Regularization techniques have been proved useful in an enormous variety of sparse optimization problem. In this paper, we introduce a new formulation of regularization with a hybrid
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The negative rejection of certain solutes is an interesting phenomenon often observed in nanofiltration (NF) process, which presents an ideal solute separation effect. In this study, the NF membrane ...pore size, electric charge property and influent ions composition were controlled to investigate the rule and mechanism of negative rejection phenomenon during SO42−/Cl− mixed salt NF. The results show that the changing of the membrane pore diameter and charge will significantly affect the NF selectivity to SO42−/Cl−, then affect the negative rejection phenomenon. Selective efficiency of Cl−/SO42− can be up to 156.04–283.20 for the negative charged NF membrane with an average pore diameter of 0.62–0.68 nm, and the Cl− was negatively rejected under many influent conditions with the lowest rejection rate of −252.36 %. The substitution of Na+ for Mg2+ and the increase of SO42−/Cl− ratio are beneficial to improve selectivity. The Donnan Steric Pore Model with dielectric exclusion model was used to calculate the rejection curve which is consistent with the experimental results. The analysis of NF mechanism shows that the negative rejection of Cl− is caused by the extra transfer power derived from the NF selectivity to Cl−, which is a compensation for the higher rejection rate of SO42−.
•Negative rejection is an extreme manifestation of NF membrane selectivity.•Pore size, chargeability and salts ratio significantly affect the NF selectivity.•The extreme selectivity factor of the PIP/TMC NF film to SO42−/Cl− is up to 283.20.•DSPM-DE can be used to calculate negative rejection and analyze the mechanism.•Osmotic force from additional cations promotes the negative rejection of Cl−.
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•Virtual water transfer related to food and energy imports was studied in Beijing.•The impact of external and local water on sustainable development was studied.•Water stress index in ...Beijing would double in absence of external water.•Some effective measures are presented to ease urban water pressure.
With the increase in population and economic development, urban water demand has increased significantly over the past decades, and physical transfer water (i.e., freshwater transported from water source regions to water intake regions through channels or pipelines) and virtual water (i.e., freshwater used in the production of goods and services along their supply chains, abbreviated as VW) have gradually become viable water sources for many cities to relieve water stress. This study used Beijing as the research object and systematically analyzed the impact of physical transfer water, VW, and local water on urban water stress from 2000 to 2016. The results show that VW inflow related to food trade has increased from 3.55 billion m3 in 2000 to 16.76 billion m3 in 2016, and that energy’s VW inflow increased from 52.76 million m3 to 137.47 million m3 over the same period. Before 2011, Beijing’s water demand was largely met by local water resources; however, after 2011, external water resources (including physical transfer water and VW) accounted for majority of the city’s water demand, and VW’s contribution increased from 47% in 2011 to 53% in 2016. Although Beijing has significantly reduced local water use in favor of external sources, its water stress index in 2016 remained considerable, far exceeding the upper limit of available water. This study also proposes some measures to ensure Beijing’s water security based on the sustainability of external water supply.
Rainfall gauges are always sparse in the arid and semi-arid areas of Northwest China, which makes it difficult to precisely study the characteristics of drought at a large scale in this region and ...similar areas. This study used the TRMM (The Tropical Rainfall Measuring Mission) multi-satellite precipitation data to study the spatial-temporal evolution of drought in the Loess Plateau based on the SPI (Standardized Precipitation Index) drought index for the period of 1998-2014. The results indicate that the monthly TRMM precipitation data are well matched with the observed precipitation, indicating that this remotely sensed data set can be reliably used to calculate the SPI drought index. Based on the study findings, the average precipitation in the Loess Plateau is showing a significant increasing trend at the rate of 4.46 mm/year. From the spatial perspective, the average annual precipitation in the Southeast is generally greater than that in the Northwest. However, the annual precipitation in the Southeast area is showing a decreasing trend, whereas, the annual precipitation in the northwest areas is showing an increasing trend. Through the SPI analysis, the 3-month SPI and 12-month SPI were both showing an increasing trend, which indicates that the drought severity in the Loess Plateau was a generally declining trend at a seasonal to annual time scale. From the spatial perspective, the SPI values in the Central and Northwest of the Loess Plateau were significantly increasing, whereas, the SPI values in the southern area of the Loess Plateau were slightly decreasing. From the seasonal characteristics, the high-risk area for drought in the spring was concentrated in the northeast and southwest part, and in the summer and autumn, the high-risk area was transferred to the south part. Through this study, it is concluded that the Loess Plateau was likely getting wetter during the time period since the Grain-for-Green Project (1999-2012) was implemented, which replaced much farmland with forestry. This is a positive signal for vegetation recovery and ecological restoration in the near future.
•Utilization of remote-sensing-based water balance assessment tool (RWBAT) model.•An optimized PDSI index based on the RWBAT model is constructed, namely RW-PDSI.•Tree-ring data were used to evaluate ...the performance of the drought index.•RW-PDSI has a better correlation with the tree-ring data than SC-PDSI and SPEI.•The drought of the Loess Plateau has weakened over the past 30 years.
Palmer Drought Severity Index (PDSI) is a widely used indicator to assess the intensity of drought based on a similar two-layer bucket (TLB) model, especially in arid and semi-arid regions. However, the TLB model cannot quantify surface water balance, effectively, which may lead to the mis-assessment of drought. Therefore, an optimized PDSI indicator named RW-PDSI based on the water balance is constructed. RW-PDSI is developed using the output of a newly proposed remote-sensing-based water balance assessment tool (RWBAT) model. The RWBAT model is constructed to depict the detailed hydrological processes on a fine spatial scale using high-resolution remote sensing data. To test its performance, we collected tree-ring data on the Loess Plateau (LP) to show the drought conditions in past decades (1991–2020). Tree-ring data provide a useful continuous multi-year data archive for drought assessment. Our results showed that the correlation between RW-PDSI and tree-ring data was statistically significant (p < 0.01) at Kongtong and Hengshan sites with 0.65 and 0.64 respectively. Meanwhile, RW-PDSI showed a greater overall correlation with the tree-ring data than the self-calibrating PDSI(SC-PDSI) and the Standardized Precipitation Evapotranspiration Index (SPEI). Results also illustrated that RW-PDSI of the LP region increased in the past three decades, indicating weakening drought frequency and intensity. The area with a significant weakening trend of drought in the investigated region accounts for 71 %. Overall, drought characteristics in LP were well represented by our drought indicators, which could provide research support for the sustainable development of the ecosystem and social economy in drought areas.
Since the implementation of the Grain for Green Project, the vegetation coverage of Loess Plateau has been greatly improved. However, the contradiction between the increasing vegetation water demand ...(VWD) and the regional rainwater utilization potential (RUP) has become an important factor threatening the sustainable development of vegetation. In order to figure out whether the available water can support the water consumption of vegetation restoration, it is necessary to quantitatively explore the balance between the RUP and the VWD. Based on these, this study utilized the Soil and Water Assessment Tool (SWAT) and Penman–Monteith (PM) method to quantitatively evaluate the vegetation–water mutual suitability of a typical area in the Loess Plateau’s Helong Region (HLR). The results showed that both RUP and VWD exhibited significant increasing trends (95 % confidence level) from 1982 to 2018, with a rate of 18.19 mm/10a and 25.22 mm/10a, respectively. Spatially, RUP was lower in the northwest and higher in the southeast and south regions, whereas VWD decreased from the southeast to the northwest. According to the evaluation results, the annual average vegetation–water mutual suitability matching degree was 0.64 in Period I (1982–1999) and 0.67 in Period II (2000–2018). The matching degree was higher in the northwest and middle regions, lower in the southeast, and above 0.60 in most regions. Under the future climate scenarios of RCP 2.6 and RCP 8.5, the matching degree of water supply and demand also improved to 0.69 and 0.72. Overall, the available water resources can basically support vegetation growth in the HLR. Future vegetation restoration in HLR should try to select annual herbaceous plants that consume less water, and it is not recommended to continue vegetation restoration in the southeast. The results of this study can provide scientific guidance and reference for vegetation restoration policies in HLR.
•Radial growth was positively correlated with precipitation.•The response of vegetation to drought is more accurate in dryland.•The description of vegetation drought by PDSI after 2000 is not ...accurate.•PDSI was more accurate than the SPEI in this region.
Since the 1990s, global warming has substantially affected the dynamic responses of forest ecosystems to drought by altering tree growth and ecosystems carbon cycling. The Loess Plateau is a typical vegetation recovery region with an arid and semiarid climate. However, the responses of the vegetation in this region to drought have not been fully studied. We therefore aimed to characterize these responses in tree-ring samples, which were obtained by drilling tree cores with a growth cone, for establishing the tree-ring width chronologies. In addition, we investigated the main factors controlling the radial growth of Chinese pine (Pinus tabulaeformis) and its dynamic responses to drought in the Loess Plateau using correlation analysis. Our results show that radial growth in Chinese pine had a positive correlation with precipitation during the last growing season, pre-growing season, and entire current growing season. The correlation between the radial growth and temperature was inconsistent between different sampling sites and time periods. These suggest that precipitation was more likely to affect radial vegetation growth than temperature. Moreover, the drought indices calculated using data before the year 2000 more accurately reflected the vegetation drought situation in Loess Plateau than data from the last 20 years. The drier the place, the more accurately the drought indices represented the responses of vegetation to drought. However, these indices cannot satisfactorily capture the drought responses of vegetation in wet regions. Furthermore, the PDSI was more accurate than the SPEI at capturing the effects of drought on radial vegetation growth. Understanding the response mechanism of the radial growth of Chinese pine to drought can provide theoretical support for ecological protection, forest management, and ecological construction under climate change.
Given the context of global warming and the increasing frequency of extreme climate events, concerns have been raised by scientists, government, and the public regarding drought occurrence and its ...impacts, particularly in arid and semi-arid regions. In this paper, the drought conditions for the forest and grassland areas in the northern region of China were identified based on 12 years of satellite-based Drought Severity Index (DSI) data. The impact of drought on dryland vegetation in terms of carbon use efficiency (CUE) and water use efficiency (WUE) were also investigated by exploring their correlations with DSI. Results indicated that 49.90% of forest and grassland experienced a dry trend over this period. The most severe drought occurred in 2001. In general, most forests in the study regions experienced near normal and wet conditions during the 12 year period. However, grasslands experienced a widespread drought after 2006. The forest CUE values showed a fluctuation increase from 2000 to 2011, whereas the grassland CUE remained steady over this period. In contrast, WUE increased in both forest and grassland areas due to the increasing net primary productivity (NPP) and descending evapotranspiration (ET). The CUE and WUE values of forest areas were more sensitive to droughts when compared to the values for grassland areas. The correlation analysis demonstrated that areas of DSI that showed significant correlations with CUE and WUE were 17.24 and 10.37% of the vegetated areas, respectively. Overall, the carbon and water use of dryland forests was more affected by drought than that of dryland grasslands.
China (excluding Hong Kong, Macao, and Taiwan).
Few studies have nationally evaluated China's spatiotemporal distribution of future runoff and per capita water resources (PCWR). Based on the ...SSP1-RCP2.6, SSP3-RCP7.0, and SSP5-RCP8.5 scenarios, the future runoff and PCWR in China under global warming levels of 1.5–4.5 °C are predicted. The calibrated Water and Energy Budget-based Distributed Hydrological Model with improved Snow physics for Global simulation (WEB-DHM-SG) was driven by the Inter-Sectoral Impact Model Intercomparison Project 3b (ISIMIP3b) protocol data to simulate runoff and future population data were used to predict the PCWR. Furthermore, the pre-industrial scenario was compared with future development scenarios to analyse the impact of human-induced climate change (HICC).
The average annual runoff would increase by 6.9–27.6 % nationally and increase in 28 provinces, whereas it would decrease in the other 3 provinces. Seasonal runoff decreased in winter but increased in the other three seasons. Runoff is affected by HICC by 4.1–30.0 %. The national average PCWR would change by −7.5 % to 20.4 %. Water shortage conditions might be further intensified in nine provinces but relatively alleviated in the other 22 provinces. Our results can provide scientific support for the future national and regional water planning and management in China.
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●Future spatio-temporal distributions of runoff and per capita water are analysed.●The attributable ratio of the impact of human-induced climate change is discussed.●The water shortage conditions maybe further intensified in nine provinces of China.
► Water demand of the grassland was analyzed, based on which the volume of water pumping was determined. ► Water yield and change of groundwater table in the well were simulated respectively within ...one year. ► Results show that groundwater resources can be exploited sustainably in the demonstration area. ► The cost of PV pumping irrigation system is much less than the diesel engine irrigation system. ► The PV system can bring about tremendous economic benefit as well as eco-environmental benefit.
Solar photovoltaic (PV) pumping irrigation system has become a widely applied solar energy technology over the past decades, in which the pump is driven by electricity produced by solar energy and lifts groundwater or surface water to irrigate the crop or grassland for agriculture. Qinghai Province, located in the Qinghai-Tibet Plateau, features abundant solar energy, but the problem of local grassland degradation and ecological deterioration has become increasingly serious. Using the clean solar energy to pump groundwater or surface water is of great significance for grassland recovery, environment protection and ecological restoration. In this study, we selected a demonstration site (with an area of 3.15ha) in Tibetan Autonomous Prefecture of Golog at the southern part of Qinghai Province and evaluated the feasibility and performance of the PV pumping irrigation system at field scale. Firstly, water demand of pasture was predicted in different hydrological level years to determine water deficiency, which should be replenished mainly by pumping groundwater according to the local water resources conditions. Secondly, through modeling the unsteady flow of partially penetrating well in unconfined aquifer, we analyzed the change of groundwater table of the pumping well in both irrigation season and non-irrigation season, and then evaluated whether the groundwater resources can satisfy the pumping water demand for the growth of grassland. Results show that groundwater resources in the demonstration area are satisfactory and water yield in the pumping well can generally fulfill the water demand of grassland. Finally, based on balance analysis between solar energy supply and demand, a set of technical parameters were given to design the PV pumping irrigation system in the demonstration area. We also made the benefit analysis for the PV pumping irrigation system. It is concluded that, the PV system has good economic and ecological performance in the demonstration site compared to the diesel engine irrigation system, showing promising prospects to be popularized in Western China at large scale.
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