Downscaled daily temperature generally compares well with observed data, but daily precipitation amounts often do not, particularly seasonal amounts and durations of wet and dry periods. Such discrepancies are important because of the highly nonlinear responses and sensitivities of dynamic vegetation growth and water use transpiration to precipitation regimes Green et al.
Allen et al. They found that the variability in recharge predictions indicates that the seasonal performance of the downscaling tool is important, and that a range of GCMs should be considered for water management planning. Yang et al. Thus, they made use of limited daily data to study sub-weekly structure, and used this information to downscale weekly sequences.
In this way the dual objectives of downscaling weekly data and simulating daily PE sequences could both be achieved. Schematic illustration of the hydrologic cycle, including rainfed and irrigated agriculture with potential groundwater abstraction Taken from Green and van Schilfgaarde Precipitation and evapotranspiration are particularly important because they directly affect groundwater recharge and indirectly affect human groundwater withdrawals or discharge. Even small changes in precipitation may lead to large changes in recharge in some semiarid and arid regions Green et al.
The current section describes recent research findings regarding how atmospheric and surface-water changes will generally affect subsurface hydrologic processes in the soil and vadose zone that control infiltration and recharge to groundwater resources. Global warming is expected to increase the spatial variability in projected precipitation producing both positive and negative changes in regional precipitation, as well as changes in seasonal patterns Cook et al. There is little agreement on the direction and magnitude of predicted evapotranspiration patterns Barnett et al.
However, higher air temperatures are likely to increase evapotranspiration, which may result in a reduction in runoff and SWC in some regions Chiew and McMahon In temperate regions where plants senesce during the winter, groundwater recharge and stream baseflow could be less affected than evapotranspiration would infer due to the seasonal timing of recharge events e.
In seasons of above average precipitation, recharge is likely to increase, and water demand, such as for irrigated agriculture , will decline because of lower temperature and solar radiation and higher humidity in such periods Rosenberg et al. In contrast, the spatial extent and temporal duration of extreme drought are predicted to increase under future climate change Bates et al.
The increased variability in precipitation, temperature, and evapotranspiration that is predicted under many climate-change scenarios will likely have variable effects on different aquifers and different locations within an aquifer depending on spatial variability in hydraulic properties and distance from the recharge area s. Chen et al. Additionally, groundwater levels at some locations of the aquifer responded to high-frequency precipitation events while groundwater levels in other areas did not respond.
The groundwater-level response to high-frequency events may indicate the existence of highly permeable channels or preferential-flow paths from land surface to the water table Chen et al. Other studies indicate that even modest increases in near-surface air temperatures will alter the hydrologic cycle substantially in snowmelt-dominated regions. Seasonal streamflow is altered because the snowpack acts as a reservoir for water storage Barnett et al.
For example, Eckhardt and Ulbrich predicted a smaller proportion of the winter precipitation will fall as snow due to warming trends in mountainous regions of central Europe and that the spring-snowmelt peak will likely be reduced while the flood risk in winter will probably increase. Unless additional reservoir storage is created to account for the earlier snowmelt runoff, the use of groundwater may increase, where available, to offset the lack of surface water later in the season when water demands are typically higher.
Spatial differences in groundwater dynamics in mountainous regions also can play a substantial role in determining streamflow responses to warming Tague et al. Tague et al. The changes in streamflow, shifting spring and summer streamflow to the winter, will likely increase competition for reservoir storage and in-stream flow for endangered species Payne et al. In mountainous regions, how will forecasted changes to the surface hydrologic regime affect infiltration, evapotranspiration, SWC distribution, and ultimately recharge?
Singleton and Moran noted that recharge mechanisms, storage capacity, and residence times of high elevation aquifers are poorly understood. The net change in recharge in mountain aquifers due to changes in the timing of snowpack melting is generally not known in direction or magnitude, making it difficult to predict the response of mountain groundwater systems to climate change Singleton and Moran How will mountain-front recharge and recharge in other types of mountainous systems be affected by predicted changes in the snowmelt-dominated regions?
A negative feedback between early timing of snowmelt and evapotranspiration may exist in snowmelt-dominated watersheds, as earlier snowmelt increases SWC in the season when potential evapotranspiration is relatively low Barnett et al. Later in the year, when potential evapotranspiration is greater, the shift in snowmelt timing may reduce SWC, which again reduces the effect of evapotranspiration change but has an unknown effect on net infiltration and recharge. These and other questions remain regarding subsurface hydrologic responses to climate-change effects on surface-water hydrology.
Climate-related variables that have a substantial control on soil water include spatiotemporal patterns in precipitation, evapotranspiration, and surface-water conditions. Land use, soil texture, slope, and other biological, chemical , and physical characteristics also are known to affect SWC Jasper et al. Seneviratne et al. Climate change and variability are expected to have profound effects on soil water and temperature Jasper et al. Soil water content and temperature are important factors in terrestrial biogeochemical reactions, land-atmosphere interactions, and a critical determinant of terrestrial climate.
Variability in vadose-zone hydrology, shallow water tables that support SWC, and ultimately infiltration that feeds aquifers are also affected by SWC and temperature Cohen et al. Spatial variations in SWC also influence atmospheric processes, such as the cumulus convective rainfall Pielke Jungkunst et al. Water evaporated from soils and transpired by plants is recirculated into the atmosphere, thus promoting a positive feedback mechanism for precipitation Salas et al. The importance of this feedback depends upon the scale of interest. At the global scale, circulation of water between the land, atmosphere, and ocean is obviously important.
Simulation of such circulation patterns is the basis for projecting future climates in GCMs. Moving down in scale, the coupling of land-atmosphere interactions may become looser. For this reason, hydrologic models are typically driven by measured precipitation without considering feedbacks.
Eltahir and Bras Koster et al. The vadose zone is the region between the land surface and saturated zone through which groundwater recharge occurs. It comprises complex interactions between thermal-hydrologic-geochemical processes that can affect groundwater quantity and quality. The timing and amount of groundwater recharge can be affected by the thickness of the vadose zone, as simulated for a temperate zone Hunt et al.
The vadose zone of some semiarid and arid regions responds slowly to terrestrial climate, and its long-term dynamics pose important challenges for understanding of the effects of climate change and variability on the vadose zone Glassley et al. Glassley et al. Groundwater is an important component of the global water balance Chap. The use of groundwater can mitigate droughts, because many aquifers have a large storage capacity and are potentially less sensitive to short-term climate variability than surface-water bodies, which often rely on groundwater discharge to maintain baseflow conditions Dragoni and Sukhija However, the ability to use groundwater storage to buffer rainfall deficits that affect surface-water resources will be constrained by the need to protect groundwater-dependent environmental systems Skinner Groundwater has and will continue to respond to changes in climate.
Paleoclimate-change conditions and subsequent responses in recharge, discharge, and changes in storage are preserved in the records of groundwater major and trace-element chemistry, stable and radioactive isotope composition, and noble gas content Bajjali and Abu-Jaber ; Castro et al. Other important components of hydrogeological systems include groundwater-fed lakes in arid and semiarid regions Gasse and temperate climates Hunt et al.
Groundwater acts as a low-pass filter and provides long time-series of reconstructed temperatures and information on atmospheric-moisture transport patterns Gasse Falling global sea levels during the last five glacial periods of the Pleistocene Ice Ages likely resulted in increased hydraulic heads in inland aquifers relative to those in the continental shelf, enhancing groundwater flow toward the coast Faure et al. Faure et al.
At present sea levels, submarine groundwater discharge is a well-established phenomenon that contributes substantial mass flux to oceans Burnett et al. Gasse recommended that future paleohydrological research needs to develop solid chronologies, but also to analyze the mechanisms of water storage and losses in aquifers, obtain quantitative reconstructions of hydrological cycles, and identify atmospheric-moisture transport patterns at regional scales that affect groundwater resources. Groundwater resources have been affected by a number of non-climatic forcings, such as contamination, reduction in streamflow reduction in recharge , and lowering of the water table and decreased storage due to groundwater mining primarily for irrigated agriculture.
Kundzewicz et al. Juckem et al. Additionally, groundwater systems often respond more slowly and have a more substantial temporal lag to climate change than surface-water systems Chen et al. Persistent and severe dry periods have even altered the hydraulic properties of aquifers, such as the transmissivity of a regional karst aquifer in France Laroque et al.
Current vulnerabilities in water resources are strongly correlated with climate variability , due largely to precipitation variability, especially for semiarid and arid regions Kundzewicz et al. Such regions are particularly vulnerable to climate change if groundwater reservoirs are small or not available. Even if groundwater resources are currently available, communities become more vulnerable to climate change if the ratio of stored groundwater volumes to recharge is smaller and if there are no other local water resources, such as in the isolated alluvial aquifers of Yemen van der Gun Groundwater levels correlate more strongly with precipitation than with temperature, but temperature becomes more important for shallow aquifers Kundzewicz et al.
The complexity is exacerbated because predictions of global precipitation spatiotemporal patterns are less certain than are predicted temperature patterns. As a result, the IPCC a stated that there is no evidence for ubiquitous climate-related trends in groundwater. These topics are summarized below. Predicting the dynamics and processes interactions affecting groundwater recharge over time requires a reliable prediction of critical climate variables Gurdak et al. Recharge occurs via two general pathways in many environments: diffuse recharge to the water table and focused recharge that occurs at locations where surface-water flow is concentrated at the land surface, including stream channels, lakes, topographic depressions, irrigated-agricultural land, and other macropore, preferential-flow pathways Small Thus, recharge is a spatially and temporally complex, sensitive function of the climate regimes, local geology and soil, topography, vegetation, surface-water hydrology, coastal flooding, and land-use activities Candela et al.
Understanding of the controls on recharge is improving Healy ; Scanlon et al.
Groundwater & Climate Change | IGRAC
These aquifers are highly renewable because precipitation exceeds evapotranspiration throughout much of year. Climate change and variability will likely have variable long-term effects on recharge rates and mechanisms Aguilera and Murillo ; Green et al. Overall, simulated trends in recharge were highly variable depending upon the base climate zone and combinations of soil and vegetation types.
Temporal climate variability , especially variability in precipitation, can have substantial effects on recharge and groundwater levels. For example, Thomsen noted that recharge in most of western Denmark at the end of the nineteenth century was only half of the recharge during the period — because of much greater winter rainfall.
Subsequently, Green et al. As noted above, estimates of recharge vary spatially with vegetation, soils and land use, and change in time depending upon the emissions scenario. Temperature-depth profiles in deep boreholes are useful for estimating ground-surface temperature history and recharge, because climate change at the ground surface is stored in the subsurface thermal regime Miyakoshi et al.
Taniguchi showed that subsurface thermal profiles near Tokyo, Japan reveal that recharge rates increased from the s to s and decreased from the s to s, in large part related to climatic variations in the precipitation regime. Climatic conditions affect the direction of groundwater flow and the relation between surface-water bodies and subsurface-water resources. Permafrost-groundwater dynamics respond to climate change at many scales, particularly in sub-permafrost groundwater that is highly climate dependent Haldorsen Recharge is likely to increase in areas of Alaska that experience permafrost thaw Dragoni and Sukhija ; Kitabata et al.
In the Qinghai-Tibet Plateau of China, groundwater flow may play an important role in permafrost degradation Cheng and Wu , where degrading permafrost caused regional lowering of the groundwater table, which has resulted in falling lake levels, shrinking wetlands, and degenerating grasslands. Climate change is expected to reduce snow cover and soil frost in boreal environments of Finland, which will increase winter floods and cause the maximum recharge and water levels to occur earlier in the year in shallow unconfined aquifers Okkonen et al.
- Evaluating the effect of climate change on groundwater resources : from local to catchment scale?
- Generalized Linear Models for Insurance Data (International Series on Actuarial Science);
- Impact of Climate Change on Groundwater Resources.
- Marzulli and Maibachs Dermatotoxicology, 7th Edition;
- Climate Impacts Group.
Groundwater is a crucial component of the hydrologic cycle and many water-resource projects. Thus, potential effects of climate change on recharge deserve more attention Dettinger and Earman Scientists currently lack the necessary tools and data, such as long-term continuous monitoring of recharge processes to confidently predict recharge responses to future climate change in most environments.
In many regions of the world, it is unknown whether recharge will increase or decrease under predicted climate change Green et al. The location and timing of recharge and associated effects on groundwater supplies are insufficiently understood under future climate change and variability Gurdak et al. However, water resources, especially in many semiarid and arid regions, are particularly vulnerable to the effects of climate change Aguilera and Murillo ; Barthel et al. Groundwater discharge is the loss of water from an aquifer to a surface-water body, the atmosphere, or abstraction for human uses.
Groundwater depletion see Chap. Over the last 50 years, groundwater depletion from direct or indirect effects of climate change and human activities, such as groundwater pumping for irrigated agriculture or urban centers Bouraoui et al. Changing global groundwater discharge has even contributed to sea-level rise during the past century Taylor et al. In particular, the rise in sea level would have been even greater if substantial quantities of water had not been stored in land-surface reservoirs or channeled into aquifers by irrigation return-flow Sahagian et al.
Some groundwater resources could be affected substantially by climate change even if the present groundwater pumping rates are not increased, such as in the Edward aquifer in Texas, USA Loaiciga et al. Direct or indirect effects of climate change on groundwater discharge include soil degradation, changes in water demand, and changes in irrigation or land-use practices Brouyere et al.
The notable increase in groundwater depletion beginning in the mids is consistent with increased population in many regions and the development of high-capacity well pumps that are used to support agricultural industries and public and private drinking-water supplies. Under some climate scenarios, many regions may receive more precipitation. Woldeamlak et al. This could have adverse effects on local aquatic life in local wetlands and riverine ecosystems that rely on groundwater discharge to support baseflow Woldeamlak et al. Quantifying submarine groundwater discharge and the biogeochemical effects on the ocean has important implications for understanding climate-change effects on oceanic processes Windom et al.
For example, high dissolved nitrogen—phosphorus ratios in SGD relative to surface waters may drive the coastal oceans toward phosphorus limitation within the coming decades, perhaps changing the present nitrogen-limited coastal primary production Slomp and Van Cappellen ; Taniguchi et al. Alley noted the critical importance of groundwater storage in successfully dealing with climate change and variability. In particular, changes in groundwater storage and agricultural groundwater pumping in active semiarid basins are substantial, yet poorly understood, components of the water balance Ruud et al.
The use of groundwater storage to moderate the effects of drought increases in importance as surface-water storage becomes more limited, especially during drought periods Alley Prior to development, the water in storage of most s worldwide was based on local-climate conditions, ecological demands, and interactions with surface water.
Water-table declines and loss of storage worldwide during the second half of the twentieth century were consistent with the development of high-capacity well pumps, aquifer development for human use, and a warming climate Kertesz and Mika Although some regions of the world, including parts of Russia Dzhamalov et al. Postel estimated that if this rate of groundwater depletion continues, the number of people globally that will live in water-stressed countries will increase from million to 3 billion by the year This problem will likely be compounded by future global-population growth, which correlates with higher groundwater pumping rates that further threaten the groundwater sustainability of many aquifers at the global scale Loaiciga Taniguchi et al.
Bultot et al. The water-table declines and loss of groundwater storage in the High Plains aquifer in the United States were consistently large from about the s, when aquifer development became widespread across the aquifer, until about the early s when rates of water-table drawdown diminished. Rosenberg et al. McGuire attributed the changes in water tables over this period to more efficient irrigation methods and economic factors, but also to the fact that precipitation in the High Plains was well above normal between and Garbrecht and Rossel The responsiveness of the High Plains aquifer , and other similar aquifers, is strongly suggestive that natural and human-induced changes in climate can profoundly affect the availability and future sustainability of groundwater resources.
The above-normal precipitation across the High Plains aquifer region between and the lates can be attributed to teleconnections from natural variations in sea-surface temperatures and atmospheric pressures across the Atlantic and Pacific Oceans Garbrecht and Rossel During the s and early s, the Pacific Decadal Oscillation PDO Mantua and Hare was in the positive phase of variability and the Atlantic Multidecadal Oscillation AMO Kerr was in the negative phase of variability, which generally results in wetter conditions and lower frequency of drought for the High Plains region McCabe et al.
Natural climate variability occurs on all time scales, from annual to decadal, centennial, and millennial time scales. Ghil noted that the complex nature of climate variability on multiple time scales is a major obstacle to the reliable characterisation of global climate change resulting from human activities. When anthropogenic effects on aquifers are on the same time scale as some natural climate variabilities, it is difficult to distinguish between the two Gurdak et al. These natural variations in climate, when combined, can have profound effects on the surface-hydrologic cycle largely because of the magnitude and phase relation that can cause average or extreme climate forcings Hanson and Dettinger , such as drought, low flow in streams, changes to water quality, and adverse effects on stream ecosystems Caruso As a result, research efforts have characterised subsurface hydrologic and geochemical responses to climate variability on interannual to multidecadal time scales because variability on these time scales has the most tangible implications for water-resource management Chen et al.
A few studies have relied on long-term historical hydrologic time series to identify climate-variability effects on groundwater levels Chen et al. Many questions remain regarding the control of natural climate forcings on subsurface hydrologic processes and how anthropogenic global warming may affect the frequency and magnitude of these forcings. Historical temporal patterns in the hydrologic cycle may not provide a reasonable guide to future climate conditions and hydrologic processes Bates et al.
Future climate conditions may have substantial consequences for groundwater management and infrastructure van der Gun Milly et al. Climate change has substantial implications for surface-water processes Gosling et al. Some studies suggest that climate change will result in less surface-water availability, which will likely increase the need for groundwater development Chen et al. For example, climate change may extend the dry season of no or very low flows in some semiarid and arid regions, which can have a substantial effect on the overall water resources of the region if no deep or otherwise reliable groundwater resources are available Giertz et al.
Surface-water storage structures can play a vital role in augmenting groundwater recharge , especially in semiarid and arid regions Sharda et al. Accurate low-flow stream measurements are important for groundwater-fed streams to assess the potential effects of climate change and variability, and to assess in-stream flow requirements and the nature of groundwater-surface interactions Berg and Allen Cohen et al. Groundwater-supported evapotranspiration varied with topography and aquifer-hydraulic conductivity, and small yet important feedbacks exist between groundwater and atmospheric processes on decadal and longer time scales.
Moreover, hydrologic sensitivity of a watershed to climate change depends on feedbacks between groundwater, overland flow, and land-surface water and energy balance Ferguson and Maxwell as well as the hydrologic regime such as lakes with and without stream outflows e. The magnitude and seasonality of groundwater feedbacks to surface hydrologic processes is highly sensitive to climate change Ferguson and Maxwell A projected increase in the frequency of droughts has implications for surface-groundwater interactions. For example, the summer of was the hottest in Europe in more than years, linked to an estimated deaths in the Netherlands alone, but this could become a close-to-normal summer by about Kabat et al.
The extremely low freshwater discharge by the river Rhine in resulted in groundwater seepage of seawater to the low-lying delta, which threatened substantial areas of Dutch agriculture and horticulture. As a result, studies are underway to develop freshwater canals and additional summer water storage facilities for the region. Across regions of the High Plains aquifer in Kansas, USA, streamflow declines are historically caused by high rates of groundwater pumping, but also correlate with climate variability since the mids Brikowski Projected climate change for the Kansas region will likely continue streamflow declines, resulting in severe consequences for surface-water supply and the strong possibility of unsustainable surface storage of water resources in the region.
This will likely create even more pressure on the groundwater resources of the already-stressed High Plains aquifer. Similar findings have been identified in other climate regions, including humid, tropical and arctic catchments. Both observations and modelling suggest that climate-warming induced permafrost degradation will markedly increase baseflows of arctic and subarctic rivers and streams Bense et al. Jacques and Sauchyn ; Walvoord and Striegl Groundwater withdrawals can affect streamflow strongly during dry periods Lee and Chung Therefore, it is critically important to accurately understand the links between climate change and variations and the cycles of supply and demand that drive recharge and withdrawal of water resources.
Accurate projections of climate change and variations and simulations of the responses in the water-resources system are required Hanson and Dettinger Most studies of the effects of climate change and variability on groundwater have focused on processes that affect water quantity. Relatively few studies of climate change and variability effects on groundwater have focused on processes that will affect groundwater quality.
Groundwater quality is a function of the chemical , physical, and biological characteristics of the resource. Thus, groundwater quality is expected to respond to changes in climate and human activities because of the influences of recharge, discharge, and land use on groundwater systems. The quality of water is related to specific water-use standards. The protection and enhancement of groundwater quality has been a high-priority environmental concern because of the direct implications for drinking-water health standards Alley Also, water quality may be a limiting factor for other uses of groundwater, such as agriculture , industry, or ecosystem needs.
Therefore, sustainability of water supplies under future climate change and variability is not only dependent on the quantity and quality of groundwater resources, but also on the physical hydrogeologic characteristics of the aquifer , laws, regulations, and socioeconomic factors that control the demand and use of groundwater Reilly et al. Global change may affect the quality of groundwater in many ways Alley ; Dragoni and Sukhija Changes to recharge rates, mechanisms, and locations can affect contaminant transport, which may lead to erroneous conclusions about temporal trends in groundwater quality, particularly if only a few samples have been collected over time Alley For example, recharge during relatively dry periods may have a greater concentration of salts and total-dissolved solids TDS , while recharge during relatively wet periods may have a relatively lower TDS concentration Sukhija et al.
Climate variability on interannual to multidecadal timescales has been linked with changes in spatiotemporal-precipitation patterns that can result in substantial infiltration events that mobilise large, pore-water chloride and nitrate reservoirs in the vadose zone of aquifers in semiarid and arid regions Gurdak et al. Groundwater quality may deteriorate substantially if these large chemical reservoirs reach the water table.
Sea-level rise, spatiotemporal changes in precipitation and evapotranspiration, which affect recharge, and increased groundwater pumping will likely result in more groundwater salinisation in many coastal regions Barrocu and Dahab ; Beuhler ; IPCC a ; Klein and Nicholls ; Kundzewicz et al.
Vandenbohede et al. Therefore, brackish and salt water present in low-lying areas will be pushed back. Salt-water intrusion may occur from the low-lying areas into dunes, which could affect the ecology of the dunes and the drainage system used in most low-lying areas Vandenbohede et al. Lambrakis and Kallergis showed that over-pumping, combined with a dry period, has led to a substantial decline in groundwater quality of many Greek coastal aquifers.
Such long periods of groundwater freshening highlight the importance of minimising the initial saltwater intrusion. The salinisation of groundwater may, in turn, affect the water quality in many rivers and estuaries Burkett et al. Due to increasing human population, agricultural development and economic activities, the shortage of fresh groundwater for domestic, agricultural, and industrial purposes becomes more striking in coastal low-lying deltaic areas like the Mississippi, Nile, Mekong, Ganges, Po, and Rhine-Scheldt deltas Oude Essink Increased groundwater pumping could induce upward leakage of groundwater with poorer-water quality, such as in the High Plains aquifer McMahon et al.
Alley also noted that the combined effects of groundwater development and climate change may lead to less dilution of contaminants in streams during low flow baseflow from groundwater than was assumed in setting stream-discharge permits. A wide range of additional climate-change effects on groundwater quality are possible. Kovalevskii showed that under projected climate change, many regions of Russia will likely have increased rates of recharge that may increase rates of contaminant transport and groundwater vulnerability to various distributed and point-source contamination.
The combination of the heat-island effect from urbanisation and global warming on subsurface temperatures has implications for groundwater quality because of changes to subsurface biogeochemical reactions Knorr et al. Additional research is needed to understand and predict the full range of effects on groundwater quality from changes in the subsurface thermal regime and various biogeochemical reactions Aureli and Taniguchi There are particularly no specific studies about the impact of climate change on aquifers, both on their recharge and on pressures associated to their increase in demand.
This situation is worsened by the fact that the knowledge on the real potential of this resource is not complete and does not extend all over the country to allow a good resource management.
Impact of Climate-Indicators on Continental-Scale Potential Groundwater Recharge in Africa
Due to this situation, the purpose of this work is to evaluate, in a preliminar and regional scale, the potential impacts that are expected because of the climate change on aquifers, indicating, above all, regions where systematic analyses are necessary to reduce these impacts. A relevant aspect to be considered is that groundwater dynamics is different from surface water.
The river, from the point of view of the water resource manager, is the "opposite" of the aquifer Table I. The river has a low capacity to store water, but, on the other hand, it can deliver a much larger instant discharge than aquifers. Additionally, the aquifer exploitation is done through wells and springs that usually have stable flows little influenced by seasonal changes , but they are usually reduced in volume when compared to surface water pumping. Groundwater exploitation is still characterized by less financial investment and by allowing scaled solutions one well after the other in the installation of large-scale supply systems, even for independent and atomized systems.
Surface water pumping, on the other hand, needs more substantial initial investments and it is not so flexible. Yet, costs of pumping and electric energy make groundwater less competitive where the aquifer transmissibility is low, where dynamic levels are deep or where the demand is high and the well yield is low Hirata et al. These two different water dynamics are not widely used in Brazil. Even in cities that use both water sources, there is still no integrated planning that will explore the advantages of each resource, and the usage of two or more water sources does not aim at lower cost or better environmental use of the water cycle Figure 1.
This complementary aspect Table I must therefore be considered in the water use planning, which obvious benefits the society and the users. Milly et al. In the period of , relative to , there is a higher tendency toward dry consecutive days in the east of the Amazon and in the Northeast and Southeast regions, whereas extremes of intense rainfall will intensify the rainy days in the west of the Amazon Marengo Orsini Although there will be more rain in some regions in Brazil, the rainfall distribution will still vary, sometimes causing longer drought periods as observed in in the Amazon region.
This means that water tends to be concentrated in specific periods. There will be more water, but it will have a more heterogeneous distribution throughout the year. In times of scarcity, aquifers become safe sources of water for supplying local population and for economic activities including irrigated agriculture. However, more demand for the groundwater resource exploitation affects aquifers and also the surface water lakes, rivers, reservoirs by reducing base flows and consequently reducing biodiversity and impacting other systems that depend on stable water levels in reservoirs, lakes and rivers.
The climate change has affected the aquifer recharge and the surface discharge. Temperature rise has the potential to reduce the total discharge in function of the elevation of evapotranspiration, as well as the discharge due to the reduction of water excess. The impact on temporal variability increase on the aquifer is closely related to the local conditions. The increase in rainfall has the potential to increase aquifer recharge, but evapotranspiration can cancel this factor mainly in semi-arid regions.
The aquifer recharge reduction, mainly in unconfined aquifers, causes a groundwater decrease in the total available since the safe yield is a fraction of this recharge. Yet, it is certain that a greater exploitation of an aquifer can induce a greater recharge. So, if the dynamics of the aquifer is known, it is possible, with good management practices, to profit the most from this induced recharge increase and, consequently, from availability , with a better use of the hydric excess by reducing the losses in the base flow. A smaller recharge also has a negative impact on the vegetation once the aquifer lowering can reduce soil moisture.
A smaller recharge will also cause the saline seawater intrusion in coastal aquifers. This effect is particularly important in large urban centers of the Northeast region Hirata et al. The recharge also plays an important role in diluting contamination caused by disperse sources, including persistent contaminators such as those originated from latrines and pit-latrines in dense urban areas, particularly nitrate.
In this case, nitrate elimination is difficult and the dilution with clean water from natural recharge is an effective mechanism to reduce impacts to aquifers. On the other hand, the increase in the aquifer water level can have harmful effects in cities, for example on the foundations of buildings and floods in tunnels, garages and other underground work. This increase can also be harmful to vegetation, with significant alterations in the phreatic level. This study estimates with a good approximation based on calibrations in semi-arid and arid conditions a reduction of the aquifer recharge, although this model is not yet capable of predicting scenarios with the necessary accuracy, so that results are still uncertain.
Studies evaluating the influence of climate change on groundwater have been intensified since the 's by assessing many impact aspects on the aquifer recharge Bates et al. However, the evaluation in the Brazilian or South American territories is still scanty. Additionally, although all these articles calculated the groundwater recharge in different scale or detail level, almost all authors complained about uncertainties in estimating hydraulic parameters and their interactions in the atmosphere-aquifer system.
In Germany Jankiewicz et al. The results of this exercise is presented in Figure 4 , in which the authors demonstrated that, although there is significant resolution differences, the recharge variations are similar. IPCC scenario A2 is pessimistic, predicting world population growth and the increase of greenhouse gases emissions in current levels. The scenario B2 is more optimistic: population and greenhouse gases emissions grow less than in scenario A2. According to it, temperature should rise between 1.
Its oceanic component has a horizontal resolution of 1. HadCM3 has equations discriminated in space and time in grids covering the whole world and integrated with time steps of about 30 minutes. The horizontal resolution is 2. In contrast, the models show that in general the recharge in the South and Southeast regions will increase.
Although some punctual differences are observed in these two estimations, the results are still valid for establishing actions to mitigate the problem caused by climate changes. It is also possible to notice a severe reduction in the recharge values in the aquifers of the Northeast region. This report, prepared by the Climate Change Technical Subcommittee of the central Puget Sound WA Regional Water Supply Planning Process , is a literature review of the impacts of climate change on groundwater, focusing on studies that may be relevant to the Puget Sound lowlands region.
The report notes that no single groundwater model has emerged as appropriate for evaluating the impacts of climate change for all watersheds. The studies reviewed suggest substantial differences in the estimates of potential impacts of climate change on groundwater.