Despite the importance of energy efficiency (EE) in promoting economic growth (EG), the empirical evidence about the growth effect of EE is quite thin. This research intends to examine the ...heterogeneous impacts of EE, renewable energy consumption (REC), and other factors on EG of BRICS countries for 1990–2014. The empirical results unveil that EE in BRICS countries is an important source for EG. The findings of fixed-effect panel quantile regression analysis clearly explain that the effects of all the selected components of EG are heterogeneous along the quantiles. The effect of EE is significantly positive across all the quantiles, but the positive effect is more robust at 50th and 60th quantiles of EG. REC significantly decreases the EG in BRICS economies, but the negative influence is more robust at the upper quantiles of EG (0.60–0.90). Moreover, the results obtained from Dumitrescu-Hurlin (D-H) heterogeneous panel causality test approve the feedback hypothesis between EE and EG in BRICS countries. The findings also provide the bidirectional causal relationship between REC and EG. Furthermore, a causal association is observed from EE to REC. It suggests that EE is also beneficial to enhance REC in BRICS countries. The study suggests that more prolific use of energy can stimulate EG in BRICS countries by improvement in EE and renewable energy (RE).
•Heterogeneous impact of energy efficiency and renewable energy use on the economic growth of BRICS countries.•Fixed effect panel quantile regression analysis is used to capture the heterogeneous effects.•Energy efficiency is an important source of economic growth in BRICS countries.•The feedback hypothesis exists between energy efficiency and economic growth.
•HYDRUS-1D model was modified by coupling with the dualKc approach.•Water–salt fate and yield were simulated for three crops under shallow water table.•Water use was evaluated in a canal system with ...fragmented crops simultaneously.•New insights were provided for improving water use efficiency and saving water.
Water saving in irrigation is a key issue in the upper Yellow River basin. Excessive irrigation leads to water waste, water table rising and increased salinity. Land fragmentation associated with a large dispersion of crops adds to the agro-hydrological complexity of the irrigation system. The model HYDRUS-1D, coupled with the FAO-56 dual crop coefficient approach (dualKc), was applied to simulate the water and salt movement processes. Field experiments were conducted for maize, sunflower and watermelon crops in the command area of a typical irrigation canal system in Hetao Irrigation District during 2012 and 2013. The model was calibrated and validated in three crop fields using two-year experimental data. Simulations of soil moisture, salinity concentration and crop yield fitted well with the observations. The irrigation water use was then evaluated and results showed that large amounts of irrigation water percolated due to over-irrigation but their reuse through capillary rise was also quite large. That reuse was facilitated by the dispersion of crops throughout largely fragmented field, thus with fields reusing water percolated from nearby areas due to the rapid lateral migration of groundwater. Beneficial water use could be improved when taking this aspect into account, which was not considered in previous researches. The non-beneficial evaporation and salt accumulation into the root zone were found to significantly increase during non-growth periods due to the shallow water tables. It could be concluded that when applying water saving measures, close attention should be paid to cropping pattern distribution and groundwater control in association with irrigation scheduling and technique improvement.
•We analyzed change trends of the climate variables ET0 and AI in an arid region of China over the past 50years.•We identified the sensitivity of ET0 and AI to the main climate variables.•We ...quantified the contributions of climate variables to the changes in ET0 and AI.•Contribution of wind speed decline to decrease of ET0 is larger than other climate variables.•The increase of precipitation contributes more than the decrease of ET0 to decrease of AI.
Temporal variations in reference evapotranspiration (ET0) and aridity index (AI) were comprehensively investigated for 23 meteorological stations during 1955–2008 in the northwest China. The quantitative contributions of the major meteorological variables to the ET0 and AI trends were evaluated and the possible causes were also investigated. The results showed that in the past 50years annual temperature, humidity and precipitation had significant increasing trends with time, and wind speed and radiation had decreasing trends. ET0 had a significant decreasing trend with an averagely value of about 3mm per year, and AI had also witnessed a decreasing trend; For ET0, wind speed was the most sensitive meteorological variable, followed by relative humidity, temperature and radiation and for AI, precipitation was the most sensitive meteorological variable. The contribution of wind speed to the decrease of ET0 is more than that of other meteorological variables. The increase of precipitation contributes more than the decrease of ET0 to decrease of AI in past 50years. This study provides an understanding of the effect of recent climate change on drought in arid northwest China.
Biodiesel has received much attention in recent years. Although numerous reports are available on the production of biodiesel from vegetable oils of terraneous oil-plants, such as soybean, sunflower ...and palm oils, the production of biodiesel from microalgae is a newly emerging field. Microalgal biotechnology appears to possess high potential for biodiesel production because a significant increase in lipid content of microalgae is now possible through heterotrophic cultivation and genetic engineering approaches. This paper provides an overview of the technologies in the production of biodiesel from microalgae, including the various modes of cultivation for the production of oil-rich microalgal biomass, as well as the subsequent downstream processing for biodiesel production. The advances and prospects of using microalgal biotechnology for biodiesel production are discussed.
•The SHAW model was modified with considering changes in soil hydrothermal properties.•Hydrothermal properties in frost heave soil can be evaluated with altered bulk density.•The modified model can ...accurately capture soil water-heat-salt dynamics.•The modified model can be used for water management in obviously frost heave areas.
Traditional agricultural or eco-hydrological models usually ignore soil deformation and its impact on hydrothermal properties when simulating soil water, heat, and salt transport under freeze–thaw conditions. As a result, significant errors may occur when these models are used in areas with considerable frost heave, such as arid areas with shallow groundwater tables. In this study, the simultaneous heat and water model (SHAW model) was modified with considering soil deformation and its impact on hydrothermal properties during the freeze–thaw period. The modified SHAW model was then validated using the experimental data collected at the Hetao Irrigation District, in the upper Yellow River basin. Comparison between the simulated and observed data showed that the modified SHAW model performed well and obviously better than the original SHAW model in simulating the soil water, heat, and salt transport. As compared with the SHAW model, the modified SHAW model averagely decreased the RMSE value by 37.5% and 23% for soil water content and soil temperature, respectively. The modified model can be used as a decision tool for water management and salinity control of farmland in cold areas with significant frost heave.
Soil salinization is one of the most common land degradation processes that impacts agricultural production, environmental health, and economic welfare. The first task in managing soil salinity is to ...understand its spatiotemporal characteristics, causal factors and influences, both over large regions and within individual fields. In this study, a typical irrigated agro-ecosystem located in the upper Yellow River basin, suffering from long-term soil salinization problems, was selected as the case study area. Field sampling experiments and investigations related to soil layer salt content, groundwater, irrigation and ground elevation were carried out at three scales (field scale, canal scale and regional scale) covering both croplands and natural vegetation patches during 2016 and 2017. Spatiotemporal characteristics of soil salinity were analyzed for the three scales based on sampling data, remote sensing, geostatistical analysis and model simulation. Results showed that, at the regional scale, the soil salinity distribution was dominated by topography and groundwater depth; at the canal scale, it was dominated by irrigation and cropping pattern; at the field scale, it was dominated by micro-topography and the uniformity of field irrigation. Scale-dependent soil salinity management strategies should be adopted to maintain agricultural production and the sustainability of natural ecosystems. It can be concluded that using integrated approaches including multi scale soil sampling, model simulation and other modern techniques is an effective way for thorough understanding and management of soil salinity.
•Soil sampling, GIS/RS and dynamic model were integrated for salinity analysis.•Salinity characteristics and their causal factors were scale dependent.•The proportion of salt-affected soil increased by 14% during the growing season.•Multiple modern techniques are needed for salt prediction and management.
Soil evaporation and its associated processes are vital for agricultural production and ecosystems in seasonal frozen regions. However, soil evaporation and its impact on salt accumulation in ...different landscapes during freeze–thaw periods have not been well elucidated. In this study, field experiments were carried out to investigate soil evaporation and salt accumulation patterns in three typical landscapes—namely, cropland, woodland, and natural land—in an arid seasonal frozen region located in the upper reaches of the Yellow River basin from November 2018 to April 2019. The results indicated the highest soil evaporation occurred on natural land with a total amount of 148.5 mm during the freeze–thaw period from 2018 to 2019, whereas woodland had the smallest soil evaporation of 56.9 mm. Over 75% of soil evaporation occurred during the thawing stage for all three landscapes. The average daily evaporation was below 1 mm d–1 for the whole freeze–thaw period and was 0.1 mm d–1 for the stable freezing stage. Compared with humidity and wind speed, temperature and soil water content had a greater impact on soil evaporation. At the end of the thawing stage, the salt content in the topsoil (0–10 cm) layer increased significantly with an increasing rate of 70–225%. Salt concentrations in the topsoil were significantly and linearly related to the cumulative soil evaporation during the freeze–thaw period. The current research is expected to provide implications for water management and salinity control in the upper reaches of the Yellow River basin and in other arid regions with similar conditions.
Household sector is the end consumer in the socio-economic water cycle and consumes a large amount of water in both physical and virtual ways. The life cycle water consumption by households, also ...denoted as Blue Water Footprint (BWF), is mostly affected by consumption expenditure and varies among different household groups. This study assessed the household BWF in China by integrating the input-output model with a national survey of household consumption expenditure. The logarithmic mean divisia index method was employed to examine the influencing factors in BWF disparity among the different household groups. We found that 1) per capita BWF, on national average, increased from 157 m3 in 2012 to 176 m3 in 2018; 2) in 2012, urban households, on average, consumed 185 m3 of water per capita annually, while rural households consumed 126 m3 per capita; there is a significant difference in dietary between rural and urban households, e.g., starchy foods predominate in rural dietary while animal-based foods are more preferred in urban regions; 3) BWF shows distinctive regional characteristics, e.g., more water was consumed on clothes in cold regions and on aquatic products in coastal regions; 4) income disparity is a key factor in causing the BWF difference. Although BWF has a positive correlation with income, its marginal growth diminishes, because of the fading consumption propensity and the switch of consumption pattern from water-consuming to water-saving, e.g., rich households are inclined to spend most of the money on education and recreation rather than food. This study is of significance in understanding how the BWF varies among different households, and how the BWF is affected by the influencing factors, including income, propensity to consume, consumption pattern, and virtual water intensity.
Display omitted
•Enhanced hydrological model (SWAT-AG) is proposed based on SWAT framework.•Close interactions of soil water, groundwater and plant growth are well described.•Hydrological processes in watershed with ...shallow aquifer are reasonably simulated.•SWAT-AG improves the model performance in agro-watershed compared with SWAT.
This article introduces the SWAT-AG (a modified SWAT for agro-hydrological modeling) as an enhanced hydrological model for simulating the hydrological processes in agricultural watershed with shallow water tables. The model is developed based on the framework of the SWAT with significant improvements on describing the interactions of the vadose zone water, groundwater, salt and plant growth. The main features of the SWAT-AG include that it can simulate the close interactions of soil water and shallow groundwater with considering the capillary rise effects; it provides functions to simulate the soil salt movement and salt-stress on plant growth; and it incorporates a balance-based module on a sub-basin scale for shallow aquifer with involving canal seepage and ditch drainage calculation. Model testing and application were conducted in Jiyuan Irrigation System located in the Hetao of upper Yellow River basin, northwest China. The comparison between simulated and observed data showed that the SWAT-AG performed well and obviously better than the original SWAT in simulating the soil water and salt dynamics, groundwater depth fluctuations, and plant growth and water consumption. The results showed that the NSE averagely increased from −17.57 to 0.57 and from 0.71 to 0.79 for soil water storage and leaf area index, respectively, in typical croplands and natural patches. In addition, the effects of shallow groundwater in sustaining the agro-ecosystems were reasonably revealed with the spatial analysis of evapotranspiration, capillary rise and salt accumulation. The test case proved that the proposed SWAT-AG could efficiently enhance the functionality and practicality of hydrological models for agricultural watersheds with shallow groundwater.
This study presents the analytical expressions of drainable and fillable porosity for layered soils under shallow groundwater environments. The expressions of drainable porosity λd and fillable ...porosity λf for two‐layered soils are first derived with water table depth change ∆d→0 under dynamic soil moisture conditions. The expressions of λd and λf consider the dynamic soil moisture conditions through the assumption of vertical fluxes in the unsaturated zone, varying as functions of water table elevation h. The analytical expressions of λd and λf have the same formula form but different values under evapotranspiration and recharge conditions, which is also verified using the numerical calculation. The case comparisons indicate that the vertical distribution of soil layers and the fluxes have significant effects on the performance of λd and λf. Our proposed expressions could effectively characterize the effects of soil layering and vertical fluxes on λd and λf. They could improve the accuracy of the previous expressions for single‐layer soils, and complement the lack of description for layered soils under dynamic soil moisture conditions in previous expressions. Furthermore, under the hydrostatic assumption (static equilibrium of soil water pressure distribution) in the unsaturated zone, the expressions of drainable porosity λd* and fillable porosity λf* for two‐layered soils with large water table fluctuations are derived based on λd and λf (asterisks in λd* and λf* is to distinguish them from λd and λf derived based on ∆d→0). Verification with drainage experimental data indicates that the proposed expressions can be extended to well capture the λd* and λf* changes for two‐layered soils. Application scenarios suggest that our analytical expressions of drainable and fillable porosity are useful to improve the application performance of related subsurface modeling and groundwater estimation for layered soils under shallow water table environments.
Key Points
Analytical expressions of drainable and fillable porosity for layered soils were proposed under vertical fluxes conditions
Expressions of drainable/fillable porosity for layered soils with large water table fluctuations were derived under hydrostatic conditions
Expressions were useful to improve the application performance of subsurface modeling and groundwater estimation for layered soils
PDF
