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1.
In glacierized catchments, meteorological inputs driving surface melting are translated into runoff outputs mediated by the glacier hydrological system: analysis of the relationship between meteorology and diurnal and seasonal patterns of runoff should reflect the functioning of that system, with the role of meltwater storage likely to be of particular importance. Daily meltwater storage is determined for a glacier at 78 °N in the Svalbard archipelago, by comparing inputs calculated from a surface energy balance model with measured outputs (proglacial discharge). Solar radiation, air temperature, wind speed and proglacial discharge are then analysed by regression and time‐series methods, in order to assess the meteorology–discharge relationship and its variation at diurnal and seasonal time‐scales. The recorded discharge time‐series can be divided into two contrasting intervals: up to early August, proglacial discharge was high and variable, mean hydrographs showed little indication of diurnal cycling, ARIMA models of discharge indicated a non‐seasonal, moving‐average generating process, and there was a net loss of meltwater from storage; from early August, proglacial discharge was low and relatively invariable, but with clearer diurnal cycles, regression models of discharge showed substantially improved correlations with air temperature and solar radiation, ARIMA models indicated a non‐seasonal, autoregressive generating process, and eventually a seasonal component, and there was a net gain in meltwater storage. The transition between the two periods is brief compared with the duration of the melt season. The runoff response to meteorology therefore lacks the strongly progressive element previously identified in mid‐latitude glacierized catchments. In particular, the glacier hydrological system only appears responsive to diurnal forcing following the depletion of the seasonal snowpack meltwater store. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

2.
An analysis of temporal variability in proglacial suspended sediment concentration is undertaken using time series data collected from three Svalbard basins which include one largely cold-based glacier (Austre Brøggerbreen), one largely warm-based glacier (Finsterwalderbreen) and one intermediate polythermal glacier (Erdmannbreen). The temporal variability in proglacial suspended sediment concentration is analysed using multiple regression techniques in which discharge is supplemented by other predictors acting as surrogates for variability in sediment supply at diurnal, medium-term and seasonal timescales. These multiple regression models improve upon the statistical explanation of suspended sediment concentration produced by simple sediment rating curves but need to account for additional stochastic elements within the time series before they may be considered successful. An interpretation of the physical processes which are responsible for the regression model characteristics is offered as a basis for comparing the different arctic glaciofluvial suspended sediment transport systems with that of their better known temperate glaciofluvial counterparts. It is inferred that the largely warm-based glacier is dominated by sediment supply from subglacial reservoirs which evolve in a similar manner to temperate glaciers and which cause a pronounced seasonal exhaustion of suspended sediment supply. The largely cold-based glacier, however, is dominated by sediment supply from marginal sources which generate a responsive system at short time scales but no significant seasonal pattern. The intermediate polythermal glacier basin, which was anticipated to be similar to the warm-based glacier, instead shows a highly significant seasonal increase in suspended sediment supply from an unusual subglacial reservoir emerging under pressure in the glacier foreland. The temperate model of glaciofluvial suspended sediment transport is therefore found to be of limited use in an arctic context. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

3.
Himalayan basins have considerable snow‐ and glacier‐covered areas, which are an important source of water, particularly during summer season. In the Himalayan region, in general, the glacier melt season is considered to be from May to October. Changes in hydrological characteristics of the runoff over the melt season can be understood by studying the variation in time to peak and time lag between melt generation and its emergence as runoff. In the present study, the runoff‐delaying characteristics of Gangotri Glacier, one of the largest glaciers in the Indian Himalayas, have been studied. For this purpose, hourly discharge and temperature data were collected near the snout of the glacier (4000 m) for three ablation seasons (2004–2006). The diurnal variations in discharge and temperature provided useful information on water storage and runoff characteristics of the glacier. In the early stages of the ablation period, poor drainage network and stronger storage characteristics of the glaciers due to the presence of seasonal snow cover resulted in a much delayed response of melt water, providing a higher time lag and time to peak as compared to the peak melt season. A comparison of runoff‐delaying parameters with the discharge ratio clearly indicated that changes in time lag and time to peak are inversely correlated with variations in discharge. Impact of such meltwater storage and delaying characteristics of glaciers on hydropower projects being planned/developed on glacier‐fed streams in India has been discussed. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
气候背景下冰川在博斯腾湖水量平衡中的作用   总被引：3，自引：1，他引：2  
孙占东  王润 《湖泊科学》2006,18(5):484-489
基于博斯腾湖水量平衡关系,对博斯腾湖水量变化做了分析,认为博斯腾湖近年水位的显著变化与占其入湖水量85%的开都河流量变化有直接关系．冰川作为开都河上游重要的水资源形势,造就了开都河稳定的基流．部分冰川在近20年全球和区域气候变化影响下发生了较大退缩,消退的冰雪直接补给了开都河径流,对开都河连年丰水起了重要作用．随着相对海拔较低的中小冰川的退缩,冰益变薄雪线升高,冰雪储量减少,冰川对气温升高的敏感性开始降低,融水补给量可能随之减少,气候变暖所带来的融水补给效应将减弱,最终影响到博斯腾湖的入流补给．  相似文献   

5.
We measured stream temperature continuously during the 2011 summer run‐off season (May through October) in nine watersheds of Southeast Alaska that provide spawning habitat for Pacific salmon. The nine watersheds have glacier coverage ranging from 0% to 63%. Our goal was to determine how air temperature and watershed land cover, particularly glacier coverage, influence stream temperature across the seasonal glacial meltwater hydrograph. Multiple linear regression models identified mean watershed elevation (related to glacier extent) and watershed lake coverage (%) as the strongest landscape controls on mean monthly stream temperature, with the weakest (May) and strongest (July) models explaining 86% and 97% of the temperature variability, respectively. Mean weekly stream temperature was significantly correlated with mean weekly air temperature in seven streams; however, the relationships were weak to non‐significant in the streams influenced by glacial run‐off. Streams with >30% glacier coverage showed decreasing stream temperatures with rising summer air temperatures, whereas those with <30% glacier coverage exhibited summertime warming. Glaciers also had a cooling effect on monthly mean stream temperature during the summer (July through September) equivalent to a decrease of 1.1 °C for each 10% increase in glacier coverage. The maximum weekly average temperature (an index of thermal suitability for salmon) in the six glacial streams was substantially below the lower threshold for optimum salmon growth. This finding suggests that although glaciers are important for moderating summer stream temperatures, future reductions in glacier run‐off may actually improve the thermal suitability of some glacially dominated streams in Southeast Alaska for salmon. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
Abstract

To assess the predictive significance of meteorological parameters for forecasting discharge from the Dokriani Glacier basin in the Himalayan region, discharge autocorrelation and correlations between discharge and meteorological factors were investigated on a monthly and a seasonal basis. Changes in correlations between discharge and meteorological variables, lagged by 0–3 days, were determined. Discharge autocorrelation was found to be very high for each individual summer month and for the melt season as a whole. This suggests that a substantial meltwater storage in the glacier, which results in a delayed response of runoff, and therefore discharge, from the highly glacierized basins is very much dependent on the previous day's discharge. A comparison of correlations between discharge and temperature, and discharge and precipitation shows that temperature has a better correlation with discharge during June and September, while precipitation has good correlation with discharge in July and August. Variations in the physical features of the glacier, weather conditions, and precipitation and its distribution with time over the basin account for changes in correlations. To forecast the runoff from the Dokriani Glacier basin, multiple linear regression equations were developed separately for each month and for the whole melt season. A better forecast was obtained using the seasonal regression equation. A comparison of correlations for the Dokriani Glacier with those for the Z'mutt Glacier basin, Switzerland, illustrates that, for both basins, the previous day's discharge (Qi-1) shows maximum autocorrelation throughout the melt period. Whereas a good correlation between discharge and temperature was observed for the Z'mutt Glacier basin for the whole melt period, for the Dokriani Glacier basin it was strong at the beginning and end of the ablation season. Runoff delaying behaviour in the Dokriani Glacier basin is found more prominent than in the Z'mutt Glacier basin early in the melt season. Water storage appears to be less significant in the Dokriani Glacier than in the Z'mutt Glacier towards the end of the ablation season. The strength of correlation between discharge and precipitation is higher for the Dokriani Glacier basin than for the Z'mutt Glacier basin. This is due to higher rainfall in the Dokriani Glacier basin. In general, for both glacier basins, maximum correlation is found between discharge and precipitation on the same day.  相似文献   

7.
In glacial studies, properties such as glacier thickness and the basement permeability and porosity are key to understand the hydrological and mechanical behaviour of the system. The seismoelectric method could potentially be used to determine key properties of glacial environments. Here we analytically model the generation of seismic and seismoelectric signals by means of a shear horizontal seismic wave source on top of a glacier overlying a porous basement. Considering a one-dimensional setting, we compute the seismic waves and the electrokinetically induced electric field. We then analyse the sensitivity of the seismic and electromagnetic data to relevant model parameters, namely depth of the glacier bottom, porosity, permeability, shear modulus and saturating water salinity of the glacier basement. Moreover, we study the possibility of inferring these key parameters from a set of very low noise synthetic data, adopting a Bayesian framework to pay particular attention to the uncertainty of the model parameters mentioned above. We tackle the resolution of the probabilistic inverse problem with two strategies: (1) we compute the marginal posterior distributions of each model parameter solving multidimensional integrals numerically and (2) we use a Markov chain Monte Carlo algorithm to retrieve a collection of model parameters that follows the posterior probability density function of the model parameters, given the synthetic data set. Both methodologies are able to obtain the marginal distributions of the parameters and estimate their mean and standard deviation. The Markov chain Monte Carlo algorithm performs better in terms of numerical stability and number of iterations needed to characterize the distributions. The inversion of seismic data alone is not able to constrain the values of porosity and permeability further than the prior distribution. In turn, the inversion of the electric data alone, and the joint inversion of seismic and electric data are useful to constrain these parameters as well as other glacial system properties. Furthermore, the joint inversion reduces the uncertainty of the model parameters estimates and provides more accurate results.  相似文献   

8.
Nowadays, Flood Forecasting and Warning Systems (FFWSs) are known as the most inexpensive and efficient non‐structural measures for flood damage mitigation in the world. Benefit to cost of the FFWSs has been reported to be several times of other flood mitigation measures. Beside these advantages, uncertainty in flood predictions is a subject that may affect FFWS's reliability and the benefits of these systems. Determining the reliability of advanced flood warning systems based on the rainfall–runoff models is a challenge in assessment of the FFWS performance which is the subject of this study. In this paper, a stochastic methodology is proposed to provide the uncertainty band of the rainfall–runoff model and to calculate the probability of acceptable forecasts. The proposed method is based on Monte Carlo simulation and multivariate analysis of the predicted time and discharge error data sets. For this purpose, after the calibration of the rainfall–runoff model, the probability distributions of input calibration parameters and uncertainty band of the model are estimated through the Bayesian inference. Then, data sets of the time and discharge errors are calculated using the Monte Carlo simulation, and the probability of acceptable model forecasts is calculated by multivariate analysis of data using copula functions. The proposed approach was applied for a small watershed in Iran as a case study. The results showed using rainfall–runoff modeling based on real‐time precipitation is not enough to attain high performance for FFWSs in small watersheds, and it seems using weather forecasts as the inputs of rainfall–runoff models is essential to increase lead times and the reliability of FFWSs in small watersheds. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

9.
Uncertainty analysis of radar rainfall enables stakeholders and users have a clear knowledge of the possible uncertainty associated with the rainfall products. Long-term empirical modeling of the relationship between radar and gauge measurements is an efficient and practical method to describe the radar rainfall uncertainty. However, complicated variation of synoptic conditions makes the radar-rainfall uncertainty model based on historical data hard to extend in the future state. A promising solution is to integrate synoptic regimes with the empirical model and explore the impact of individual synoptic regimes on radar rainfall uncertainty. This study is an attempt to introduce season, one of the most important synoptic factor, into the radar rainfall uncertainty model and proposes a seasonal ensemble generator for radar rainfall using copula and autoregressive model. We firstly analyze the histograms of rainfall-weighted temperature, the radar-gauge relationships, and Box and Whisker plots in different seasons and conclude that the radar rainfall uncertainty has strong seasonal dependence. Then a seasonal ensemble generator is designed and implemented in a UK catchment under a temperate maritime climate, which can fully model marginal distribution, spatial dependence, temporal dependence and seasonal dependence of radar rainfall uncertainty. To test its performance, 12 typical rainfall events (4 for each season) are chosen to generate ensemble rainfall values. In each time step, 500 ensemble members are produced and the values of 5th to 95th percentiles are used to derive the uncertainty bands. Except several outliers, the uncertainty bands encompass the observed gauge rainfall quite well. The parameters of the ensemble generator vary considerably for each season, indicating the seasonal ensemble generator reflects the impact of seasons on radar rainfall uncertainty. This study is an attempt to simultaneously consider four key features of radar rainfall uncertainty and future study will investigate their impacts on the outputs of hydrological models with radar rainfall as input or initial conditions.  相似文献   

10.
Water temperature dynamics in High Arctic river basins   总被引：2，自引：0，他引：2  
Despite the high sensitivity of polar regions to climate change and the strong influence of temperature upon ecosystem processes, contemporary understanding of water temperature dynamics in Arctic river systems is limited. This research gap was addressed by exploring high‐resolution water column thermal regimes for glacier‐fed and non‐glacial rivers at eight sites across Svalbard during the 2010 melt season. Mean water column temperatures in glacier‐fed rivers (0.3–3.2 °C) were lowest and least variable near the glacier terminus but increased downstream (0.7–2.3 °C km–1). Non‐glacial rivers, where discharge was sourced primarily from snowmelt runoff, were warmer (mean: 2.9–5.7 °C) and more variable, indicating increased water residence times in shallow alluvial zones and increased potential for atmospheric influence. Mean summer water temperature and the magnitude of daily thermal variation were similar to those of some Alaskan Arctic rivers but low at all sites when compared with alpine glacierized environments at lower latitudes. Thermal regimes were correlated strongly (p < 0.01) with incoming short‐wave radiation, air temperature, and river discharge. Principal drivers of thermal variability were inferred to be (i) water source (i.e. glacier melt, snowmelt, groundwater); (ii) exposure time to the atmosphere; (iii) prevailing meteorological conditions; (iv) river discharge; (v) runoff interaction with permafrost and buried ice; and (vi) basin‐specific geomorphological features (e.g. channel morphology). These results provide insight into the potential changes in high‐latitude river systems in the context of projected warming in polar regions. We hypothesize that warmer and more variable temperature regimes may prevail in the future as the proportion of bulk discharge sourced from glacial meltwater declines and rivers undergo a progressive shift towards snow water and groundwater sources. Importantly, such changes could have implications for aquatic species diversity and abundance and influence rates of ecosystem functioning in high‐latitude river systems. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

11.
Meltwater from glaciers is not only a stable source of water but also affects downstream streamflow dynamics. One of these dynamics is the interannual variability of streamflow. Glaciers can moderate streamflow variability because the runoff in the glacierized part, driven by temperature, correlates negatively with the runoff in the non-glacierized part of a catchment, driven by precipitation, thereby counterbalancing each other. This is also called the glacier compensation effect (GCE), and the effect is assumed to depend on relative glacier cover. Previous studies found a convex relationship between streamflow variability and glacier cover of different glacierized catchments, with lowest streamflow variability at a certain optimum glacier cover. In this study, we aim to revisit these previously found curves to find out if a universal relationship between interannual streamflow variability and glacier cover exists, which could potentially be used in a space-for-time substitution analysis. Moreover, we test the hypothesis that the dominant climate drivers (here precipitation and temperature) switch around the suggested optimum of the curve. First, a set of virtual nested catchments, with the same absolute glacier area but varying non-glacierized area, were modelled to isolate the effect of glacier cover on streamflow variability. The modelled relationship was then compared with a multicatchment data set of gauged glacierized catchments in the European Alps. In the third step, changes of the GCE curve over time were analysed. Model results showed a convex relationship and the optimum in the simulated curve aligned with a switch in the dominant climate driver. However, the multicatchment data and the time change analyses did not suggest the existence of a universal convex relationship. Overall, we conclude that GCE is complex due to entangled controls and changes over time in glacierized catchments. Therefore, care should be taken to use a GCE curve for estimating and/or predicting interannual streamflow variability in glacierized catchments.  相似文献   

12.
Mountain water resources management often requires hydrological models that need to handle both snow and ice melt. In this study, we compared two different model types for a partly glacierized watershed in central Switzerland: (1) an energy‐balance model primarily designed for snow simulations; and (2) a temperature‐index model developed for glacier simulations. The models were forced with data extrapolated from long‐term measurement records to mimic the typical input data situation for climate change assessments. By using different methods to distribute precipitation, we also assessed how various snow cover patterns influenced the modelled runoff. The energy‐balance model provided accurate discharge estimations during periods dominated by snow melt, but dropped in performance during the glacier ablation season. The glacier melt rates were sensitive to the modelled snow cover patterns and to the parameterization of turbulent heat fluxes. In contrast, the temperature‐index model poorly reproduced snow melt runoff, but provided accurate discharge estimations during the periods dominated by glacier ablation, almost independently of the method used to distribute precipitation. Apparently, the calibration of this model compensated for the inaccurate precipitation input with biased parameters. Our results show that accurate estimates of snow cover patterns are needed either to correctly constrain the melt parameters of the temperature‐index model or to ensure appropriate glacier surface albedos required by the energy‐balance model. Thus, particularly when only distant meteorological stations are available, carefully selected input data and efficient extrapolation methods of meteorological variables improve the reliability of runoff simulations in high alpine watersheds. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
Rainfall threshold (RT) method is one of the evolving flood forecasting approaches. When the cumulative rainfall depth for a given initial soil moisture condition intersects the threshold rainfall curve, the peak discharge is expected to be equal or greater than the threshold discharge for flooding at the target site. Besides the total rainfall depth, spatial and temporal distribution of rainfall impacts the flood peak discharge and the time to peak. To revisit a previous study conducted by the authors, in which spatially independent rainfall pattern was assumed, the spatial distribution of rainfall was simulated following a Monte Carlo approach. The structure of the spatial dependence among sub‐watersheds' rainfalls was taken into account under three different scenarios, namely independent, bivariate copula (2copula) and multivariate Gaussian copula (MGC). For each set of generated random dimensionless rainfalls, the probabilistic RT curves were derived for dry moisture condition. Results were evaluated with both historical and simulated events. For the simulated events, threshold curves were assessed by means of categorical statistics, such as hit rate, false rate and critical success index (CSI). Results revealed that the best performance based on the CSI criterion corresponded to 50% curve in 2copula and MGC scenarios as well as 90% curve in the independent scenario. The recognition of 50% curve in 2copula and MGC scenarios is in agreement with our expectations that the mean probable curve should have the best performance. Moreover, the proposed inclusion of spatially dependent rainfall scenario improved the performance of RT curves by about 25% in comparison with the presumed spatially uniform rainfall scenario. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

14.
This paper addresses the problem of identification of the modal parameters for a structural system using measured non‐stationary response time histories only. A Bayesian time‐domain approach is presented which is based on an approximation of the probability distribution of the response to a non‐stationary stochastic excitation. It allows one to obtain not only the most probable values of the updated modal parameters and stochastic excitation parameters but also their associated uncertainties using only one set of response data. It is found that the updated probability distribution can be well approximated by a Gaussian distribution centred at the most probable values of the parameters. Examples using simulated data are presented to illustrate the proposed method. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

15.
The summer discharge pattern of the Skeldal River, which drains a 560 km2 partly glacierized catchment in north‐east Greenland, is dominated by diurnal oscillations reflecting variations in the melt rate of snow and ice in the basin. Superimposed on this diurnal pattern are numerous short‐lived discharge fluctuations of irregular periodicity and magnitude. The larger fluctuations are described and attributed to both rainfall events and periodic collapse of the glacier margin damming flow from beneath the Skelbrae glacier. Other minor fluctuations are less readily explained but are associated with changes in the channelized and distributed reservoirs and possibly temporary blockage of subglacial conduits caused by ice melt with subsequent damming. Fluctuations in suspended sediment concentration (SSC) are normally associated with discharge fluctuations, although examples of ‘transient flushes’ were observed where marked increases in SSC occurred in the absence of corresponding discharge variations. A strong relationship between the event discharge increase and event SSC increase for rainfall‐induced events was established, but no such relationship existed for non‐rainfall‐induced events. There is some evidence for an exhaustion effect in the SSC patterns both at the event time‐scale and as the month proceeds. A mean suspended sediment load of 1765 ± 0·26 t day?1 was estimated for the study period, which would be equivalent to a suspended sediment yield of 732 ± 4 t km?2 year?1. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

16.
In glacier‐fed rivers, melting of glacier ice sustains streamflow during the driest times of the year, especially during drought years. Anthropogenic and ecologic systems that rely on this glacial buffering of low flows are vulnerable to glacier recession as temperatures rise. We demonstrate the evolution of glacier melt contribution in watershed hydrology over the course of a 184‐year period from 1916 to 2099 through the application of a coupled hydrological and glacier dynamics model to the Hood River basin in Northwest Oregon, USA. We performed continuous simulations of glaciological processes (mass accumulation and ablation, lateral flow of ice and heat conduction through supra‐glacial debris), which are directly linked with seasonal snow dynamics as well as other key hydrologic processes (e.g. evapotranspiration and subsurface flow). Our simulations show that historically, the contribution of glacier melt to basin water supply was up to 79% at upland water management locations. We also show that supraglacial debris cover on the Hood River glaciers modulates the rate of glacier recession and progression of dry season flow at upland stream locations with debris‐covered glaciers. Our model results indicate that dry season (July to September) discharge sourced from glacier melt started to decline early in the 21st century following glacier recession that started early in the 20th century. Changes in climate over the course of the current century will lead to 14–63% (18–78%) reductions in dry season discharge across the basin for IPCC emission pathway RCP4.5 (RCP8.5). The largest losses will be at upland drainage locations of water diversions that were dominated historically by glacier melt and seasonal snowmelt. The contribution of glacier melt varies greatly not only in space but also in time. It displays a strong decadal scale fluctuations that are super‐imposed on the effects of a long‐term climatic warming trend. This decadal variability results in reversals in trends in glacier melt, which underscore the importance of long‐time series of glacio‐hydrologic analyses for evaluating the hydrological response to glacier recession. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

17.
There are still relatively few hydrochemical studies of glacial runoff and meltwater routing from the high latitudes, where non-temperate glacier ice is frequently encountered. Representative samples of glacier meltwater were obtained from Scott Turnerbreen, a ‘cold-based’ glacier at 78° N in the Norwegian high Arctic archipelago of Svalbard, during the 1993 melt season and analysed for major ion chemistry. Laboratory dissolution experiments were also conducted, using suspended sediment from the runoff. Significant concentrations of crustal weathering derived SO2−4 are present in the runoff, which is characterized by high ratios of SO2−4: (SO2−4+HCO−3) and high p(CO2). Meltwater is not routed subglacially, but flows to the glacier terminus through subaerial, ice marginal channels, and partly flows through a proglacial icing, containing highly concentrated interstitial waters, immediately afront the terminus. The hydrochemistry of the runoff is controlled by: (1) seasonal variations in the input of solutes from snow- and icemelt; (2) proglacial solute acquisition from the icing; and (3) subaerial chemical weathering within saturated, ice-cored lateral moraine adjoining drainage channels at the glacier margins, sediment and concentrated pore water from which is entrained by flowing meltwater. Diurnal variations in solute concentration arise from the net effects of variable sediment pore water entrainment and dilution in the ice marginal streams. Explanation of the hydrochemistry of Scott Turnerbreen requires only one major subaerial flow path, the ice marginal channel system, in which seasonally varying inputs of concentrated snowmelt and dilute icemelt are modified by seepage or entrainment of concentrated pore waters from sediment in lateral moraine, and by concentrated interstitial waters from the proglacial icing, supplied by leaching, slow drainage at grain intersections or simple melting of the icing itself. The ice marginal channels are analogous neither to dilute supra/englacial nor to concentrated subglacial flow components. © 1998 John Wiley & Sons, Ltd.  相似文献   

18.
Near-surface processes on glaciers, including water flow over bare ice and through seasonal snow and firn, have a significant effect on the speed, volume and chemistry of water flow through the glacier. The transient nature of the seasonal snow profoundly affects the water discharge and chemistry. Water flow through snow is fairly slow compared with flow over bare ice and a thinning snowpack on a glacier decreases the delay between peak meltwater input and peak stream discharge. Furthermore, early spring melt flushes the snowpack of solutes and by mid-summer the melt water flowing into the glacier is fairly clean by comparison. The firn, a relatively constant feature of glaciers, attenuates variations in water drainage into the glacier by temporarily storing water in saturated layer. Bare ice exerts opposite influences by accentuating variations in runoff by water flowing over the ice surface. The melt of firn and ice contributes relatively clean (solute-free) water to the glacier water system.  相似文献   

19.
Under a climate change, the physical factors that influence the rainfall regime are diverse and difficult to predict. The selection of skilful inputs for rainfall forecasting models is, therefore, more challenging. This paper combines wavelet transform and Frank copula function in a mutual information‐based input variable selection (IVS) for non‐linear rainfall forecasting models. The marginal probability density functions (PDFs) of a set of potential rainfall predictors and the rainfall series (predictand) were computed using a wavelet density estimator. The Frank copula function was applied to compute the joint PDF of the predictors and the predictand from their marginal PDFs. The relationship between the rainfall series and the potential predictors was assessed based on the mutual information computed from their marginal and joint PDFs. Finally, the minimum redundancy maximum relevance was used as an IVS stopping criterion to determine the number of skilful input variables. The proposed approach was applied to four stations of the Nigerien Sahel with rainfall series spanning the period 1950–2016 by considering 24 climate indices as potential predictors. Adaptive neuro‐fuzzy inference system, artificial neural networks, and random forest‐based forecast models were used to assess the skill of the proposed IVS method. The three forecasting models yielded satisfactory results, exhibiting a coefficient of determination between 0.52 and 0.69 and a mean absolute percentage error varying from 13.6% to 21%. The adaptive neuro‐fuzzy inference system performed better than the other models at all the stations. A comparison made with KDE‐based mutual information showed the advantage of the proposed wavelet–copula approach.  相似文献   

20.
The inversion of induced‐polarization parameters is important in the characterization of the frequency electrical response of porous rocks. A Bayesian approach is developed to invert these parameters assuming the electrical response is described by a Cole–Cole model in the time or frequency domain. We show that the Bayesian approach provides a better analysis of the uncertainty associated with the parameters of the Cole–Cole model compared with more conventional methods based on the minimization of a cost function using the least‐squares criterion. This is due to the strong non‐linearity of the inverse problem and non‐uniqueness of the solution in the time domain. The Bayesian approach consists of propagating the information provided by the measurements through the model and combining this information with a priori knowledge of the data. Our analysis demonstrates that the uncertainty in estimating the Cole–Cole model parameters from induced‐polarization data is much higher for measurements performed in the time domain than in the frequency domain. Our conclusion is that it is very difficult, if not impossible, to retrieve the correct value of the Cole–Cole parameters from time‐domain induced‐polarization data using standard least‐squares methods. In contrast, the Cole–Cole parameters can be more correctly inverted in the frequency domain. These results are also valid for other models describing the induced‐polarization spectral response, such as the Cole–Davidson or power law models.  相似文献   

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