Impact of Climate Change on Groundwater Resources

Impact of Climate Change on Groundwater Resources C. P. KumarScientist ‘F’ : 

Impact of Climate Change on Groundwater Resources C. P. KumarScientist ‘F’ National Institute of Hydrology Roorkee – 247667 (India)

Presentation overview : 

Presentation overview Groundwater in Hydrologic Cycle What is Climate Change? Hydrological Impact of Climate Change Impact of Climate Change on Groundwater Climate Change Scenario for Groundwater in India Status of Research Studies Methodology to Assess the Impact of Climate Change on Groundwater Resources Concluding Remarks

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Types of Terrestrial Water Ground water Soil Moisture Surface Water

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Unsaturated Zone / Zone of Aeration / Vadose (Soil Water) Pores Full of Combination of Air and Water Zone of Saturation (Ground water) Pores Full Completely with Water

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Groundwater Important source of clean water More abundant than Surface Water Linked to SW systems Sustains flows in streams Baseflow

Why include groundwater in climate change studies? : 

Why include groundwater in climate change studies? Although groundwater accounts for small percentage of Earth’s total water, groundwater comprises approximately thirty percent of the Earth’s freshwater. Groundwater is the primary source of water for over 1.5 billion people worldwide. Depletion of groundwater may be the most substantial threat to irrigated agriculture, exceeding even the buildup of salts in soils. (Alley, et al., 2002)

“Natural” Groundwater Recharge : 

“Natural” Groundwater Recharge Natural groundwater recharge accounts for: Components of the hydrologic cycle: precipitation, evaporation, transpiration, runoff, infiltration, recharge, and baseflow. Heterogeneity of geological structures, local vegetation, and weather conditions. (Alley et al., 2002)

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Pollution Groundwater Concerns Groundwater mining Subsidence

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Problems with groundwater Groundwater overdraft / mining / subsidence Waterlogging Seawater intrusion Groundwater pollution

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Groundwater An important component of water resource systems. Extracted from aquifers through pumping wells and supplied for domestic use, industry and agriculture. With increased withdrawal of groundwater, the quality of groundwater has been continuously deteriorating. Water can be injected into aquifers for storage and/or quality control purposes.

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Groundwater contamination by: Hazardous industrial wastes Leachate from landfills Agricultural activities such as the use of fertilizers and pesticides Management of a groundwater system, means making such decisions as: The total volume that may be withdrawn annually from the aquifer. The location of pumping and artificial recharge wells, and their rates. Decisions related to groundwater quality.

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What is Climate Change? IPCC usage: Any change in climate over time, whether due to natural variability or from human activity. Alternate: Change of climate, attributed directly or indirectly to human activity, that Alters composition of global atmosphere and Is in addition to natural climate variability observed over comparable time periods

GLOBAL CIRCULATION MODELS : 

GLOBAL CIRCULATION MODELS Formulated to simulate climate sensitivity to increased concentrations of greenhouse gases such as carbon dioxide, methane and nitrous oxide.

Global Climate Models (GCMs) : 

Global Climate Models (GCMs) Divide the globe into large size grids Physical equations Lots of computing Predict the climatological variables

Global Climate Models translated to local impacts : 

Global Climate Models translated to local impacts Five step process outlined by Glieck & Frederick (1999) Look at several Global Climate Models (GCMs) and look for consensus & ranges Downscale to level needed (statistical and dynamical methods) Apply impact ranges to hydrologic modeling Develop systems simulation models Assessment of the results (historic and GCMs) at representative time frames

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Overview of the Climate Change Problem Source: IPCC Synthesis Report 2001

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Hydrological Impact of Climate Change According to the Technical Paper VI (2008) of Intergovernmental Panel on Climate Change (IPCC), the best-estimate in global surface temperature from 1906 to 2005 is a warming of 0.74°C (likely range 0.56 to 0.92°C), with a more rapid warming trend over the past 50 years. Temperature increases also affect the hydrologic cycle by directly increasing evaporation of available surface water and vegetation transpiration. Consequently, these changes can influence precipitation amounts, timings and intensity rates, and indirectly impact the flux and storage of water in surface and subsurface reservoirs (i.e., lakes, soil moisture, groundwater). In addition, there may be other associated impacts, such as sea water intrusion, water quality deterioration, potable water shortage, etc.

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While climate change affects surface water resources directly through changes in the major long-term climate variables such as air temperature, precipitation, and evapotranspiration, the relationship between the changing climate variables and groundwater is more complicated and poorly understood. The greater variability in rainfall could mean more frequent and prolonged periods of high or low groundwater levels, and saline intrusion in coastal aquifers due to sea level rise and resource reduction. Groundwater resources are related to climate change through the direct interaction with surface water resources, such as lakes and rivers, and indirectly through the recharge process. The direct effect of climate change on groundwater resources depends upon the change in the volume and distribution of groundwater recharge.

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Therefore, quantifying the impact of climate change on groundwater resources requires not only reliable forecasting of changes in the major climatic variables, but also accurate estimation of groundwater recharge. A number of Global Climate Models (GCM) are available for understanding climate and projecting climate change. There is a need to downscale outputs of GCM on a basin scale and couple them with relevant hydrological models considering all components of the hydrological cycle. Output of these coupled models such as quantification of the groundwater recharge will help in taking appropriate adaptation strategies due to the impact of climate change.

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Impact of Climate Change on Groundwater It is important to consider the potential impacts of climate change on groundwater systems. Although the most noticeable impacts of climate change could be fluctuations in surface water levels and quality, the greatest concern of water managers and government is the potential decrease and quality of groundwater supplies, as it is the main available potable water supply source for human consumption and irrigation of agriculture produce worldwide. Because groundwater aquifers are recharged mainly by precipitation or through interaction with surface water bodies, the direct influence of climate change on precipitation and surface water ultimately affects groundwater systems. As part of the hydrologic cycle, it can be anticipated that groundwater systems will be affected by changes in recharge (which encompasses changes in precipitation and evapotranspiration), potentially by changes in the nature of the interactions between the groundwater and surface water systems, and changes in use related to irrigation.

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(a) Soil Moisture The amount of water stored in the soil is fundamentally important to agriculture and has an influence on the rate of actual evaporation, groundwater recharge, and generation of runoff. Soil moisture contents are directly simulated by global climate models, albeit over a very coarse spatial resolution, and outputs from these models give an indication of possible directions of change. The local effects of climate change on soil moisture, however, will vary not only with the degree of climate change but also with soil characteristics. The water-holding capacity of soil will affect possible changes in soil moisture deficits; the lower the capacity, the greater the sensitivity to climate change. For example, sand has lower field capacity than clay. Climate change may also affect soil characteristics, perhaps through changes in cracking, which in turn may affect soil moisture storage properties.

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(b) Groundwater Recharge Groundwater is the major source of water across much of the world, particularly in rural areas in arid and semi-arid regions, but there has been very little research on the potential effects of climate change. Aquifers generally are replenished by effective rainfall, rivers, and lakes. This water may reach the aquifer rapidly, through macro-pores or fissures, or more slowly by infiltrating through soils and permeable rocks overlying the aquifer. A change in the amount of effective rainfall will alter recharge, but so will a change in the duration of the recharge season. Increased winter rainfall, as projected under most scenarios for mid-latitudes, generally is likely to result in increased groundwater recharge. However, higher evaporation may mean that soil deficits persist for longer and commence earlier, offsetting an increase in total effective rainfall.

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Various types of aquifers will be recharged differently. The main types are unconfined and confined aquifers. An unconfined aquifer is recharged directly by local rainfall, rivers, and lakes, and the rate of recharge will be influenced by the permeability of overlying rocks and soils. Unconfined aquifers are sensitive to local climate change, abstraction, and seawater intrusion. However, quantification of recharge is complicated by the characteristics of the aquifers themselves as well as overlying rocks and soils. A confined aquifer, on the other hand, is characterized by an overlying bed that is impermeable, and local rainfall does not influence the aquifer. It is normally recharged from lakes, rivers, and rainfall that may occur at distances ranging from a few kilometers to thousands of kilometers.

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Several approaches can be used to estimate recharge based on surface water, unsaturated zone and groundwater data. Among these approaches, numerical modelling is the only tool that can predict recharge. Modelling is also extremely useful for identifying the relative importance of different controls on recharge, provided that the model realistically accounts for all the processes involved. However, the accuracy of recharge estimates depends largely on the availability of high quality hydrogeologic and climatic data. The medium through which recharge takes place often is poorly known and very heterogeneous, again challenging recharge modelling. Determining the potential impact of climate change on groundwater resources, in particular, is difficult due to the complexity of the recharge process, and the variation of recharge within and between different climatic zones. In general, there is a need to intensify research on modeling techniques, aquifer characteristics, recharge rates, and seawater intrusion, as well as monitoring of groundwater abstractions.

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(c) Coastal Aquifers Coastal aquifers are important sources of freshwater. However, salinity intrusion can be a major problem in these zones. Changes in climatic variables can significantly alter groundwater recharge rates for major aquifer systems and thus affect the availability of fresh groundwater. Sea-level rise will cause saline intrusion into coastal aquifers, with the amount of intrusion depending on local groundwater gradients. For many small island states, seawater intrusion into freshwater aquifers has been observed as a result of overpumping of aquifers. Any sea-level rise would worsen the situation.

Sea Level Rise: A Global Concern : 

Sea Level Rise: A Global Concern Mean sea level has risen globally by 25 cm (1 - 2.5 mm/yr) on average over the last century (IPCC, 2001). Global warming is also occurring, causing temperatures to gradually increase worldwide. Global warming is exacerbating sea level rise, due to the increase in glacial melt and thermal expansion of the water which results from temperature change. Based on IPCC estimates, sea level could rise by another 50 cm (5 mm/yr) by 2100. Increased sea levels will vastly affect coastal regions. Increased sea levels will lead to increased frequency of severe floods.

Source: Intergovernmental Panel on Climate Change (2001) : 

Source: Intergovernmental Panel on Climate Change (2001) Future sea level rise = 1.990 - 2.100 meters Even if greenhouse gas concentrations are stabilised, sea level will continue to rise for hundreds of years. After 500 years, sea level rise from the thermal expansion of oceans may have reached only half its eventual level, glacier retreat will continue and ice sheets will continue to react to climate change. Thermal expansion and land ice changes were calculated using a simple climate model calibrated separately for each of seven air/ocean global climate models (AOGCMs). Light shading shows range of all models (in the next slide) -

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A link between rising sea level and changes in the water balance is suggested by a general description of the hydraulics of groundwater discharge at the coast. The shape of the water table and the depth to the freshwater/saline interface are controlled by the difference in density between freshwater and salt water, the rate of freshwater discharge and the hydraulic properties of the aquifer. To assess the impacts of potential climate change on fresh groundwater resources, we should focus on changes in groundwater recharge and impact of sea level rise on the loss of fresh groundwater resources in water resources stressed coastal aquifers.

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Climate Change Scenario for Groundwater in India Impact of climate change on the groundwater regime is expected to be severe. Due to rampant drawing of the subsurface water, the water table in many regions of the country has dropped significantly in the recent years resulting in threat to groundwater sustainability. The most optimistic assumption suggests that an average drop in groundwater level by one metre would increase India’s total carbon emissions by over 1%, because withdrawal of the same amount of water from deeper depths will increase fuel consumption. Climate change is likely to affect groundwater due to changes in precipitation and evapotranspiration. Rising sea levels may lead to increased saline intrusion into coastal and island aquifers, while increased frequency and severity of floods may affect groundwater quality in alluvial aquifers. Sea-level rise leads to intrusion of saline water into the fresh groundwater in coastal aquifers and thus adversely affects groundwater resources.

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For two small and flat coral islands at the coast of India, the thickness of freshwater lens was computed to decrease from 25 m to 10 m and from 36 m to 28 m, respectively, for a sea level rise of only 0.1 m (Mall et al., 2006). Agricultural demand, particularly for irrigation water, which is a major share of total water demand of the country, is considered more sensitive to climate change. A change in field-level climate may alter the need and timing of irrigation. Increased dryness may lead to increased demand, but demand could be reduced if soil moisture content rises at critical times of the year. It is projected that most irrigated areas in India would require more water around 2025 and global net irrigation requirements would increase relative to the situation without climate change by 3.5–5% by 2025 and 6–8% by 2075 (Mall et al., 2006). In India, roughly 52% of irrigation consumption across the country is extracted from groundwater; therefore, it can be an alarming situation with decline in groundwater and increase in irrigation requirements due to climate change (Mall et al., 2006). In a number of studies, it is projected that increasing temperature and decline in rainfall may reduce net recharge and affect groundwater levels. However, little work has been done on hydrological impacts of possible climate change for Indian regions/basins.

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Status of Research Studies There have been many studies relating the effect of climate changes on surface water bodies. However, very little research exists on the potential effects of climate change on groundwater. Available studies show that groundwater recharge and discharge conditions are reflection of the precipitation regime, climatic variables, landscape characteristics and human impacts such as agricultural drainage and flow regulation. Hence, predicting the behavior of recharge and discharge conditions under future climatic and other changes is of great importance for integrated water management. Previous studies have typically coupled climate change scenarios with hydrological models, and have generally investigated the impact of climate change on water resources in different areas. The scientific understanding of an aquifer’s response to climate change has been studied in several locations within the past decade. These studies link atmospheric models to unsaturated soil models, which, in some cases, were further linked into a groundwater model. The groundwater models used were calibrated to current groundwater conditions and stressed under different predicted climate change scenarios. Some of the recent studies on impact of climate change on groundwater resources are mentioned here.

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Bouraoui et al. (1999) Presented a general approach to evaluate the effect of potential climate changes on groundwater resources. A general methodology is proposed in order to disaggregate outputs of large-scale models and thus to make information directly usable by hydrologic models. Two important hydrological variables: rainfall and potential evapotranspiration are generated and then used by coupling with a physically based hydrological model to estimate the effects of climate changes on groundwater recharge and soil moisture in the root zone.

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Sherif and Singh (1999) Investigated the possible effect of climate change on sea water intrusion in coastal aquifers. Using two coastal aquifers, one in Egypt and the other in India, this study investigated the effect of likely climate change on sea water intrusion. Under conditions of climate change, the sea water levels will rise which will impose additional saline water heads at the sea side and therefore more sea water intrusion is anticipated. A 50 cm rise in the Mediterranean sea level will cause additional intrusion of 9.0 km in the Nile Delta aquifer. The same rise in water level in the Bay of Bengal will cause an additional intrusion of 0.4 km.

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Ghosh Bobba (2002) Analysed the effects of human activities and sea-level changes on the spatial and temporal behaviour of the coupled mechanism of salt-water and freshwater flow through the Godavari Delta of India. The density driven salt-water intrusion process was simulated with the use of SUTRA (Saturated-Unsaturated TRAnsport) model. The results indicate that a considerable advance in seawater intrusion can be expected in the coastal aquifer if current rates of groundwater exploitation continue and an important part of the freshwater from the river is diverted for irrigation, industrial and domestic purposes.

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Allen et al. (2004) Used the Grand Forks aquifer, located in south-central British Columbia, Canada as a case study area for modeling the sensitivity of an aquifer to changes in recharge and river stage consistent with projected climate-change scenarios for the region. Results suggested that variations in recharge to the aquifer under the different climate-change scenarios, modeled under steady-state conditions, have a much smaller impact on the groundwater system than changes in river-stage elevation of the Kettle and Granby Rivers, which flow through the valley.

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Brouyere et al. (2004) Developed an integrated hydrological model (MOHISE) in order to study the impact of climate change on the hydrological cycle in representative water basins in Belgium. This model considers most hydrological processes in a physically consistent way, more particularly groundwater flows which are modelled using a spatially distributed, finite-element approach. The groundwater model is described in detail and results are discussed in terms of climate change impact on the evolution of groundwater levels and groundwater reserves. Most tested scenarios predicted a decrease in groundwater levels in relation to variations in climatic conditions.

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Holman (2006) Described an integrated approach to assess the regional impacts of climate and socio-economic change on groundwater recharge from East Anglia, UK. Important sources of uncertainty and shortcomings in recharge estimation were discussed in the light of the results. Changes to soil properties are occurring over a range of time scales, such that the soils of the future may not have the same infiltration properties as existing soils. The potential implications involved in assuming unchanging soil properties were described.

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Mall et al. (2006) Examined the potential for sustainable development of surface water and groundwater resources within the constraints imposed by climate change and future research needs in India. He concluded that the Indian region is highly sensitive to climate change. The National Environment Policy (2004) also advocated that anthropogenic climate changes have severe adverse impacts on India’s precipitation patterns, ecosystems, agricultural potential, forests, water resources, coastal and marine resources. Large-scale planning would be clearly required for adaptation measures for climate change impacts, if catastrophic human misery is to be avoided.

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Ranjan et al. (2006) Evaluated the impacts of climate change on fresh groundwater resources specifically salinity intrusion in five selected water resources stressed coastal aquifers. The annual fresh groundwater resources losses indicated an increasing long-term trend in all stressed areas, except in the northern Africa/Sahara region. They also found that precipitation and temperature individually did not show good correlations with fresh groundwater loss. They also discussed the impacts of loss of fresh groundwater resources on socio-economic activities, mainly population growth and per capita fresh groundwater resources.

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Scibek and Allen (2006) Developed a methodology for linking climate models and groundwater models to investigate future impacts of climate change on groundwater resources. Climate change scenarios from the Canadian Global Coupled Model 1 (CGCM1) model runs were downscaled to local conditions using Statistical Downscaling Model (SDSM). The recharge model (HELP) simulated the direct recharge to the aquifer from infiltration of precipitation. MODFLOW was then used to simulate four climate scenarios in 1-year runs (1961–1999, 2010–2039, 2040–2069, and 2070‑2099) and compare groundwater levels to present. The predicted future climate for the Grand Forks area (Canada) from the downscaled CGCM1 model will result in more recharge to the unconfined aquifer from spring to the summer season. However, the overall effect of recharge on the water balance is small because of dominant river-aquifer interactions and river water recharge.

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Woldeamlak et al. (2007) Modeled the effects of climate change on the groundwater systems in the Grote-Nete catchment, Belgium. Seasonal and annual water balance components including groundwater recharge were simulated using the WetSpass model, while mean annual groundwater elevations and discharge were simulated with a steady-state MODFLOW groundwater model. Results show that average annual groundwater levels drop by 50 cm.

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Hsu et al. (2007) Adopted a numerical modeling approach to investigate the response of the groundwater system to climate variability to effectively manage the groundwater resources of the Pingtung Plain in southwestern Taiwan. A hydrogeological model (MODFLOW SURFACT) was constructed based on the information from geology, hydrogeology, and geochemistry. The modeling result shows decrease of available groundwater in the stress of climate change, and the enlargement of the low-groundwater-level area on the coast signals the deterioration of water quantity and quality in the future.

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Toews (2007) Modeled the impacts of future predicted climate change on groundwater recharge for the arid to semi-arid south Okanagan region, British Columbia. Climate change effects on recharge were investigated using stochastically-generated climate from three GCMs. Spatial recharge was modelled using available soil and climate data with the HELP 3.80D hydrology model. A transient MODFLOW groundwater model simulated rise of water table in future time periods, which is largely driven by irrigation application increases.

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These studies are still at infancy and more data, in terms of field information, are to be generated. This will also facilitate appropriate validation of the simulation for the present scenarios. However, it is clear that the global warming threat is real and the consequences of climate change phenomena are many and alarming. Concluding Remarks on the Research Studies

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Methodology to Assess the Impact of Climate Change on Groundwater Resources The methodology consists of three main steps. To begin with, climate scenarios can be formulated for the future years such as 2050 and 2100. Secondly, based on these scenarios and present situation, seasonal and annual recharge are simulated with the UnSat Suite (HELP module for recharge) or WetSpass model. Finally, the annual recharge outputs from UnSat Suite or WetSpass model are used to simulate groundwater system conditions using steady-state groundwater model setups, such as MODFLOW, for the present condition and for the future years.

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The influence of climate changes on goundwater levels and salinity, due to: Sea level rise Changes in precipitation and temperature Methodology Develop and calibrate a density-dependent numerical groundwater flow model that matches hydraulic head and concentration distributions in the aquifer. Estimate changes in sea level, temperature and precipitation downscaled from GCM outputs. Estimate changes in groundwater recharge. Apply sea level rise and changes in recharge to numerical groundwater model and make predictions for changes in groundwater levels and salinity distribution.

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The main tasks that are involved in such a study are: Describe hydrogeology of the study area. Analyze climate data from weather stations and modelled GCM, and build future predicted climate change datasets with temperature, precipitation and solar radiation variables (downscaled to the study area). Define methodology for estimating changes to groundwater recharge under both current climate conditions and for the range of climate-change scenarios for the study area. Use of a computer code (such as UnSat Suite or WetSpass) to estimate groundwater recharge based on available precipitation and temperature records and anticipated changes to these parameters.

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Quantify the spatially distributed recharge rates using the climate data and spatial soil survey data. Development and calibration of a three-dimensional regional-scale groundwater flow model (such as Visual MODFLOW). Simulate groundwater levels using each recharge data set and evaluate the changes in groundwater levels through time. Undertake sensitivity analysis of the groundwater flow model.

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A typical flow chart for various aspects of such a study is given below. The figure shows the connection from the climate analysis, to recharge simulation, and finally to a groundwater model. Recharge is applied to a three-dimensional groundwater flow model, which is calibrated to historical water levels. Transient simulations are undertaken to investigate the temporal response of the aquifer system to historic and future climate periods.

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Concluding Remarks Although climate change has been widely recognized, research on the impacts of climate change on the groundwater system is relatively limited. The impact of future climatic change may be felt more severely in developing countries such as India, whose economy is largely dependent on agriculture and is already under stress due to current population increase and associated demands for energy, freshwater and food. If the likely consequences of future changes of groundwater recharge, resulting from both climate and socio-economic change, are to be assessed, hydrogeologists must increasingly work with researchers from other disciplines, such as socio-economists, agricultural modelers and soil scientists.

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THANK YOU