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Satellite-based land surface temperature (Ts) with continuous global coverage is increasingly used as a complementary measure for air temperature (Ta), yet whether they observe similar decadal trends remains unknown. Here, we systematically analyzed the trend of the difference between satellite-based Ts and station-based Ta (Ts–Ta) over 2003–2018. We found the global land warming rate based on Ts was on average 56.7% slower than that on Ta (Ts–Ta trend: -0.0166℃ yr-1, p

Serving as a medium between source water and cellulose, leaf water contributes to the isotope ratios (

Rising atmospheric CO2 impacts on vegetation physiological processes can alter land feedbacks on precipitation and water resources, but understanding of regional differences in these changes is uncertain. We investigate the impact of rising CO2 on land water resources for different wetness levels using four Earth system models. We find an overall tendency of runoff to increase across all wetness levels. However, runoff increases in wet regions are much larger than those in dry regions, especially in wet seasons. This substantial amplification of contrasts between wet and dry regions increases at 3% per 100 ppm increase in CO2 relative to the historical period, reaching 18% for a quadrupling of CO2, quantified by a new wetting contrast index (WCI). Physiological effects suppress evapotranspiration more in wet than dry regions, which has a larger contribution than radiative forcing to the amplification of runoff contrast, reshaping the spatial distribution of future land water resources.

Water stable isotopes have been widely used as natural tracers to investigate soil-plant-atmosphere interactions. Recent developments in induction module cavity ring-down spectroscopy (IM-CRDS) have made it possible to rapidly complete isotope analyses, and to combust co-extracted organic compounds at the same time. However, the agreement between IM-CRDS and isotope ratio mass spectrometry (IRMS) analyses has generally been poor and was primarily attributable to spectral interference of IM-CRDS. Here we evaluated the impacts of organic contamination on the isotope ratios using IM-CRDS with two different methods. No spectral interference was observed for solid samples measured directly by IM-CRDS, whereas clear organic contamination occurred in isotope analyses for pre-extracted plant stem and leaf samples. Our results demonstrate that IM-CRDS can fully combust co-extracted organic compounds by in-line oxidation in the direct measurement of solid samples, although this may not guarantee that the IM-CRDS can obtain better isotopic data than IRMS. It may be risky to evaluate the performance of IM-CRDS by measuring pre-extracted water samples because cryogenic vacuum distillation is likely to introduce extra organic compounds, which may not be fully removed during subsequent IM-CRDS measurement. In addition, spectral variables are useful for post-processing corrections.

The global monsoon is characterised by transitions between pronounced dry and wet seasons, affecting food security for two-thirds of the world’s population. Rising atmospheric CO2 influences the terrestrial hydrological cycle through climate-radiative and vegetation-physiological forcings. How these two forcings affect the seasonal intensity and characteristics of monsoonal precipitation and runoff is poorly understood. Here we use four Earth System Models to show that in a CO2-enriched climate, radiative forcing changes drive annual precipitation increases for most monsoon regions. Further, vegetation feedbacks substantially affect annual precipitation in North and South America and Australia monsoon regions. In the dry season, runoff increases over most monsoon regions, due to stomatal closure-driven evapotranspiration reductions and associated atmospheric circulation change. Our results imply that flood risks may amplify in the wet season. However, the lengthening of the monsoon rainfall season and reduced evapotranspiration will shorten the water resources scarcity period for most monsoon regions.

Quantifying the transpiration fraction of evapotranspiration (T/ET) is crucial for understanding plant functionality in ecosystem water cycles, land‐atmosphere interactions, and the global water budget. However, the controls and mechanisms underlying the temporal change of T/ET remain poorly understood in arid and semiarid areas, especially for remote regions with sparse observations such as the Tibetan Plateau (TP). In this study, we used combined high‐frequency laser spectroscopy and chamber methods to constrain estimates of T/ET for an alpine meadow ecosystem in the central TP. The three isotopic end members in ET (δET), soil evaporation (δE), and plant transpiration (δT) were directly determined by three newly customized chambers. Results showed that the seasonal variations of δET, δE, and δT were strongly affected by the precipitation isotope (R2 = 0.53). The δ18O‐based T/ET agreed with that of δ2H. Isotope‐based T/ET ranged from 0.15 to 0.73 during the periods of observation, with an average of 0.43. This mean result was supported by T/ET derived from a two‐source model and eddy covariance observations. Our overarching finding is that at the seasonal timescale, surface soil water content (θ) dominated the change of T/ET, with leaf area index playing only a secondary role. Our study confirms the critical impact of soil water on the temporal change of T/ET in water‐limited regions such as the TP. This knowledge sheds light on diverse land‐surface processes, global hydrological cycles, and their modeling.

RATIONALE Measuring δ18 O and δ2 H values in water using wavelength-scanned cavity ring down spectroscopy (WS-CRDS) requires multiple injections of up to six (and sometimes eight or more) of one sample to remove the memory effect, which decreases the sample throughput and increases the consumables cost. Thus, improved methods for removing the memory effect are required. METHODS We calculated the memory coefficients by sequential WS-CRDS measurement of two lab standard waters with isotopic differences, and used them to establish calibration equations. We then used these equations to correct the measured δ18 O and δ2 H values by removing the memory effect, instead of using multiple injections in the routine daily measurements. RESULTS By using this method, the number of injections per sample was reduced to one. The reproducibility (one standard deviation) of the δ18 O and δ2 H values obtained for quality control sample was less than 0.05‰ and 0.5‰ for an annual average, respectively. CONCLUSIONS By measuring the memory coefficients and establishing the calibration equations, a highly effective method was developed for determining the δ18 O and δ2 H values of water, which could significantly improve sample throughput for liquid water dual isotope measurement without sacrificing the precision.

Understanding the climatic significance of stable isotope in precipitation and ice cores on the Tibetan Plateau (TP) is of critical for the paleoclimate rebuilding. However, there is a gap between the seasonal control of precipitation and long-term isotope record from ice core. Here we present a well-dated ice core isotope record from the middle of the TP (mid-TP). Isotope variations in the past decades from this ice core show strong anti -phase relation with Southern Oscillation Index, confirming unequivocally that the large scale atmospheric circulation through the El Nino Southern Oscillation cycle, rather local climate parameters, controls the interannual signal in ice cores from the mid-TP. Results also show that the cloud top height in the northern Indian Ocean is in association with the interannual variations, confirming the same mechanism controlling the precipitation δ 18 O in southwest Asia and southeast Asia. The study will improve the understanding of the interannual change of Tibetan Plateau ice core isotope signal, and also the hydrological cycle in the southwest Asian region.

Rationale The recent development of isotope ratio infrared spectroscopy (IRIS) was quickly followed by the addition of online extraction and analysis systems, making it faster and easier to measure soil and plant water isotopes. However, memory and sample size effects limit the efficiency and accuracy of these new setups. In response, this study presents a scheme dedicated to estimating and eliminating these two effects. Methods Memory effect was determined by injecting two standard waters alternately. Each standard was injected nine times in a row and analyzed using induction module cavity ring-down spectroscopy (IM-CRDS). Memory coefficients were calculated using a new “multistage jump” algorithm. Sample size effects were evaluated by injecting water volumes ranging from 1 μL to 6 μL. Finally, the influence of cellulose filter paper on the isotopic measurements, the memory, and the sample size effect was evaluated by comparing it with glass filter paper. Results Memory effects were detected for both δ18O and δ2H values, with the latter being stronger. Isotopic differences between replicates of the same plant or soil sample showed a clear decrease after memory correction. A small water volume effect was found only when the injected water volume was larger than 3 μL. However, while the correction method performed well for laboratory-made samples, it did not for field samples, due to the heterogeneity of the isotopic composition of the samples. Stronger memory and water volume effects were found for cellulose filter paper. Conclusions The memory coefficients and the water volume–isotope relationship improved the consistency and accuracy of both laboratory and field data. Our results indicate that cellulose filter paper may not be a suitable medium to measure standard waters and evaluate memory and water volume effects. Finally, a detailed correction and calibration protocol is suggested, along with notes on best practices to obtain good-quality IM-CRDS data. Copyright © 2017 John Wiley & Sons, Ltd.

The global monsoon is characterised by transitions between pronounced dry and wet seasons, affecting food security for two-thirds of the world’s population. Rising atmospheric CO2 influences the terrestrial hydrological cycle through climate-radiative and vegetation-physiological forcings. How these two forcings affect the seasonal intensity and characteristics of monsoonal precipitation and runoff is poorly understood. Here we use four Earth System Models to show that in a CO2-enriched climate, radiative forcing changes drive annual precipitation increases for most monsoon regions. Further, vegetation feedbacks substantially affect annual precipitation in North and South America and Australia monsoon regions. In the dry season, runoff increases over most monsoon regions, due to stomatal closure-driven evapotranspiration reductions and associated atmospheric circulation change. Our results imply that flood risks may amplify in the wet season. However, the lengthening of the monsoon rainfall season and reduced evapotranspiration will shorten the water resources scarcity period for most monsoon regions., Monsoon systems have strong impacts on precipitation and food security over large areas of the world. Here, the authors show that plant responses to rising CO2 concentrations in the atmosphere play a key role in modulating seasonal rainfall and water resources over global land monsoon regions.

The numerous lakes on the Tibetan Plateau (TP) play an important role in the regional hydrological cycle and water resources, but systematic observations of the lake water balance are scarce on the TP. Here we present a detailed study on the water cycle of Cona Lake, at the headwater of Nujiang-Salween River, based on three years (2011-2013) of observations of δ18O and δ2H, including samples from precipitation, upper lake water, and outlet surface water. Short-term atmospheric water vapor was also sampled for isotope analyses. The δ2H-δ18O relationship in lake water (δ2H = 6.67δ18O – 20.37) differed from that of local precipitation (δ2H = 8.29δ18O + 12.50) and the deuterium excess (d-excess) in the lake water (-7.5‰) was significantly lower than in local precipitation (10.7‰), indicating an evaporative isotope enrichment in lake water. The ratio of evaporation to inflow (E/I) of the lake water was calculated using both d-excess and δ18O. The E/I ratios of Cona lake ranged from 0.24 to 0.27 during the three years. Observations of atmospheric water vapor isotopic composition (δA) improved the accuracy in E/I ratio estimate over a simple precipitation equilibrium model, though a correction factor method provided nearly identical estimates of E/I ratio. The work demonstrates the feasibility of d-excess in the study of the water cycle for lakes in other regions of the world and provides recommendations on sampling strategies for accurate calculations of E/I ratio. This article is protected by copyright. All rights reserved.

Water isotopes in precipitation provide new insight on the controlling factors for moisture source variations on the Tibetan Plateau. However, understanding the intra-annual water isotope cycle is difficult for a region lack of winter precipitation. Here, we reported water vapor δ18O and δ2H time series over two and half years at Lhasa on the southern Tibetan Plateau. We compare our values with concurrent daily precipitation isotopes to assess the seasonal controls of vapor isotopes and possible correlation to precipitation isotopes. Results show an intra-seasonal dependence of water vapor δ18O on large scale meteorological regime. During the winter months, vapor water δ18O shows positive dependence on regional-scale temperature, confirming a Rayleigh-distillation controlling moisture transport. During the summer months, lower vapor δ18O is weekly in association with the heavy precipitation over tropical Indian Ocean and on the Tibetan Plateau, and this relation is further enhanced by the evaporation of precipitation at the sampling site. We also found a weak seasonal variation of vapor d-excess, likely resulted from climate seasonality over the large moisture sources region. Moreover, the isotope dataset contains a high-frequency of fluctuations for both δ18O and d-excess lasting several days during the summer monsoon season. These high frequency fluctuations are in phase with precipitation events, confirming significant local evaporation effects on the short-term water cycle, which further complicated the control of near surface water vapor isotopes. These findings improve our regional scale understanding of hydrological cycle on the southern Tibetan Plateau, and will potentially improve our understanding of isotope variations in proxy archives in the Tibetan Plateau.

The recent development of isotope ratio infrared spectroscopy (IRIS) was quickly followed by the addition of online extraction and analysis systems, making it faster and easier to measure soil and plant water isotopes. However, memory and sample size effects limit the efficiency and accuracy of these new setups. In response, this study presents a scheme dedicated to estimating and eliminating these two effects.Memory effect was determined by injecting two standard waters alternately. Each standard was injected nine times in a row and analyzed using induction module cavity ring-down spectroscopy (IM-CRDS). Memory coefficients were calculated using a new "multistage jump" algorithm. Sample size effects were evaluated by injecting water volumes ranging from 1 μL to 6 μL. Finally, the influence of cellulose filter paper on the isotopic measurements, the memory, and the sample size effect was evaluated by comparing it with glass filter paper.Memory effects were detected for both δThe memory coefficients and the water volume-isotope relationship improved the consistency and accuracy of both laboratory and field data. Our results indicate that cellulose filter paper may not be a suitable medium to measure standard waters and evaluate memory and water volume effects. Finally, a detailed correction and calibration protocol is suggested, along with notes on best practices to obtain good-quality IM-CRDS data. Copyright © 2017 John WileySons, Ltd.

The Northern Hemisphere experienced its warmest temperatures in the early 21st century, and this clearly increased glacier melting on the Tibetan Plateau. This study analyzed the glacier change in the area, their terminus positions and surface elevations over the last decade (2003 to 2013) in the Naimona'Nyi region of the western Himalayas, by comparing remote sensing data and differential global position system (dGPS) data from in situ surveys. The results show an accelerating glacier retreat over the past decade in this region. The area covered by glaciers was reduced by a total of 13.2 � 0.0022 km 2 over this period. The terminus of the Naimona'Nyi main glacier studied in the paper retreated by over 191 � 35 m. We also compared the ice cloud and elevation satellite elevation data with in situ measured decimeter accuracy dGPS elevation data, thus providing changes in glacier surface elevations in different periods. The maximum measured glacier thinning rate reached to 0.58 � 0.06 m∕a between 2009 and 2013. In addition to the dependence on elevation and glacier size, we found a larger retreat on the north facing slopes than on the south facing slopes in the region. Meteorological data show that glacier changes within the study area can probably be attributed to the observed rapid temperature rise. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.8.083508)