• The stable isotopes and water origins were investigated in the vicinity of Japan. • The effect of cyclone route on the stable isotopes and water origins was clarified. • The Sea of Japan cyclone induced higher δ 2 H and d-excess in the Pacific Ocean. • The Pacific cyclone caused lower δ 2 H and d-excess in the Pacific Ocean. • Results have implications for hydrological and paleoclimate studies using δ values. Isotopic composition and their corresponding moisture sources of precipitation are important for understanding water cycles and reconstructing paleoclimate. To clarify the isotopic composition and water origins, we sampled precipitation diurnally at Sapporo, Northern Japan, and simulated the isotopic composition and moisture sources by using an isotopic regional spectral model for the 2014/2015 winter period. During the period, ten intensified extratropical cyclones, approached Northern Japan, were classified as Sea of Japan cyclone and Pacific cyclone according to the cyclone route. For precipitation at Sapporo, the Sea of Japan cyclone induced higher δ 2 H with more moisture from the Kuroshio region, whereas the Pacific cyclone triggered precipitation to Sapporo with lower δ 2 H and more moisture from the North Pacific Ocean. Regarding moisture transport within the extratropical cyclone frontal system for both cyclone types, moisture transported by the warm conveyor belt from the Kuroshio region mainly condensed in the cold and eastern warm fronts with high δ 2 H and d-excess, resulting from a high sea surface temperature and low humidity during evaporation; in contrast, vapors transported by the cold conveyor belt from the North Pacific Ocean precipitated in the western warm front and cyclone center with low δ 2 H and d-excess, arising from a low sea surface temperature and high humidity. With respect to the cyclone route effect on the geographical distribution of isotopic characteristics around Japan, when the Sea of Japan cyclone occurred, condensation in the Pacific Ocean showed higher δ 2 H and d-excess with more moisture from the Kuroshio via the warm conveyor belt. In contrast, during passage of the Pacific cyclone, condensation in the Pacific Ocean exhibited lower δ 2 H and d-excess with more vapors from the North Pacific Ocean via the cold conveyor belt. These phenomena observed around Japan could be applied in other midlatitude regions and for hydrological, biogeochemical, and paleoclimate studies. 

Isotopic composition and moisture sources of precipitation in midlatitude regions characterized by extratropical cyclones’ route

Abstract This study explores the spatiotemporal characteristics of Global Navigation Satellite System (GNSS) Precipitable Water Vapor (PWV) and its relationship with the Meiyu process. Using multiple sources of atmospheric PWV data and meteorological information, the study quantitatively analyzes PWV's spatiotemporal characteristics and its association with the onset and withdrawal of the Meiyu season. The research findings are as follows: (1)PWV's spatiotemporal evolution provides indications for the Meiyu season. The daily variation of water vapor content generally follows a camelback shape. Before the Meiyu season begins, PWV exhibits an upward trend with content below 40mm. After the onset of the Meiyu season, PWV gradually accumulates during the early Meiyu season with content exceeding 50mm, accompanied by rainfall. In the late Meiyu season, water vapor releases, leading to a decrease in PWV content. After the Meiyu season ends, PWV gradually declines but remains relatively high, linked to moisture transport during the Jianghuai flood season. (2)Anomaly analysis reveals that water vapor activity is highest during the Meiyu season, showing good correspondence with special Meiyu years. This provides new insights for monitoring and forecasting abnormal Meiyu events. (3)Spatially, PWV distribution during the Meiyu season exhibits a pattern of more water vapor in southern regions and less in northern areas. This pattern is influenced by the stronger atmospheric water storage capacity in low-latitude areas and the gradual weakening of monsoon water vapor during northward and westward transport. 

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Response of Meiyu Process Considering the Temporal and Spatial Characteristics of GNSS PWV

An inland river grassland basin is a fragile ecosystem, and precipitation is of great significance to its resilience. However, the knowledge of where precipitation-forming water vapor originated is not well understood, limiting the predictability of future precipitation provided climate change. The objective of this study was to characterize the hydrogen (δD) and oxygen (δ18O) isotopes and hydro-chemical compositions of precipitation as well as decipher atmospheric water vapor sources in a typical Eurasian steppe river basin. In this regard, this study collected 59 water samples from 44 storm events in 2019 and 2020. The samples were analyzed in our laboratory for ions, δD, and δ18O, which in turn were used to examine the stable isotopic features, hydro-chemical characteristics, and water vapor transport at different temporal scales by a backward trajectory model and correlation and redundancy analyses. The results showed negative δD and δ18O during the wet season with a trend of positive deuterium excess, indicating that precipitation effect was significant. In comparison with a linear model of global meteoric water levels, the local meteoric water lines had smaller slopes and intercepts, with a maximum slope in August and a minimum slope in July. In addition, HCO3− and Ca2+ were the primary hydro-chemical ions in precipitation. Ca2+ and Mg2+ were significantly correlated with HCO3− and Na+, indicating that they shared terrestrial and marine sources. NH4+ originated mainly from human activities and chemical reactions, whereas K+ originated primarily from continental and marine processes. Further, the atmospheric water vapor was mainly transported from the northeast, northwest, and southeast directions into the study basin, as affected by the westerly wind circulation, the East Asian summer monsoon, northeast anticyclone circulation, and local evapotranspiration. Moreover, the water vapor was from both onsite and offsite sources: over 40% from Eurasia, 10 to 25% from the Arctic Ocean, and 35 to 45% from the Pacific Ocean. 

Isotopes-Based Characterization of Precipitation Compositions and Atmospheric Water Vapor Sources Over Typical Eurasian Steppes in South Mongolian Plateau

Moisture sources and isotopic composition of a record-breaking heavy Meiyu-Baiu rainfall in southwestern Japan in early July 2020

Paleoclimatic records in the East Asian monsoon region (EAM) depend on precipitation isotopes as proxies for past hydroclimatic variability. However, the potential mechanisms controlling precipitation isotopic variability in this region remain poorly understood. This study collected daily precipitation isotopes in the middle-lower reaches of the Yangtze River Basin from 2017 to 2020 to explore how convective behaviors and moisture sources determining the variability of precipitation stable isotopes. Daily precipitation δ18O presented a weak inverse relationship with local precipitation amount and air temperature. Results of correlation analysis showed that the maximum correlation zones of precipitation δ18O between different cloud levels and outgoing long wave radiation were identified in the upstream regions such as the Indian Peninsula, BoB, and Indo-China Peninsula during the rainy season. Back-trajectory analysis showed that substantial water vapor from maritine sources in the Indian Ocean and the Bay of Bengal (BoB) largely contributed to the lower δ18O values during the rainy season (-7.5 ‰) because of intense rainout processes in the upstream sourced regions, demonstrated by significant regional correlation between precipitation δ18O and regional precipitation amount. The regional correlations were stronger in the upstream regions than the local influences, indicating that precipitation isotopes in this region are more influenced by regional convective processes in the upstream region during the rainy season. Using the modified Stewart model, the mean subcloud evaporation fraction estimated was greater in rainy season (24.1 % vs 36.1 % for HK and HZ, respectively) than that in dry season (15.1 % vs 19.9 % for HK and HZ, respectively). These findings highlight the importance of upstream processes in controlling precipitation isotopes in the EAM region and provide reliable evidence on the interpretation of monsoonal climate variability. 

Atmospheric processes control the stable isotopic variability of precipitation in the middle–lower reaches of the Yangtze River Basin, East Asian monsoon region

In this study, the stable isotopic compositions (δ18O, δ2H and d-excess) in daily precipitation from October 2017 to May 2020 in the lower reach of the Yangtze River (LYR) were examined to understand the relationship between stable isotopic compositions in precipitation and synoptic atmospheric circulation patterns (SACPs). Atmospheric circulations over the LYR were classified into seven patterns according to the Kirchhofer method with three, one and three SACPs in the East Asian winter monsoon period (EAWM), the monsoon transition period and the East Asian summer monsoon period (EASM), respectively. Precipitation events between most SACPs are distinguishable for either δ18O or d-excess, except for two SACPs in the EAWM, and two SACPs in the EASM. Local meteorological variables are primary factors determining the variation of isotopic compositions in precipitation for three SACPs in the EAWM. Though the precipitation-producing air masses come from different seas under two different SACPs in the EASM, i.e., the South China Sea for one and the western Pacific for the other, neither δ18O nor d-excess is distinguishable. Nevertheless, the relationships between isotopic composition and meteorological variables appear to be distinguishable between these two SACPs. The SACP dominant in the monsoon transition tends to have higher δ18O (mean value) and δ2H (mean value) in precipitation than all other SACPs. The d-excess in precipitation of this SACP is more likely altered by subcloud evaporation, and the retrieval of moisture source d-excess information should be treated with cautions. Similarly, d-excess in Meiyu rain, classified in one of the SACPs in the EASM period, is very likely altered by moisture recycling along the atmospheric moisture transport pathway, evident from the significant negative relationship between d-excess in precipitation and mean specific humidity along the backward trajectories. Thus d-exess of Meiyu rain is very likely positively deviated from its oceanic moisture source. Overall, the findings can provide valuable insights for understanding the relationship between stable isotopes in precipitation and SACPs in the East Asian monsoon region. 

Relationship between precipitation isotopic compositions and synoptic atmospheric circulation patterns in the lower reach of the Yangtze River

&amp;lt;p&amp;gt;Climate change has a significant impact on the environment by increasing the frequency of extreme precipitation events. Underestimating the potential risks of such events and lack of climate resilience will result in a substantial crisis in terms of water security. Understanding the hydrological consequences is difficult due to complexities and additional environmental feedbacks, depending on landuse/landcover, soil and climate.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Gravity Recovery and Climate Experiment (GRACE) has provided an unprecedented perspective on global fluctuations in terrestrial water storage (TWS) over the past decade. While numerous studies have correlated different hydrological variables against TWS, no study has tested different rainfall thresholds (intensity) impacting TWS. Existing studies mostly have explored the relationship between TWS anomalies and hydrological variables using individual responses, while few have looked at multi-variable interaction. Single indicators (e.g., standardized precipitation index) may limit ecohydrological understanding of soil-vegetation-atmosphere water transfer, as many factors play essential roles in land-atmosphere interactions. In particular, rainfall characteristics can significantly impact the interaction between hydrological factors by accelerating or slowing processes. Hence, including appropriate temporal resolution of precipitation in analyses is essential; e.g., monthly data are not a good indicator for understanding ecohydrological interactions. Therefore, this research aims to improve our understanding of the spatiotemporal response of TWS to climate change impacts on rainfall characteristics. Monthly GRACE TWS time series anomalies are analyzed against aggregated monthly rainfall with different daily thresholds (intensities). The obtained results are used to find explanatory variables such as land use/land cover, soil type, and climatic zones that determine the significance between TWS and various variables. The methodology provides a valuable insight into the mechanisms in which TWS is affected by rainfall characteristics at different spatiotemporal scales across various hydrological contexts across Australia.&amp;lt;/p&amp;gt; 

Impact of rainfall intensity on GRACE total water storage across Australia

&amp;lt;p&amp;gt;Since the first stoma appeared about 400 million years ago, moisture exchange between lands and the atmosphere extends into the root zone. However, due to its invisibility from the surface, root distribution and its temporal variation are difficult to estimate, which greatly hinders investigation of root zone moisture dynamics, soil-plant water relations, and transpiration modelling. Plant water potential reflects dynamic water condition in vegetation, which is determined by moisture supply in the root zone, atmospheric demand, and plant physiological control. Thus, dynamic water potential can provide a &amp;amp;#8220;periscope&amp;amp;#8221; to observe root zone hydraulic conditions. Based on this hydraulic connection in the soil-plant-atmosphere continuum (SPAC), plant individuals work very likely as &amp;amp;#8220;observation wells&amp;amp;#8221; to the whole root zone at predawn, and as &amp;amp;#8220;pumping test wells&amp;amp;#8221; in daytime. Meanwhile, stable isotopic composition of water in plant xylem approximately reflects the isotopic signature of bulk root accessible moisture. These hydraulic and isotopic root-zone periscopes provide information to estimate root-zone and plant hydraulic states and their dynamics, and hydraulic properties. In this presentation, we will show how this root-zone periscope concept, based on continuous monitoring of plant water potential, sapflow, and/or isotopic composition of xylem water, has been successfully applied in SPAC model development, root water uptake model improvement, transpiration model parameterisation, as well as investigation of ecohydrological separation.&amp;lt;/p&amp;gt; 

Tin Agustina Karnawati

Papers

Relationship between precipitation isotopic compositions and synoptic atmospheric circulation patterns in the lower reach of the Yangtze River

Impact of rainfall intensity on GRACE total water storage across Australia

Root-zone &#8220;Periscope&#8221; and its applications for investigating plant-soil water relations and transpiration modelling&#160;

Tin Agustina Karnawati

Papers

Relationship between precipitation isotopic compositions and synoptic atmospheric circulation patterns in the lower reach of the Yangtze River

Impact of rainfall intensity on GRACE total water storage across Australia

Root-zone &amp;#8220;Periscope&amp;#8221; and its applications for investigating plant-soil water relations and transpiration modelling&amp;#160;

Root-zone “Periscope” and its applications for investigating plant-soil water relations and transpiration modelling 