The coupled terrestrial-atmospheric water cycle: model development, cross-compartment observations and data assimilation

Understanding the complex interactions of the coupled terrestrial-atmospheric water cycle requires cross-compartment strategies encompassing coupled modeling from the bedrock to the top of the atmosphere, integrated hydro-meteorological observations and datasets, novel data assimilation schemes and multivariable validation approaches. The objective of the session is to create opportunities for interdisciplinary exchange of ideas and experiences among members of the Earth System and hydrology communities. Contributions are invited dealing with the complex interactions between groundwater, surface water, land surface and atmospheric processes with a specific focus on the development, application and validation of novel one-way (both deterministic and ensemble) or fully-coupled hydrometeorological modeling systems for process understanding and predictions and projections across various space- and time scales. This includes also combined dynamical-statistical approaches and studies addressing data assimilation in coupled models. An additional focus is placed on the use of field experiments and testbeds equipped with complex sensors and measurement systems allowing cross-compartment and multivariable validation of these modeling systems.

Co-organized by AS5
Convener: Harald Kunstmann | Co-conveners: Gabriëlle De Lannoy, Martin Drews, Harrie-Jan Hendricks Franssen, Stefan Kollet, Insa Neuweiler, Alfonso Senatore
vPICO presentations
| Fri, 30 Apr, 15:30–17:00 (CEST)

Session assets

Session materials

vPICO presentations: Fri, 30 Apr

Chairpersons: Harrie-Jan Hendricks Franssen, Alfonso Senatore, Gabriëlle De Lannoy
Craig R. Ferguson, Shubhi Agrawal, and Lance F. Bosart

The U.S. Great Plains low-level jet (LLJ) is active on 26% and 62% of May-September days in the northern and southern Plains, respectively. Characterized by a diurnally-oscillating low-level wind maximum below 700 hPa, large vertical wind shear, and enhanced atmospheric moisture convergence, LLJs have been shown to fuel extreme wind- and precipitation generating mesoscale convective systems. Overall, they explain 30-50% of May-September precipitation in the Plains. The considerable societal impacts of LLJs, which span agriculture, severe weather, and wind energy, have long motivated meteorologist-led investigations into their dynamics and predictability. The sensitivity of LLJs to regional soil moisture gradients was established over thirty years ago. However, it was only recently that our work provided the first estimates of the added-value of satellite soil moisture data assimilation (DA) to LLJ forecasts.

In this presentation, we review and expand upon our previous analysis of 75 NASA Unified WRF LLJ case studies simulated with- and without weakly-coupled NASA Soil Moisture Active Passive (SMAP) soil moisture DA. Of the 75-jet cases, 43 are uncoupled LLJs and 32 are coupled LLJs. Their dynamical classification corresponds with the probable efficacy of land data assimilation. Cyclone-induced coupled LLJs, found in the warm sector of frontal systems, are strongly driven by synoptics and less likely to be influenced by land forcing. Conversely, uncoupled LLJs that occur during quiescent conditions of an anticyclonic high pressure ridge system are likely to be more strongly affected by terrain and soil moisture gradient-induced circulations.

It is shown that SMAP DA is generally more effective in uncoupled LLJ cases. However, significant SMAP DA-induced wind speed differences are noted for both LLJ types at their core and exit regions. Notably, the range of SMAP DA-induced wind speed differences between LLJs of the same class (i.e., uncoupled LLJs) is comparable to the range of differences between LLJs of different classes (i.e., coupled vs. uncoupled). Follow-on analyses presented here address the question of what differs between LLJs with small and large SMAP DA effects. Specifically, we explore attribution of event-scale differences in the added-value of SMAP DA to factors including SMAP spatial coverage, antecedent soil moisture, and the strength of synoptic forcing. Finally, a closer look is given to the verification of jet exit region SMAP DA-induced wind speed shifts using Rapid Refresh.

How to cite: Ferguson, C. R., Agrawal, S., and Bosart, L. F.: The importance of satellite soil moisture assimilation for low-level jet forecasts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2862, https://doi.org/10.5194/egusphere-egu21-2862, 2021.

Focus Data Assimilation
Lukas Strebel, Heye Bogena, Harry Vereecken, and Harrie-Jan Hendricks Franssen

Land surface models are important tools to improve our understanding of interacting ecosystem processes, but their predictions are associated with uncertainties related to model forcings, parameters and process simplifications. As high-quality observations become more and more available, they can be used to constrain the uncertainty of land surface model predictions. In this study, we use data assimilation for the fusion of data into the Community Land Model 5.0 (CLM5). CLM5 simulates a broad variety of important land surface processes including moisture and energy partitioning, surface runoff, subsurface runoff, photosynthesis and carbon and nitrogen storage in vegetation and soil. Here, we focus on water movement in soils and related soil hydraulic parameters and assimilate in-situ soil moisture data into CLM5 to improve the estimate of model states and soil hydraulic parameters. To do this, we have coupled the Parallel Data Assimilation Framework (PDAF) with CLM5. This coupling is based on the online variant of PDAF, i.e., data assimilation occurs during simulation runtime in the main memory and not via input/output files. Online coupling requires modification of the model source code, but we aim to keep the modifications to the CLM5 code minimal so that maintenance of the ongoing CLM5 developments remains straightforward. To this end, our approach reuses the existing CLM5 ensemble mode with only necessary adjustments to connect the PDAF parallel communicators. Furthermore, we developed the coupling in the framework of the Terrestrial System Modeling Platform (TSMP). TSMP is a highly modular modeling system for the fully integrated soil-vegetation-atmosphere system. To illustrate the potential of this coupling, we use the ensemble Kalman Filter to perform simultaneous state and parameter updates in a forest headwater catchment.

How to cite: Strebel, L., Bogena, H., Vereecken, H., and Hendricks Franssen, H.-J.: Coupling the Community Land Model 5.0 with the Parallel Data Assimilation Framework, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11805, https://doi.org/10.5194/egusphere-egu21-11805, 2021.

Bernd Schalge, Barbara Haese, Bastian Waldowski, Natascha Brandhorst, Emilio Sanchez, Ching Pui Hung, Shaoning Lv, Lennart Schüler, Harald Kunstmann, Olaf Cirpka, Sabine Attinger, Stefan Kollet, Insa Neuweiler, Harrie-Jan Hendricks Franssen, and Clemens Simmer

We present a data assimilation (DA) system for the atmosphere-land-surface-subsurface system on the catchment scale. The Neckar catchment in SW-Germany served as the specific case where the DA in combination with the coupled atmosphere-land surface-subsurface model TSMP was used. TSMP couples the atmospheric model COSMO, the land-surface model CLM and the hydrological model ParFlow to the DA framework PDAF. We will discuss how the ensemble system is set up in order to work properly and what issues we faced during our initial testing. For the atmosphere we found that it is important to have a good ensemble of lateral forcings as changing internal parameters for various parametrizations does not introduce sufficient variability on its own due to the rather small size of our domain. For the sub-surface the choice of parameters becomes most important and as such parameter estimation will be a valuable tool for improving DA results significantly. Finally, we are showing some first DA results with our system concerning soil moisture with two different assimilation methods with a fully coupled model setup. In the first assimilation scenario in-situ soil moisture data measured by cosmic ray probes are assimilated, while in the second assimilation scenario remotely sensed near surface soil moisture is assimilated. The first results are encouraging and we discuss additional planned simulation scenarios with the fully coupled atmosphere-land surface-subsurface modelling system as well as plans to test strongly coupled DA, where measurements are used to update states across compartments, possibly resulting in additional accuracy gain compared to traditional uncoupled DA.


How to cite: Schalge, B., Haese, B., Waldowski, B., Brandhorst, N., Sanchez, E., Pui Hung, C., Lv, S., Schüler, L., Kunstmann, H., Cirpka, O., Attinger, S., Kollet, S., Neuweiler, I., Hendricks Franssen, H.-J., and Simmer, C.: Building a coupled data assimilation system for the atmosphere, land-surface and subsurface on the catchment scale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7439, https://doi.org/10.5194/egusphere-egu21-7439, 2021.

The Role of Different Sources of Uncertainty in Data Assimilation with Coupled Land Surface - Subsurface Models
Eduardo Emilio Sanchez-Leon, Natascha Brandhorst, Bastian Waldowski, Ching Pui Hung, Insa Neuweiler, Harrie-Jan Hendricks Franssen, and Olaf A. Cirpka
Ching Pui Hung, Bernd Schalge, Gabriele Baroni, Emilio Sanchez, Olaf Cirpka, Stefan Kollet, Insa Neuweiler, Clemens Simmer, and Harrie-Jan Hendricks Franssen

Estimating states and fluxes of the water cycle with terrestrial system models needs a large amount of input data, including soil and vegetation parameters, resulting in large uncertainties in model predictions. Assimilation of pressure head and/or soil moisture data can better constrain states and parameters of a terrestrial system model. Here we assimilate pressure head data and soil moisture data in a terrestrial system model over the Neckar catchment (13928 km2) with a spatial horizontal resolution of 800 m. We use the Terrestrial System Modeling Platform (TSMP), which consists of an atmospheric model component (not used in this work), the Community Land Model version 3.5 (CLM3.5), and the subsurface hydrological model Parflow, coupled by OASIS. TSMP is coupled to the Parallel Data Assimilation Framework (PDAF), which allows the assimilation of land surface and subsurface observations to estimate the model states and parameters. In this work the localized Ensemble Kalman Filter (LEnKF) was used to update hydraulic head, soil moisture and/or saturated hydraulic conductivity by assimilating hydraulic head or in situ soil moisture observations for a period of one year. Ensembles of soil properties, leaf area index and atmospheric forcings were generated. The ensemble of atmospheric forcings considered correlations among four variables, and spatio-temporal correlations of the atmospheric variables using a geostatistical procedure. The characterization of the water table depth and river discharge without data assimilation and for different scenarios of pressure head and soil moisture data assimilation were compared.

How to cite: Hung, C. P., Schalge, B., Baroni, G., Sanchez, E., Cirpka, O., Kollet, S., Neuweiler, I., Simmer, C., and Hendricks Franssen, H.-J.: Estimation of water table, soil states and parameters of integrated subsurface-land surface models by data assimilation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15529, https://doi.org/10.5194/egusphere-egu21-15529, 2021.

Natascha Brandhorst and Insa Neuweiler

Soil moisture is an important variable for land surface processes. To make good model predictions of soil moisture, the flow processes in the subsurface need to be captured well. Flow in the subsurface strongly depends on the soil hydraulic parameters. Information about model parameters is often not available, at least not for the entire domain of interest. The resulting parameter uncertainty needs to be accounted for in the applied model. Data assimilation can account for parameter and model errors as well as for all other possible sources of uncertainty if observations are available that can be used to condition the model states. Thus, the parameter uncertainty might be reduced and model predictions improved. However, including the parameters increases the size of the state vector and thus the computational burden. Especially for large models, this can be a problem. Furthermore, the updates can produce unphysical parameter combinations which in unsaturated zone models often lead to numerical problems.

In this work, we test the effect of updating the soil hydraulic parameters along with soil moisture in a 3D subsurface hillslope model. We use the ensemble Kalman filter for data assimilation and synthetic observations of soil moisture. In a similar study using a 1D unsaturated flow model, parameter updates were found to be the best way to handle parameter uncertainty. Updating parameters resulted in improved predictions of soil moisture, although not necessarily in more realistic model parameters. The parameter updates should rather be considered a method of treating parameter uncertainty than a method for parameter identification. In the 1D settings, updating all uncertain parameters led to the best results. Whether this still holds and is feasible for a more complex 3D model is the question addressed in this presentation.

How to cite: Brandhorst, N. and Neuweiler, I.: Updating the soil hydraulic parameters in a 3D subsurface model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7392, https://doi.org/10.5194/egusphere-egu21-7392, 2021.

Timothy Lahmers, Sujay Kumar, Aubrey Dugger, David Gochis, and Joseph Santanello

In late 2019 widespread wildfires impacted much of the New South Wales province in south east Australia, and this loss of vegetation contributed to increased surface runoff and consequently major flooding caused by extreme rainfall by early 2020. The recently developed NASA LIS/WRF-Hydro system enables the data assimilation (DA) capabilities of the NASA Land Information System (LIS) and the surface hydrological modeling capabilities of the WRF-Hydro model to be combined in a single model architecture. Combining the DA capabilities of the LIS system with WRF-Hydro, which has been used for both research and operational hydrologic simulations, we investigate the impacts of vegetation DA on the simulated floods in several basins across New South Wales, with varying degrees of burn severity from the 2019 fires. We also consider the impacts of the wildfires, as realized through vegetation DA on water partitioning and the surface energy budget, which both have implications for L-A interactions. For DA, we utilize the leaf area index retrievals from MODIS and vegetation optical depth from SMAP. For the present study, we will quantify the impact of the changes to the landscape brought about by the wildfires on hydrologic response, including flood severity, which would not be possible without the DA capabilities of the LIS/WRF-Hydro system.

How to cite: Lahmers, T., Kumar, S., Dugger, A., Gochis, D., and Santanello, J.: Impacts of wildfires on the 2020 floods in southeast Australia: A vegetation data-assimilation case study  using the NASA coupled LIS/WRF-Hydro system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9006, https://doi.org/10.5194/egusphere-egu21-9006, 2021.

Focus Coupled Modeling, Model Development, Feedbacks
Alfonso Senatore, Giorgia Verri, Luca Furnari, Giovanni Coppini, and Giuseppe Mendicino

AdriaClim is a project funded by the Italy-Croatia CBC Programme aimed at improving climate change information and providing monitoring and management tools for adaptation strategies in Adriatic coastal areas. Among the innovative tools planned, an integrated online coupled (Hydro-Meteo-Ocean-Wave-Biogeochemistry) model for the Adriatic Sea will be developed, which will run high-resolution simulations for the present/past time and future newly developed scenarios. The concept behind the integrated model is a comprehensive high-resolution representation of the hydrological cycle at the regional (Adriatic basin) level, overcoming classical approaches partitioning the description of the main physical processes into different compartments (i.e., ocean, atmosphere and terrestrial hydrology) interacting poorly each other and possibly missing crucial feedback, especially for long-term (climate) analyses.

This note presents the coupling approach for the atmospheric-hydrological component, introducing the main features that will be developed and the pilot areas used as test cases. The modelling system will be based on the WRF-Hydro architecture, which provides an extensible, multi-scale and multi-physics modelling capability for land-atmosphere coupling studies. WRF-Hydro modelling system will be applied over the whole Adriatic Basin, encompassing many catchments extending over six countries. A single 6 km-resolution domain will be used concerning atmospheric processes, with a further downscaling until 600 m-resolution for hydrological modelling. The hydrological model will be preliminary calibrated against multiple discharge observations in river sections as close to the rivers' mouths as possible with one full year simulation. Later, climatic simulations will be executed in fully coupled fashion for the historical period 2001-2020 and the future period 2031-2050 using the available EUROCORDEX ensembles as regional climate forcings.

First results of the ongoing activities will be presented, highlighting both the main outcomes in terms of modelling performance and the potential of further coupling to ocean, waves and biogeochemistry modelling components. The complete modelling system will be used for addressing a wide range of issues, including inundation/storm surge, salt wedge intrusion, sediment transport, transport and diffusion of E. coli, deterioration of transitional and coastal waters.

How to cite: Senatore, A., Verri, G., Furnari, L., Coppini, G., and Mendicino, G.: An integrated atmospheric-hydrological model for high-resolution climate projections in the Adriatic Sea basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14026, https://doi.org/10.5194/egusphere-egu21-14026, 2021.

Luca Furnari, Linus Magnusson, Giuseppe Mendicino, and Alfonso Senatore

Mediterranean coastal areas are prone to hydrometeorological extremes. Their complex orography often enhances the severity of high impact events and, at the same time, makes forecasts more challenging, particularly in the medium range. Nevertheless, global operational forecasts significantly improved their accuracy in the last decades, while several novelties in mesoscale modelling are emerging, such as the atmospheric-hydrological fully coupled approach, which explicitly describes the complex interactions between the Planetary Boundary Layer (PBL) and land surface including terrestrial lateral water transport. Overall, several clues open new perspectives to define new standards in medium-range forecast performances in the Mediterranean basin.

This study investigates the skills of the Advanced Research WRF (ARW) mesoscale model both one-way and two-way coupled with the hydrological extension WRF-Hydro in providing a medium-range (7 days) forecast of a severe event hitting the Calabrian peninsula (southern Italy) in November 2019. Such event was simulated in a classical ensemble approach, using the European Center for Medium-Range Weather Forecasting (ECMWF) ensemble product (Ensemble Prediction System – EPS), which consists of 50 members providing the initial and boundary conditions to the mesoscale model. WRF model was applied in two one-way nested domains with 10 km and 2 km horizontal resolutions, encompassing most of the Mediterranean basin. WRF-Hydro was applied in the innermost domain, with NOAH-MP as Land Surface Model. Surface and subsurface routing was performed adopting 200 m as horizontal resolution.

Results highlighted that the fully coupled approach increased soil moisture and latent heat flux from land in an increasing way in the days preceding the event. Such an increase partially affected the lower PBL layers. However, when shoreward moisture transport from surrounding sea rapidly increased becoming the dominant process, only a weak signature of moisture contribution from land to the atmosphere could be detected, resulting in only slightly higher precipitation forecast and slightly increased hydrological response. Overall, the proof-of-concept carried out in this study highlighted a remarkable performance of the medium-range ensemble forecasts, suggesting a profitable use of the fully coupled approach in the selected study area for forecasting purposes in circumstances in which soil moisture dynamics and exchanges with the atmosphere are of particular interest.

How to cite: Furnari, L., Magnusson, L., Mendicino, G., and Senatore, A.: Impact of the atmospheric-hydrological fully coupled approach in a high-resolution medium-range forecasts: a case study in the Mediterranean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10883, https://doi.org/10.5194/egusphere-egu21-10883, 2021.

Mahdad Talebpour, Claire Welty, and Elie Bou-Zeid

Urban areas have distinct features (e.g. impervious surfaces) which modify the energy-water balance at the upper subsurface, lower atmosphere, and over the land surface. Moreover, the atmosphere and groundwater are strongly coupled in places with shallow groundwater. To improve the understanding of urban atmospheric-hydrological processes, their interconnections, and their impacts on other environmental processes, a new fully-coupled urban atmosphere-surface-subsurface hydrometeorological model was developed. The new model brings together WRF-PUCM (Princeton Urban Canopy Model) with ParFlow (a 3D variably saturated groundwater model with an integrated 2D overland flow component) to build WRF-PUCM-PF. The new model and the original non-coupled WRF-PUCM were both applied to a small watershed (10.64 km2) in a heavily urbanized area in the Baltimore metropolitan region as a demonstration test case. To capture atmospheric-hydrological processes at scales closer to urban heterogeneous land cover, models were run at a 90-m horizontal resolution using the LES mode in WRF. The analysis period after the two models were spun up to an identical initial condition spanned 96 hours from July 19 to July 23, 2008. The period was selected as it started with a drydown period for 40 hours followed by several intense rain events. This period allowed evaluation of both models' responses to dry-down and rain events. First the models were run with homogeneous similar hydrogelogic input to isolate the effect of terrestrial hydrology implementations in each model. In response to rain events, the homogeneous WRF-PUCM model output gained and retained a 40% greater amount of soil moisture (area-averaged) compared to the homogeneous WRF-PUCM-PF case. WRF-PUCM performed poorly in lateral distribution of water due to its 1D implementation of subsurface hydrology and lack of overland flow parameterization. The spatial distribution of soil moisture at the end of the simulation in a homogeneous WRF-PUCM model looked similar to the cumulative spatial distribution rain at the end of the simulation with no indication of surface topography impact on soil moisture distribution. On the other hand, lateral movement of water in WRF-PUCM-PF resulted in a more realistic distribution of soil moisture following topography. To further analyze the impact of urban areas, results of WRF-PUCM-PF simulations incorporating heterogeneous subsurface hydrogeology  were compared with WRF-PUCM with its 2D implementation of hydrogeology units for the region. The heterogeneous WRF-PUCM model generated a 10-fold greater area-averaged soil moisture increase compared to the heterogeneous WRF-PUCM-PF case. Influenced by lateral hydrology and impervious surfaces, the heterogeneous WRF-PUCM-PF model output, generated lower latent heat flux, resulting in half of the domain having higher land surface temperatures (2-10 ◦C), compared to the heterogeneous WRF-PUCM model. Overall, the new model provides a tool that can enhance simulation of urban areas by combining ParFlow’s representation of terrestrial hydrology, PUCM’s improved representation of the urban heterogeneous energy and water balance, and incorporation of higher-resolution urban heterogeneous microclimatic variations.

How to cite: Talebpour, M., Welty, C., and Bou-Zeid, E.: A new fully-coupled atmospheric-hydrological model for urban areas: development and testing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6727, https://doi.org/10.5194/egusphere-egu21-6727, 2021.

Jianhui Wei, Joël Arnault, Zhenyu Zhang, Patrick Laux, Benjamin Fersch, Sven Wagner, Ningpeng Dong, Qianya Yang, Chuanguo Yang, Zhongbo Yu, and Harald Kunstmann

Land surface characteristics and processes may have complex interactions with the physical and dynamical processes of the atmosphere. However, adequate methods for systemically understanding individual processes of the nonlinearly coupled land-atmosphere continuum are still rare. Therefore, in this study, the age-weighted evaporation tagging approach of Wei et al. (2016) and the three-dimensional online atmospheric water budget analysis of Arnault et al. (2016) were implemented into the Weather Research and Forecast (WRF) model. In addition to the total and tagged atmospheric water states of matter, the latter approach was further extended for age-weighted tagged atmospheric water states of matter, thereby providing a prognostic equation of the residence time of state variables in the atmospheric water cycle. This extension allows to systematically quantify the fate of evaporated and transpired water in terms of magnitude, location, composition, and residence time. The extended WRF model was tested for a land use and land cover change study for the Poyang Lake basin, the largest freshwater lake in China. Two hypothetical scenarios, i.e., a dried-up lake and a forest restoration scenario, were simulated and then compared to a real-case control simulation using the original land-use data. The results of the basin-scale precipitation recycling in the context of evapotranspiration partitioning and the modified atmospheric water cycle due to both scenarios will be presented and discussed. We conclude that our newly developed modelling framework and the proposed analysis strategy have the potential to be applied for better understanding and quantifying the nonlinearly intertwined processes between the land and the atmosphere.


Arnault, J., Knoche, R., Wei, J., & Kunstmann, H. (2016). Evaporation tagging and atmospheric water budget analysis with WRF: A regional precipitation recycling study for West Africa. Water Resources Research, 52(3), 1544–1567. https://doi.org/10.1002/2015WR017704

Wei, J., Knoche, R., & Kunstmann, H. (2016). Atmospheric residence times from transpiration and evaporation to precipitation: An age-weighted regional evaporation tagging approach. Journal of Geophysical Research: Atmospheres, 121(12), 6841–6862. https://doi.org/10.1002/2015JD024650

How to cite: Wei, J., Arnault, J., Zhang, Z., Laux, P., Fersch, B., Wagner, S., Dong, N., Yang, Q., Yang, C., Yu, Z., and Kunstmann, H.: How is the atmospheric residence time of evapotranspired water altered with a dried-up lake or a forest restoration scenario and what is the impact on precipiation?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7368, https://doi.org/10.5194/egusphere-egu21-7368, 2021.

Carl Hartick, Carina Furusho-Percot, Klaus Goergen, and Stefan Kollet

In the year 2018, Central Europe experienced a meteorological drought and a heatwave, which led to a subsequent evolution of a hydrological drought that is still detectable in subsurface water storage anomalies today. Most likely, the drought also led to significant changes in the energy balance between solar radiation, latent and sensible heat fluxes. In conjunction with water scarcity in the subsurface, these changes may lead to feedbacks that mitigate or enforce drought conditions in the context of land-atmosphere coupling. Understanding these feedbacks is of great interest, especially under various large-scale weather patterns that strongly influence the water and energy budgets over Europe at the interannual time scale. We improve our understanding by applying the Terrestrial Systems Modeling Platform (TSMP) over the 12km resolution pan-European CORDEX model domain simulating the water and energy cycles from the groundwater to the top of the atmosphere. TSMP couples a hydrological, land-surface and atmospheric model, facilitating studies of feedbacks between total water storage anomalies, the energy budget and atmospheric processes. To investigate the feedbacks, we performed TSMP ensemble simulations of three anomalously dry water years (September to August) over Central Europe. The ensembles were initialized with the surface and subsurface states of the end of August of the drought years 2011, 2018 and 2019 from an ERA-Interim driven climatology simulated continuously with TSMP from 1989 to 2019. Every ensemble consists of 22 members, each representing a full subsequent water year, sampled from ERA-Interim reanalysis meteorological boundary conditions from 1996 to 2019, thereby simulating the influence of drought conditions over a wide range of large-scale weather patterns that occurred in Europe since 1996. In addition, to illustrate the potential range of feedbacks we also ran idealized experiments with a completely dry or wet subsurface. The results show that drought conditions may have a significant impact on cloud water and solar radiation at interannual timescales. Effects in winter are negligible, while in summer, an impact of the drought conditions of the previous year on cloud water and solar radiation is detectable in all three ensembles. The results suggest that positive feedbacks between dry subsurface water storage anomalies and atmosphere processes are not negligible and may intensify drought conditions also at the interannual time scale.

How to cite: Hartick, C., Furusho-Percot, C., Goergen, K., and Kollet, S.: Exploring the mechanism behind successive droughts: Intensification of continental droughts due to positive feedbacks between subsurface water storage anomalies and atmospheric process, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8625, https://doi.org/10.5194/egusphere-egu21-8625, 2021.

Yi Yao, Sean Swenson, David Lawrence, Danica Lombardozzi, Inne Vanderkelen, and Wim Thiery

Many observational and modelling studies have highlighted the important role that irrigation plays in the terrestrial hydrological and energy cycle. Land surface models are a key tool to study these interactions, underlining the importance of an accurate representation of irrigation in these models. However, most land surface models either ignore irrigation or represent it in a crude way. Here we improve and evaluate the implementation of irrigation in the Community Terrestrial Systems Model (CTSM), the land component of the Community Earth System Model (CESM). In this improvement, we consider three irrigation techniques (flood, sprinkler and drip), which differ in the amount and way of water applied. By combining global maps of the area equipped for irrigation with the distribution of different irrigation techniques, we represent the transient spatial distribution of irrigation techniques. Subsequently, we evaluate the performance of CTSM with the improved irrigation module. Three experiments are conducted: one with irrigation switched off, the second with the original irrigation module and the third with the improved irrigation module implemented. All three outputs are evaluated against observed or remotely sensed land surface energy fluxes and near-surface climate datasets. We anticipate that the results will reveal how our new irrigation schemes improve or reduce the performance of the land surface model.

How to cite: Yao, Y., Swenson, S., Lawrence, D., Lombardozzi, D., Vanderkelen, I., and Thiery, W.: Evaluation of the new irrigation implementation in CTSM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4253, https://doi.org/10.5194/egusphere-egu21-4253, 2021.

Anthony Schrapffer, Jan Polcher, Anna Sörensson, and Lluis Fita

Floodplains are flat regions close to rivers which are temporarily or permanently flooded. When they are next to large streamflow, their flooding is mainly related to the river overflow and, thus, to the precipitation occurring in the upstream regions. Large floodplains are important for the regional water cycle, the hydrological resources, the ecological services they provide and, when they are located in tropical regions, for their interaction with the atmosphere. Large tropical floodplains exist in the Amazon, the Mississippi, the Congo, the Paraguay and the Nile basins. 

On the one hand, floodplains are regions with scarce ground observations which lead to difficulties to assess the accuracy of the satellite products that limits their calibration. One the other hand, the dynamic of the floodplains is usually not integrated in Land Surface Models and even less in Earth System Models although they may be important for land-atmosphere interactions. There is a need to develop numerical schemes in order to be able to represent the impact of the floodplains on the water cycle. These schemes will also allow us to better understand the hydrological dynamics in these regions. 

The Land Surface component of the IPSL Earth System Model, ORCHIDEE (CMIP6 version) includes a river routing scheme with a floodplains scheme at a resolution of 0.5°. This scheme allows the water from the precipitation over the upstream region to flood and evaporate over the floodplains. Recent developments in ORCHIDEE driven by the need for a higher resolution routing scheme, based on sub-grid hydrological units, allowed us to implement a floodplain scheme which improves the representation of the overbank flow and the spatial distribution of ponded water with respect to the CMIP6 version of ORCHIDEE. 

This study focuses on the Pantanal region which is the world’s largest tropical floodplains and is located in the La Plata Basin, in the Upper Paraguay River (South America). ORCHIDEE’s sensitivity to the activation of floodplain schemes has been assessed through simulations performed at various resolutions. These simulations have shown the importance of representing floodplains to simulate the water cycle in the area. Combining these simulations and observations, we estimated the evapotranspiration loss by models when the floodplains scheme is deactivated to 90 mm/year over the Pantanal. The higher resolution scheme shows realistic simulations of the river discharge over the floodplains and is expected to improve the spatial distribution of the flooded area and, thus, the representation of evapotranspiration.

How to cite: Schrapffer, A., Polcher, J., Sörensson, A., and Fita, L.: Floodplains representation in Land Surface Model : toward higher resolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9735, https://doi.org/10.5194/egusphere-egu21-9735, 2021.

Inne Vanderkelen, Nicole P. M. van Lipzig, William J. Sacks, David M. Lawrence, Martyn Clark, Naoki Mizukami, Yadu Pokhrel, and Wim Thiery

By now, humans have constructed more than 45 000 large reservoirs across the globe, increasing the global lake area with 8%. These reservoirs have large impacts on freshwater processes and resources by impounding continental runoff and altering river flows. So far, the impact of reservoirs on the climate remains largely unknown, as they are typically not represented in current Earth System Models (ESMs). This is remarkable, as two-way interactions between reservoirs and climate are likely to alter hydrological extremes and impact future water availability.

Here we present the implementation of the role of reservoirs in the Community Terrestrial Systems Model (CTSM), a land surface model, by accounting for the increase in open water surfaces due to reservoir construction throughout the 20th century. To this end, we allow lake area to expand in the model, while ensuring that the surface energy and mass balances remain closed. We use reservoir and lake extent  from the state-of-the-art Global Reservoir and Dams (GRanD) and HydroLAKES data sets.

By conducting both land-only and coupled simulations with CTSM and the Community Earth System Model (CESM), we assess the added value of accounting for reservoir expansion in the land surface model performance and investigate their impacts on the mean climate and extremes. Globally, the effect of reservoirs on temperatures and the surface energy balance is small, but  responses can be substantial locally, in particular for grid cells where reservoirs make up a large fraction. Our results show that reservoirs reduce temperature extremes and moderate the seasonal temperature cycle, by up to -1.5 K (for reservoirs covering > 15% of the grid cell).

This study is an important step towards incorporating human water management in ESMs.


How to cite: Vanderkelen, I., van Lipzig, N. P. M., Sacks, W. J., Lawrence, D. M., Clark, M., Mizukami, N., Pokhrel, Y., and Thiery, W.: The impact of global reservoir expansion on the present-day climate  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-723, https://doi.org/10.5194/egusphere-egu21-723, 2021.

Focus Tracers and Isotopes
Christopher Diekmann, Matthias Schneider, Franziska Aemisegger, Fabienne Dahinden, Benjamin Ertl, Frank Hase, Farahnaz Khosrawi, Stephan Pfahl, Andries de Vries, Heini Wernli, Peter Knippertz, and Peter Braesicke

Three-dimensional distributions of atmospheric moisture with high spatial and temporal variability arise from the complex interaction of the various branches in the hydrological cycle. By studying abundances of stable water isotopes, one can retrieve fundamental information about the physical processes acting in these branches. Differences in the molecular structure lead to characteristic responses of each water isotope to phase change processes, which reflects on characteristic ratios of water isotopes in different branches of the hydrological cycle.

In this study, we use tropospheric distributions of H2O and HDO (denoted as δD) to identify dominant processes in the hydrological cycle during the wet phase of the West African Monsoon in boreal summer. Here, large gradients in water vapor, strong convective activity and continental recycling lead to high variability of tropospheric moisture and its isotopic composition. This complexity makes a direct attribution of observed water vapor signals to underlying processes challenging.

To address this challenge, we use remotely sensed {H2O, δD} – pair data retrieved from spectra of the thermal infrared satellite sensor IASI, which are available daily and globally from October 2014 to June 2019. For an improved understanding of the IASI data, we add high-resolution model data from the regional isotope-enabled model COSMO-iso and generate Lagrangian backward trajectories for the Sahelian troposphere. This provides valuable insights into geometrical and moisture pathways along the history of Sahelian air masses that were observed from IASI. Further, after applying a retrieval simulator on the COSMO-iso data, we can conduct direct satellite-to-model comparisons.
By drawing these datasets together, we document and analyze the characteristic variability of the {H2O, δD} – pairs for the Sahelian troposphere on interannual, seasonal and convective scales. We identify distinct effects on {H2O, δD} – pairs of (1) synoptic-scale and boundary air mass mixing, (2) rain condensation during convection and (3) partial evaporation and isotope equilibration of rain drops during convection.

This study reveals the potential of using MUSICA IASI {H2O, δD} – pair data together with high-resolution modeling for investigating the tropospheric hydrological cycle. This approach is promising for understanding the relative importance of large-scale dynamics against microphysical phase transitions during convection on the tropical moisture distribution.

How to cite: Diekmann, C., Schneider, M., Aemisegger, F., Dahinden, F., Ertl, B., Hase, F., Khosrawi, F., Pfahl, S., de Vries, A., Wernli, H., Knippertz, P., and Braesicke, P.: Analysis of stable water isotopes in tropospheric moisture during the West African Monsoon, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10121, https://doi.org/10.5194/egusphere-egu21-10121, 2021.

Joel Arnault, Gerlinde Jung, Barbara Haese, Benjamin Fersch, Thomas Rummler, Jianhui Wei, Zhenyu Zhang, and Harald Kunstmann

Water isotopologues, as natural tracers of the hydrological cycle on Earth, provide a unique way to assess the skill of climate models in representing realistic atmospheric and terrestrial water pathways. In the last decades, many global and regional models have been developed to represent water isotopologues and enable a direct comparison with observed isotopic concentrations. This study presents the recently developed regional model, WRF-Hydro-iso, which is a version of the coupled atmospheric – hydrological modeling system WRF-Hydro enhanced with a joint soil-vegetation-atmospheric description of water isotopologues motions. WRF-Hydro-iso is applied to two regions in Europe and Southern Africa under present climate condition. The setup includes an outer domain with a 10 km grid-spacing, an inner domain with a 5 km grid-spacing, and a subdomain with a 500 m grid spacing that can be coupled with the inner domain in order to represent lateral terrestrial water flow. A 10-year slice is simulated for 2003-2012, using ERA5 reanalyses for the boundary condition. The boundary condition of the isotopic variables is specifically provided with climatological values deduced from a 10-year simulation with the Community Earth System Model Version 1. For both Europe and Southern Africa, WRF-Hydro-iso realistically reproduces the climatological variations of the isotopic concentrations δP18O and δP2H from the Global Network of Isotopes in Precipitation. In a sensitivity analysis, it is found that land surface evaporation fractionation increases the isotopic concentrations in the rootzone soil moisture and slightly decreases the isotopic concentrations in precipitation, an effect that is modulated by the change in evaporation – transpiration partitioning caused by lateral terrestrial water flow. The ability of WRF-Hydro-iso to account for a detailed description of terrestrial water transport makes it as a good candidate for the dynamical downscaling of global paleoclimate simulations and for the comparison to isotopic measurements in proxy data such as plant wax fossils.

How to cite: Arnault, J., Jung, G., Haese, B., Fersch, B., Rummler, T., Wei, J., Zhang, Z., and Kunstmann, H.: A joint soil-vegetation-atmospheric modeling procedure of water isotopologues with WRF-Hydro-iso: Implementation and application to present-day climate in Europe and Southern Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2759, https://doi.org/10.5194/egusphere-egu21-2759, 2021.

Alain Zuber, Wolfgang Stremme, Adolfo Magaldi, Michel Grutter, Caludia Rivera, Alejandro Bezanilla, Noemie Taquet, Thomas Blumenstock, Frank Hase, and Matthias Schneider

Knowledge about water vapor isotopologues is a useful tool in the study of the hydrological cycle. Total columns of water vapor isotopologues (H216O, H218O and HD16O) are measured by ground-based solar absorption FTIR spectroscopy at Altzomoni (3985 m.a.s.l, 19.12ºN, 98.66ºW), a high altitude subtropical remote background site in central Mexico (Barthlott et al., 2017). In the contribution we present the time series of the isotopic composition of water vapor columns and profiles above central Mexico and analyze differences in the isotopic ratios of H216O, H218O and HD16O between the rain and dry seasons of the year: in the rain season, changes in the isotopic ratios might be dominated by the diurnal cycle, which correlates with the relative humidity, temperature and dew point, while isotopic ratio in the dry season might depend more on the origin of the air parcels and transportation. We discuss the hydrological cycle in central Mexico using the relationship between light and heavy isotopes, and how this relationship gives valuable information about the pathways, sources and transport.

How to cite: Zuber, A., Stremme, W., Magaldi, A., Grutter, M., Rivera, C., Bezanilla, A., Taquet, N., Blumenstock, T., Hase, F., and Schneider, M.: Water vapor isotopologues (H216O, H218O and HD16O) by ground-based FTIR spectroscopy in central Mexico, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13433, https://doi.org/10.5194/egusphere-egu21-13433, 2021.

Sakina Takache, Thomas Dubos, and Sylvain Mailler

The distribution of tracers in the atmosphere results from the presence and emission of gaseous and particulate matter, as well as their transport, sedimentation and (photo-)chemical transformations. Understanding and quantifying these processes in the atmosphere can be addressed through the use of global-scale or regional-scale chemistry-transport numerical models such as CHIMERE (Mailler et al., 2016).

 While possible in principle, it is impractical to use this model to represent long-range transport of dense plumes of gas and aerosols, resulting for instance from massive emissions by volcanic eruptions, forest fires and desertic aerosol tempests. Indeed such studies requiring both large domains and high resolution have a prohibitive numerical cost due to the formulation of CHIMERE on a regular Cartesian mesh. This limitation is shared by all currently operational chemistry-transport models. Additionally, traditional Cartesian meshes pose a numerical singularity at the poles, where the longitude lines converge.

 These limitations may be lifted by replacing CHIMERE’s Cartesian mesh by a fully unstructured mesh. This would allow modelers to vary resolution in space, and hence to focus computational resources in key regions with sharp variations (e.g. volcanic eruptions) where high spatial and temporal resolution is required.

 As a first step in this direction, we compare the numerical performance of transport schemes formulated on Cartesian meshes and schemes formulated on unstructured meshes (Dubey et al., 2015). To focus on differences due to numerics, the unstructured mesh is a quasi-uniform icosahedral mesh such as the one used by global dynamical core DYNAMICO (Dubos et al., 2015). Spatial and temporal coupled and de-coupled schemes of various order are implemented in each mesh framework. A suite of test cases is used to evaluate different properties of the mesh-scheme pairings.To avoid the Cartesian pole singularity, the Cartesian mesh covers a limited domain excluding the poles. Analytical wind fields adapted to this limited domain are used. Metrics are evaluated using the quantities obtained in the simulations, such as convergence using root mean square errors, shape preservation using non-linear tracer relations, and diffusion using total entropy. The stability and monotonicity of the used schemes are also numerically validated.

 We find that a scheme of the Van Leer family on the unstructured mesh has a performance slightly inferior to a similar scheme on a Cartesian mesh. However, since this loss in quality remains moderate, it should be possible to more than compensate for it with a variable resolution. We are currently investigating this question and will present variable-resolution results if this ongoing work is timely completed. If successful, fully unstructured meshes would be a significant step forward in the modeling of scale interactions in atmospheric chemistry, and would potentially allow breakthrough for the understanding of such interactions.

How to cite: Takache, S., Dubos, T., and Mailler, S.: 2D tracer transport on Cartesian and icosahedral grids: scheme comparisons for idealized test cases, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15082, https://doi.org/10.5194/egusphere-egu21-15082, 2021.