Water is the key limiting factor in socioeconomic and ecological development, but it is adversely affected by climate change. The novel virtual water (VW) concept and water, energy, food, biodiversity, and human health (WEFBH) nexus approach are powerful tools to assess the sustainability of a region through the lens of climate change. Climate change-related challenges and water are complex and intertwined. This paper analyzed the significant WEFBH sectors using the multicriteria decision-making (MCDM) and analytic hierarchy process (AHP) model. The AHP model demonstrated quantitative relationships among WEFBH nexus sustainability indicators in the Greater Horn of Africa countries. Besides, the net VW imports and water footprints of major staple crops were assessed. The composite WEFBH nexus indices varied from 0.10 to 0.14. The water footprint of crops is increasing period by period. The results also revealed that most countries in the study area are facing WEFBH domains unsustainability due to weak planning or improper management strategies. The strong policy constancy among the WEFBH sector is vital for dissociating the high-water consumption from crop production, energy, environmental, and human health system. Thus, this study enhances insights into the interdependencies, interconnectedness, and interactions of sectors thereby strengthening the coordination, complementarities, and synergies among them. To attain sustainable development, we urgently call all public and private entities to value the amount of VW used in their daily activities and design better policies on the complex WEFBH nexus and future climate change.

Streams are regionally important sources of CH₄ to the atmosphere, but the temporal variability in and control on CH₄ concentrations and emissions are not well understood. Especially, lack of long‐term data hampers our ability to predict CH₄ emissions from streams. Here, we present a 7‐year data set of biweekly CH₄ concentration and underlying potential drivers from two adjacent small German streams with contrasting riparian area characteristics. Over the 7‐year study period, mean CH₄ concentration and emissions were 0.20 and 0.07 μmol L⁻¹ and 2.01 and 0.84 mmol m⁻² d⁻¹ for the two streams, respectively. Our findings suggest that the combination of seasonality and topography ultimately shaped the considerable temporal variations of CH₄. CH₄ oxidation and production in the streams were probably of minor importance. Instead, fluctuations in CH₄ concentrations likely reflected a temporal pattern of CH₄ input from soils of the riparian zone with larger CH₄ variations in the stream with more riparian lands. Structural equation modeling revealed dissolved organic carbon and nitrate as important predictors of CH₄ concentration. However, we did not identify predictors of the considerable short‐term variability, nor the explicit pathways of CH₄ delivery to streams. The discrepancy of the CH₄ flux between streams was likely triggered by different connectivities to riparian soils with higher CH₄ emissions in the hydrologically more connected stream. Interannual comparison showed that changing hydrologic conditions, rather than warming, may impact future CH₄ emissions from temperate streams. We predict that higher CH₄ emissions occur in wetter years in streams with close connectivity to riparian soils.

It is important to strengthen the studies on the response of soil respiration components to tillage practices and natural precipitation in cropland. Therefore, soil heterotrophic respiration (R_H) and autotrophic (R_A) respiration were monitored by a root exclusion method in the North China Plain (NCP). The tillage practices included no-tillage (NT) and conventional tillage (CT), and the study periods were the summer maize growth stages in 2018 and 2019. R_H, R_A, soil water content and temperature were measured continuously for 113 days by an automatic sampling and analysis system. The soil R_H values on bright days and rain-affected days were higher under NT in 2018 (14.22 and 15.06 g CO₂ m⁻² d⁻¹, respectively) than in 2019 (8.25 and 13.30 g CO₂ m⁻² d⁻¹, respectively). However, the R_A values on bright days and rain-affected days were lower under NT in 2018 (4.74 and 4.97 g CO₂ m⁻² d⁻¹, respectively) than in 2019 (5.67 and 6.93 g CO₂ m⁻² d⁻¹, respectively). Moreover, NT decreased R_H but increased R_A compared to CT in 2019. Compared to bright days, the largest increase in both R_H and R_A after rain pulses was under CT in 2019 (6.75 and 1.80 g CO₂ m⁻² d⁻¹, respectively). Soil water content and soil temperature were higher in 2018 than in 2019. Moreover, NT increased soil water content and decreased soil temperature on bright days compared to CT in 2019. Furthermore, soil temperature accounted for more variations in R_H on bright days and rain-affected days, but soil water content had a greater influence on R_A on bright days. However, after precipitation, higher soil water content decreased R_A under NT in 2018, while soil water content was positively related to R_A under CT in 2019. This study determined the differential response of R_H and R_A to tillage practices and natural precipitation pulses, and we confirmed that excessively dry soil increases soil carbon loss after rain events in the NCP.

Climate change and human activities lead to freshwater shortage, soil salinization, and food security crises in arable land. To explore the natural and irrigation factors on soil water and salt movement, this study quantitatively analyzed the dynamic characteristics of soil water and salt movement under precipitation, groundwater irrigation, and brackish water irrigation conditions for the next 30 years using Hydrus-1D model-based parameters obtained from the winter wheat–summer maize rotation experiments in the Yellow River Irrigation District. The results showed that precipitation was the key factor of climate change affecting soil water and salt migration, especially in the 0–20 cm soil layer. Under both SSP585 and SSP245 climate scenarios, rainfall in normal and wet years promoted salt leaching up to 1 m below the surface soil. But in dry years, salt washing treatment was required for the tillage layer to prevent salt accumulation. The higher the groundwater level was, the higher the soil water and salt content was in the 0–100 cm soil layer. In this soil layer, a 2 m groundwater level contributed 30% to wheat water needs, while a 3 m groundwater level contributed 18%, and no significant contribution was observed for a 4 m groundwater level. The salinity of the soil profile showed an overall increasing trend with irrigation using 1–3 g/L brackish water for 30 years. However, the salinity in the 0–100 cm soil layer was below the salt tolerance threshold of winter wheat and summer maize with salts accumulated in the 1–2 m soil layer. Considering the salinization of the root zone and crop water needs, it is recommended that the safe groundwater level for brackish water irrigation should be 3 m in the study region. This study provides scientific reference for groundwater–farmland ecosystems to utilize brackish water and treat saline–alkali lands.