Probabilistic forecasting of seasonal droughts in the Pearl River basin,China

Forecasting of droughts is essential for developing measures for mitigation of drought hazards and for reducing drought-induced loss. In this study, droughts were characterized by the standardized precipitation-evapotranspiration index with a time scale of 3 months. Copula-based probabilistic forecasting models were developed to predict drought occurrences. Results indicated higher probability of occurrence of seasonal droughts after the occurrence of more severe seasonal droughts, and extreme drought in winter tended to persist with higher probability till spring, whereas extreme drought in autumn might not probably last to winter. Furthermore, results indicated high probability of occurrence of droughts in southeast parts of the Pearl River basin during spring to winter. Thus, droughts in the Pearl River basin are subject to lengthening duration, particularly in the southeastern part of the basin. It should be noted here that the southeastern part is densely populated with a high degree of socioeconomic development. Thus, higher probability of droughts in the southeastern part should attract considerable concern. Higher drought risk was also identified in the western part of the basin. Results of this study provide a theoretical framework for water resources management and conservation of eco-environment in the Pearl River basin in a changing climate, and may serve as a reference for evaluation of drought risk in other regions of the world.     

Frequency analysis of droughts using the Plackett copula and parameter estimation by genetic algorithm

This study aims to model the joint probability distribution of drought duration, severity and inter-arrival time using a trivariate Plackett copula. The drought duration and inter-arrival time each follow the Weibull distribution and the drought severity follows the gamma distribution. Parameters of these univariate distributions are estimated using the method of moments (MOM), maximum likelihood method (MLM), probability weighted moments (PWM), and a genetic algorithm (GA); whereas parameters of the bivariate and trivariate Plackett copulas are estimated using the log-pseudolikelihood function method (LPLF) and GA. Streamflow data from three gaging stations, Zhuangtou, Taian and Tianyang, located in the Wei River basin, China, are employed to test the trivariate Plackett copula. The results show that the Plackett copula is capable of yielding bivariate and trivariate probability distributions of correlated drought variables.     

Zn(II) Ion Biosorption onto Surface of Eucalyptus Leaf Biomass: Isotherm,Kinetic, and Mechanistic Modeling

Bioremediation of Zn(II) by biosorption across aqueous phase on to surface of eucalyptus leaf powder has been investigated in present research work. The adsorptive potential of eucalyptus leaf powder was evaluated as function of pH, temperature, contact time, agitation rate and particle size. Maximum metal ion uptake and percentage removal capacity of eucalyptus leaf powder were 23.5 mg g⁻¹ and 94%, respectively, at optimized pH 5, 20 ± 1°C, contact time 6 h, particle size 0.5 mm and agitation rate 200 rpm. The biomass surface analysis revealed the fact that the biomass surface was heterogeneous and porous in nature. The functional groups like amine, amide, carboxyl, hydroxyl, and methyl groups, significantly important for metal ion binding were present on biomass surface in tremendous amount. Additionally, the Fourier transformation IR spectrum analysis of acid and base activated eucalyptus leaf biomass ruled out all the possibilities of the presence of surface functional groups mentioned above. The reaction rate was studied by applying two rate limiting models pseudo first and pseudo second order. Pseudo second order model was found to be more suitable (R² = 0.998) in comparison to pseudo first order (R² = 0.724). Adsorption equilibrium of batch stirred reaction data fitting shows the dominance of Langmuir isotherm (R² = 0.99) against Freundlich isotherm (R² = 0.887) model with equipartitional involvement of both film and intra particle diffusion as rate limiting steps at differential status of contact time.     

Self-organized Fractal Seismicity of Reservoir Triggered Earthquakes in the Koyna-Warna Seismic Zone,Western India

— Analysis of the Koyna-Warna earthquake catalog (1968–1996) shows that on an average there is a positive correlation between the b value (decrease) and fractal dimensions (decrease in both D₂^s and D₂^t) of earthquake epicenters 0.5 and 2.5 years prior to 1973 (M5.2) and 1980 (M5.5) events, respectively, except a negative correlation for about five years (1988–1993) prior to the 1993/1994 sequence (M5.4). This positive correlation indicates a weaker clustering, or that the epicenters tend to fill the two-dimensional plane. While the origin of the negative correlation seems to be that during periods of large events (low b value), there is strong clustering around the main shock epicenter (high fractal dimension). Interestingly, during the last year (1995–1996) of the studied period both the b value and correlation dimensions rose significantly, suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity, suggesting an increased risk of larger magnitude events. Incidentally, during 2000 three earthquakes of magnitude M 5.0, one earthquake of M 4.0, 45 earthquakes of magnitude M 3.0–3.9, and several thousand earthquakes of M < 3 have occurred in the region. Thus it can be inferred that at local scales the relationship yields both positive and negative correlation that appears to be controlled by different modes of failure within the active fault complex.Acknowledgement. The authors are grateful to Dr. B.K. Rastogi of NGRI for providing the catalog of Koyna earthquakes and for useful scientific discussions. The comments of Dr. I. G. Main have improved the quality of paper for which we extend to him our sincere thanks. One of the authors (AOM) thanks the Third World Academy of Science and the Council of Scientific and Industrial Research, India for the Postdoctoral Fellowship award under which this work was carried out.     

Existence of libration points in the generalised photogravitational restricted problem of three bodies

In this paper we have proved the existence of libration points for the generalised photogravitational restricted problem of three bodies. We have assumed the infinitesimal mass of the shape of an oblate spheroid and both of the finite masses to be radiating bodies and the effect of their radiation pressure on the motion of the infinitesimal mass has also been taken into account. It is seen that there is a possibility of nine libration points for small values of oblateness, three collinear, four coplanar and two triangular.     

Automatic recognition of geologic prospects

Computer recognition of prospective areas through the processing of digital exploration data can be effective if the statistical tests for the determination of the prospects are pertinent to the presence of the desired mineral. Where exploration involves the application of polynomial trend analysis to structure contour maps in the search for petroleum and natural gas, standard analysis of variance tests may not indicate the best exploration maps. Variance tests may be completely invalid where isolated dips and clustered samples cause the surfaces generated by some of the most common trend programs to oscillate, creating a false impression of variance. On the other hand, tests that directly compare the position of residual features with areas of known production consistently indicate the best map for the determination of new prospects. They are simple to apply and appear to offer the most opportunity for the automatic recognition of prospective areas.     

Comment on “The stability of UO2OH+ and UO2(HPO4)22− complexes at 25°C” by G. Dongarra and D. Langmuir

Equilibrium calculations have shown that all the solutions in the experiments of Dongarra and Langmuir (1980) were super-saturated with respect to uranyl triphosphate; the degree of super-saturation varied from 3 to 857. In spite of the super-saturation, for all of their experiments n? and molal % UO₂(HPO⁴)₂^2? have been found to be <0.5 and <12 respectively. Similarly in all of their experiments 88–98% of ∑U(VI) existed as UO₂²⁺ or hydroxo complexes. Based on the analysis of their data it has been shown that their experimental conditions were not appropriate for determining the stability constant of UO₂(HPO⁴)₂^2?. The significance of careful design of experiments has been demonstrated. The uncertainty in log β (±0.2) as reported by these authors is too small in view of the very small $\text{n}\text{?}$ as well as negligible pH change during titrations. Furthermore, the fact that the β determined by Dongarra and Langmuir is very close to that of Moskvin et al. (1967) certainly does not serve to validate the work of Dongarra and Langmuir, since Dongarra and Langmuir, as well as this writer, have found several problems in the work of Moskvin et al.     

Precipitation extremes in the Yangtze River Basin,China: regional frequency and spatial–temporal patterns

Regional frequency analysis and spatial–temporal patterns of precipitation extremes are investigated based on daily precipitation data covering 1960–2009 using the index-flood L-moments method together with some advanced statistical tests and spatial analysis techniques. The results indicate that: (1) the entire Yangtze River basin can be divided into six homogeneous regions in terms of extreme daily precipitation index. Goodness-of-fit test indicates that Pearson type III (PE3, three parameters), general extreme-value (GEV, three parameters), and general normal (GNO, three parameters) perform well in fitting regional precipitation extremes; (2) the regional growth curves for each homogeneous region with 99 % error bands show that the quantile estimates are reliable enough and can be used when return periods are less than 100 years, and the results indicate that extreme precipitation events are highly probable to occur in regions V and VI, and hence higher risk of floods and droughts; and (3) spatial patterns of annual extreme daily precipitation with return period of 20 years indicate that precipitation amount increases gradually from the upper to the lower Yangtze River basin, showing higher risks of floods and droughts in the middle and lower Yangtze River basin, and this result is in good agreement with those derived from regional growth curves.     

Spatiotemporal variations of precipitation regimes across Yangtze River Basin,China

Daily precipitation data during the period of 1960 to 2005 from 147 rain gauging stations over the Yangtze River Basin are analyzed to investigate precipitation variations based on precipitation indices and also consecutive rainfall regimes in both space and time. Results indicate decreasing annual/monthly mean precipitation. Distinct decreases in rainfall days are observed over most parts of the Yangtze River Basin, but precipitation intensity is increasing over most parts of the Yangtze River Basin, particularly the lower Yangtze River Basin. Besides, durations of precipitation regimes are shortening; however, the fractional contribution of short-lasting precipitation regimes to the total precipitation amount is increasing. In this sense, the precipitation processes in the Yangtze River Basin are dominated by precipitation regimes of shorter durations. These results indicate intensified hydrological cycle reflected by shortening precipitation regimes. This finding is different from that in Europe where the intensifying precipitation changes are reflected mainly by lengthening precipitation regimes, implying different regional responses of hydrological cycle to climate changes. The results of this study will be of considerable relevance in basin-scale water resources management, human mitigation of natural hazards, and in understanding regional hydrological responses to changing climate at regional scales.