Development of a flood forecasting system using IFAS: a case study of scarcely gauged Jhelum and Chenab river basins

Development of a well-calibrated, distributed hydrological model for flood forecasting based on rainfall and snowmelt is quite challenging, especially when in situ data is limited or unavailable. This paper presents the study carried out to parameterise the Integrated Flood Analysis System (IFAS) model for the trans-boundary, scarcely gauged catchments of Jhelum and Chenab rivers in Pakistan. Rainfall-runoff analysis was performed with a two-layered tank configuration, integrating snowmelt and dam and barrage operation from the very upstream in India to Trimmu Barrage in Pakistan. A grid size of 5?×?5 km was considered. Global map topography, land cover and soil data was utilised. The model was tested considering different magnitudes of floods of the years 2014, 2015 and 2017. The results showed that the satellite rainfall product, i.e. Global Satellite Mapping of Precipitation (GSMaP-NRT), underestimated the rainfall volume, compared to the ground-gauged rainfall. The GSMaP-IF correction method showed poor performance owing to the lack of ground observatory rainfall data for correcting the trans-boundary part of the basin. The GSMaP-Type1 correction method showed good results, except for the confluence point where complex flow conditions were not properly reproduced by the model. In addition, the incorporation of dam and barrages in the model improved the simulated flow results. It is concluded that the satellite rainfall estimates must be corrected to improve the results. Snowmelt module estimated the snowmelt contribution as 3 to 7% and 4 to 23% of the average daily discharge during the monsoon season at Mangla Dam and Marala Barrage, respectively, during 2014 and 2015. This study assessed various correction methods and concluded that the model and methodology used in the study functioned well with suitable precipitation.     

A New Semi-supervised Classification Method Based on Mixture Model Clustering for Classification of Multispectral Data

A new method for semi-supervised classification of remotely-sensed multispectral image data is developed in this study. It consists of unsupervised-clustering for data labelling and supervised-classification of clusters in multispectral image data (MID) using spectral signatures. Mixture model clustering, based on model selection, is proposed for finding the number and determining the structures of clusters in MID. The best mixture model, for the best clustering of data, finds the number and determines the structure of clusters in MID. The number of elements in the best mixture model fits to the number of clusters in MID. The elements of the best mixture model fits to the structure of clusters in MID. Clusters in MID is supervised-classified using spectral signatures. Euclidean distance is used as the discrimination function for the supervised-classification method. The values of Euclidean distances are used as decision rule for the supervised-classification method.     

Analyzing the occurrence of floods and droughts in connection with climate change in Punjab province,Pakistan

Natural Hazards - Frequency and intensity of extreme weather events are immensely changing throughout the world. This study aims to give insight into the changing climatic patterns leading to...     

Bayesian inference for the Errors-In-Variables model

We discuss the Bayesian inference based on the Errors-In-Variables (EIV) model. The proposed estimators are developed not only for the unknown parameters but also for the variance factor with or without prior information. The proposed Total Least-Squares (TLS) estimators of the unknown parameter are deemed as the quasi Least-Squares (LS) and quasi maximum a posterior (MAP) solution. In addition, the variance factor of the EIV model is proven to be always smaller than the variance factor of the traditional linear model. A numerical example demonstrates the performance of the proposed solutions.     

断层含水层在非等温条件下的构造性渗流——一种震前热前兆异常产生的机理

本文用一个简单的解析模式来计算,在被断层带切断的含水层,由于形变产生的渗流引起的热量瞬时流动。在这个模式中,含水层流体的补给被假定只是通过弱隔水层垂向渗流。在这种条件下,能量平衡方程要计算由于含水层体积变化和形变产生的水力压头变化引起的流体水平向和垂直向流动的单位热量传递。数值模拟的结果表明在应力增加期,当渗流的地下水与含水层的地下水混合的时候,地温就表现为瞬时的升高。相应地,当这一渗流过程停止的时候,地温迅速回到平衡状态。利用此解析模型,可以重建观测记录中的地温前兆异常特征。按照模型的结果,地温升高达到稳定状态的时间和流体的补给率相关。热异常的幅度与弱隔水层的温度梯度有关,弱隔水层与含水层之间的渗透率也起到很重要的作用。模型的结果表明热前兆异常只是在离断层近的区域表现明显,由于在这个区域构造渗流的过程对含水层的水力压头有直接的影响。如果断层面对形变敏感,应力模式的改变会使得构造渗流率发生永久的改变,从而很容易使区域的温度场产生剧烈的、不可恢复的改变。在某些构造活跃区域的井孔地温记录中,一些短临异常变化的特征和按照“构造渗流”模型的预测结果非常相似。在土库曼斯坦的Firjusa、乔治亚州的Didiweli和日本的Izu peninsnla都有这种震前热前兆模型的例子。研究表明,与小规模构造形变相关的热前兆异常并不是罕见的。热前兆异常的监测要有合适的井孔和高精度的监测仪器,其观测时间至少要与区域地震复发周期相当。     

Possible role of magnetosphere-ionosphere coupling in auroral arc generation

Three models for the magnetosphere-ionosphere coupling feedback instability are considered. The first model is based on demagnetization of hot ions in the plasma sheet. The instability takes place in the global magnetosphere-ionosphere system when magnetospheric electrons drift through a spatial gradient of hot magnetospheric ion population. Such a situation exists on the inner and outer edges of the plasma sheet where relatively cold magnetospheric electrons move earthward through a radial gradient of hot ions. This leads to the formation of field-aligned currents. The effect of upward field-aligned current on particle precipitation and the magnitude of ionospheric conductivity leads to the instability of this earthward convection and to its division into convection streams oriented at some angle with respect to the initial convection direction. The growth rate of the instability is maximum for structures with sizes less than the ion Larmor radius in the equatorial plane. This may lead to formation of auroral arcs with widths about 10 km. This instability explains many features of such arcs, including their conjugacy in opposite hemispheres. However, it cannot explain the very high growth rates of some auroral arcs and very narrow arcs. For such arcs another type of instability must be considered. In the other two models the instability arises because of the generation of Alfven waves from growing arc-like structures in the ionospheric conductivity. One model is based on the modulation of precipitating electrons by field-aligned currents of the upward moving Alfven wave. The other model takes into consideration the reflection of Alfven waves from a maximum in the Alfven velocity at an altitude of about 3000 km. The growth of structures in both models takes place when the ionization function associated with upward field-aligned current is shifted from the edges of enhanced conductivity structures toward their centers. Such a shift arises because the structures move at a velocity different from the E × B drift. Although both models may work, the growth rate for the model, based on the modulation of the precipitating accelerated electrons, is significantly larger than that of the model based on the Alfven wave reflection. This mechanism is suitable for generation of auroral arcs with widths of about 1 km and less. The growth rate of the instability can be as large as 1 s^-1, and this mechanism enables us to justify the development of auroral arcs only in one ionosphere. It is hardly suitable for excitation of wide and conjugate auroral arcs, but it may be responsible for the formation of small-scale structures inside a wide arc.Polar Geophysical Institute, Apatity, Russia     

Desert pavement characteristics on wadi terrace and alluvial fan surfaces: Wadi Al-Bih, U.A.E. and Oman

In arid mountain areas, the dating and correlation of alluvial depositional surfaces is often uncertain. Especially in regions where the geomorphology is not well known, surface modification by the development of soil and desert pavement may allow the correlation of geomorphic surfaces and estimation of at least their relative ages. Pleistocene wadi terraces and associated alluvial fans occur in Wadi Al-Bih, U.A.E. and Oman, for which correlations and age relationships are not known. Three age-related groups of fans and terraces have been identified and mapped on the basis of their morphostratigraphic relationships. Deposition of the oldest terrace sediments and associated fans followed a long period of sustained incision after Miocene uplift of the region. The younger two groups of terraces and fans are inset within the older group. To identify the gross effects of pavement development, comparisons have been made between terrace surface and subsurface particle-size distributions. The older terraces have finer surface sediments and a greater contrast between finer surface and subsurface sediments than the younger terraces. This reflects the degree of pavement development. Particle size on the fan surfaces is comparable with that on the equivalent terrace surfaces. Criteria for the classification of pavements were developed based on clast fracturing and angularity, size, sorting, packing, and surface texture, from which a simple index of pavement development has been derived. Other properties, rock varnish and weathering characteristics, were also recorded; but these proved to be less discriminatory than pavement characteristics. The pavement data have been augmented by observations on soils. Detailed studies of pavements on terraces (8 sites, 12 samples covering the three age groups) and fans (5 sites, 10 samples covering the three age groups) allow differentiation between age-groups. The three terraces show three different age-related pavement types, expressed by differences in the pavement development index. Weakly-developed pavements (little fracturing, sub-rounded clasts, some modification of the depositional fabric, incipient soil development, stage I CaCO₃ accumulation) occur on the youngest terrace and fan surfaces. Moderately-developed pavements (clast fracturing, sub-angular clasts, moderate sorting and packing, deeper soil development, stage II CaCO₃ accumulation) occur on the middle terrace and fan surfaces. Well-developed pavements (complete clast fracturing into small angular fragments, mature sorting and packing of the pavement surface, deep soil development with strong horizonation, stage III CaCO₃ accumulation) occur on the highest terrace and oldest fan surfaces. There are minor differences between the youngest pavements on terraces and fans, which reflect initial sedimentological differences. These differences become less as the pavements develop. On the basis of comparative studies, the oldest terrace is estimated to date from sometime prior to ca. 100 ka BP, the second terrace and the most extensive fan surface from the Late Pleistocene, and the youngest terrace and fan phase from the Latest Pleistocene or Early Holocene.     

Hot plasma waves in Schwarzschild magnetosphere

In this paper we examine the wave properties of a hot plasma living in a Schwarzschild magnetosphere. The 3+1 GRMHD perturbation equations are formulated for this scenario. These equations are Fourier analyzed and then solved numerically to obtain the dispersion relations for a non-rotating, rotating non-magnetized and rotating magnetized plasma. The wave vector is evaluated, which is used to calculate the refractive index. These quantities are shown in graphs which are helpful to discuss the dispersive properties of the medium near the event horizon.     

Microphysical characteristics of rainfall during different seasons over a coastal tropical station using disdrometer

Drop size distribution (DSD) over the tropical region exhibit pronounced variations during different monsoon seasons. Measurements from an impact type Joss–Waldovgel disdrometer is used for characterization of drop size distribution and its integral parameters over a tropical coastal station (Thiruvananthapuram, 8.31°N, 76.54°E, 20 m asl). Rain events were identified during the winter, premonsoon, summer monsoon and postmonsoon seasons from 8 years, computed rain duration (min) and accumulated rain water (mm). Rain intensity (mm h^?1), mean drop diameter (D_m, mm) and total number concentration of raindrops (N_T, m^?3) were calculated on each sampling interval and classified in to different bins. The different range bins of rain intensity and their relative contributions towards total rainfall are different for different seasons. Maximum events were reported on the R2 (heavy drizzle/light rain) type, but the contribution of rainfall (mm) is mainly registered on R4 (heavy rain) type. Similarly, the N_T and D_m are also showing different characteristics during different monsoon seasons. Frequency of occurrence of D_m is higher in D_m2 (1–2 mm) followed by D_m1 (D_m < 1 mm) and then D_m3 (2–3 mm) with difference in magnitudes for different seasons. On analysing relative rainfall contribution from different mean diameter bins, it can be observed that D_m2 and D_m3 (1–3 mm) are the major contributors to the total rainfall. In the case of N_T, both frequency and accumulated water are almost same or comparable for the different bins during all the seasons. The D_m and N_T are positively related with different intensity bins. The lower rainfall intensity bins show higher duration during the summer monsoon season and lower duration during the premonsoon season, the higher intensity range bins show lower duration for the premonsoon season and higher duration for the postmonsoon season.     

Temporal and depth distribution of microepiphytes on Posidonia oceanica (L.) Delile leaves in a meadow off Tunisia

A survey on the epiphytic microorganisms growing on Posidonia oceanica leaves was conducted along a depth transect along the coast of Eastern Tunisia (Mahdia). Samples were collected by SCUBA diving at depths of 3, 5, 10 and 12 m in July 2008 and January 2009. A total of 58 microepiphyte taxa were identified. Multivariate analyses revealed temporal and spatial variation of the abundance of epiphytic microalgae. Water motion, light availability, temperature and motility of species seem to be responsible of temporal and bathymetric variations of epiphytic microalgae. Unlike diatoms, dinoflagellates were more abundant in deep waters, suggesting that they are more vulnerable to hydrodynamics. The significant correlation between leaf area index and abundance of epiphytic species indicates that the phenological parameters of the host plant influence the abundance of the epiphytic microorganisms. Among the epiphytic dinoflagellates, our data showed a great number of potentially toxic species (Alexandrium minitum, Amphidinium carterae, Karenia selliformis, Coolia monatis, Karlodinium veneficum, Ostreopsis siamensis, Prorocentrum concavum, Prorocentrum minimum, Prorocentrum rathymum and Prorocentrum lima). These species were more abundant in the deep station under more sheltered conditions than found at inshore shallower stations, which are subjected to high water motion.