Search

Altitude is one of the important factors influencing the spatial distribution of precipitation, especially in a complex topography, and simulations of isotope-enabled climate models can be improved by altitude correlation. Here we compiled isotope observations at 12 sites in Lanzhou, and examined the relationship between isotope error and altitude in this valley in the Chinese Loess Plateau using isoGSM2 isotope simulations. Before altitude correction, the performance using the nearest four grid boxes to the target site is better than that using the nearest box; the root mean square error in δ18O using the nearest four grid boxes averagely decreases by 0.37‰ compared to that using the nearest grid boxes, and correlation coefficient increases by 0.05. The influences of altitude on precipitation isotope errors were examined, and the linear relationship between altitude error and isotope simulations was calculated. The strongest altitude isotopic gradient between δ18O mean bias error and altitude error is in summer, and the weakest is in winter. The regression relationships were used to correct the simulated isotope composition. After altitude correction, the root mean square error decreases by 1.21‰ or 0.86‰ using the nearest one or four grid boxes, respectively, and the correlation coefficient increases by 0.13 or 0.08, respectively. The differences between methods using the nearest one or four grids are also weakened, and the differences are 0.02‰ for root mean square error and −0.01 for the correlation coefficient. The altitude correction of precipitation isotopes should be considered to downscale the simulations of climate models, especially in complex topography. [ABSTRACT FROM AUTHOR]

Based on the precipitation samples collected in Minxian in the western Loess Plateau from 2019 to 2021, this study analyzes the influence of moisture sources on precipitation isotopes. Through the specific humidity correction of the backward trajectory, it is found that Xinjiang and the middle and lower reaches of the Yangtze River may be the main moisture sources. Through cluster analysis of backward trajectories, it is found that in the summer half-year, the water vapor from the east and northeast leads to the precipitation with a depleted isotope ratio, while the water vapor from the south and northwest leads to the precipitation with an enriched isotope ratio; in the winter half, water vapor from the east leads to precipitation with enriched isotope ratios, while water vapor from the northwest and northeast leads to precipitation with depleted isotope ratios. In addition, the precipitation isotope values showed a tendency to deplete with the duration of water vapor transport in the summer half-year, but this tendency was not obvious in the winter half-year. The relationship between precipitation isotopes and water vapor transport height showed a positive correlation in both the winter half-year and summer half-year. Using the Potential Source Contribution Factor analysis methods and the backward trajectory after the specific humidity revision, it was found that the potential evaporation source areas in the summer half-year are larger in extent, mainly distributed in the eastern and southern regions of the sampling site, and the contribution of local recycled vapor to precipitation is 32.17%; while the potential evaporation source areas in the winter half-year are smaller in extent, they are only distributed in the southern region of the sampling site, and the contribution of local recycled vapor to precipitation is 24.66%. [ABSTRACT FROM AUTHOR]

Quantitatively assessing the evaporation‐caused stable water isotope fractionation in precipitation below the cloud base is of great significance to understand the modern hydrological circulation especially in a plateau climate. Based on the hourly meteorological data at eight meteorological stations of the Gannan Plateau at the eastern margin of Qinghai‐Tibet Plateau in 2020, we examined the spatial and temporal variations of below‐cloud evaporation effect on precipitation isotopes, and then discussed the factors influencing the below‐cloud evaporation across the Gannan Plateau. The contemporary observation of precipitation isotopes at one site in the Gannan Plateau is also applied to understand the local meteoric water line associated with the below‐cloud evaporation. From 9:00 to 21:00 Beijing Time, the impact of below‐cloud evaporation is greater than that during the rest periods. Within the study region, the below‐cloud evaporation in the central area is usually stronger than that of the surrounding area. The diurnal and monthly variability of relative humidity is highly consistent with that of the remaining raindrop mass fraction after evaporation as well as the isotope variation in raindrop below the cloud base. When the relative humidity is greater than 95%, there is a linear relationship between the remaining raindrop mass fraction and the below‐cloud deuterium‐excess variation of approximate 1.1‰/%. Global warming will increase the below‐cloud evaporation effect across the Gannan Plateau. The findings are useful to understand the below‐cloud evaporation and isotope fractionation under a plateau climate. [ABSTRACT FROM AUTHOR]

Based on daily meteorological records for 651 sites across China during the period 1960–2018, we estimated the changes in isotopic variations in raindrops as they descend from cloud base to ground over past decades, and tested the sensitivity of isotopic variations to climate parameters like air temperature and relative humidity. Air temperature correlates positively and relative humidity correlates negatively with below‐cloud isotopic variation. Generally, the below‐cloud evaporation effect on precipitation isotopes in the arid and semi‐arid regions of China is much greater than that in the humid and semi‐humid regions, although the impact might be reduced under cold‐arid or hot‐humid conditions. With aridity increasing with distance from the coast, the continental effect of precipitation isotopes is modified due to the below‐cloud evaporation. The seasonal pattern of the measured isotopic composition in precipitation near the ground and estimated at cloud base, is still similar in most regions, although the seasonal range is higher at the ground. During the last five decades, the below‐cloud evaporation effect has enhanced for the cold and arid regions of China especially across Qinghai‐Tibet Plateau and Inner Mongolia, due to combined effects of increasing air temperature and decreasing relative humidity. Although the below‐cloud evaporation effect is not always the dominant factor influencing the variability of stable isotopes, it needs to be considered as one of the contributing factors. This enhanced effect may impact the interpretation of past climate based on stable water isotopes, particularly in paleoclimate studies using speleothems and tree rings. Key Points: Below‐cloud evaporation effect on precipitation isotopes is assessed nationwideThe variability of below‐cloud evaporation effect is controlled by the warming climateEnhanced below‐cloud evaporation may affect interpretation of long‐term isotope records [ABSTRACT FROM AUTHOR]

Different water sources exploited for public use have different exposure to risks associated with climatic and environmental change. Isotope ratios of tap water have previously been studied as a potential tool to link public supply waters with water source characteristics at local to continental scales, providing information on the footprint of and potential risks associated with the water sources used. Work that combines intensive spatial and temporal sampling with independent water management data has been limited, however. In this study, an extensive observation network was established during 2014–2016 to provide monthly tap water sampling across China. We show that the spatial distribution of annual mean tap water isotope ratios is generally consistent with that of local precipitation across China. We identify seasonal correlation between tap water and precipitation isotope ratios in south China, where use of surface water is prevalent. In contrast, relatively invariant tap water isotope ratios elsewhere in China, which are not correlated with seasonal variation of precipitation isotope ratios, can be attributed to use of groundwater or water from river basins with longer storage times. The tap water isotope signatures identified here could be widely applied to characterize water supplies and associated sustainability challenges in different regions worldwide. Key Points: A new nationwide network of tap water isotope data across China was establishedConnection between monthly stable isotopes in tap water and precipitation is identifiedDiagnostic patterns of tap water isotopes are associated with water resource use [ABSTRACT FROM AUTHOR]

Terrestrial moisture contributed by surface evaporation and transpiration, also known as recycled moisture, plays an important role in hydrological processes especially across arid central Asia. The stable hydrogen and oxygen isotopes can be used for water budget analysis to calculate the contribution of recycled moisture to precipitation between two locations along the moisture flow. Based on a three-component isotopic mixing model, the moisture recycling in oasis stations of arid central Asia during summer months is assessed. At large oases of Urumqi, the proportional contribution of recycled moisture to local precipitation is approximately 16.2%, and the mean proportions of surface evaporation and transpiration are 5.9% ± 1.5% and 10.3% ± 2.2%, respectively. At small oases like Shihezi and Caijiahu the contribution of recycled moisture is less than 5%, and the proportion of surface evaporation is much less than that of transpiration. The vegetative cover in arid central Asia is generally sparse, but the evapotranspiration contribution to precipitation cannot be ignored at the widely distributed oases. The oasis effect shows great variability depending on locations and water availability for evapotranspiration. [ABSTRACT FROM AUTHOR]

Approximately one-third of the Earth's arid areas are distributed across central Asia. The stable isotope composition of precipitation in this region is affected by its aridity, therefore subject to high evaporation and low precipitation amount. To investigate the factors controlling stable water isotopes in precipitation in arid central Asia, an observation network was established around the Tianshan Mountains in 2012. Based on the 1052 eventbased precipitation samples collected at 23 stations during 2012-2013, the spatial distribution and seasonal variation of δD and δ18O in precipitation were investigated. The values of δD and δ18O are relatively more enriched in the rainfall dominant summer months (from April to October) and depleted in the drier winter months (from November to March) with low D-excess due to subcloud evaporation observed at many of the driest low elevation stations. The local meteoric water line (LMWL) was calculated to be δD=7.36δ18O+0.50 (r²=0.97, p<0.01) based on the event-based samples, and δD=7.60δ18O+2.66 (r²=0.98, p<0.01) based on the monthly precipitation-weighted values. In winter, the data indicate an isotopic rain shadow effect whereby rainout leads to depletion of precipitation in the most arid region to the south of the Tianshan Mountains. The values of d18Osignificantly correlate with air temperature for each station, and the best-fit equation is established as δ18O=0.78T - 16.01 (r²=0.73, p<0.01). Using daily air temperature and precipitation derived from a 0.5° (latitude)?0.5° (longitude) gridded data set, an isoscape of δ18Oin precipitation was produced based on this observed temperature effect. [ABSTRACT FROM AUTHOR]

Based on the precipitation samples obtained at Lanzhou City (36°06′N, 103°44′E, 1,548 m a.s.l.) in western China and its surrounding counties (Yongdeng, Gaolan, and Yuzhong) from April 2011 to February 2013, the characteristics of stable isotopes in precipitation and the correlations between δO and meteorological factors were analyzed. The LMWL (local meteoric water line) of Lanzhou City and its surrounding areas was calculated, and the order of LMWL slopes in the four stations is Yuzhong (7.70) > Lanzhou (7.57) > Yongdeng (7.24) > Gaolan (6.80). Both the slope and intercept of the LMWLs for each station are less than those of the global meteoric water line. There is a weakly positive correlation between δO and air temperature, and the correlation between δO and precipitation amount is weakly negative. Evidenced from the slope and intercept of LMWL and the relationship between δO and relative humidity, there is secondary evaporation when the precipitation falls from clouds to the ground. [ABSTRACT FROM AUTHOR]

The local meteoric water lines (LMWLs) reflect water sources and the degree of sub-cloud evaporation at a specific location. Lanzhou is a semi-arid city located at the margin of the Asian monsoon, and the isotope composition in precipitation around this region has aroused attention in hydrological and paleoclimate studies. Based on an observation network of stable isotopes in precipitation in Lanzhou, LMWLs at four stations (Anning, Yuzhong, Gaolan and Yongdeng) are calculated using the event-based/monthly data and six regression methods (i.e., ordinary least squares, reduced major axis, major axis regressions, and their counterparts weighted using precipitation amount). Compared with the global meteoric water line, the slope and intercept of LMWL in Lanzhou are smaller. The slopes and intercepts calculated using different methods are slightly different. Among these methods, precipitation-weighted least squares regression (PWLSR) usually had the minimum average value of root mean sum of squared error (rmSSEav), indicating that the result of the precipitation weighted method is relatively stable. Higher precipitation amount and lower air temperature result in larger slopes and intercepts on an annual scale, which is out of accordance with the summertime. [ABSTRACT FROM AUTHOR]

Deuterium excess and stable oxygen isotopes in precipitation have been widely applied to trace the source of water vapor. In this study, hydrogen and oxygen isotope analyses of samples were collected on seven sampling stations in Dingxi area from April 2019 to April 2020. The seasonal variation of hydrogen and oxygen stable isotopes as well as the d-excess indicate that the source of water vapor in Dingxi area is mostly from a single source. However, there are different sources of water vapor in the summer. Meanwhile, water vapor sources were analyzed using the Lagrange algorithm, indicating two different principal water vapor sources for precipitation in the area: some locally recycled water vapor in summer and autumn, and most water vapor from the westerly belt. Further studies using the PSCF and CWT analysis methods show that the locally recycled water vapor contributes more to its precipitation in the northwest of Dingxi area. [ABSTRACT FROM AUTHOR]

The proportional contribution of recycled moisture to local precipitation is a geographically dependent parameter that cannot be ignored in water budgets. Stable hydrogen and oxygen isotopes are sensitive to environmental changes and can be applied to investigate the modern water cycle. In this study, a three-component mixing model is used to calculate the contribution of different water vapors (advection, evaporation and transpiration) to summer precipitation in Lanzhou city, Northwest China. The results show that for all sampling sites in Lanzhou, the contribution of advection vapor to precipitation is the largest, followed by the plant transpiration vapor, and the contribution of surface evaporation water vapor is usually the least, with the average values of 87.96%, 9.1% and 2.9%, respectively. The spatial differences of plant transpiration vapor are generally larger than those of advection vapor and surface evaporation vapor, and the high values appear in Yongdeng, Daheng and Gaolan. [ABSTRACT FROM AUTHOR]

The deuterium excess in precipitation is an effective indicator to assess the existence of sub-cloud evaporation of raindrops. Based on the synchronous measurements of stable isotopes of hydrogen and oxygen (δ2H and δ18O) in precipitation for several sites in Lanzhou, western China, spanning for approximately four years, the variations of deuterium excess between the ground and the cloud base are evaluated by using a one-box Stewart model. The deuterium excess difference below the cloud base during summer (−17.82‰ in Anning, −11.76‰ in Yuzhong, −21.18‰ in Gaolan and −12.41‰ in Yongdeng) is greater than that in other seasons, and difference in winter is weak due to the low temperature. The variations of deuterium excess in precipitation due to below-cloud evaporation are examined for each sampling site and year. The results are useful to understand the modification of raindrop isotope composition below the cloud base at a city scale, and the quantitative methods provide a case study for a semi-arid region at the monsoon margin. [ABSTRACT FROM AUTHOR]

The deuterium excess (d) in precipitation, determined by the stable hydrogen and oxygen isotopes (δ2H and δ18O), is a widely applied parameter in tracing the water vapor source. Based on the multiple-year observations of stable water isotopes in precipitation at four stations in the Lanzhou city, Northwest China, we analyzed the variations in deuterium excess in precipitation at the Asian monsoon margin region. The mean value of deuterium excess at the study region is 11.0‰ in the dry season and 8.0‰ in the wet season. The d value in precipitation negatively correlates with air temperature and vapor pressure. The low d value during the wet season reflects the monsoon moisture transported from long distances. During the dry season, the continental air masses correspond to the higher d value in precipitation. The moisture regimes based on reanalysis data are generally consistent with the findings using a stable isotopic approach, and the monsoon moisture is highlighted in summer precipitation at these monsoon margin sites. [ABSTRACT FROM AUTHOR]

The stable isotopes in precipitation provide a new understanding for the mechanism study of water cycles in the Loess Plateau. However, there has never been an introduction for the Tianshui area, which is transitioning from semi-humid to semi-arid. We analyzed the time series changes of stable isotopes in precipitation at seven sampling points during pre-monsoon, monsoon and post-monsoon periods (April to October) in the Tianshui area. The results show that the temperature effect not only shows spatial differences but also seasonal changes and a weak precipitation effect is only found during the monsoon period. At the same time, the variation characteristics of precipitation isotopes before and after the monsoon clearly record the advancing and retreating time of the monsoon. We captured this important time node around 7 May and 21 September. Due to the influence of the regional microclimate formed by different natural conditions, the kinetic fractionation effect of isotopes in precipitation cause obvious differences in the slope and intercept of the meteoric water line in different natural regions, which shows that the stable isotopes in precipitation with high-resolution changes in a short period of time are of great significance to deeply explore the hydrological process of regional microclimates. [ABSTRACT FROM AUTHOR]

Stable isotopes (e.g., δ2H and δ18O) in tap water are important tools to understand the local climate or environment background, water sources and the state of regional water supply. Based on 242 tap water samples, 35 precipitation samples and 24 surface water samples gathered in the urban area of Lanzhou, the basic spatiotemporal characteristics of isotopes in tap water, their connection with isotopes in other water bodies and change during the process from raw water to tap water are discussed in detail, combining the information of local tap water supply and water source. It can provide reliable help for understanding the isotope characteristics of local tap water, regional water supply management and determination of tap water source of in a small area. Except for the establishment of a new data set of isotopes in tap water with complete time series and uniform spatial distribution of sampling sites, other results show that: (1) The Local Tap Water Line (LTWL) of Lanzhou is δ2H = (6.03 ± 0.57) δ18O + (−8.63 ± 5.44) (r2 = 0.41, p < 0.01). (2) For seasonal variations, δ2H and δ18O in tap water both are higher in autumn and lower in spring. The diurnal and daily variations of isotopes in tap water are not large. As for spatial variations, the monthly mean values of δ2H and δ18O in tap water at each sampling site show little difference. The isotopes in tap water collected from one single sampling site can be considered as a representative for isotopes in tap water in the area with a single tap water source. (3) Isotopes in tap water show weak connection with precipitation isotopes, but exhibit good connection (consistent seasonal variation, similar numerical range, small numerical difference and high correlation) with isotopes in surface water, which is the direct water source. Isotopes in water change little from raw water to tap water. Isotopic composition of tap water in Lanzhou can be used as a representative of isotopes in surface water. [ABSTRACT FROM AUTHOR]