In July 2021, the Taklamakan Desert (TD) experienced an unprecedented rainstorm with daily precipitation exceeding 61.1 mm, triggering mudslides and landslides, highlighting the increasing frequency of extreme precipitation events even in arid regions under global warming. The water vapor sources and transport paths of this rainstorm are still puzzling due to the insufficient representation of physical processes in previous analytical models, leading to possible deviations from reality. Here, using the online Eulerian Weather Research and Forecasting model with water vapor tracer (WRF-WVT), we aim for an improved understanding of water vapor sources of the rainfall event. Results demonstrate that the most important water source for this event is water vapor from local evapotranspiration, contributing to 32.77% of the rainstorm moisture. Water vapor from Upstream Westerlies (28.95%) and East Asian Drylands (28.54%) are transported over the precipitation area by the westerlies owing to the strong lower-level low-pressure system, being the second-most important precipitation source. These sources contribute significantly more than other regions, including the Arabian Sea (5.56%), the Tibetan Plateau (2.16%), and the South Asian Monsoon (0.77%). External moisture sources collectively provide over 65.98% of the precipitation, underscoring their important role. Notably, local evapotranspiration significantly influences precipitation, exceeding the contributions from other individual sources. By comparing with the 2016 precipitation event, it is found that a low-pressure trough extending southward to the west of the TD plays a significant role in the 2021 rainstorm event. The presence of the trough significantly enhances the moisture transport of the westerlies and the upward motion, contributing to the occurrence of extreme precipitation events.

How to cite: Gong, Y. and Yu, H.: The Water Vapor Origin of a Rainstorm Event in the Taklamakan Desert, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2539, https://doi.org/10.5194/egusphere-egu25-2539, 2025.

Global warming is accelerating the global water cycle. However, quantification of the acceleration and regional analyses remain open. Accordingly, in this study we address the fundamental hydrological question: Is the water cycle regionally accelerating/decelerating under global warming? For our investigation we have implemented the age-weighted regional water tagging approach into the Weather Research and Forecasting WRF model, namely WRF-age, to follow the atmospheric water pathways and to derive atmospheric water residence times defined as the age of tagged water since its source. We apply a three-dimensional online budget analysis of the total, tagged, and aged atmospheric water into WRF-age to provide a prognostic equation of the atmospheric water residence times and to derive atmospheric water transit times defined as the age of tagged water since its source originating from a particular physical or dynamical process. The newly developed, physics-based WRF-age model is used to regionally downscale the reanalysis of ERA-Interim and the MPI-ESM Representative Concentration Pathway 8.5 scenario exemplarily for an East Asian monsoon region, i.e., the Poyang Lake basin (the tagged water source area), for historical (1980-1989) and future (2040-2049) times. In the warmer (+1.9 °C for temperature and +2% for evaporation) and drier (-21% for precipitation) future, the residence time for the tagged water vapor will regionally decrease by 1.8 hours (from 14.3 hours) due to enhanced local evaporation contributions, but the transit time for the tagged precipitation will increase by 1.8 hours (from 12.9 hours) partly due to slower fallout of precipitating moisture components. These findings reveal the physical mechanisms behind dry-getting-dryer at regional scales.

How to cite: Wei, J., Arnault, J., Rummler, T., Fersch, B., Zhang, Z., Laux, P., and Kunstmann, H.: Acceleration of the Hydrological Cycle under Global Warming for the Poyang Lake Basin in Southeast China: An Age-Weighted Regional Water Tagging Approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4013, https://doi.org/10.5194/egusphere-egu25-4013, 2025.

Hourly rainfall data from 81 Self Recording Rain Gauge stations were analyzed to study the temporal change of the diurnal cycle of rainfall across India between the two periods: 1969-1991 (past) and 1992-2014 (recent). Except east and northeast (ENE) and west India (WI), majority of the stations showed delayed phase of the diurnal cycle of rainfall in recent period.Both frequency and intensity diurnal cycle contributes to the delayed phase over central India (CI) whereas only the intensity diurnal cycle is responsible for advanced phase over WI. Decrease in the number of heavy rainfall events in the past phase contributes most to the delayed phase in CI while increase in the intensity of heavy rainfall events in the recent phase primarily contributes to the advanced phase over WI. Besides, increase in the number of break days over CI is also responsible its delayed phase. The decrease (increase) in CAPE over WI (CI) is responsible for advanced (delayed) phase.

How to cite: Chutia, T. and Chakraborty, A.: Temporal Evolution of Diurnal Cycle of Rainfall Using Rain Gauge Data Over India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14484, https://doi.org/10.5194/egusphere-egu25-14484, 2025.

Extratropical cyclones are essential for the redistribution of energy, moisture, and momentum from the equator to the poles. Although wintertime extratropical cyclones are relatively well studied, less is known about summertime cyclones. Therefore, this research aims to improve our understanding of how summertime extratropical cyclones in the Northern Atlantic shape the global water cycle. More specifically, we focused on determining the moisture sources of these cyclones and analysed how precipitating air parcels were transported to the cyclone center. Changes in the moisture uptake and transport characteristics during the cyclone life cycle were also evaluated. To this end, 8-day backward trajectories were computed for the 20% most intense storms for three different stages in their life cycle: intensification, time of maximum intensity, and decay. Trajectory calculations were performed for all precipitating air parcels in a 500 km radius surrounding the cyclone center using the Lagrangian analysis tool LAGRANTO. Subsequently, moisture uptakes along the trajectories of only precipitating parcels were identified using the moisture source diagnostic WaterSip. We find that the bulk of the precipitation falls close to the cyclone center and along the fronts, mostly during the intensification phase. The origins of this moisture correspond to areas of high evaporation, with hotspots over the Gulf Stream region and its northeastern extension, and continental sources for cyclones in the Labrador Sea. The source distance is large during intensification, while local evaporation becomes more important during decay. Finally, we discuss the differences between summer and winter, as they have different dependencies on preceding "parent" cyclones for moisture supply.

How to cite: Selten, F., Stoffels, R., Weijenborg, C., and Benedict, I.: Moisture sources and transport pathways of summertime intense extratropical cyclones in the North-Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18111, https://doi.org/10.5194/egusphere-egu25-18111, 2025.

The age of water vapor in the atmosphere is often invoked to explain a well known discrepancy in the change of the hydrologic cycle with global warming. Although moisture increases at a rate of 7% per degree of global warming, precipitation increases only at a rate of 2% per degree of global warming. The difference between these rates can be explained by a 5% increase in water vapor age per degree of global warming. Although this explanation works on a global scale, it does not explain the spatial distribution in the increase of the age, or the dynamical mechanisms which are responsible for this increase in age.

In this project, we demonstrate the potential of a 3D Eulerian age tracking system for the age of water vapor in a simplified atmospheric general circulation model. The age tracking system works by computing the moments of the age distribution, which form a recursive system. The moments themselves exist as passive tracers, so they can be transported with the water vapor using a consistent transport calculation. This method allows us to track the age of water vapor online in any configuration where the model can be run, including both control and climate change simulations. Our intial tests with an aquaplanet model show a relative increase with age with height and towards the poles, with a decrease over the midlatitude eddies and an increase in the updraft of the Hadley cell. Additionally by resolving the standard deviation of the age distribution we can calculate the shape parameter of the distribution (raio of mean to standard deviation), which shows which regions of the atmosphere are affected by transport from a single pathway and which regions are affected by transport from multiple pathways. We further demonstrate the ability of our age tracking system in more realistic model configurations and climate change scenarios. 

How to cite: Fajber, R. and Boulanger, P.: 3D Eulerian Calculation of water vapor age moments for climate change and atmospheric dynamics studies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14470, https://doi.org/10.5194/egusphere-egu25-14470, 2025.

On December 19-21 2018, an atmospheric river hit the French-Italian Concordia station, located at Dome C, East Antarctic Plateau, 3 269 m above sea level. It induced a significant surface warming (+ 15°C in 3 days), combined with high specific humidity (multiplied by 3 in 3 days) and a strong isotopic anomaly in water vapour (+ 15 ‰ for δ¹⁸O). The isotopic composition of water vapour monitored during the event may be explained by (1) the isotopic signature of long-range water transport, and by (2) local moisture uptake during the event. In this study, we use continuous meteorological and isotopic water vapour observations, together with the atmospheric general circulation model LMDZ6iso, to describe this event and to quantify the influence of each of these processes. The presence of mixed-phase clouds during the event induced a significant increase in downward longwave radiative fluxes, which led to high turbulent mixing in the boundary layer. These fluxes are well represented by LMDZ6iso, as are the near-surface temperature and specific humidity. The surface vapour δ¹⁸O is accurately simulated during the event, despite an overestimated amplitude in the diurnal cycle outside of the event. Using this LMDZ6iso simulation, we perform a water vapour mass budget in the boundary layer and we show that the primary driver of the positive δ¹⁸O anomaly in vapour is surface sublimation, which becomes significantly stronger during the event compared to typical diurnal cycles. The second contribution arises from large-scale moisture advection associated with the atmospheric river. Consequently, the isotopic signal monitored in water vapour during this atmospheric river event reflects both long-range moisture advection and interactions between the boundary layer and the snowpack. Only specific meteorological conditions driven by the atmospheric river can explain these strong interactions. Enhancing the representation of local processes in climate models, especially by incorporating isotopic fractionation during sublimation, could substantially improve the simulation of the isotopic signal over Antarctica. Given the importance of air-snow vapour exchanges at the surface and in the atmosphere and their influence on the isotopic composition of surface snow, such simulations could provide valuable insights into how moisture advection events might affect the climate-scale isotope signal in ice cores.

How to cite: Dutrievoz, N., Agosta, C., Landais, A., Davrinche, C., Risi, C., Nguyen, S., Leroy-Dos Santos, C., Ollivier, I., Fourré, E., Berchet, A., and Wille, J.: Water vapour isotope anomalies during an atmospheric river event at Dome C, East Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18530, https://doi.org/10.5194/egusphere-egu25-18530, 2025.

The Amazon region is recognized as one of the world's most significant active convective areas, generating precipitation systems that regulate the climate and weather across the region. Climate projections indicate increased convection over South America, expected to intensify extreme events and amplify their impacts on society. Stable water isotopes are a valuable tool for investigating the formation and evolution of extreme rainfall events in tropical regions. This study presents high-frequency (5-30 minutes) isotope data for rainfall (n=115) and vapor (Picarro Inc., USA L2140i analyzer) from 19 convective events at the ATTO tower site (25/Jan-08/Feb 2024), coupled with various meteorological data (Rain Micro Radar, ATTO tower, Reanalysis, GOES-16). Rainfall and vapor exhibited distinct isotopic signatures with similar temporal trends, with vapor being more depleted in 𝛿¹⁸O (-13.78 to -8.92‰) than rainfall (-6.28 to +1.03‰).  Rainfall events were short-lived (< 1 hour) and associated with lower cloud top temperature (-33ºC to +9°C). The averaged 𝛿¹⁸O variability within (intra-) and between events (intra: -6.28 to -4.03‰, between: -5.13‰ and +1.03‰), suggests a complex interplay of factors influencing precipitation formation. These factors likely include moisture transport, limited vertical development, and the incorporation of forest evapotranspiration. This study provides valuable insights into the intricate relationship between the Amazon rainforest and rainfall formation. The generated knowledge and data can contribute to improving atmospheric models and understanding the potential impacts of climate change on the Amazon's hydroclimatic system.

How to cite: Gastmans, D., Santos, V., Komiya, S., Sánchez-Murillo, R., Jones, S., Santos, Z. C. S., Gomes, R. R., Trumbore, S., Gleixner, G., and Duran-Quesada, A. M.: High-Frequency Isotopic Analysis Unveils the Complexity of Convective Rainfall Dynamics in the Central Amazon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3310, https://doi.org/10.5194/egusphere-egu25-3310, 2025.

Observations on the variability of the isotopic composition of rainfall have been used to understand the effects of climate change, but there is a gap in this type of analysis in tropical regions. Studies in tropical regions are extremely important to assess the influence of meteorological parameters on the isotopic composition of rainfall, as these regions have a unique climate that greatly influences the distribution of rainfall regimes. The aim of this study is to evaluate the historical series of isotopic data from the GNIP station at Rio Claro, located in Southeast region of Brazil, since the climate in this area is directly influenced by a variety of atmospheric systems that impact the variation in isotopic composition of rainfall. This study presents the analysis of a 10-year dataset of daily isotopic precipitation data (δ¹⁸O, δ²H, and d-excess). The isotopic signatures for δ¹⁸O ranged from -21.74‰ to 9.09‰ VSMOW, and for δ²H the variation was from -158.45‰ to 44.9‰ VSMOW, determining the Local Meteoric Water Line (LMWL) of Rio Claro as δ²H = 7.76 * δ¹⁸O + 10.97. The values of the LMWL are close to the Global Meteoric Water Line (GMWL), demonstrating a balance between evaporation and vapor recirculation processes. The rainy season LMWL (δ²H = 7.72 * δ¹⁸O + 10.3) is also close to the LMWL for Rio Claro. However, when considering data from the dry season, which represents 24% of the rainfall data, the LMWL indicates stronger vapor recirculation processes (δ²H = 7.7 * δ¹⁸O + 12.12), caused by rainfall initiated by cold fronts. Trend analysis using the Mann-Kendall test revealed a decreasing trend for δ²H and d-excess, while rainfall showed an increasing trend over the study period. These findings highlight the significance of determining the LMWL for Rio Claro, as it provides a valuable reference for isotopic studies in the region. Moreover, the analysis offers a comprehensive overview of the isotopic dataset, which can be further expanded and refined through the integration of synoptic meteorological data.

How to cite: Soares, A., Gastmans, D., and dos Santos, V.: Long-term isotopic monitoring in Southeast region of Brazil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12038, https://doi.org/10.5194/egusphere-egu25-12038, 2025.

The monsoon system is a dynamic and complex component of the atmospheric water cycle, profoundly impacting weather, climate, and human activities. A variety of meteorological observations are used to understand the monsoon system. The isotopic technique provides a unique perspective on moisture dynamics, enhancing our understanding of the monsoon system. The isotopic signature of precipitation is shaped by numerous geographical and environmental variables, making only select regions suitable for in-depth monsoon isotopic studies. The central Indian region, a pivotal monsoon zone, exhibits distinct characteristics ideal for studying monsoon dynamics. Key features include the passage of the monsoon trough- a modified Intertropical Convergence Zone, and frequent low-pressure systems (LPS) from the northern Bay of Bengal, contributing significantly to summer monsoon rainfall. Notably, rainfall variability in central India shows an out-of-phase relationship with northeastern India. Furthermore, central Indian rainfall strongly correlates with the All-India Summer Monsoon Rainfall, serving as a reliable proxy. Despite its potential, the isotopic technique remains underutilized in this core monsoon zone (CMZ: approximately defined by an area 18-28^oN, 65-88^oE) for monsoon research.

We report a multi-year (2016-2021) precipitation isotopic record obtained from Sagar, a site in the CMZ of India. We explore the relationship between isotopic signatures and regional-scale atmospheric processes mediated by diabatic heating and its vertical distribution pattern, the LPSs, moisture source dynamics, monsoon trough variability, and other meteorological conditions. We also examine the role of recycled rainfall in modulating the precipitation isotopic variability.

We have computed the diabatic heating profiles over India's CMZ. The calculated heating profiles are strongly associated with the monsoon rainfall variability expressed through a precipitation index over the CMZ. We observed a strong association between precipitation isotopic depletion and tropospheric heating. Our analysis reveals that LPSs significantly influence rainfall isotopic values through their origin, trajectory, and intensity. These systems and associated convective activity yield depleted isotopic signatures. A strong inverse relationship exists between LPS intensity and corresponding precipitation isotopic values.

Terrestrial evaporation, leading to substantial recycled rainfall, plays a pivotal role in modulating precipitation isotopic variability. A notable inverse correlation exists between precipitation isotopes and recycled rainfall. The isotopic depletions resulting from diabatic heating, LPSs, and recycled rainfall collectively manifest the amount effect, highlighting a common link among these processes.

The out-of-phase isotopic patterns observed in central and northeastern India mirror the region's dipolar rainfall variability, rendering the CMZ an optimal location for proxy-based reconstructions of past rainfall variability.

How to cite: Chakraborty, S., Trivedi, N., and Trivedi, R.: Isotopic Signatures of Precipitation: Linking Tropospheric and Surface Processes in India's Core Monsoon Zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-736, https://doi.org/10.5194/egusphere-egu25-736, 2025.