Extensive Groundwater Pumping Research Articles

Widespread potential for streamflow leakage across Brazil

River-aquifer interactions play a crucial role in water availability, influencing environmental flows and impacting climate dynamics. Where groundwater tables lie below river water levels, stream water can infiltrate into the underlying aquifer, reducing streamflow. However, the prevalence of these “losing” rivers remains poorly understood due to limited national-wide in situ observations. Here we analyze water levels in 17,972 wells across Brazil to show that most of them (55%) lie below nearby stream surfaces, implying that these nearby streams are likely seeping into the subsurface. Our results demonstrate the widespread potential for stream water losses into underlying aquifers in many regions of the country, especially in areas with extensive groundwater pumping. Our direct observations underscore the importance of conjunctively managing groundwater and surface water, and highlight the widespread risk of streamflow losses to aquifers, which could impact global water access and ecosystems that rely on rivers.

Evaluation of Terrestrial Water Storage and Flux in North China by Using GRACE Combined Gravity Field Solutions and Hydrometeorological Models

To enrich the understanding of the dynamic evolution of the water resources in North China, terrestrial water storage anomalies (TWSA) from January 2003 to June 2017 are derived using the new GRACE time-variable gravity field model Tongji-GraceCom. Additionally, the spatiotemporal characteristics of terrestrial water fluxes (TWF) at multiple time scales are analyzed based on the water budget theory in conjunction with hydrometeorological and statistical data. The results show that the quality of the Tongji-GraceCom model is superior to the state-of-art spherical harmonic models (CSR RL06 and JPL RL06), with the signal-to-noise ratio improving by 10–16%. After correcting the leakage errors with a reliable correction method, the inferred TWSA in North China presents a significant downward trend, amounting to −1.61 ± 0.05 cm/yr, with the most serious TWSA depletion mainly clustering in the south-central area. The TWFs derived from GRACE and from hydrometeorological elements are in good agreement and both exhibit significant seasonal fluctuations induced by tracking the periodic movements of meteorological factors. However, unlike precipitation which manifests in an increasing trend, both TWFs reflect the obvious decreasing trends, indicating that North China is suffering from severe water deficits, which are mainly attributed to the enhanced evaporation and extensive groundwater pumping for agricultural irrigation.

Khettaras in the Tafilalet oasis (Morocco): contribution to the promotion of tourism and sustainable development

The khettaras constitute a hydraulic system for mobilising water by gravity from the water table to the surface to irrigate fields in oases. This system, which has been fairly widespread in North Africa, in particular in Algeria (foggara) and Morocco (khettaras), was introduced several centuries ago in the oases of southeastern Morocco and has continued to operate despite various natural and anthropic constraints. Based on these ingenious and millennial hydraulic systems, successive civilisations living in these environments have been able to establish laws and regulations for the management and mobilisation of natural resources, especially water. Indeed, to get the most out of these systems, users have had to abide by rules (Al Orf/Azref) designed to protect, promote, and care for the systems to enhance their sustainability. These hydraulic systems have declined in recent years, notably due to extensive groundwater pumping, climate variability (severe droughts), and the local population’s disinterest for this type of development. Therefore, we have unfortunately witnessed the loss of a thousand-year-old local ancestral know-how that had been developed by different succeeding civilisations in the area. Recent initiatives (2008–2011) have been undertaken by the Moroccan government for the restoration and development of some abandoned khettaras in the Tafilalet Oasis so that they could be utilised in the development of an oasis-based cultural tourism and integrated in a tourist circuit known as Majhoul. This initiative, still in its infancy, has constituted an alternative and a fairly encouraging development for this national and world heritage.

Evaluation of water-level trends in the Mimbres Basin, southwest New Mexico (USA), using spatiotemporal kriging

Groundwater-level trends over the past 40 years in the Mimbres Basin of southwest New Mexico (USA) were characterized with sequential water-level maps and maps of water-level change generated via spatiotemporal kriging. In the region of the most abundant irrigated agriculture, water levels have declined up to 24 m and cones of depression have expanded greatly. Increases in area of irrigated land and groundwater withdrawals in the past 10 years are coeval with water-level declines near the USA-Mexico border. Known areas of groundwater recharge from streamflow infiltration, and springs discharging deep-sourced water, show evidence of net water-level rises in the past 40 years, but declines in the last 10 years, in concert with declining precipitation over the basin. Formerly irrigated lands exhibit water-level rises, suggestive of flattening of cones of depression after cessation of extensive groundwater pumping. Manual water-level measurements are vital for understanding and managing groundwater resources, yet they are expensive and laborious to collect, which has resulted in much fewer data in recent years. Spatiotemporal kriging is more complex in mathematical development and implementation than spatial kriging, but it yields improved precision and accuracy, predictions at times with no data as well as at locations with no data, and fewer artifacts due to changing well networks. Its ability to leverage historical data recommends its use in hydrologic studies dependent on water-level maps and changes in water levels over time.

Assessing groundwater salinity across Africa

In Africa groundwater is the principal source of drinking water (https://washdata.org/) and has significant potential to improve food production as a source of irrigation water. Although volumes of stored groundwater are high when compared to surface water, not all the available groundwater is suitable for irrigation. One of the principal factors that limit the development of groundwater is salinity, but quantitative evidence regarding the scale of salinization in Africa has been lacking. This paper presents an initial analysis of the extent of groundwater salinization in Africa, bringing together groundwater salinity data (n = 12,255) from across the continent. In our dataset c.80% of the samples have electrical conductivity values less than 2000 μS/cm. Samples with high conductivity values of more than 2000 μS/cm are restricted to limited geological and climatic environments. The data reveals salinity does not affect the water security status of most countries in Africa. However, salinity compounds water insecurity issues in arid low groundwater recharge environments. The paper discusses the role of anthropogenic processes such as river valley water resources development, extensive groundwater pumping, inter-basin groundwater transfer, and irrigation in altering the salinity of groundwater bodies. The paper further elucidates the origin of groundwater salinity by critically reviewing the natural and human-induced factors that control the salinization of the various groundwater bodies across Africa. Existing case studies reveal several causes of salinization, including i) human-induced salinization, ii) climate and hydrological change-induced paleo groundwater salinity, iii) rock dissolution, and iv), saltwater encroachment.

Widespread potential loss of streamflow into underlying aquifers across the USA

Most rivers exchange water with surrounding aquifers1,2. Where groundwater levels lie below nearby streams, streamwater can infiltrate through the streambed, reducing streamflow and recharging the aquifer3. These 'losing' streams have important implications for water availability, riparian ecosystems and environmental flows4-10, but the prevalence of losing streams remains poorly constrained by continent-wide in situ observations. Here we analyse water levels in 4.2 million wells across the contiguous USA and show that nearly two-thirds (64 per cent) of them lie below nearby stream surfaces, implying that these streamwaters will seep into the subsurface if it is sufficiently permeable. A lack of adequate permeability data prevents us from quantifying the magnitudes of these subsurface flows, but our analysis nonetheless demonstrates widespread potential for streamwater losses into underlying aquifers. These potentially losing rivers are more common in drier climates, flatter landscapes and regions with extensive groundwater pumping. Our results thus imply that climatic factors, geological conditions and historic groundwater pumping jointly contribute to the widespread risk of streams losing flow into surrounding aquifers instead of gaining flow from them. Recent modelling studies10 have suggested that losing streams could become common in future decades, but our direct observations show that many rivers across the USA are already potentially losing flow, highlighting the importance of coordinating groundwater and surface water policy.

Impact process of the aquitard to regional arsenic accumulation of the underlying aquifer in Central Yangtze River Basin.

The clayey aquitard has the potential to release geogenic poisonous chemicals such as arsenic (As) to the adjacent aquifer owing to complex hydrologic or biogeochemical processes. However, it remains unclear whether the aquitard has effect on As enrichment in the underlying aquifer in regions without extensive groundwater pumping, and the related processes have been poorly known. Based on piezometer water chemistry, stable water isotopes, sediment chemistry and reactive-transport model, this study aims to reveal the impact process of the aquitard to As accumulation of underlying aquifer from central Yangtze River Basin, a As-affected area without extensive groundwater pumping. On the whole, As migrated from top to bottom of the aquitard (especially the depth over 10m) and significantly influenced the As accumulation in the underlying aquifer. Nonetheless, the results of three topical boreholes showed two different hydrogeological conditions affected As release in the aquitard and enrichment in the underlying aquifer. Different hydrogeological conditions could result in the input of different species organic carbon and then impact As concentrations in the aquifer. When the aquitard was near surface water bodies, the reductive dissolution of iron oxides was the main driver for As release and the aquitard had a significant influence on the enrichment of arsenic in the aquifer. At areas without surface water bodies nearby, the desorption of As(V) from minerals was the main source of As and the concentrations of As in pore water were quite low; this pattern had little effect on the enrichment of arsenic in the aquifer.

Methane emissions from groundwater pumping in the USA

Atmospheric methane accumulation contributes to climate change, hence quantifying methane emissions is essential to assess and model the impacts. Here, we estimate methane emissions from groundwater pumping in the Los Angeles Basin (LAB), north-eastern Pennsylvania, and the Principal aquifers of the USA using the average concentrations of methane in groundwater and annual groundwater pumping volumes. High average methane concentrations, 44.1 mg/L, and extensive groundwater pumping, ~3.1 × 1011 L/a in the LAB, result in the annual emission of ~2.9 × 10−3 Tg of microbial methane. Ethane emissions in the LAB were 3.5 × 10−6 Tg/a. Lower methane emissions estimated for NE Pennsylvania, ~3.0 × 10−6 Tg/a, reflect lower methane concentrations and groundwater pumping, 0.7 mg/L and 4.27 × 109 L/a, respectively. Methane concentrations and groundwater withdrawals, 1.06 × 1014 L/a, across the USA enabled the estimation of the total emissions of methane from Principal aquifers (92% of total pumping) of 0.044 Tg/a in the year 2000, which represents a small percentage (~0.2%) of the total annual US methane emissions, but a previously unquantified flux in the global methane budget. Globally, groundwater-pumping methane emissions were estimated to be 0.53 Tg/a, 0.2% of global methane emissions, by adopting a global estimate for groundwater extraction, and an average methane concentration in older groundwater of 0.44 mg/L.

Agricultural Water Policy during Drought: A Strategy for Including Groundwater Permits in Future Irrigation Buyout Auctions in the Flint River Basin

Georgia’s Flint River Basin has water management challenges from extensive groundwater pumping for agriculture and in-stream flow requirements. The state has experimented with buying out irrigation permits through auctions. Past auctions were relegated to surface water permits. Recently, the state has allowed groundwater permit holders to participate in future auctions. The Flow-Impact Offer (FIO) developed in this paper provides a way to reconcile the disparate impacts of groundwater and surface water withdrawals on in-stream flows when comparing offers in a buyout auction. The techniques suggested here to operationalize the FIO are applicable to other regions of the world as well.

Urban environment and major challenges in sustainable development: Experience from Dhaka City in Bangladesh

Sustainable development is one of the most discussed and desired issues for the last few decades in Bangladesh and also throughout the world. But due to various challenges it is really tough to prepare and execute a proper plan for achieving sustainable development. The objective of this study is to find out the major challenges that the urban environment has been facing in sustainable development in Dhaka city. The qualitative study was done purposively and data collection methods were 10 Key Informants Interviews (KII) and 10 Focus Group Discussions (FGDs). KII were conducted among university teachers and Government officials as well as FGDs were conducted among city duelers in Dhaka. Urbanization process providing reasonable housing and infrastructure for duelers of all financial gain categories is a nice challenge for capital of Bangladesh town. Lack of swamp, open places, public parks, land with tree cover up causes environmental degradation and also creates aesthetic discomfort is another challenge in urban areas. Surface water is becoming useless because of having extensive pumping of groundwater in capital of Bangladesh. City dwellers didn’t follow the environmental rules and pollutes the surface waters with freedom. Impenetrable population with quick urbanization, industrialization and the lack of land coming up with has created major environmental problem to establish sustainable development. In future we need to study on identify the implementation strategy to sustainable development of urban environment.South East Asia Journal of Public Health Vol.7(1) 2017: 12-16

Evaluation of groundwater tritium content and mixing behavior of Tatapani geothermal systems, Chhattisgarh, India

Isotopic investigations were carried out on hot springs, groundwater and surface water to evaluate the mixing processes within the geothermal system. Physico-chemical parameter (EC, pH, Temp.) and tritium content of groundwater, hot springs and surface water were measured. The temperature of the hot springs were varied from 60 to 98.8 °C and EC from 674 to 728 μS/cm. The tritium content of groundwater varies from 1.5 to 5 TU whereas, geothermal water have slightly less tritium and their values ranges from 1.4 to 4.4 TU. Low tritium, higher EC and high temperature of a few hot springs indicate insignificant mixing whereas high tritium, lower EC and low temperature indicates significant mixing of thermal and non-thermal water. The degree of mixing for geothermal springs is estimated. It is found that the groundwater components present in the diluted thermal waters are about 25–80%. It is also observed that mixing process is prominent along the fault and in the area where groundwater exploitation is more. Extensive pumping of groundwater causes an increase in the rate of mixing of thermal and non-thermal water. The tritium content of groundwater, surface water and hot springs are indicating, it is of modern recharge.

Estimated seepage rates from selected ditches, ponds, and lakes at the Camas National Wildlife Refuge, eastern Idaho

The Camas National Wildlife Refuge (Refuge) in eastern Idaho, established in 1937, contains wetlands, ponds, and wet meadows that are essential resting and feeding habitat for migratory birds and nesting habitat for waterfowl. Initially, natural sources of water supported these habitats. However, during the past few decades, changes in climate and surrounding land use have altered and reduced natural groundwater and surface-water inflows, resulting in a 5-meter decline in the water table and an earlier, and more frequent, occurrence of no flow in Camas Creek at the Refuge. Due to these changes in water availability, water management that includes extensive groundwater pumping is now necessary to maintain the wetlands, ponds, and wet meadows.These water management activities have proven to be inefficient and expensive, and the Refuge is seeking alternative water-management options that are more efficient and less expensive. More efficient water management at the Refuge may be possible through knowledge of the seepage rates from ditches, ponds, and lakes at the Refuge. With this knowledge, water-management efficiency may be improved by natural means through selective use of water bodies with the smallest seepage rates or through engineering efforts to minimize seepage losses from water bodies with the largest seepage rates.The U.S. Geological Survey performed field studies in 2015 and 2016 to estimate seepage rates for selected ditches, ponds, and lakes at the Refuge. Estimated seepage rates from ponds and lakes ranged over an order of magnitude, from 3.4 ± 0.2 to 103.0 ± 0.5 mm/d, with larger seepage rates calculated for Big Pond and Redhead Pond, intermediate seepage rates calculated for Two-way Pond, and smaller seepages rates calculated for the south arm of Sandhole Lake. Estimated seepage losses from two reaches of Main Diversion Ditch were 21 ± 2 and 17 ± 2 percent/km. These losses represent seepage rates of about 890 and 860 mm/d, which are one- to two-orders-of-magnitude larger than seepage rates from the ponds and lake.The depth-integrated vertical hydraulic conductivity (Kv) for sediment underlying the ponds and lake was the primary control of seepage rates. The Kv's were 30 and 34 m/d for Big Pond, 14 and 18 m/d for Toomey Pond, 8 and 10 m/d for Two-way Pond, and 47 m/d for the north arm of Sandhole Lake.

An integrated study on the characterization of freshwater lens in a coastal aquifer of Southern India

The hydrogeochemical characterization of groundwater helps to assess the trend of salinization and freshening of the groundwater. The present study was carried out to understand the lateral and vertical variation of groundwater salinity and the process of salinization and freshening of the groundwater in a coastal aquifer comprising a freshwater lens. The partially isolated unconfined aquifer selected for the present study is lying just south of the Chennai City, one of the densely populated cities on the east coast of South India. Critical problems affecting this aquifer include a thin aquifer which is connected/surrounded by saltwater on all the sides, overexploitation of the groundwater, surface impermeabilization due to increasing residential areas, and destruction of existing dune morphology by conversion of barren land to the residential area which causes a reduction in their barrier effect to seawater intrusion. The process of salinization and freshening of the groundwater was studied and monitored by using electrical resistivity survey and hydrogeochemical analysis. The vertical electrical sounding was carried out at 17 locations, and 400 water samples were collected and analyzed from 50 locations during the period from August 2008 to May 2010 for this study. The apparent resistivity values were analyzed and compared with groundwater quality to demarcate the zone of seawater intrusion. The regional flow direction of the groundwater is westward and eastward with respect to the central stretch and groundwater level ranges from 4.96 m MSL at the dune morphology to 0 m MSL along the boundary on all the sides. Base exchange index indicates that salinization trend in the northern part of the study area is due to the extensive groundwater pumping which increases the possibility of seawater intrusion. The increase of base exchange index towards southern part indicates a better groundwater quality of the aquifer due to proper land use practices. A strong trend of quality alteration is clearly visible from the base exchange index in response to the seasonal change between monsoon and dry season. In the western side, the monsoonal variation in the salinization and freshening of the groundwater was not noticed; however, the salinity is slightly higher than freshwater due to the presence of clay.

River bank geomorphology controls groundwater arsenic concentrations in aquifers adjacent to the Red River, Hanoi Vietnam

AbstractMany aquifers that are highly contaminated by arsenic in South and Southeast Asia are in the floodplains of large river networks. Under natural conditions, these aquifers would discharge into nearby rivers; however, large‐scale groundwater pumping has reversed the flow in some areas so that rivers now recharge aquifers. At a field site near Hanoi Vietnam, we find river water recharging the aquifer becomes high in arsenic, reaching concentrations above 1000 µg/L, within the upper meter of recently (< ∼10 years) deposited riverbed sediments as it is drawn into a heavily pumped aquifer along the Red River. Groundwater arsenic concentrations in aquifers adjacent to the river are largely controlled by river geomorphology. High (>50 µg/L) aqueous arsenic concentrations are found in aquifer regions adjacent to zones where the river has recently deposited sediment and low arsenic concentrations are found in aquifer regions adjacent to erosional zones. High arsenic concentrations are even found adjacent to a depositional river reach in a Pleistocene aquifer, a type of aquifer sediment which generally hosts low arsenic water. Using geochemical and isotopic data, we estimate the in situ rate of arsenic release from riverbed sediments to be up to 1000 times the rates calculated on inland aquifer sediments in Vietnam. Geochemical data for riverbed porewater conditions indicate that the reduction of reactive, poorly crystalline iron oxides controls arsenic release. We suggest that aquifers in these regions may be susceptible to further arsenic contamination where riverine recharge drawn into aquifers by extensive groundwater pumping flows through recently deposited river sediments before entering the aquifer.

The socioecohydrology of rainwater harvesting in India: understanding water storage and release dynamics across spatial scales

Abstract. Rainwater harvesting (RWH), the small-scale collection and storage of runoff for irrigated agriculture, is recognized as a sustainable strategy for ensuring food security, especially in monsoonal landscapes in the developing world. In south India, these strategies have been used for millennia to mitigate problems of water scarcity. However, in the past 100 years many traditional RWH systems have fallen into disrepair due to increasing dependence on groundwater. This dependence has contributed to accelerated decline in groundwater resources, which has in turn led to increased efforts at the state and national levels to revive older RWH systems. Critical to the success of such efforts is an improved understanding of how these ancient systems function in contemporary landscapes with extensive groundwater pumping and shifted climatic regimes. Knowledge is especially lacking regarding the water-exchange dynamics of these RWH tanks at tank and catchment scales, and how these exchanges regulate tank performance and catchment water balances. Here, we use fine-scale, water-level variation to quantify daily fluxes of groundwater, evapotranspiration (ET), and sluice outflows in four tanks over the 2013 northeast monsoon season in a tank cascade that covers a catchment area of 28 km2. At the tank scale, our results indicate that groundwater recharge and irrigation outflows comprise the largest fractions of the tank water budget, with ET accounting for only 13–22 % of the outflows. At the scale of the cascade, we observe a distinct spatial pattern in groundwater-exchange dynamics, with the frequency and magnitude of groundwater inflows increasing down the cascade of tanks. The significant magnitude of return flows along the tank cascade leads to the most downgradient tank in the cascade having an outflow-to-capacity ratio greater than 2. At the catchment scale, the presence of tanks in the landscape dramatically alters the catchment water balance, with runoff decreasing by nearly 75 %, and recharge increasing by more than 40 %. Finally, while water from the tanks directly satisfies ∼ 40 % of the crop water requirement across the northeast monsoon season via surface water irrigation, a large fraction of the tank water is "wasted", and more efficient management of sluice outflows could lead to tanks meeting a higher fraction of crop water requirements.

A statistical model for karst spring discharge estimation under extensive groundwater development and extreme climate change

ABSTRACTTo acquire better understanding of spring discharge under extreme climate change and extensive groundwater pumping, this study proposed an extreme value statistical decomposition model, in which the spring discharge was decomposed into three items: a long-term trend; periodic variation; and random fluctuation. The long-term trend was fitted by an exponential function, and the periodic variation was fitted by an exponential function whose index was the sum of two sine functions. A general extreme value (GEV) model was used to obtain the return level of extreme random fluctuation. Parameters of the non-linear long-term trend and periodic variation were estimated by the Levenberg-Marquardt algorithm, and the GEV model was estimated by the maximum likelihood method. The extreme value statistical decomposition model was applied to Niangziguan Springs, China to forecast spring discharge. We showed that the modelled spring discharge fitted the observed data very well. Niangziguan Springs discharge is likely to continue declining with fluctuation, and the risk of cessation by August 2046 is 1%. The extreme value decomposition model is a robust method for analysing the nonstationary karst spring discharge under conditions of extensive groundwater development/pumping, and extreme climate changes.Editor D. Koutsoyiannis; Associate editor J. Ward

Evaluating Farmers’ Perceptions on Causes of Water Scarcity and Coping Strategies: a Case Study Example from Tehsil Karazat District Pishin

This paper probes into the major causes of water scarcity and farmers coping strategies in tehsil Karazat of district Pishin, Balochistan. Both primary and secondary data were used for the study. A well-structured questionnaire was constructed to collect primary data from sample respondents. Systematic random sampling technique was used for the selection of sample respondents. This study employed both descriptive analysis and econometric model to quantify the key variables. The econometric model used in this study includes multiple regression model to predict the effects of various factors causing water scarcity. The dependent variable fallow Land other than Current fallow FLOTCF is taken as a proxy for showing the effect of water scarcity. The model results showed that among other variables, family size and lack of government control on tubewells installation significantly affect the dependent variable. While the other variables such as subsidized electricity, awareness about water as a scarce resource, inappropriate cropping pattern, over irrigation of crops and orchards, extensive pumping of groundwater, mass installation of tubewells, the availability of proper water management practices, and lack of water storage reservoirs were though non-significant but influencing the dependent variable as per prior expectations. To meet water scarcity, the farmers’ coping strategies were also analyzed. The results show that among other strategies, changes from flooding to control/basin irrigation was ranked first by the farmers, followed by changes in the irrigation interval, increase in number of tubewells, water courses lining, and installation of delivery pipes at the farm.

Evaluating Farmers’ Perceptions on Causes of Water Scarcity and Coping Strategies: a Case Study Example from Tehsil Karazat District Pishin

This paper probes into the major causes of water scarcity and farmers coping strategies in tehsil Karazat of district Pishin, Balochistan. Both primary and secondary data were used for the study. A well-structured questionnaire was constructed to collect primary data from sample respondents. Systematic random sampling technique was used for the selection of sample respondents. This study employed both descriptive analysis and econometric model to quantify the key variables. The econometric model used in this study includes multiple regression model to predict the effects of various factors causing water scarcity. The dependent variable fallow Land other than Current fallow FLOTCF is taken as a proxy for showing the effect of water scarcity. The model results showed that among other variables, family size and lack of government control on tubewells installation significantly affect the dependent variable. While the other variables such as subsidized electricity, awareness about water as a scarce resource, inappropriate cropping pattern, over irrigation of crops and orchards, extensive pumping of groundwater, mass installation of tubewells, the availability of proper water management practices, and lack of water storage reservoirs were though non-significant but influencing the dependent variable as per prior expectations. To meet water scarcity, the farmers’ coping strategies were also analyzed. The results show that among other strategies, changes from flooding to control/basin irrigation was ranked first by the farmers, followed by changes in the irrigation interval, increase in number of tubewells, water courses lining, and installation of delivery pipes at the farm.

Quantifying water and energy budgets and the impacts of climatic and human factors in the Haihe River Basin, China: 1. Model and validation

We have developed an operational model to simulate water and energy fluxes in the Haihe River Basin (231,800 km(2) in size) for the past 28 years. This model is capable of estimating water and energy fluxes of irrigated croplands and heterogeneous grids. The model was validated using actual evapotranspiration (ETa) measured by an eddy covariance system, measured soil moisture in croplands, groundwater level measurements over the piedmont plain and runoff observations in a mountainous catchment. A long-term time series of water and energy balance components were then simulated at a daily time step by integrating remotely sensed information and meteorological data to examine the spatial and temporal distribution and changes in water and energy fluxes in the basin over the past 28 years. The results show that net radiation (R-n) in the mountainous regions is generally higher than that in the plain regions. ETa, in the plain regions is higher than that in the mountainous regions mostly because of higher air temperature and larger areas of irrigated farmland. Higher sensible heat flux (H) and lower ETa in the urban areas are possibly due to less vegetation cover, an impervious surface, rapid drainage, and the heat island effect of cities. During the study period, a water deficit continuously occurred in the plain regions because of extensive pumping of groundwater for irrigation to meet the crop water requirements. Irrigation has led to significant groundwater depletion, which poses a substantial challenge to the sustainability of water resources in this basin. (C) 2015 Elsevier B.V. All rights reserved.

A Bayesian analysis of nonstationary generalized extreme value distribution of annual spring discharge minima

In many areas throughout the world, extensive groundwater pumping has facilitated significant social development and economic growth, but has typically resulted in a decrease in groundwater level and a decline and change in spring discharge. The declining trend and changing seasonality of spring discharge lead to nonstationarity in hydrological processes. When we apply the generalized extreme value distribution to karst spring discharge, several assumptions including independence, identical distribution, and stationarity must be met. To investigate the response of spring discharge to extensive groundwater development and extreme climate change, a nonstationary generalized extreme value (NSGEV) model is proposed by assuming the location parameter to be the sum of a linear and a periodic temporal function to describe the declining trend and seasonality of spring discharge. Bayes’ theorem treats parameters as random variables and provides ways to convert the prior distribution of parameters into a posterior distribution. Statistical inferences based on posterior distribution can provide a more comprehensive representation of the parameters. In this paper we use Markov Chain Monte Carlo method, which can solve high-dimensional integral computation in the Bayes equation, to estimate the parameters of NSGEV model. Then the NSGEV model was used to calculate the distribution of minimum discharge values of Niangziguan Springs in North China. The results show that NSGEV model is able to represent the distribution of minimum values and to predict the cessation time of Niangziguan Springs discharge with two controllable variables: time and return period. With a 100-year return level, flow cessation of Niangziguan Springs would occur in April 2022. Moreover, the probability of Niangziguan Springs discharge cessation is 1/27 in 2025, and 1/19 in 2030. This implies that the probability of Niangziguan Springs cessation will increase dramatically with time.