The response of idealized aquifer/river systems to climate change

Abstract

A study of the effect of changes in climate on aquifer storage and river recharge using a simple model of an idealized aquifer/river system shows the combined influence of aquifer properties and climate change scenario on the system response. The study shows that changes in the seasonal distribution of recharge may have a critical effect on low flows in rivers supported by baseflow. However, rivers supported by slowly responding aquifers may show a considerable delay in response to climate change allowing an opportunity for water resources planning over an extended period.     

Dynamics of a headwater system and peatland under current conditions and with climate change

Interactions between headwater aquifers and peatlands have received limited scientific attention. Hydrological stresses, including those related to climate change, may adversely impact these interactions. In this study, the dynamics of a southern Québec headwater system where a peatland is present is simulated under current conditions and with climate change. The model is calibrated in steady state on field‐measured data and provides satisfactory results for transient‐state conditions. Under current conditions, simulations confirm that the peatland is fed by the fractured bedrock aquifer year‐round and provides continuous baseflow to its outlets. Climate change is simulated through its impact on groundwater recharge. Predicted precipitation and temperature data from a suite of regional climate model scenarios provide a net precipitation variation range from +10% to ?30% for the 2041–2070 horizon. Calibrated recharge is modified within this range to perform a sensitivity analysis of the headwater model to recharge variations (+10%, ?15% and ?30%). Total contribution from the aquifer to rivers and streams varies from +14% to ?44% of the baseline for +10% to ?30% recharge changes from spring 2010 data, for example. With higher recharge, the peatland receives more groundwater, which could significantly change its vegetation pattern and eventually ecosystem functions. For a ?30% recharge, the peatland becomes perched above the aquifer during the summer, fall and winter. Recharge reductions also induce sharp declines in groundwater levels and drying streams. Copyright © 2013 John Wiley & Sons, Ltd.     

Proglacial groundwater storage dynamics under climate change and glacier retreat

Proglacial aquifers are an important water store in glacierised mountain catchments that supplement meltwater-fed river flows and support freshwater ecosystems. Climate change and glacier retreat will perturb water storage in these aquifers, yet the climate-glacier-groundwater response cascade has rarely been studied and remains poorly understood. This study implements an integrated modelling approach that combines distributed glacio-hydrological and groundwater models with climate change projections to evaluate the evolution of groundwater storage dynamics and surface-groundwater exchanges in a temperate, glacierised catchment in Iceland. Focused infiltration along the meltwater-fed Virkisá River channel is found to be an important source of groundwater recharge and is projected to provide 14%–20% of total groundwater recharge by the 2080s. The simulations highlight a mechanism by which glacier retreat could inhibit river recharge in the future due to the loss of diurnal melt cycling in the runoff hydrograph. However, the evolution of proglacial groundwater level dynamics show considerable resilience to changes in river recharge and, instead, are driven by changes in the magnitude and seasonal timing of diffuse recharge from year-round rainfall. The majority of scenarios simulate an overall reduction in groundwater levels with a maximum 30-day average groundwater level reduction of 1 m. The simulations replicate observational studies of baseflow to the river, where up to 15% of the 30-day average river flow comes from groundwater outside of the melt season. This is forecast to reduce to 3%–8% by the 2080s due to increased contributions from rainfall and meltwater runoff. During the melt season, groundwater will continue to contribute 1%–3% of river flow despite significant reductions in meltwater runoff inputs. Therefore it is concluded that, in the proglacial region, groundwater will continue to provide only limited buffering of river flows as the glacier retreats.     

Is there a superior conceptual groundwater model structure for baseflow simulation?

Previous work has shown that streamflow response during baseflow conditions is a function of storage, but also that this functional relationship varies among seasons and catchments. Traditionally, hydrological models incorporate conceptual groundwater models consisting of linear or non‐linear storage–outflow functions. Identification of the right model structure and model parameterization however is challenging. The aim of this paper is to systematically test different model structures in a set of catchments where different aquifer types govern baseflow generation processes. Nine different two‐parameter conceptual groundwater models are applied with multi‐objective calibration to transform two different groundwater recharge series derived from a soil‐atmosphere‐vegetation transfer model into baseflow separated from streamflow data. The relative performance differences of the model structures allow to systematically improve the understanding of baseflow generation processes and to identify most appropriate model structures for different aquifer types. We found more versatile and more aquifer‐specific optimal model structures and elucidate the role of interflow, flow paths, recharge regimes and partially contributing storages. Aquifer‐specific recommendations of storage models were found for fractured and karstic aquifers, whereas large storage capacities blur the identification of superior model structures for complex and porous aquifers. A model performance matrix is presented, which highlights the joint effects of different recharge inputs, calibration criteria, model structures and aquifer types. The matrix is a guidance to improve groundwater model structures towards their representation of the dominant baseflow generation processes of specific aquifer types. Copyright © 2014 John Wiley & Sons, Ltd.     

Modification of the SWAT model to simulate regional groundwater flow using a multicell aquifer

The soil and water assessment tool (SWAT) has been widely used and thoroughly tested in many places in the world. The application of the SWAT model has pointed out that 2 of the major weaknesses of SWAT are related to the nonspatial reference of the hydrologic response unit concept and to the simplified groundwater concept, which contribute to its low performance in baseflow simulation and its inability to simulate regional groundwater flow. This study modified the groundwater module of SWAT to overcome the above limitations. The modified groundwater module has 2 aquifers. The local aquifer, which is the shallow aquifer in the original SWAT, represents a local groundwater flow system. The regional aquifer, which replaces the deep aquifer of the original SWAT, represents intermediate and regional groundwater flow systems. Groundwater recharge is partitioned into local and regional aquifer recharges. The regional aquifer is represented by a multicell aquifer (MCA) model. The regional aquifer is discretized into cells using the Thiessen polygon method, where centres of the cells are locations of groundwater observation wells. Groundwater flow between cells is modelled using Darcy's law. Return flow from cell to stream is conceptualized using a non‐linear storage–discharge relationship. The SWAT model with the modified aquifer module, the so‐called SWAT‐MCA, was tested in 2 basins (Wipperau and Neetze) with porous aquifers in a lowland area in Lower Saxony, Germany. Results from the Wipperau basin show that the SWAT‐MCA model is able (a) to simulate baseflow in a lowland area (where baseflow is a dominant source of streamflow) better than the original model and (b) to simulate regional groundwater flow, shown by the simulated groundwater levels in cells, quite well.     

Effect of climate change on sea water intrusion in coastal aquifers

There is increasing debate these days on climate change and its possible consequences. Much of this debate has focused in the context of surface water systems. In many arid areas of the world, rainfall is scarce and so is surface runoff. These areas rely heavily on groundwater. The consequences of climate change on groundwater are long term and can be far reaching. One of the more apparent consequences is the increased migration of salt water inland in coastal aquifers. Using two coastal aquifers, one in Egypt and the other in India, this study investigates the effect of likely climate change on sea water intrusion. Three realistic scenarios mimicking climate change are considered. Under these scenarios, the Nile Delta aquifer is found to be more vulnerable to climate change and sea level rise. Copyright © 1999 John Wiley & Sons, Ltd.     

Modelling the water level of the alluvial aquifer of an ephemeral river in south-western Zimbabwe

ABSTRACT

Water from the alluvium of ephemeral rivers in Zimbabwe is increasingly being used. These alluvial aquifers are recharged annually from infiltrating floodwater. Nonetheless, the size of this water resource is not without limit and an understanding of the hydrological processes of an alluvial aquifer is required for its sustainable management. This paper presents the development of a water balance model, which estimates the water level in an alluvial aquifer recharged by surface flow and rainfall, while allowing for abstraction, evaporation and other losses. The model is coupled with a watershed model, which generates inflows from upland catchment areas and tributaries. Climate, hydrological, land cover and geomorphological data were collected as inputs to both models as well as observed flow and water levels for model calibration and validation. The sand river model was found to be good at simulating the observed water level and was most sensitive to porosity and seepage.     

Hydrological extremes in a southwestern Ontario river basin under future climate conditions/Extrêmes hydrologiques dans un basin versant du sud-ouest de l'Ontario sous conditions climatiques futures

Abstract

The global climate change may have serious impacts on the frequency, magnitude, location and duration of hydrological extremes. Changed hydrological extremes will have important implications on the design of future hydraulic structures, flood-plain development, and water resource management. This study assesses the potential impact of a changed climate on the timing and magnitude of hydrological extremes in a densely populated and urbanized river basin in southwestern Ontario, Canada. An ensemble of future climate scenarios is developed using a weather generating algorithm, linked with GCM outputs. These climate scenarios are then transformed into basin runoff by a semi-distributed hydrological model of the study area. The results show that future maximum river flows in the study area will be less extreme and more variable in terms of magnitude, and more irregular in terms of seasonal occurrence, than they are at present. Low flows may become less extreme and variable in terms of magnitude, and more irregular in terms of seasonal occurrence. According to the evaluated scenarios, climate change may have favourable impacts on the distribution of hydrological extremes in the study area.     

Using periodic hydrologic and geochemical sampling with limited continuous monitoring to characterize remote karst aquifers in the Kaweah River Basin,California, USA

Hydrogeologic field work in remote settings is often challenging: assessing spring behaviour and aquifer characteristics can be expensive in both time commitment and resources needed to assess these systems. In this study, we document the hydrology and geochemistry of 47 perennial karst springs in the Kaweah River, a mountain river basin in the Sierra Nevada, California. After preliminary hydrogeochemical characterization and grouping, selected springs were continuously monitored to further assess aquifer characteristics in each group. Later, in areas without previous dye‐tracing work, traces were conducted to establish connections between large sinking streams and springs. The springs have a wide range of inter‐spring and intra‐spring variability in discharge and geochemistry. We assessed this variability by performing statistical comparisons with spring chemistry and principal components analysis of all measured variables. Results show that springs can be divided into two distinct groups: high elevation springs of the Mineral King Valley and lower elevation springs throughout the rest of the basin. Continuous discharge, temperature and specific conductivity data from four springs (two from each group) were then used to characterize the hydrograph recession behaviour of springs in each group. Both groups showed statistically similar baseflow recession slopes, suggesting that both groups contain baseflow storage compartments with similar hydrogeologic properties. The biggest difference between each group is the variability in amount of water remaining in the aquifer during baseflow conditions. High elevation springs have lower baseflow discharges, relative to peak flow, than lower elevation springs, despite the fact that more precipitation falls at higher elevation. This is likely caused by differences in the amount of soil and epikarst storage, which are related to recent geomorphic events: high elevation aquifers were glaciated as recent as 41 thousand years ago (kya), while there is no evidence that low elevation aquifers were glaciated. As a result, lower elevations have developed thicker soils, weathered bedrock and epikarst. Copyright © 2016 John Wiley & Sons, Ltd.     

Semi‐Arid Aquifer Responses to Forest Restoration Treatments and Climate Change

The purpose of this study was to develop an interpretive groundwater‐flow model to assess the impacts that planned forest restoration treatments and anticipated climate change will have on large regional, deep (>400 m), semi‐arid aquifers. Simulations were conducted to examine how tree basal area reductions impact groundwater recharge from historic conditions to 2099. Novel spatial analyses were conducted to determine areas and rates of potential increases in groundwater recharge. Changes in recharge were applied to the model by identifying zones of basal area reduction from planned forest restoration treatments and applying recharge‐change factors to these zones. Over a 10‐year period of forest restoration treatment, a 2.8% increase in recharge to one adjacent groundwater basin (the Verde Valley sub‐basin) was estimated, compared to conditions that existed from 2000 to 2005. However, this increase in recharge was assumed to quickly decline after treatment due to regrowth of vegetation and forest underbrush and their associated increased evapotranspiration. Furthermore, simulated increases in groundwater recharge were masked by decreases in water levels, stream baseflow, and groundwater storage resulting from surface water diversions and groundwater pumping. These results indicate that there is an imbalance between water supply and demand in this regional, semi‐arid aquifer. Current water management practices may not be sustainable into the far future and comprehensive action should be taken to minimize this water budget imbalance.     

Effect of extreme rainfall events on the water resources of the Jordan River

As a response to climate change, shifting rainfall trends including increased multi-year droughts and an escalation in extreme rainfall events are expected in the Middle East. The purpose of this study is to evaluate the potential impact of these shifting trends on stream flow in the Jordan River and its tributaries. We use a non-homogeneous hidden Markov model to generate artificial daily rainfall simulations which capture independently shifting trends of increased droughts and escalated extreme. These simulations are then used as input into a hydrological model calibrated for the upper catchments of the Jordan River to compare the impact on stream flow and water resources between the different rainfall scenarios. We compare the predicted baseflow and surface flow components of the tested watersheds, and find that while an increase in extreme rainfall events increases the intensity and frequency of surface flow, the over all flow to the Jordan River, and the characteristics of the baseflow in the Jordan River system is not largely impacted. In addition, though it has been suggested that in the case of a multi-year drought the karstic nature of the aquifer might lead to more intense, non-linear reductions in stream flow, here we quantify and show the conditions when annual stream flow reduce linearly with rainfall, and when these relations will become non-linear.     

Water balance of Lake Victoria: update to 2000 and climate change modelling to 2100 / Bilan hydrologique du Lac Victoria: mise à jour jusqu’en 2000 et modélisation des impacts du changement climatique jusqu’en 2100

Abstract

Abstract An annual water balance model of Lake Victoria is derived for the period 1925–2000. Regression techniques are used to derive annual inputs to the water balance, based on lake rainfall data, measured and derived inflows and estimated evaporation during the historical period. This approach acknowledges that runoff is a nonlinear function of lake rainfall. A longer inflow series is produced here which is representative of the whole inflow to the lake, rather than just from individual tributaries. The results show a good simulation of annual lake levels and outflows and capture the high lake level in 1997–1998. Climate change scenarios, from a recent global climate model experiment, are applied to the lake rainfall inflow series and evaporation data to estimate future water balances of the lake. The scenarios produce a potential fall in lake levels by the 2030s horizon, and a rise by the 2080s horizon. A discussion of the application of climate change data to this complex hydrological system is presented.     

Effects of variations of river stage and hydraulic conductivity on temporal scaling of groundwater levels: numerical simulations

It was found in previous studies that groundwater levels may fluctuate as a temporal fractal. In this study numerical simulations of groundwater level fluctuations in an unconfined aquifer near a river were conducted to investigate the effects of aquifer heterogeneity and river stage variations on the fractal behavior of the water levels, h(t). Groundwater recharge was taken to be a white-noise process. The aquifer heterogeneity was simulated with a second-order stationary field of hydraulic conductivity (K) with an exponential variogram model. The results showed that groundwater levels fluctuate as a temporal fractal in both homogeneous and heterogeneous aquifers as long as K is less than 10 m/d. Most aquifers may indeed act as a fractal filter which takes a random non-fractal recharge inputs and produces a fractal responses of groundwater level fluctuations. A crossover in temporal scaling of h(t) may appear in more permeable aquifers. Fluctuations of the groundwater level in a homogeneous aquifer are dominated by the recharge process when the river stage is constant or by the river stage variations when the river stage varies in highly permeable aquifers. Heterogeneity plays an important role in the temporal scaling of h(t) in more permeable aquifers: the stronger the heterogeneity, the stronger the temporal scaling of h(t).     

Flow–duration curve integration into digital filtering algorithms for simulating climate variability based on river baseflow

ABSTRACT

A baseflow separation methodology combining the outcomes of the flow–duration curve and the digital filtering algorithms to cope with the restrictions of traditional procedures has been assessed. Using this methodology as well as the monitored and simulated hydro-climatological data, the baseflow annual variations due to climate change and human-induced activities were determined. The outcomes show that the long-term baseflow index at the upstream sub-basin is nearly half of that at the downstream from October to April, whereas they are close to each other for the remaining months. Some of the groundwater reacts to precipitation and an evident rise in the groundwater contribution was detected for the hydrological years 1998–2001 and 2006–2008. The contrary was recorded for1987. The water released from the reservoir in the dry periods led to distinctions in the detected baseflow index between the pre-damming and post-damming periods of the river.     

Simulated groundwater interaction with rivers and springs in the Heihe river basin

Surface water and groundwater in the Heihe river basin of China are interconnected and the pattern of water resources exploitation has a direct effect on the interaction of groundwater and surface water, especially on a downstream oasis. A three‐dimensional groundwater flow simulation model with eight model layers was established to simulate the regional groundwater flow in the multilayered aquifer system and the interaction among the rivers, springs, and groundwater. The model was calibrated not only with historical water levels but also with the investigated baseflow and spring flux. The simulation results of the numerical model match reasonably well with the observed groundwater levels, baseflow to rivers, and spring flux. The numerical simulation also demonstrates that the hydraulic connection between the river and the aquifers has transferred from the coupling to decoupling at some reaches. It is suggested that there is a vital need to reduce groundwater withdrawal and to rationalize the use of both groundwater and surface water in order to maintain sustainable development in the study area. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of multi-annual climate variability on the hydrodynamic evolution (1833 to present) in a shallow aquifer system in northern Belgium

Abstract

Using a groundwater flow model and long historical meteorological time series data, the evolution of the groundwater flow regime in a multi-layered groundwater flow basin in northern Belgium during the last one and a half centuries (since 1833) is reconstructed. Model output parameters such as piezometric levels, depth to water table, seepage fluxes in the valleys and calculated baseflow to the river system are presented and inter-annual and decadal variations are evaluated against seasonal fluctuations. The main time-varying boundary condition in the model is the aquifer recharge which was estimated using the method of Thornthwaite and Mather based on precipitation and temperature data. The model does not take into account changes in boundary conditions due to changes in land use (deforestation, drainage of cultivated land) or groundwater exploitation. Variations in model output parameters are therefore only due to climatological forcing. Only the natural non-exploited state of the aquifer is considered. Although few historical piezometric measurements are available to verify model output, the results give an indication of the natural hydrodynamic variations on a time scale of decades.

Citation Van Camp, M., Coetsiers, M., Martens, K. & Walraevens, K. (2010) Effects of multi-annual climate variability on the hydrodynamic evolution (1833 to present) in a shallow aquifer system in northern Belgium. Hydrol. Sci. J. 55(5), 763–779.     

Spatial measurements of stream baseflow,a relevant method for aquifer characterization and permeability evaluation. Application to a hard‐rock aquifer,the Oman ophiolite

The structure, functioning and hydrodynamic properties of aquifers can be determined from an analysis of the spatial variability of baseflow in the streams with which they are associated. Such analyses are based on simple low‐cost measurements. Through interpreting the hydrological profiles (Q = f(A)) it is possible to locate the aquifer(s) linked to the stream network and to determine the type of interrelated flow, i.e. whether the stream drains or feeds the aquifer. Using an analytical solution developed for situations with a positive linear relationship, i.e. where the baseflow increases linearly with increasing catchment size, it is also possible to estimate the permeability of the aquifer(s) concerned at catchment scale. Applied to the hard‐rock aquifers of the Oman ophiolite, this method shows that the ‘gabbro’ aquifer is more permeable than the ‘peridotite’ aquifer. As a consequence the streams drain the peridotites and ‘leak’ into the gabbro. The hydrological profiles within the peridotite are linear and positive, and indicate homogeneity in the hydrodynamic properties of these formations at the kilometre scale. The permeability of the peridotite is estimated at 5 · 10^?7 to 5 · 10^?8 m/s. Copyright © 2004 John Wiley & Sons, Ltd.     

Groundwater impact on environmental flow needs of streams in sandy catchments in the Netherlands

Abstract

During recent years, water managers and water users in the Netherlands experienced water shortages in numerous streams. Besides low rainfall amounts and high temperatures, anthropogenic alterations to the groundwater system are also responsible for the reduced baseflow in streams. These alterations may reduce resilience and increase a risk to streams as more droughts are expected in the Netherlands due to climate change. We propose a methodology to assess the impact of groundwater-related alterations and climate change on baseflow and environmental flow needs (EFN). Application of this methodology for two sandy catchments showed that, under average meteorological conditions, baseflow in the main streams still meets the EFN requirements. During dry years, baseflow is probably insufficient in the upper parts of the catchments. Anthropogenic alterations show a significant impact: drainage caused 25–40% baseflow reduction, groundwater abstractions caused 5–28% and climate change will potentially cause an additional reduction of 33–70% by 2050.

Editor D. Koutsoyiannis; Guest editor M. Acreman     

Estimation of uncertainty sources in the projections of Lithuanian river runoff

Particular attention is given to the reliability of hydrological modelling results. The accuracy of river runoff projection depends on the selected set of hydrological model parameters, emission scenario and global climate model. The aim of this article is to estimate the uncertainty of hydrological model parameters, to perform sensitivity analysis of the runoff projections, as well as the contribution analysis of uncertainty sources (model parameters, emission scenarios and global climate models) in forecasting Lithuanian river runoff. The impact of model parameters on the runoff modelling results was estimated using a sensitivity analysis for the selected hydrological periods (spring flood, winter and autumn flash floods, and low water). During spring flood the results of runoff modelling depended on the calibration parameters that describe snowmelt and soil moisture storage, while during the low water period—the parameter that determines river underground feeding was the most important. The estimation of climate change impact on hydrological processes in the Merkys and Neris river basins was accomplished through the combination of results from A1B, A2 and B1 emission scenarios and global climate models (ECHAM5 and HadCM3). The runoff projections of the thirty-year periods (2011–2040, 2041–2070, 2071–2100) were conducted applying the HBV software. The uncertainties introduced by hydrological model parameters, emission scenarios and global climate models were presented according to the magnitude of the expected changes in Lithuanian rivers runoff. The emission scenarios had much greater influence on the runoff projection than the global climate models. The hydrological model parameters had less impact on the reliability of the modelling results.     

Prediction of the arrival of peak nitrate concentrations at the water table at the regional scale in Great Britain

A simple process‐based approach to predict regional‐scale loading of nitrate at the water table was implemented in a GIS for Great Britain. This links a nitrate input function, unsaturated zone thickness, and lithologically dependent rate of nitrate unsaturated zone travel to estimate arrival time of nitrate at the water table. The nitrate input function is the loading at the base of the soil and has been validated using unsaturated zone porewater profiles. The unsaturated zone thickness uses groundwater levels based on regional‐scale observations infilled by interpolated river base levels. Estimates of the rate of unsaturated zone travel are attributed from regional‐scale hydrogeological mapping. The results indicate that peak nitrate loading may have already arrived at the water table for many aquifers, but that it has not where the unsaturated zone is relatively thick There are contrasting outcomes for the two main aquifers which have similar unsaturated zone velocities, the predominantly low relief Permo‐Triassic sandstones, and the Chalk, which forms significant topographic features. For about 60% of the Chalk, the peak input has not yet reached the water table and will continue to arrive over the next 60 years. The methodology is readily transferable and provides a robust method for estimating peak arrival time for any diffuse conservative pollutant where an input function can be defined at a regional scale and requires only depth to groundwater and a hydrogeological classification. The methodology is extendable in that if additional information is available this can easily be incorporated into the model scheme. British Geology Survey © NERC 2011. Hydrological Process © 2011 John Wiley & Sons, Ltd