Sustainable groundwater management on the small island of Manukan,Malaysia

Numerical models are capable of simulating various groundwater scenarios and relate it towards groundwater management. This paper focuses on numerical modeling and water balance approaches in the search for a sustainable management plan in Manukan Island. The impacts of pumping and recharge rates represented by groundwater scenarios were investigated by means of hydraulic heads, chloride concentrations and water balance components. Overpumping and inconsistency in recharge rate are the stresses shown in Scenario A. Scenario B involved with reduction pumping rate by 25% has shown an increase in groundwater levels, chloride concentration and groundwater storage. Scenario C showed the most promising finding compared with Scenarios A and B. Highest hydraulic heads, lowest chloride concentration (1,552.2 mg/L) and positive groundwater storage (254.3 m³/day) were obtained in Scenario C. Chloride concentration in pumping wells still exceeds World Health Organization International Standard limit in Scenario C which illustrates an additional water treatment is needed. Nevertheless, in view of a compromise groundwater management plan in study area, Scenario C is the best plan so far to protect the groundwater resources in the study area. More understanding of the artificial recharge method (percolation tank) and study site by means of modeling studies is needed. Additionally, further progress is needed in obtaining the water usage data from each part to determine the best pumping rate. A sustainable groundwater management plan is crucial to maintain the natural resources and social benefits as well as to protect the ecological balance of Manukan Island.     

Effects of climate change on groundwater resources at Shelter Island, New York State, USA

Rising sea levels due to climate change are expected to negatively impact the fresh-water resources of small islands. The effects of climate change on Shelter Island, New York State (USA), a small sandy island, were investigated using a variable-density transient groundwater flow model. Predictions for changes in precipitation and sea-level rise over the next century from the Intergovernmental Panel on Climate Change 2007 report were used to create two future climate scenarios. In the scenario most favorable to fresh groundwater retention, consisting of a 15% precipitation increase and 0.18-m sea-level rise, the result was a 23-m seaward movement of the fresh-water/salt-water interface, a 0.27-m water-table rise, and a 3% increase in the fresh-water lens volume. In the scenario supposedly least favorable to groundwater retention, consisting of a 2% precipitation decrease and 0.61-m sea-level rise, the result was a 16-m landward movement of the fresh-water/salt-water interface, a 0.59-m water-table rise, and a 1% increase in lens volume. The unexpected groundwater-volume increase under unfavorable climate change conditions was best explained by a clay layer under the island that restricts the maximum depth of the aquifer and allows for an increase in fresh-water lens volume when the water table rises.     

Pumping dry: an increasing groundwater budget deficit induced by urbanization,industrialization, and climate change in an over-exploited volcanic aquifer

A methodology is proposed to improve the groundwater budget model by determining the past, present, and future recharge and discharge rates. The model is applied to an increasingly urbanized and industrialized region with drying tendencies: the Toluca Valley, Mexico. This study includes spatially variable recharge determined from the historical climate data, the climate change predictions, and the multiple parameters used in the Hydrologic Evaluation of Landfill Performance (HELP3) model. Using HELP3 a spatial discretization for the average recharge is obtained and estimated at 376 million cubic meters per year (Mm³/year). When considering climate change predictions, by 2050 the average scenario projects recharge to decrease by 15 Mm³/year (from 376 to 361 Mm³/year), and in a worst case scenario up to a maximum decrease of 88 Mm³/year (from 376 to 288 Mm³/year). Groundwater pumping has increased steadily since 1970 and is estimated at 495 Mm³/year for 2010. The current average deficit estimated for 2010 is 172 Mm³/year with average projections increasing to over 292 Mm³/year by 2050. This study of two of the most important components of the water cycle (recharge and discharge) clearly shows that the decreasing water availability in the Toluca basin is due mainly to groundwater pumping and that the current pumping rates are not sustainable. The current deficit can be considered problematic and projections based on expected water consumption and climate change reinforce the need for management of the water resources to be addressed.     

Assessing the impacts of climate change on sustainable management of coastal aquifers

Water is a vital resource for the survival of not only human population, but also almost all ecosystems. Constituting 30 % of all freshwater, groundwater is the main source of available freshwater. Coastal aquifers, which serve as the major freshwater source for densely populated zones, are of vital importance and quite vulnerable to climate change. This paper examines the significant consequences of climate change, decreasing recharge rates, sea-level rise and increasing freshwater demand on the sustainable management of coastal aquifers, via a hypothetical case study. A 3-D numerical model is developed using SEAWAT, to simulate a circular island aquifer in the form of a freshwater lens surrounded by saltwater. Issues such as sloping land surface resulting in landward migration of the coastal boundary and transient response of the system due to pumping are considered through a set of predictive simulations. To assess the sensitivity of the model results to important parameters, a sensitivity analysis is performed. Results of this research, revealing the effects of mentioned pressures on the long-term sustainability of the freshwater resource, are evaluated on the basis of groundwater reserves and intrusion of the freshwater–saltwater interface in lateral and vertical directions. These outcomes are further used to determine the sustainable pumping rate of the system, considering both quantity and quality of the groundwater resources.     

A comparison of stochastic and deterministic downscaling methods for modelling potential groundwater recharge under climate change in East Anglia, UK: implications for groundwater resource management

Groundwater resource estimates require the calculation of recharge using a daily time step. Within climate-change impact studies, this inevitably necessitates temporal downscaling of global or regional climate model outputs. This paper compares future estimates of potential groundwater recharge calculated using a daily soil-water balance model and climate-change weather time series derived using change factor (deterministic) and weather generator (stochastic) methods for Coltishall, UK. The uncertainty in the results for a given climate-change scenario arising from the choice of downscaling method is greater than the uncertainty due to the emissions scenario within a 30-year time slice. Robust estimates of the impact of climate change on groundwater resources require stochastic modelling of potential recharge, but this has implications for groundwater model runtimes. It is recommended that stochastic modelling of potential recharge is used in vulnerable or sensitive groundwater systems, and that the multiple recharge time series are sampled according to the distribution of contextually important time series variables, e.g. recharge drought severity and persistence (for water resource management) or high recharge years (for groundwater flooding). Such an approach will underpin an improved understanding of climate change impacts on sustainable groundwater resource management based on adaptive management and risk-based frameworks.     

Impacts of climate change on groundwater recharge in Küçük Menderes River Basin in Western Turkey

Groundwater is an important component of the global freshwater supply and is affected by climate. There is a strong need to understand and evaluate the impacts of climate change over the long term, in order to better plan and manage precious groundwater resources. Turkey, located in Mediterranean basin, is threatened by climate change. The purpose of this study was, through a quantitative overview, to determine the impacts of climate change on the groundwater recharge rates in Küçük Menderes River Basin in western Turkey. According to the data of Ödemi? and Selçuk meteorological stations located in the basin, there is a significantly decreasing trend in precipitation combined with increasing trends in temperature and evaporation observed in 1964–2011. The calculations of groundwater recharge with hydrologic budget method for the observation period showed an approximately 15% decline in groundwater recharge in the basin. Thus, the combined impacts of climate change and excessive groundwater pumping, due to increasing water demand, have caused a significant decline in groundwater levels. Consequently, the proper management of the groundwater resources threatened by climate change requires effective governance to both mitigate the adverse impacts of climate change and facilitate the adaptation of sustainable integrated water management policies.     

Modelling the response of shallow groundwater levels to combined climate and water-diversion scenarios in Beijing-Tianjin-Hebei Plain,China

A three-dimensional groundwater flow model was implemented to quantify the temporal variation of shallow groundwater levels in response to combined climate and water-diversion scenarios over the next 40 years (2011–2050) in Beijing-Tianjin-Hebei (Jing-Jin-Ji) Plain, China. Groundwater plays a key role in the water supply, but the Jing-Jin-Ji Plain is facing a water crisis. Groundwater levels have declined continuously over the last five decades (1961–2010) due to extensive pumping and climate change, which has resulted in decreased recharge. The implementation of the South-to-North Water Diversion Project (SNWDP) will provide an opportunity to restore the groundwater resources. The response of groundwater levels to combined climate and water-diversion scenarios has been quantified using a groundwater flow model. The impacts of climate change were based on the World Climate Research Programme’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset for future high (A2), medium (A1B), and low (B1) greenhouse gas scenarios; precipitation data from CMIP3 were applied in the model. The results show that climate change will slow the rate of decrease of the shallow groundwater levels under three climate-change scenarios over the next 40 years compared to the baseline scenario; however, the shallow groundwater levels will rise significantly (maximum of 6.71 m) when considering scenarios that combine climate change and restrictions on groundwater exploitation. Restrictions on groundwater exploitation for water resource management are imperative to control the decline of levels in the Jing-Jin-Ji area.     

Assessing the impact of future climate change on groundwater recharge in Galicia-Costa, Spain

Climate change can impact the hydrological processes of a watershed and may result in problems with future water supply for large sections of the population. Results from the FP5 PRUDENCE project suggest significant changes in temperature and precipitation over Europe. In this study, the Soil and Water Assessment Tool (SWAT) model was used to assess the potential impacts of climate change on groundwater recharge in the hydrological district of Galicia-Costa, Spain. Climate projections from two general circulation models and eight different regional climate models were used for the assessment and two climate-change scenarios were evaluated. Calibration and validation of the model were performed using a daily time-step in four representative catchments in the district. The effects on modeled mean annual groundwater recharge are small, partly due to the greater stomatal efficiency of plants in response to increased CO₂ concentration. However, climate change strongly influences the temporal variability of modeled groundwater recharge. Recharge may concentrate in the winter season and dramatically decrease in the summer–autumn season. As a result, the dry-season duration may be increased on average by almost 30 % for the A2 emission scenario, exacerbating the current problems in water supply.     

Modeling of seawater intrusion in a coastal aquifer of Karaburun Peninsula,western Turkey

Seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could be easily influenced by seawater. This study presents the development of a conceptual and numerical model for the coastal aquifer of Karareis region (Karaburun Peninsula) in the western part of Turkey. The study also presents the interpretation and the analysis of the time series data of groundwater levels recorded by data loggers. The SEAWAT model is used in this study to solve the density-dependent flow field and seawater intrusion in the coastal aquifer that is under excessive pumping particularly during summer months. The model was calibrated using the average values of a 1-year dataset and further verified by the average values of another year. Five potential scenarios were analyzed to understand the effects of pumping and climate change on groundwater levels and the extent of seawater intrusion in the next 10 years. The result of the analysis demonstrated high levels of electrical conductivity and chloride along the coastal part of the study area. As a result of the numerical model, seawater intrusion is simulated to move about 420 m toward the land in the next 10 years under “increased pumping” scenario, while a slight change in water level and TDS concentrations was observed in “climate change” scenario. Results also revealed that a reduction in the pumping rate from Karareis wells will be necessary to protect fresh groundwater from contamination by seawater.     

Evapotranspiration capture and stream depletion due to groundwater pumping under variable boreal climate conditions: Sudogda River Basin,Russia

Groundwater pumping and changes in climate-induced recharge lead to lower groundwater levels and significant changes in the water balance of a catchment. Water previously discharged as evapotranspiration can become a source of pumpage. Neglecting this effect leads to overestimated streamflow depletion. A small river basin (Sudogda River Basin, Russia) with a boreal climate and with long-term records of groundwater head and streamflow rate (showing that the measured stream depletion is less than the pumping rate) was investigated. The role of evapotranspiration in the water balance was analyzed by a hydrogeological model using MODFLOW-2005 with the STR package; the annual variation in recharge was obtained with the codes Surfbal and HYDRUS. The Sudogda River Basin was classified according to landscape and unsaturated-zone texture classes, and for each classified zone, the unsaturated-zone flow simulation was used to calculate the annual recharge dynamics for the observation period. Calibration of the regional flow model was conducted using flow and head observations jointly for two steady-state flow conditions—natural (before pumping started) and stressed (pumping). The simulations showed that pumped water originates from three sources: intercepted baseflow (75% of the annual total pumping rate), the capture of groundwater evapotranspiration discharge plus increased groundwater recharge (17%), and induced stream infiltration (8%). Additionally, multi-year precipitation records were analyzed to detect any long-term recharge and pumping water-budget changes. The results showed that increasing groundwater recharge by natural precipitation leads to (1) decreased intercepted baseflow and induced streamflow infiltration and (2) increased intercepted evapotranspiration discharge, thereby reducing stream depletion.     

Climate change and groundwater conditions in the Mekong Region–A review

Changes in the climatic system introduce uncertainties in the supply and management of water resources. The Intergovernmental Panel on Climate Change(IPCC) predicts an increase of 2 to 4 °C over the next 100 years. Temperature increases will impact the hydrologic cycle by directly increasing the evaporation of surface water sources. Consequently, changes in precipitation will indirectly impact the flux and storage of water in surface and subsurface reservoirs(i.e., lakes, soil moisture, groundwater, etc.). In addition, increases in temperature contribute to increases in the sea level, which may lead to sea water intrusions, water quality deterioration, potable water shortages, etc. Climate change has direct impacts on the surface water and the control of storage in rivers, lakes and reservoirs, which indirectly controls the groundwater recharge process. The main and direct impact of climate change on groundwater is changes in the volume and distribution of groundwater recharge. The impact of climate change on groundwater resources requires reliable forecasting of changes in the major climatic variables and accurate estimations of groundwater recharge. A number of Global Climate Models(GCMs) are available for understanding climate and projecting climate change.These GCMs can be downscaled to a basin scale, and when they are coupled with relevant hydrological models, the output of these coupled models can be used to quantify the groundwater recharge, which will facilitate the adoption of appropriate adaptation strategies under the impact of climate change.     

Hydrogeology and sustainable future groundwater abstraction from the Agua Verde aquifer in the Atacama Desert,northern Chile

The hyper-arid conditions prevailing in Agua Verde aquifer in northern Chile make this system the most important water source for nearby towns and mining industries. Due to the growing demand for water in this region, recharge is investigated along with the impact of intense pumping activity in this aquifer. A conceptual model of the hydrogeological system is developed and implemented into a two-dimensional groundwater-flow numerical model. To assess the impact of climate change and groundwater extraction, several scenarios are simulated considering variations in both aquifer recharge and withdrawals. The estimated average groundwater lateral recharge from Precordillera (pre-mountain range) is about 4,482 m³/day. The scenarios that consider an increase of water withdrawal show a non-sustainable groundwater consumption leading to an over-exploitation of the resource, because the outflows surpasses inflows, causing storage depletion. The greater the depletion, the larger the impact of recharge reduction caused by the considered future climate change. This result indicates that the combined effects of such factors may have a severe impact on groundwater availability as found in other groundwater-dependent regions located in arid environments. Furthermore, the scenarios that consider a reduction of the extraction flow rate show that it may be possible to partially alleviate the damage already caused to the aquifer by the continuous extractions since 1974, and it can partially counteract climate change impacts on future groundwater availability caused by a decrease in precipitation (and so in recharge), if the desalination plant in Taltal increases its capacity.     

基岩海岛地下水与海水相互作用研究

中国北方基岩海岛水文地质条件独特,气候变化和人类活动不同程度地影响着海岛地下水与海水相互作用过程,然而对包括海水入侵(SWI)和海底地下水排泄(SGD)的水文过程的定量认识比较缺乏。本研究基于2012—2016年我国北方某基岩群岛降水、地下水水位、水质动态监测数据,运用数理统计、空间插值和水力学方法,分析了基岩海岛地下水与海水相互作用的特征和影响因素。结果表明,降水和开采是影响地下水、海水相互作用的主要因素,地下水水位变化滞后于降水事件约10 d;南岛东北岸、南岸的大部分地区没有发生海水入侵,地下水向海排泄过程较稳定,2012—2016年SGD速率均值为0.2 m/d,向海NO₃^-N通量均值为81.8 mmol/(m²·d);北岛东南地区是海水入侵的严重区域,地下水水位长期低于海平面且逐年下降,2012—2016年SWI速率均值为0.3 m/d,向陆NO₃^-N通量均值为69.6 mmol/(m2·d)。分别计算南、北两岛枯水季(2014年4月)、丰水季(2013年9月)SGD水...     

Conceptual hydrogeological model of volcanic Easter Island (Chile) after chemical and isotopic surveys

Most human activities and hydrogeological information on small young volcanic islands are near the coastal area. There are almost no hydrological data from inland areas, where permanent springs and/or boreholes may be rare or nonexistent. A major concern is the excessive salinity of near-the-coast wells. Obtaining a conceptual hydrogeological model is crucial for groundwater resources development and management. Surveys of water seepages and rain for chemical and environmental isotope contents may provide information on the whole island groundwater flow conditions, in spite of remaining geological and hydrogeological uncertainties. New data from Easter Island (Isla de Pascua), in the Pacific Ocean, are considered. Whether Easter Island has a central low permeability volcanic “core” sustaining an elevated water table remains unknown. Average recharge is estimated at 300–400 mm/year, with a low salinity of 15–50 mg/L Cl. There is an apron of highly permeable volcanics that extends to the coast. The salinity of near-the-coast wells, >1,000 mg/L Cl, is marine in origin. This is the result of a thick mixing zone of island groundwater and encroached seawater, locally enhanced by upconings below pumping wells. This conceptual model explains what is observed, in the absence of inland boreholes and springs.     

1956—2016年新疆平原区地下水资源量变化及其影响因素分析

探索变化环境下新疆平原区地下水资源量的变化趋势,是识别地下水环境问题、加强地下水资源管理的基础工作。基于水利部门历次水资源调查评价成果、水利统计资料汇编等数据,对1956—2016年新疆平原区地下水资源量变化及其影响因素进行分析,对变化原因进行探讨。结果表明:1956—2016年新疆平原区地下水资源量呈减少趋势,其中地下水天然补给量基本稳定,地表水体转化补给量持续减少;从地下水补给结构分析,渠系渗漏补给量大幅减少,导致地下水资源量减少;河道渗漏补给量增加,抵消了地下水资源量的减幅。平原区灌溉面积扩大导致的农田灌溉耗水量增大是地下水资源量减少的根本原因,人类活动对地下水资源量的影响大于气候变化。     

Evaluation of climate change effects in a coastal aquifer in Morocco using a density-dependent numerical model

A density-dependent numerical groundwater model was applied to study the climate change impact in a shallow aquifer in the Mediterranean coast of Morocco, the Saïdia aquifer. The stresses imposed to the model were derived from the IPCC emission scenarios and included recharge variation and sea level rise. The main effect of the climate change in the Saïdia aquifer will be a decrease in renewable resources, which in the worst-case scenario may decrease to 50–60% of present-day values, due to the decline in recharge and to a reduced inflow from the adjacent Triffa aquifer. The water quality will be affected mostly in the area immediately adjacent to the seashore, where salinity may increase up to 30 g/l. Localised areas may see a decrease in salinity due to the induced freshwater recharge from Oued Moulouya River and diminished inflow from high-salinity springs.     

Salinization and Deterioration of Groundwater Quality by Nitrate and Fluoride in the Chittur Block,Palakkad, Kerala

Chittur block represents a mid-land region of Palakkad district, Kerala and the block differs from the rest of the blocks in its climate and availability of groundwater. About 75% of the people depend on agriculture for their livelihood. Results showed that groundwater salinity levels (up to 1,963 mg/L TDS),fluoride (up to 6.3 mg/L) and nitrate (up to 141 mg/L) contents have increased significantly in tandem with the increase in groundwater abstraction. Before human intervention the chemical weathering of gneisses and granites was the main process impinging on the chemical signature of groundwater. The initial chemical equilibrium conditions change with increasing groundwater withdrawal rates and fertilizer input, in a milieu of lower natural groundwater recharge. The appearance of higher levels of bicarbonate, linked to denitrification processes, and the decrease in calcium, due to calcite precipitation, can lead to increased content of sodium and fluoride in groundwater. In this scenario the use of groundwater resources for human consumption and agriculture represents a public health risk if water management actions do not change the trend in water use in the near future. The potential loss of fertile soil by groundwater salinization must also be considered when planning sustainable policies in a region with over dependence on groundwater resources.     

Climate change and groundwater resources in Cambodia

Climate change has become a major global concern and threatens the security of natural environmental resources, including groundwater, especially for Cambodia. In this study, literature reviews related to climate change and groundwater resources in Cambodia were evaluated to address the impact of climate change on the groundwater environment. In Cambodia, global climate change will likely affect available water resources by driving changes in the groundwater recharge and usage pattern. Despite a general increase in the mean annual rainfall, a reduction in rainfall is anticipated during the dry season, which could lead to shortages of fresh water during the dry season. The impact of climate change on water resource environments can significantly affect national economic development. Thus, strategic management plansfor groundwater in response to climate change should be established to ensure the security of water resources in Cambodia.     

Application of Numerical Modeling for Groundwater Flow System Analysis in the Akaki Catchment,Central Ethiopia

A three dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze the subsurface hydrodynamics in the Akaki catchment by giving particular emphasis to the well field that supplies water to the city of Addis Ababa. The area is characterized by Tertiary volcanics covered with thick residual and alluvial soils. The model is calibrated using head observations from 131 wells. The simulation is made in a two layer unconfined aquifer with spatially variable recharge and hydraulic conductivities under well-defined boundary conditions. The calibrated model is used to forecast groundwater flow pattern, the interaction of groundwater and surface water, and the effect of pumping on the well field under different scenarios. The result indicates that the groundwater flows regionally to the south converging to the major well field. Reservoirs and rivers play an important role in recharging the aquifer. Simulations made under different pumping rate indicate that an increase in pumping rate results in substantial regional groundwater level decline, which will lead to the drying of springs and shallow hand dug wells. Also, it has implications of reversal of flow from contaminated rivers into productive aquifers close to main river courses. The scenario analysis shows that the groundwater potential is not enough to sustain the ever-growing water demand of the city of Addis Ababa. The sensitivity and scenario analysis provided important information on the data gaps and the specific sites to be selected for monitoring, and may be of great help for transient model development. This study has laid the foundation for developing detailed predictive groundwater model, which can be readily used for groundwater management practices.     

Response of the groundwater system in the Guanzhong Basin (central China) to climate change and human activities

The Guanzhong Basin in central China features a booming economy and has suffered severe drought, resulting in serious groundwater depletion in the last 30 years. As a major water resource, groundwater plays a significant role in water supply. The combined impact of climate change and intensive human activities has caused a substantial decline in groundwater recharge and groundwater levels, as well as degradation of groundwater quality and associated changes in the ecosystems. Based on observational data, an integrated approach was used to assess the impact of climate change and human activities on the groundwater system and the base flow of the river basin. Methods included: river runoff records and a multivariate statistical analysis of data including historical groundwater levels and climate; hydro-chemical investigation and trend analysis of the historical hydro-chemical data; wavelet analysis of climate data; and the base flow index. The analyses indicate a clear warming trend and a decreasing trend in rainfall since the 1960s, in addition to increased human activities since the 1970s. The reduction of groundwater recharge in the past 30 years has led to a continuous depletion of groundwater levels, complex changes of the hydro-chemical environment, localized salinization, and a strong decline of the base flow to the river. It is expected that the results will contribute to a more comprehensive management plan for groundwater and the related eco-environment in the face of growing pressures from intensive human activities superimposed on climate change in this region.