Search

Study region: The Mainstream in the Tarim River Basin, Southern Xinjiang, China Study focus: Climate change and human activities have significantly altered the water cycle, and water security evaluation and management are urgent. In arid and semi-arid areas, the assessment of blue and green water is particularly important. In this study, the MIKE SHE model is used to simulate the spatial and temporal changes of blue and green water resources in the mainstream of the Tarim River Basin (TRB) from 1990 to 2050 under land use and climate change conditions. The scarcity and vulnerability of blue-green water are introduced to evaluate the water security of the basin. The impacts of different land uses on blue-green water resources were also calculated according to the model zoning. New hydrological insights for the region: The results indicate that from 1990 to 2050, blue water resources show a spatial pattern of gradual decrease from upstream to downstream. Compared to blue water, green water is dispersed more evenly over space. Future climatic scenarios will impact water security, as will changes in blue and green water security in terms of time and space. By comparing the influence of ecological water transport on the change of blue and green water before and after 2000, it was found that environmental water transport plays a certain role in improving the blue water scarcity in downstream of the TRB. The study is significant in maintaining regional water security and ecosystem stability.

Mountains are important suppliers of freshwater to downstream areas, affecting large populations in particular in High Mountain Asia (HMA). Yet, the propagation of water from HMA headwaters to downstream areas is not fully understood, as interactions in the mountain water cycle between the cryo-, hydro- and biosphere remain elusive. We review the definition of blue and green water fluxes as liquid water that contributes to runoff at the outlet of the selected domain (blue) and water lost to the atmosphere through vapor fluxes, that is evaporation from water, ground, and interception plus transpiration (green) and propose to add the term white water to account for the (often neglected) evaporation and sublimation from snow and ice. We provide an assessment of models that can simulate the cryo-hydro-biosphere continuum and the interactions between spheres in high mountain catchments, going beyond disciplinary separations. Land surface models are uniquely able to account for such complexity, since they solve the coupled fluxes of water, energy, and carbon between the land surface and atmosphere. Due to the mechanistic nature of such models, specific variables can be compared systematically to independent remote sensing observations – providing vital insights into model accuracy and enabling the understanding of the complex watersheds of HMA. We discuss recent developments in spaceborne earth observation products that have the potential to support catchment modeling in high mountain regions. We then present a pilot study application of the mechanistic land surface model Tethys & Chloris to a glacierized watershed in the Nepalese Himalayas and discuss the use of high-resolution earth observation data to constrain the meteorological forcing uncertainty and validate model results. We use these insights to highlight the remaining challenges and future opportunities that remote sensing data presents for land surface modeling in HMA. [ABSTRACT FROM AUTHOR]

Mountains are important suppliers of freshwater to downstream areas, affecting large populations in particular in High Mountain Asia (HMA). Yet, the propagation of water from HMA headwaters to downstream areas is not fully understood, as interactions in the mountain water cycle between the cryo-, hydro- and biosphere remain elusive. We review the definition of blue and green water fluxes as liquid water that contributes to runoff at the outlet of the selected domain (blue) and water lost to the atmosphere through vapor fluxes, that is evaporation from water, ground, and interception plus transpiration (green) and propose to add the term white water to account for the (often neglected) evaporation and sublimation from snow and ice. We provide an assessment of models that can simulate the cryo-hydro-biosphere continuum and the interactions between spheres in high mountain catchments, going beyond disciplinary separations. Land surface models are uniquely able to account for such complexity, since they solve the coupled fluxes of water, energy, and carbon between the land surface and atmosphere. Due to the mechanistic nature of such models, specific variables can be compared systematically to independent remote sensing observations – providing vital insights into model accuracy and enabling the understanding of the complex watersheds of HMA. We discuss recent developments in spaceborne earth observation products that have the potential to support catchment modeling in high mountain regions. We then present a pilot study application of the mechanistic land surface model Tethys & Chloris to a glacierized watershed in the Nepalese Himalayas and discuss the use of high-resolution earth observation data to constrain the meteorological forcing uncertainty and validate model results. We use these insights to highlight the remaining challenges and future opportunities that remote sensing data presents for land surface modeling in HMA.

Exploring the spatiotemporal impacts of climate change and human activities on freshwater resources through the concepts of blue and green water can effectively improve the sustainability of basin water resource management. However, previous relevant studies have not considered the specific impacts of different climate models and land use changes on the future simultaneously. To mitigate this issue, this study proposes a hydrological modeling framework by integrating geographic detectors, Future Land Use Simulation (FLUS) models, and the Soil and Water Assessment Tool (SWAT) model. This framework was capable of identifying the major driving factors of land use changes, predicting future land use patterns, and assessing the spatiotemporal characteristics of water resources under different future climate scenarios and land use distributions. Applying the framework to the Wei River Basin (WRB) in northwest China, it identified the primary drivers of land use change in the WRB and quantitatively analyzed the spatiotemporal changes of blue and green water resources in the WRB under four scenarios. The results show that: 1) FLUS model and SWAT model can effectively simulate land use change and runoff process with high simulation accuracy; 2) Precipitation, temperature and GDP are the main drivers of land use change; 3) The amount of blue and green water in the middle and lower reaches of the basin is significantly higher than that in the tributaries and upper reaches. Blue water and green water flow are more affected by climate than land use, while green water storage is more sensitive to land use change. This study can provide effective information for basin land planning and rational allocation of water resources.

Study region: The study area was Nanjing, Jiangsu Province, eastern China. Study focus: Blue-green water utility assessment in crop cultivation is profound to better sustainability of regional resources, agriculture and ecosystems. The aim of current study is to establish a blue-green water differentiation and efficiency evaluation methods for paddy fields, based on daily water migration observation under four irrigation-drainage protocols. The blue-green water use performance under different irrigation-drainage protocols and precipitation patterns in paddy fields and the advantage of the water resources analysis model proposed in the current study were analyzed and discussed. New hydrological insights for the region: The green and blue water efficiency indices (GWE and BWE) were significantly affected by precipitation. GWE (0.495) was 35.1% higher in dry years than in wet years, and BWE was mainly affected by precipitation distribution during the crop growth season. The green and blue water productivity indices (GWP and BWP) showed pronounced differences among various irrigation-drainage measures, and the controlled irrigation (COI) performs the best. BWE and GWP obtained by previous method were 48.9% and 38.9% greater than those reported here, showing that the neglect of interactive blue-green water migration process would overestimate the field irrigation efficiency. The methods employed and results obtained in the present study suggest that it is important to assess the water footprint and blue-green performance for crop cultivation systems.

Study region: Kaidu River Basin, an arid region of China Study focus: Water resources are scarce and unstable. Adverse changes in blue-green water resources can disrupt water balance and availability in arid regions. Therefore, it is crucial to effectively assess and predict future blue-green water resources in arid areas. This study utilizes the Soil and Water Assessment Tool (SWAT), Patch-generating Land Use Simulation (PLUS), and Global Circulation Models (GCMs) to analyze the interactive impacts of climate and land use/cover changes (LUCC) on blue-green water in arid basin from 1990 to 2050. New hydrological insights for the region: This work identified key factors influencing blue-green water changes, including forests, grasslands, and snowmelt. In the historical scenarios, the Kaidu River basin exhibited significant interannual variations in blue water and precipitation. In the future scenarios, blue water increases (+3.6%), and green water decreases (−1.8%) under SSP245 (medium emissions). Under SSP585 (high emissions), blue water decreases (−2.4%), and green water increases (+1.8%). Under SSP126 (low emissions), both blue water (+8.5%) and green water (+0.73%) show an increasing trend. The change in snowmelt is the main reason for the first peak of blue water in April May. Under historical and future snowmelt conditions, blue water shows a significant upward or downward trend with the amount of snowmelt. The findings provided practical hints for the enhancement of the management and allocation of precious water resources.

The process of blue water used in crop cultivation has both natural and economic properties due to the intervention of irrigation facilities. This study revealed crop water use (CWU) from 1999 to 2018 in each province of China based on water footprint theory, and then established the blue water dependence index (BDI) to evaluate the dependence of agricultural cultivation on irrigation water from the perspective of water withdraw, and conducted a spatial and temporal pattern analysis.The influencing factors and structural pathways of BDI were explored using least squares structural equation modeling (PLS-SEM) at national and regional scales. Results indicated that the annual amount of water used for crop production in China exceeded 900.0 Gm³. The growth in CWU from 1999 to 2018 for cash crops and grain crops was 145.4 Gm³ and 74.4 Gm³, respectively.BDI of all crops was 0.281 over the study period in China, with grain crops being 2.6 times more dependent on blue water resources than cash crops. Xinjiang, with annual average BDI of 0.716, 0.805, and 0.620 for all, grain and cash crops, respectively, has the highest irrigation demand. The PLS-SEM results showed a significant causal relationship between the economy and BDI, with obvious regional differences in structural path analysis. Based on the analysis of agricultural water use, the regions can adjust the structure of crop cultivation, optimize the allocation of water and soil resources, expand the cultivation of fodder grains and promote steady economic growth, to achieve a ''win-win'' situation of ensuring food security and sustainable use of agricultural water resources.

Different canopy characteristics of industrial eucalyptus may lead to differences in water evaporation and availability to plants. This study aims to understand rainfall partitioning in a young clonal plantation (age of 2–4.5 years) of three eucalyptus species by relating tree parameters: diameter at breast height, total height, and leaf area index. We measured rainfall, throughfall, stemflow and litter interception, along with the tree parameters. The eucalyptus trees had rainfall interception varying between 22 mm (for 178 mm of rainfall) and 42 mm (for 87 mm of te rainfall), throughfall between 106 mm (for 186 mm of rainfall) and 44 mm (for 74 mm of rainfall), and stemflow between 0.5 mm (for 92 mm of rainfall) and 1.4 mm (for 24 mm of rainfall). For the three species, rainfall interception varied between 12 and 48%, throughfall between 57 and 90%, and stemflow between 0.3 and 5.4%. The coefficient of determination between interception and rainfall was 0.76, indicating interception depends on other variables, possibly including antecedent rainfall, rainfall intensity, and seasonality. Interception decreased with a reduction in leaf area index caused by eucalyptus defoliation. The E. benthamii had 0.75 mm of throughfall per 1 mm of rainfall, whereas in E. dunnii and E. saligna, these ratios were 0.71 and 0.68, respectively. Stemflow in E. benthamii and E. dunii had a higher positive relationship with the diameter at breast height of the trees, whereas in E. saligna the highest relationship was with the rainfall. These results contribute to establishing management strategies, such as choosing suitable eucalyptus species to local climate, and to improve the synchronization of crop-demand versus soil-water-supply while maintaining streamflow to fulfill ecological and production needs.

It is of great significance to study the hydrological effect of no-tillage of rice for the popularization of no-tillage technology and the sustainable development of agriculture.However,previous studies were mainly conducted at station scale,and the effect of no-tillage of rice on blue-green water at basin scale is still unclear.Taking the Xiangjiang River Basin as the test area,based on the land use data,digital elevation data,soil data,agricultural management data in 2000 and meteorological data-driven SWAT model,this paper simulates the effect of no-tillage of rice on blue water (water yield+deep groundwater recharge) and green water (actual evapotranspiration+soil moisture content) in the basin.The results show that:Compared with traditional tillage,no-tillage of rice had a greater influence on recharge of deep groundwater,resulting in a decrease of 5.62%,which was 5.35% higher than that of water yield.However,the change of blue water was mainly attributed to the change of water yield,whose contribution was 72.46%.The green water flow (actual evapotranspiration) decreased by 8.460×107 m3 due to no-tillage of rice,but the increase of green water reservoir (soil moisture content) offset these and eventually resulted in the increase of green water.Therefore,the change of blue-green water distribution under no-tillage of rice was mainly achieved by changing water yield and soil moisture content.The water yield mainly caused the change of blue water,while the soil moisture content mainly resulted in the change of green water.Due to the mutual offset of hydrological factors,there was no significant final effect of no-tillage rice on the blue-green water of the whole basin,but large spatial differences within the basin.No-tillage of rice increased the proportion of green water in the total water resources,and increased the ecological water available in the farmland ecosystem,so it played a positive role.

Graphical abstract Highlights • Water footprint scarcity (WFS) was quantified based on blue-green water availability and appropriation. • WFS increased in drought agriculture-based region and dropped in economic developed area. • WFS increased in drought agriculture-based region and dropped in economic developed area. • Controlling the development of irrigation can reduce WFS and alleviate regional water scarcity. Abstract The mitigation of water stress in crop production is important for relieving the growing global water shortage. The water footprint scarcity (WFS) for regional water stress evaluation integrating blue and green water resources and the water footprint of the crop production industry were developed in this paper. Three subregions in China, industry-based southern Jiangsu (SJS), agriculture-based northern Jiangsu (NJS) and middle-type central Jiangsu (CJS), were selected to study the spatiotemporal pattern and driving mechanism of WFS. The results show that green water accounts for 56.6% and 71.8% of agricultural water resources available (AWA) and crop water footprint (CWF) of Jiangsu Province. The WFS of Jiangsu was calculated to be 2.26, and almost all prefectures for every year from 1996 to 2015 faced very high water stress (WFS > 1.20). The WFS value increased in NJS and CJS and decreased in SJS over time; meteorological and social factors affected the WFS at the same time. Land irrigation was the main factor to explain the growing water stress in the agriculture-based NJS. The WFS revealed the water shortage more clearly, especially in the water-poor agriculture-based areas, than the results of the conventional water stress index. The strategies for environmental change adaptation suggested by this study are to use WFS for agricultural water suitability evaluation and water resource management policy formulation; to reduce WFS through irrigation efficiency and crop variety promotion worldwide; and to implement compensation measures for agricultural products and virtual water trade to help underdeveloped agricultural production areas improve their agricultural production technology and control irrigation expansion. [ABSTRACT FROM AUTHOR]

Efficient utilization of water resources contributes to regional food, water and ecological security. An indicator, generalized efficiency (GE), was established based on a blue-green water framework for evaluating regional effective use of water resources. GE is defined as the ratio of total water consumption (TWC) to total water inflow (TWI) into an agricultural production system over a single year. Then, the spatial pattern of GE in the irrigated, rain-fed and total cropland of China in 2010 was analysed based on the quantification of provincial TWI and TWC, taking grain production as a case study. The results show that TWI in China was approximately 978.6 Gm 3 , of which rain water was close to 70.0%; national TWC was approximately 577.5 Gm 3 in the study year, including 72.0% green and 28.0% blue water; and rain-fed cropland made up approximately 33.0% of the TWI and TWC. The spatial distributions of TWI and TWC per unit arable land differs greatly; national GE in irrigated, rain-fed and total cropland were 0.584, 0.603 and 0.590, respectively; and regional rain-fed GE was larger than that in irrigated farmland due to the uneven distribution of precipitation. This work expanded the applicability of evaluation of effective use rate of water resources from blue water and irrigated cropland, to generalized water resources and any designated region. GE cannot be replaced by other exciting indicators in either scientific connotation or spatial distribution. Hence, the establishment of GE is a more advanced agricultural water use efficiency evaluation indicator system. [ABSTRACT FROM AUTHOR]

The increasing shortage of water resources and the growing demand for crops make water use efficiency a decisive factor for the sustainable and healthy development of the agricultural system. In order to evaluate agricultural water use efficiency from the water footprint perspective, the current study constructed the comprehensive water efficiency (CWE) index based on eight single agricultural water use efficiency performance parameters. The water resources utilization and efficiency in the wheat production system of China from 2006 to 2015 were analyzed and the sensitivity of single indices for CWE was identified. The results show that the national crop water footprint (CWF) for wheat production was estimated to be, including 46.3% blue, 36.6% green and 17.0% blue components, respectively. The spatial distribution patterns of water use efficiency performance indices were different. CWE of the country was 0.387, showing an upward trend over time and decreased from the southeast to the northwest geographically. Crop water productivity (CWP), productive water ratio (PWR) and rainwater consumption ratio (RCR) turned out to be the first three sensitive parameters for CWE in China. The improvement of China's overall CWE relied on reducing inefficient blue-green water use and increasing the output capacity for per unit water. Advanced agricultural water-saving technologies were in high need for goal achievement, especially for the Huang-Huai-Hai plain, which held more than 70% of Chinese wheat production and CWF. The results provide support for efficient utilization and sustainable development of water resources in the agricultural system. [ABSTRACT FROM AUTHOR]