF and \(I_\mathrm{geo}\) values indicated very high contamination with respect to Cu followed by As and Zn in the agricultural soils. The values of PLI, \(R_{I}\) and Nemerow index, which considered the overall effect of all the studied metals on the soils, revealed that 50% of the locations were highly polluted with respect to metals. The pollution levels varied with the proximity to the copper mining and processing units. Consequently, the results advocate the necessity of periodic monitoring of the agricultural soils of the area and development of proper management strategies to reduce the metal pollution.     

Biodegradation of Nonylphenol Ethoxylate Surfactants in Biofilm Reactors

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)%.