Water Balance Processes Research Articles

Water management in the world of globalization

Abstract Water management is changing its paradigm. The millennia of economic indoctrination are to be replaced by the logic of ecology. The economic sector satisfying the demands for water and water‐related services guided until now by its own ideology and institutions, is gradually becoming an integral part of environmental protection and eco‐economy. Within the great diversity of national water policies, efforts towards sustainability are a dominant common objective. Discussions of the World Water Fora and other initiatives indicate that ecologically oriented water management is the emerging new challenge for achieving this objective. Ecological orientation emphasizes the unified system of the world water balance processes as transmitters of various human impacts leading to economic externalities. Water management is becoming a component of the processes of globalization primarily through its externalities requiring a comprehensive informational infrastructure as well as adequate institutional competence for their management. The paper analyzes fundamental features of the conceptual models incorporating such informational and institutional arrangements. The outlook of water is inseparably tied to the world order of the future, and water management in the world of globalization can either promote a genuine worldwide collaboration or can become a source of dangerous international tensions and conflicts.

Relations of Water Management and Degradation Processes in PEFC

The life-time of fuel cells is one of the most critical issues for the commercialization of fuel cells. The decrease of the performance induced by the degradation of the fuel cell components together with failure which yield in the loss of the fuel cell functionality are the processes which limit the fuel cell life-time. The water balance in polymer electrolyte membrane fuel cells (PEFC) is a crucial factor for the electrochemical performance. Therefore, the relation between water management in PEFC and the degradations processes are highly important. Consequently, the interactions between water balance and degradation processes - meaning which degradation processes influence the water balance and which degradation processes are influenced by the water balance - have to be investigated and to be discussed, which are the content of this paper.

Ecohydrology and the Partitioning AET Between Transpiration and Evaporation in a Semiarid Steppe

Water availability defines and is the most frequent control on processes in arid and semiarid ecosystems. Despite widespread recognition of the importance of water in dry areas, knowledge about key processes in the water balance is surprisingly limited. How water is partitioned between evaporation and transpiration is an area about which ecosystem ecologists have almost no information. We used a daily time step soil water model and 39 years of data to describe the ecohydrology of a shortgrass steppe and investigate how manipulation of soil and vegetation variables influenced the partitioning of water loss between evaporation and transpiration. Our results emphasize the overwhelming importance of two environmental factors in influencing water balance processes in the semiarid shortgrass steppe; high and relatively constant evaporative demand of the atmosphere and a low and highly variable precipitation regime. These factors explain the temporal dominance of dry soil. Annually and during the growing season 60–80% of the days have soil water potentials less than or equal to −1.5 MPa. In the 0–15 cm layer, evaporation accounts for half of total water loss and at 15–30 cm it accounts for one third of the loss. Annual transpiration/actual evapotranspiration (T/AET) ranged from 0.4–0.75 with a mean of 0.51. The key controls on both T/AET and evaporation/actual evapotranspiration in order of their importance were aboveground biomass, seasonality of biomass, soil texture, and precipitation. High amounts of biomass and late timing of the peak resulted in the highest values of T/AET.

The impact of groundwater–surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern Germany

AbstractThe glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics.A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time‐variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM‐ETH‐I with the three‐dimensional finite‐difference‐based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km2), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km2 catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain‐dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd.

The effect of sub-grid rainfall variability on the water balance and flux exchange processes resolved at climate scale: the European region contrasted to Central Africa and Amazon rainforests

Abstract. This paper investigates the effect of sub-grid rainfall variability on the simulation of land surface hydrologic processes of three regions (Europe, Africa and Amazon) with contrasting precipitation and vegetation characteristics. The sub-grid rainfall variability is defined in terms of the rainfall coverage fraction at the model's grid cells, and the statistical distribution of rain rates within the rain-covered areas. A statistical-dynamic approach is devised to incorporate the above variability properties into the canopy interception process of a land surface model. Our results reveal that incorporation of sub-grid rainfall variability significantly impacts the land-atmosphere water vapor exchanges. Specifically, it alters the partitioning between runoff and total evapotranspiration as well as the partitioning among the three components of evapotranspiration (canopy interception loss, ground evaporation and plant transpiration). This further influences the soil water, and to a lesser effect surface/vegetation temperatures and surface heat fluxes. It is shown that, overall, rainfall variability exerts less of an impact on the land-atmosphere flux exchanges over Europe compared to Africa and Amazon.

Multiobjective calibration of land surface model evapotranspiration predictions using streamflow observations and spaceborne surface radiometric temperature retrievals

Physically based models of surface water and energy balance processes typically require a large number of soil and vegetation parameters as inputs. Accurate specification of these parameters is often difficult without resorting to calibration of model predictions against independent observations. Along with streamflow observations from gauging stations, spaceborne surface radiometric temperature retrievals offer the only independent observation of land surface model output commonly available at regional spatial scales (i.e., >502 km2). This analysis examines the potential benefits of incorporating spaceborne radiometric surface temperature retrievals and streamflow observations in a multiobjective calibration framework to accurately constrain regional‐scale model evapotranspiration predictions. Results for the VIC (Variable Infiltration Capacity) model over the Southern Great Plains of the United States suggest that multiobjective model calibration against radiometric skin temperatures and steamflow observations can reduce error in model monthly evapotranspiration predictions by up to 20% relative to single‐objective model calibration against streamflow alone.

Correcting Land Surface Model Predictions for the Impact of Temporally Sparse Rainfall Rate Measurements Using an Ensemble Kalman Filter and Surface Brightness Temperature Observations

Current attempts to measure short-term (<1 month) rainfall accumulations using spaceborne radiometers are characterized by large sampling errors associated with low observation frequencies for any single point on the globe (from two to eight measurements per day). This degrades the value of spaceborne rainfall retrievals for the monitoring of surface water and energy balance processes. Here a data assimilation system, based on the assimilation of surface L-band brightness temperature (TB) observations via the ensemble Kalman filter (EnKF), is introduced to correct for the impact of poorly sampled rainfall on land surface model predictions of root-zone soil moisture and surface energy fluxes. The system is evaluated during the period from 1 April 1997 to 31 March 1998 over two sites within the U.S. Southern Great Plains. This evaluation includes both a data assimilation experiment, based on synthetically generated TB measurements, and the assimilation of real TB observations acquired during the 1997 Southern Great Plains Hydrology Experiment (SGP97). Results suggest that the EnKF-based assimilation system is capable of correcting a substantial fraction (>50%) of model error in root-zone (40 cm) soil moisture and latent heat flux predictions associated with the use of temporally sparse rainfall measurements as forcing data. Comparable gains in accuracy are demonstrated when actual TB measurements made during the SGP97 experiment are assimilated.

Quantitative description of human skin water dynamics by a disposition-decomposition analysis (DDA) of trans-epidermal water loss and epidermal capacitance.

In vivo water assessment would greatly benefit from a dynamical approach since the evaluation of common related variables such as trans-epidermal water loss or "capacitance" measurements is always limited to instantaneous data. Mathematical modelling is still an attractive alternative already attempted with bi-exponential empirical models. A classical two-compartment interpretation of such models raises a number of questions about the underlying fundamentals, which can hardly be experimentally confirmed. However, in a system analysis sense, skin water dynamics may be approached as an ensemble of many factors, impossible to discretize, but conceptually grouped in terms of feasible properties of the system. The present paper explores the applicability of this strategy to the in vivo water dynamics assessment. From the plastic occlusion stress test (POST) skin water balance is assessed by modelling trans-epidermal water loss (TEWL) and "capacitance" data obtained at skin's surface. With system analysis (disposition-decomposition analysis) the distribution function, H(t), modelled as a sum of exponential terms, covers only the distribution characteristics of water molecules traversing the skin. This may correspond macroscopically to the experimental data accessed by "corneometry". Separately, the hyperbolic elimination function Q(TEWL) helps to characterise the dynamic aspects of water influx through the skin. In the observable range there seems to be a linear relationship between the net amount of water lost at the surface by evaporation, and the capability of the system to replenish that loss. This may be a specific characteristic of the system related to what may be described as the skin's "intrinsic hydration capacity" (IHC) a new functional parameter only identified by this strategy. These new quantitative tools are expected to find different applicabilities (from the in vivo skin characterisation to efficacy testing) contributing to disclose the dynamical nature of the skin water balance process.

A continental scale water balance model: a GIS-approach for Southern Africa

A distributed GIS-based hydrological model is developed using GIS and computational hydrology techniques. The model is based on water balance consideration of the surface and subsurface processes. The surface water balance processes include precipitation infiltration, overland runoff, evapo-transpiration and canopy surface interception losses on daily time steps; The subsurface process considers soil moisture accounting on a monthly basis. The model was used to estimate generated runoff from matrix of specific geo-referenced grids representing Southern Africa. All regional and seasonal dispensation of water balances have been based on standard GIS formats for storage, spatial display and interpretation of results. Considering the 1961–1990 climatic period, we have mapped the regional variation of the mean annual soil moisture (SM), actual evapo-transpiration (AET), and generated runoff (ROF) across Southern Africa or known as the SADC region. The model estimates the mean SM of the region to be about 148 mm/year. There is a wide spatial range in the distribution of SM over the region due to the fact that the absolute soil moisture is dependent on the water retention properties of the soils considered across the region. The model prediction of the mean annual AET in the region reaches a maximum of 1500 mm, with mean 420 mm. The mean annual generated runoff from the land catchment in the region is about 151 mm/year although there is a significant inter-regional variation among the SADC countries, which is a function of the variation in the vegetation cover, soil and climate variation. Lower runoff regimes are dominant in arid areas in Botswana, Namibia and south-western part of the Republic of South Africa. Higher runoff regimes are the Northern and Western Tanzania, along the east coastal portions of Mozambique, central Mozambique, western Zambia and Malawi.

Short-term evaporation and water budget comparisons in shallow Arctic lakes using non-steady isotope mass balance

Shallow lakes in a continental, low Arctic setting are found to undergo substantial fluctuations in heavy-isotope content during the annual cycle due to extreme seasonality in water balance processes. Progressive isotope enrichment during the ice-free period occurs as a consequence of isotope exchange during evaporation under seasonally arid conditions, while enhanced input and flushing by heavy-isotope depleted precipitation and snowmelt during late fall and spring tend to deplete the lakes in heavy isotopes once again. Time-series sampling surveys in a group of nearby lakes, ranging in volume from 41,000 to 2,250,000 m 3, was carried out for two consecutive ice-free periods, in conjunction with a comprehensive hydrological measurement program in a detailed study lake, to assess models that describe isotopic enrichment in lakes and to test their suitability for comparing evaporation rates and water balance. From a non-steady isotope balance analysis, it is found that isotope enrichment rates in lakes during the ice-free period are determined primarily by evaporation rates and volume of the lakes, and are less sensitive to water balance variations for short time intervals when evaporation is less than 50 mm or so. A basic assessment of best-fit and step-wise models is presented which suggests that the former are useful only for predicting evaporation and water balance during month-long periods with relatively stable atmospheric and hydrologic conditions. A step-wise isotope balance approach is presented which demonstrates how isotope-based estimates of evaporation rates can be applied to effectively compare short-term (weekly) water balance in nearby lakes. Practical applications in the region include water balance assessments to assist in design and maintenance of tailings ponds for gold and diamond mining operations.

A soil‐vegetation‐atmosphere transfer scheme for the modeling of water and energy balance processes in high latitudes: 2. Application and validation

In support of the overall scientific objective of the Boreal Ecosystem‐Atmosphere Study (BOREAS), which encompasses the improved understanding of the interactions between the boreal forest and the atmosphere, a process‐based water and energy balance model is applied to observed forcing data, and the results are presented and discussed. Observed tower forcing and validation data are analyzed. A consistent diurnal pattern in the energy balance closure of the validation data is obtained. Simulations are performed for a number of BOREAS flux tower sites. The model successfully simulates the temporally averaged Bowen ratio and the evaporative part of precipitation over the different BOREAS flux tower sites during the 1994 and 1996 intensive field campaigns. At finer temporal scales a small phase shift in sensible heat flux and net radiation exists between the observed and model‐derived quantities. The ground heat flux is found to be slightly larger than the observations during the course of the day. It is suggested that the sensitivity of the model to parameters such as the moss thickness, thermal conductivity, and heat capacity is responsible for these differences. The moss moisture content and the different components of the energy balance were very well matched for a continuous simulation during 1996. Overall, the accuracy performance of the model is equivalent to the accuracy of the input forcing data.

A soil‐vegetation‐atmosphere transfer scheme for the modeling of water and energy balance processes in high latitudes: 1. Model improvements

This paper describes the development of a process‐based water and energy balance model for use in high latitudes under both summertime and wintertime conditions. The model is developed as a part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). The model differs from its original version in the representation of hydrological processes specific to climatic and ecologic conditions in high latitudes: the impact of an organic layer on the water and energy balance of the boreal forest; the parameterization of frozen ground and snow accumulation and ablation; and the effect of open water bodies on the calculation of the radiative energy and water budget. The model can be run either in a fully distributed or an aggregated statistical mode. The resulting macroscale hydrological model can be used, off line, to study the energy and water balance of the boreal forest and potentially can be used as a land‐atmosphere parameterization in atmospheric models.

A soil‐vegetation‐atmosphere transfer scheme for modeling spatially variable water and energy balance processes

In support of the eventual goal to integrate remotely sensed observations with coupled land‐atmosphere models, a soil‐vegetation‐atmosphere transfer scheme is presented which can represent spatially variable water and energy balance processes on timescales of minutes to months. This scheme differs from previous schemes developed to address similar objectives in that it: (1) represents horizontal heterogeneity and transport in a TOPMODEL framework, and (2) maintains computational efficiency while representing the processes most important for our applications. The model is based on the original TOPMODEL‐based land surface‐atmosphere transfer scheme [Famiglietti and Wood, 1994a] with modifications to correct for deficiencies in the representation of ground heat flux, soil column geometry, soil evaporation, transpiration, and the effect of atmospheric stability on energy fluxes. These deficiencies were found to cause errors in the model predictions in quantities such as the sensible heat flux, to which the development of the atmospheric boundary layer is particularly sensitive. Application of the model to the entire First International Satellite Land Surface Climatology Project Field Experiment 1987 experimental period, focusing on Intensive Field Campaigns 3 and 4, shows that it successfully represents the essential processes of interest.

Modeling energy and water cycle in a forested headwater basin

A physical-mathematical model is proposed to describe hourly dynamics of water and heat transfers in a forested watershed which is conceptually divided into seven sub-compartments. Hourly, daily and annual water yield, evapotranspiration loss and canopy-soil temperatures are simulated. Inter-connecting energy budget and water balance processes are integrated by simultaneously solving related equations with a specific feedback-iteration method. Emphasis is placed on interaction of transpiration and soil water status, on nonlinear and nonuniform overland flow, and on the controlling function of each storage on water fluxes. The model is calibrated by using the SIMPLEX optimization, at the Shirakawatani catchment in Western Japan, with hydrometeorology data for 2 years. Simulated annual water yield deviated from the observations by only 1.65%, hourly, or daily runoff was statistically correlated to observed runoff at a level of 0.916 or 0.976, and flood process, leaf and soil temperature patterns were fitted well.

Study of the changes of hydrological processes induced by afforestation in mediterranean mountainous abandoned fields

Ongoing experimental research is conducted to analyze the differences of water balance processes between grassed and forested patches in an area where the abandonment of agricultural activities facilitates the spontaneous overgrowth of pine forest. The ultimate aim of this work is to test and adapt the findings and models recently developed about forest interception in wetter climates for Mediterranean mountain environments, where water resources are crucial and threatened by environmental change. Provisional results demonstrate that the higher rainfall interception in forest patches clearly dominates the water balance, but common physically-based interception models seem to fail to account for the observed interception rates.

Multiscale modeling of spatially variable water and energy balance processes

This paper presents the model development component of a body of research which addresses aggregation and scaling in multiscale hydrological modeling. Water and energy balance models are developed at the local and catchment scales and at the macroscale by aggregating a simple soil‐vegetation‐atmosphere transfer scheme (SVATS) across scales in a topographic framework. A spatially distributed approach is followed to aggregate the SVATS to the catchment scale. A statistical‐dynamical approach is utilized to simplify the large‐scale modeling problem and to aggregate the SVATS to the macroscale. The resulting macroscale hydrological model is proposed for use as a land surface parameterization in atmospheric models. It differs greatly from the current generation of land surface parameterizations owing to its simplified representation of vertical process physics and its statistical representation of horizontally heterogeneous runoff and energy balance processes. The spatially distributed model formulation is explored to understand the role of spatial variability in determining areal‐average fluxes and the dynamics of hydrological processes. The simpler macroscale formulation is analyzed to determine how it represents these important dynamics, with implications for the parameterization of runoff and energy balance processes in atmospheric models.

Wetland vulnerability in East Anglia: The range of validity of a generalized classification approach

AbstractWetlands are under threat from a variety of human activities and in response to this various assessment schemes have been devised. A recent hydrological vulnerability assessment procedure has been advanced by Lloyd et al. (1993) for East Anglia, UK, which deals with hydrological threats to fens. The assessment starts with a desk study which classifies a wetland into a particular hydrological class, and from this general statements can be made with regard to the wetland's likely vulnerability to such activities as water abstraction and pollution. No type of desk study, however, will always be able to predict the hydrological consequences of an activity with certainty. Thus, if protection of the wetland is of high priority, Lloyd et al. (1993) propose further stages of investigation of increasing expense and difficulty, involving hydrological monitoring and modelling.The purpose of this article is to explore how much desk‐study classifications such as that of Lloyd et al. (1993) can reveal about wetland hydrological vulnerability, using East Anglian field investigation and hydrological monitoring evidence. Three sites in East Anglia have been examined over a 2 year period, and the water balance and hydrological processes, together with the hydrological vulnerability of each site, deduced. Comparing these data with the conclusions from the desk study indicates that the classification procedure was able generally to identify the vulnerability of wetlands correctly at the regional scale, but the detailed studies showed that local features, below the scale resolvable by the classification and desk‐study procedure, can easily lead to incorrect assessments.The results of the East Anglian field investigations suggest that although classification procedures are adequate for providing general conclusions about the vulnerability of wetlands in a given region, they cannot be relied upon to be correct for a specific site and ensure its protection against any given hydrological threat. In the case of the assessment of important wetland sites, there is therefore no substitute for detailed hydrological and geological investigations. Because of the importance of seasonal hydrological data for detailed investigations and vulnerability assessment, it is also recommended that hydrological monitoring at a single point on important wetland sites should start well before an impact is envisaged.

The Role of the Lymphatic System in Water Balance Processes in the Toad Bufo marinus (L.)

The cutaneous uptake of tritiated water was assessed in chronically catheterized, freely moving Bufo marinus. The isotope appeared rapidly (within 2.5 min) in the lymph and the plasma after addition to the ambient water, with significantly higher levels detected in the lymph than in the plasma from 15 min onward. A different pattern of isotope distribution was observed after injection of the tritiated water into the blood circulation. Within 5 min of injection, the plasma and lymph concentrations of tritiated water did not differ significantly from one another, and they remained similar for an additional 115 min. The site of lymph sampling did not affect the results. A bolus injection of arginine vasotocin (AVT) administered 1 h after the addition of the isotope to the ambient bath resulted in an immediate, although brief (10 min), increase in the rate of uptake of the tritiated water to both the lymph and the plasma, with the response being first observed in the lymph. The data suggest that some or most ...

Quantification of the water balance and hydrogeological processes in the vicinity of a small groundwater-fed wetland, East Anglia, UK

Badley Moor Fen exists in a region of the UK where potential evapotranspiration exceeds annual rainfall. The wetland is maintained by an input of Chalk groundwater in an area where the groundwater aquifer is regionally confined below boulder clay. The large groundwater contribution to the water balance arises from a unique local geological situation on the margin of the valley floor that allows the vertical movement of groundwater to the surface under a strong upward head gradient. The groundwater contribution is the dominant water input and maintains saturation within the immediate vicinity of the source of groundwater. Surface water outflow, via adjacent drainage channels, is the major output. The groundwater component is also important in that, as a result of hydrochemical change in the groundwaters with flow towards the surface, tufa has been precipitated. The calcium bicarbonate rich groundwater and tufa accumulation have given the site a unique character, with an exceptionally rich calcareous fen community.

Cloning and expression of an ATP-regulated human retina C-type natriuretic factor receptor guanylate cyclase.

The natriuretic factors are structurally related polypeptide hormones that regulate the hemodynamics of the physiological processes of diuresis, water balance, and blood pressure. Presumably, these hormones act through the activation of guanylate cyclases which are also the specific receptors of these hormones. Two such structurally similar cell surface receptors are known; the ligand for one is atrial natriuretic factor (ANF) and for the other is C-type natriuretic peptide (CNP). Studies with ANF receptor guanylate cyclase (ANF-RGC) have indicated that its ligand binding site is extracellular and the catalytic site is intracellular, but the mere ligand binding to the receptor domain does not activate the cytosolic catalytic domain. An intervening ATP-mediated event is obligatory: ATP binds to a defined ATP-regulated module (ARM) sequence and bridges the events of ligand binding and signal transduction. The mechanism of CNP signaling is not known, although CNP in intact cells transfected with CNP receptor guanylate cyclase (CNP-RGC) stimulates the formation of cyclic GMP. Furthermore, there is no prior evidence of the presence of CNP signal transduction system in retina, although the presence of ANF-RGC has been documented. We now report the molecular cloning and expression of CNP-RGC from human retina and show that ATP is obligatory in CNP signaling also.(ABSTRACT TRUNCATED AT 250 WORDS)