Coupled Surface and Groundwater Hydrological Modeling in a Changing Climate

Many current watershed modeling efforts now incorporate surface water and groundwater for managing water resources since the exchanges between groundwater and surface water need a special focus considering the changing climate. The influence of groundwater dynamics on water and energy balance components is investigated in the Snake River Basin (SRB) by coupling the Variable Infiltration Capacity (VIC) and MODFLOW models (VIC‐MF) for the period of 1986 through 2042. A 4.4% increase in base flows and a 10.3% decrease in peak flows are estimated by VIC‐MF compared to the VIC model in SRB. The VIC‐MF model shows significant improvement in the streamflow simulation (Nash‐Sutcliffe efficiency [NSE] of 0.84) at King Hill, where the VIC model could not capture the effect of spring discharge in the streamflow simulation (NSE of ?0.30); however, the streamflow estimates show an overall decreasing trend. Two climate scenarios representing median and high radiative‐forcings such as representative concentration pathways 4.5 and 8.5 show an average increase in the water table elevations between 2.1 and 2.6 m (6.9 and 8.5 feet) through the year 2042. The spatial patterns of these exchanges show a higher groundwater elevation of 15 m (50 feet) in the downstream area and a lower elevation of up to 3 m (10 feet) in the upstream area. Broadly, this study supports results of previous work demonstrating that integrated assessment of groundwater‐surface water enables stakeholders to balance pumping, recharge and base flow needs and to manage the watersheds that are subjected to human pressures more sustainably.     

Effects of the Land Use and Check Dams on Flood in Upper Catchment of Fuping Hydrological Station by Hydrological Modeling

Flood peaks and volumes had been detected a downward trend in Fuping hydrological station. To quantify the effects of check dams on flood peaks and volumes, a hydrological model integrating land use was established. The model performed well in flood processes simulation, and the Nash efficiency of the model was 0.72. Then the model was used to identify the comprehensive effects of land use and land cover change on flood processes by comparing the simulation results of the selected flood events under 1980 and 2000 land use and land cover conditions. 24.5, 37.7 and 51.3% decrease in flood peaks for flood events of greater than 10 years, 5~10 years and less than 5 years return periods, respectively, and 16.3, 27.9 and 28.5% decrease in flood volumes for the three groups flood events of different return periods. Contributions of land use change and check dams to decrease in flood peak and volume were simulated, and it was found that peak discharge and volume for each flood event responded differently to the two factors. The results in this study can provide valuable information on design flood calculation in the basin under land use and land cover change.     

气候变化对沅江流域径流影响研究

温室气体排放量增加造成气候变化,对全球资源环境产生重要影响.本文在水量平衡基础上,建立考虑气象要素和地形变化的月水文模型,利用实测径流资料对模型在时空尺度上进行验证.利用全球气候模型(GCMs)预测的未来气候变化情形,对处于湿润区的沅江流域径流过程进行预测.分析结果表明,该区域径流过程对降雨和气温变化十分敏感.根据英国Hadcm2模型对本世纪中叶气候变化预测结果,沅江流域未来年降雨量减少0.43%气温升高1.55℃,丰水期降雨增加,而枯水期将有较大幅度减少.年径流量相应减少6.8%,丰水期径流量增大11%,枯水期径流减少47%,不利于防洪和水资源开发利用.     

东亚季风的气候变化及其时间序列模型

本文运用统计方法分析了东亚季风指数的观测序列;同时还揭示了不同时期的东亚季风变化趋势和年代际变化.自1873年以来,东亚季风逐渐减少,同时年代际的变化也十分明显.在1891-1900年间和1971-1980年间,夏季季风指数的十年平均达到极大,另外还出现两个极小值,它们分别出现在1921-1930年和1991-2000年.为了对东亚季风变化进行模拟,我们首先简要地介绍了动力系统的自忆性原理,然后叙述了一个新的时间序列分析方法——基于数据的机制自记忆模型(DAMSM).DAMSM被应用于东亚季风指数研究并且证明了它对东亚季风的拟合及预报能力.     

Climate Change Impact on Hydrological Extremes: Preliminary Results from the Polish-Norwegian Project

This paper presents the background, objectives, and preliminary outcomes from the first year of activities of the Polish–Norwegian project CHIHE (Climate Change Impact on Hydrological Extremes). The project aims to estimate the influence of climate changes on extreme river flows (low and high) and to evaluate the impact on the frequency of occurrence of hydrological extremes. Eight “twinned” catchments in Poland and Norway serve as case studies. We present the procedures of the catchment selection applied in Norway and Poland and a database consisting of near-natural ten Polish and eight Norwegian catchments constructed for the purpose of climate impact assessment. Climate projections for selected catchments are described and compared with observations of temperature and precipitation available for the reference period. Future changes based on those projections are analysed and assessed for two periods, the near future (2021–2050) and the far-future (2071–2100). The results indicate increases in precipitation and temperature in the periods and regions studied both in Poland and Norway.     

Assessment of Climate Change Impact on the Gharesou River Basin Using SWAT Hydrological Model

The evaluation of climate change and its side effects on the hydrological processes of the basin can increasingly help in dealing with the challenges that water resource managers and planners face in future courses. These side effects are investigated using the simulation of hydrological processes with the help of physical rainfall‐runoff model. Hydrological models provide a framework for examining the relationship between climate and water resources. This research aims at the investigation of the effect of climate change on the runoff of Gharesou, which is one of the main branches of the “Karkheh” River in Iran during the periods 2040–2069. To achieve this, the distributed hydrological model Soil and Water Assessment Tool (SWAT) – a model that is sensitive to the changes in land, water, and climate – has been used with the aim of evaluating the impact of climate change on the hydrology of the Gharesou Basin. For this reason, first, the continuous distributed model of rainfall‐runoff SWAT for the period 1971–2000 has been calibrated and validated. Next, with the aim of evaluating the impact of climate change and global warming on the basin hydrology for the period 2040–2069, HadCM3‐AR4 global climate model data under the A2 scenario – from the SRES scenario set‐haves been downscaled. Eventually, the downscaled climate data haves been introduced in the SWAT model, and the future runoff changes have been studied. The results showed that the temperature increases in most of the months, and the precipitation rate exhibits a change in the range of ±30%. Moreover, the produced runoff in this period changes from ?90 to 120% during different months.     

Hydrological Response of Runoff to Climate Change of Typical Tributaries in Ebinur Lake Basin of Xinjiang

In recent years, the natural hydrology behaviors were greatly influenced by climate change. The relation between runoff and climate change are always the core of scientific hydrological study in arid region. This paper presents a multi-variate time series controlled auto-regressive (CAR) model based on hydrological and climatic data of typical tributaries Jinghe River in Ebinur Lake Basin of Xinjiang covering the period from 1957 to 2012. The aim is to study the climate change and its effects on runoff of the Jinghe River, Northwest China. The results showed the following: the runoff of the Jinghe River was unevenly distributed and has obvious seasonal changes throughout the year. It was concentrated in summer and has along dry season with less runoff. The monthly maximum river runoff was from June to September and accounted for 74% of annual runoff. The river runoff increased since the 1980s till the 1990s; in the 21st century there was a trend of decreasing. The oscillatory period of annual runoff series in the Jinghe River Basin was 21a and 13a, and these periods were more obvious, followed by 32a and 9a. The oscillation with a time scale of 21a and 13a was a fulltimed domain. The MRE is 6.54%, the MAE is 0.84 × 10⁸ m³, and the RMSE is 0.039. The CAR model passed the F-test and residual test, and the change trend of calculated and measured values of annual runoff is consistence, which means that the model was reasonable.     

Integrated Hydrologic Modeling to Untangle the Impacts of Water Management During Drought

Over the past century, groundwater levels in California's San Joaquin Valley have dropped by more than 30 m in some areas mostly due to excessive groundwater extraction used to irrigate agricultural lands and sustain a growing population. Between 2012 and 2015, California experienced the worst drought in its recorded history, depleting surface water supplies and further exacerbating groundwater depletion in the region. Due to a lack of groundwater regulation, exact quantities of extracted groundwater in California are unknown and hard to quantify. Recent adoption of the Sustainable Groundwater Management Act has intensified efforts to identify sustainable groundwater use. However, understanding sustainable use in a highly productive agricultural system with an extremely complex surface water allocation system, variable groundwater use, and spatially extensive and diverse irrigation practices is no easy task. Using an integrated hydrologic model coupled with a land surface model, we evaluated how water management activities, specifically a suite of irrigation and groundwater pumping scenarios, impact surface water–groundwater fluxes and storage components and how those activities and the relationships between them change during drought. Results showed that groundwater pumping volume had the most significant impact on long-term water storage changes. A comparison with total water storage anomaly (TWSA) estimates from NASA's Gravity Recover and Climate Experiment (GRACE) provided some insight regarding which combinations of pumping and irrigation matched the GRACE TWSA estimates, lending credibility to these scenarios. In addition, the majority of long-term water storage changes during the recent drought occurred in groundwater storage in the deeper subsurface.     

On the Forecast of Long-Term Changes in the Hydrological Regime of Rivers Using the Results of Climate Modeling

Water Resources - A method is proposed for probabilistic forecasting of river flow under non-stationary conditions based on the Bayesian approach and using the results of climatic system modeling....     

人工神经网络模型预测气候变化对博斯腾湖流域径流影响

温室气体排放量增加造成气候变化,对全球资源环境产生重要影响．本文利用人工神经网络模型建立月降水、气温与径流关系,利用开都河流域降水、气温、径流资料对模型进行训练和验证,通过试算法确定网络模型结构,气温升高和降水量增加对径流影响的敏感程度分析表明,气温升高和降水增加对该区域径流影响较大,且气温升高的影响更为显著,径流增加主要集中在夏季,根据区域气候模型（RCMs）推算的CO2加倍情况下西北地区气候的可能变化,预测位于博斯腾湖流域的开都河大山口站年径流量增加38．6％,其中夏季增加71．8％,冬季增加11．4％。     

Predicting Aquifer Response Time for Application in Catchment Modeling

It is well established that changes in catchment land use can lead to significant impacts on water resources. Where land‐use changes increase evapotranspiration there is a resultant decrease in groundwater recharge, which in turn decreases groundwater discharge to streams. The response time of changes in groundwater discharge to a change in recharge is a key aspect of predicting impacts of land‐use change on catchment water yield. Predicting these impacts across the large catchments relevant to water resource planning can require the estimation of groundwater response times from hundreds of aquifers. At this scale, detailed site‐specific measured data are often absent, and available spatial data are limited. While numerical models can be applied, there is little advantage if there are no detailed data to parameterize them. Simple analytical methods are useful in this situation, as they allow the variability in groundwater response to be incorporated into catchment hydrological models, with minimal modeling overhead. This paper describes an analytical model which has been developed to capture some of the features of real, sloping aquifer systems. The derived groundwater response timescale can be used to parameterize a groundwater discharge function, allowing groundwater response to be predicted in relation to different broad catchment characteristics at a level of complexity which matches the available data. The results from the analytical model are compared to published field data and numerical model results, and provide an approach with broad application to inform water resource planning in other large, data‐scarce catchments.     

Investigating Impacts of Climate Change on Irrigation Water Demands and Its Resulting Consequences on Groundwater Using CMIP5 Models

In this study, the impacts of climate change on crop water requirements and irrigation water requirements on the regional cropping pattern were evaluated using two climate change scenarios and combinations of 20 GCM models. Different models including CROPWAT, MODFLOW, and statistical models were used to evaluate the climate change impacts. The results showed that in the future period (2017 to 2046) the temperature in all months of the year will increase at all stations. The average annual precipitation decline in Isfahan, Tiran, Flavarjan, and Lenj stations for RCP 4.5 and RCP 8.5 scenarios are 18.6 and 27.6%, 15.2 and 18%, 22.5 and 31.5%, and 10.5 and 12.1%, respectively. The average increase in the evapotranspiration for RCP 4.5 and RCP 8.5 scenarios are about 2.5 and 4.1%, respectively. The irrigation water demands increases considerably and for some crops, on average 18%. Among the existing crops in the cropping pattern, barley, cumin, onion, wheat, and forage crops are more sensitive and their water demand will increase significantly. Results indicate that climate change could have a significant impact on water resources consumption. By considering irrigation efficiency in the region, climate change impacts will result in about 35 to 50 million m³/year, over-extraction from the aquifer. This additional exploitation causes an extra drop of 0.4 to 0.8 m in groundwater table per year in the aquifer. Therefore, with regard to the critical condition of the aquifer, management and preventive measures to deal with climate change in the future is absolutely necessary.     

Groundwater Quality Impacts from a Full‐Scale Integrated Constructed Wetland

The concept of integrated constructed wetlands (ICW) promotes in‐situ soils to construct and line wetland cells. The integrity of soil material, however, may provide a potential pathway for contaminants to flow into the underlying groundwater. This study assessed the extent of groundwater quality deterioration due to the establishment of a full‐scale ICW system treating domestic wastewater in Ireland. The ICW is located at Glaslough in Co. Monaghan, Ireland. It consists of two sedimentation ponds and a sequence of five shallow vegetated wetland cells. The ICW cells were lined with 500‐mm thick local subsoil material, which comprised a mixture of alluvium, organic soils, tills, and gravel. Groundwater samples and head data were collected from eight piezometers, which were installed around the ICW cells. The groundwater and wetland water samples were analysed for water quality parameters such as bulk organic matter, nutrients, and pathogens. Overall, the quality of groundwater underlying the ICW system recorded some contamination with bulk organic matter and some inorganic nutrients. Significantly higher contaminant concentrations were recorded in monitoring wells upgradient and near to the distal wetland cells than downgradient ones, which were near to the proximal cells. For the downgradient piezometers, concentrations seldomly exceeded the natural background levels. Detailed analyses through the application of chemometrics models indicated that the source of contamination was largely of geogenic origin. Findings suggest that ICW systems pose a minimal risk to the groundwater quality; the greatest risk was associated with the distal wetland cells.     

Implementing Integrated Catchment Management in the upper Limpopo River basin: A situational assessment

A three-phase study was initiated as a way to promote Integrated Catchment Management approaches in the Limpopo River basin. This paper presents the situational assessment, which should enable De Beers to understand how their Venetia Mine operations are located within a broader and highly dynamic socio-economic and ecohydrological landscape as it pertains to water risks. The second phase, Risk assessment, aims to develop conservation interventions in the identified areas; the third phase will develop mechanisms for implementing water stewardship schemes to mitigate the shared water risks.Analysis of the social-ecological system (hydrological, climatic, ecological, socio-economic and governance systems) of the Limpopo River basin indicates that the institutional arrangement of the Limpopo River basin is neither simple nor effective. The basin is rapidly approaching closure in the sense that almost all of the available supplies of water have already been allocated to existing water users. If the proposed ecological flow requirements were to be met for all of the tributaries, the basin would be ‘closed’. On-going and projected land use changes and water resources developments in the upper reaches of the basin, coupled with projected rainfall reductions and temperature increases, and allocation of the flows for the ecological reserve, are likely to further reduce downstream river flows. The coupled increase in temperature and decrease in rainfall is of great concern for everyone in the basin, especially the poorer communities, who rely on rain-fed agriculture for their livelihoods. Increased temperatures also lead to increased evaporation from reservoirs and therefore result in a decrease in water availability. This will lead to increased abstraction of groundwater, especially from alluvial aquifers, and consequently an increase in river transmission losses and a decrease in river flows.     

Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna

In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m² plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies.