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My Earth System research program

My research program focuses on four broad, partially-overlapping themes: 1) storage-plant transpiration processes 2) groundwater-stream network interactions 3) climate change-induced changes in land atmospheric coupling 4) land use change-induced changes in residence time and land atmospheric coupling. 
@University of Zurich (July 23 - Present) 
Funding: EU Horizon 2020, Marie Skłodowska-Curie grant (101033274)
Future resiLient forest in a chAnging cliMatE 

Previous studies have attempted to improve the mechanistic understanding of ecosystem response to dry conditions or climate change by focusing either on vegetation water availability or plant physiological adaptation strategies, but the combined effects of shifting terrestrial water availability and atmospheric demand have not been mechanistically investigated. FLAME will use a newly developed high-frequency in-situ measurements of stable water isotopes (18O and 2H) in soil and xylem as a unique natural signature to trace the origin of vegetation water uptake and its residence time in subsurface. It will combine these observations with a high resolution physically based water and vegetation uptake model to track water flow paths and constrain the spatiotemporal heterogeneities in terrestrial ecosystems at the soil-vegetation interface. 

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Related key publications 
  • ​Zweifel et al., Networking the forest infrastructure towards near real-time monitoring – a white paper, Science of the total Environment, 872:162167, 2023.  doi: 10.1016/j.scitotenv.2023.162167. [pdf].
@ ETH Zurich (Sep 20 - Jun 22)

Groundwater - Surface water interactions


River networks are a striking reflection of the processes that shape Earth’s surface, but it is still unclear what mechanisms created these distinctive geometric signatures. Branching angles of river networks tend to be narrower in regions with dry climate and wider in regions with humid climates, but the mechanisms behind this relationship remain unclear. By combining new continental datasets of groundwater well levels, river water levels, and river junction angle across the United States, we reveal the first continental-scale observational evidence on the potential contribution of groundwater to shaping river network branching angles, and thus to the development of large-scale drainage patterns. 

Related key publications 
  • ​Elham Rouholahnejad Freund, Hansjörg Seybold, Scott Jesechko, James W. Kirchner, Groundwater's fingerprint in stream network branching angles, Geophysical Research Letters, 2023, accepted, DOI: 10.1029/2023GL10359.
@ UC Berkeley and University of Freiburg (Jul 18 - Aug 20)
Swiss National Science Foundation, SNSF advanced postdoc mobility grant (P300P2-177713)

Eco-hydrological connectivity and groundwater contribution to transpiration

​Quantitatively partitioning of terrestrial precipitation into evapotranspiration, runoff, soil and other subsurface water storage reservoirs, and groundwater recharge is challenging due to the heterogeneity of the subsurface and the complex patterns of plant water uptake and use. The further partitioning of evapotranspiration into its two components, transpiration and evaporation, is crucial for better understanding eco-hydrological processes and their underlying mechanisms. Several water sources can contribute to plant transpiration, including groundwater, which sustains transpiration in many arid ecosystems. However, groundwater's contribution to plant water uptake is difficult to reliably quantify, yet crucial for understanding how land surface processes and the sensitivity of ecosystems respond to climate change. During my SNSF advanced postdoc mobility fellowship hosted jointly by the group of Prof. Weiler in Freiburg and the group of Prof. Dawson at Berkeley, USA, I studied terrestrial systems’ hydrochemical properties and vegetation water uptake dynamics in forested sites undergoing substantial deforestation. I identified major hydrological shifts, namely increase in stream flow and excessive evaporation fractionation at the deforested sites, associated with change of land cover by tracking isotopic signature of several water sources at the sites. In another study we beech trees reduce their water uptake from the drying topsoil during drought, but don not compensate their water deficit by water uptake from deeper soil layers. 

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Related key publications 
  • Gessler, Arthur, Bächli, Lukas, Rouholahnejad Freund, Elham, Treydte, Kerstin, Schaub, Marcus, Haeni, Matthias, Weiler, Markus, Seeger, Stefan, Marshall, John, Hug, Christian, Zweifel, Roman, Hagedorn, Frank, Rigling, Andreas, Saurer, Matthias, Meusburger, Katrin, Drought reduces water uptake in beech from the drying topsoil, but no compensatory uptake occurs from deeper soil layers, New Phytologist,, 2021. [pdf]. 
  • E. Rouholahnejad Freund, P. Königer, E. Du, T. Link, M. Weiler, The effects of forest canopy change on water uptake dynamics, evidence from stable isotope observations, in prep.
@ University of Ghent, Belgium (Jan 17- Jun 18)
Funding: Swiss National Science Foundation, SNSF early postdoc mobility grant (

Does groundwater regulate our Climate?


Evaporation is a key process in land-climate interactions. While evaporation from ocean surfaces is likely to increase with rising temperatures (because warmer air can hold more water vapor), it is unclear whether evaporation from land surfaces could similarly increase, due to possible limitations imposed by soil moisture content and vegetation physiology.

Observations suggest that groundwater (GW) has an important role in the hydrological budget and soil moisture variability in many regions, providing moisture supply for evaporation during dry seasons. The soil water storage is often underestimated by neglecting the lateral movement of water from topographically higher altitudes to valley bottoms in most land surface models. Modeling studies suggest that GW is often close enough to the surface to interact with atmosphere, and in those cases GW dynamics can enhance soil moisture and evaporation. In this project, I focused on identifying where and when GW is an important source for terrestrial water storage across the globe. I developed a groundwater module for the GLEAM global diagnostic evaporation model. I assimilated GRACE remotely sensed observations of storage into the land surface model, GLEAM, to understand the importance of deeper water storages for terrestrial evaporation at global scale.

Related key publications 
  • E. Rouholahnejad Freund, B. Martens, D. Miralles, Assimilating GRACE observation in GLEAM evaporation model, in prep. 

@ ETH Zurich, (Sep 14 - Dec 16)

Lateral transport and heterogeneity in earth System models

Evapotranspiration (ET) influences land–climate

interactions, regulates the hydrological cycle, and contributes to the Earth’s energy balance. Due to its feedback to largescale hydrological processes and its impact on atmospheric dynamics, ET is one of the drivers of droughts and heatwaves. Existing land surface models differ substantially, both in their estimates of current ET fluxes and in their projections of how ET will evolve in the future. Any bias in estimated ET fluxes will affect the partitioning between sensible and latent heat and thus alter model predictions of temperature and precipitation.

Most earth system models are based on grid-averaged soil columns that do not communicate with one another, and that average over considerable sub-grid heterogeneity in land surface properties, precipitation (P), and potential evapotranspiration (PET).  These models also typically ignore topographically driven lateral redistribution of water (either as groundwater or surface flows), both within and between model grid cells.  Here we present a first attempt to quantify the effects of spatial heterogeneity and lateral redistribution on grid-cell-averaged evapotranspiration (ET) as seen from the atmosphere over heterogeneous landscapes. We show that averaging over sub-grid heterogeneity in P and PET, and overlooking lateral transfers of water in subsurface as typical Earth System Models do, leads to overestimates of average ET.  Our analysis shows that this heterogeneity bias is more pronounced in mountainous terrain, in landscapes where spatial variations in P and PET are inversely correlated, and in regions with temperate climates and dry summers. We also show that this heterogeneity bias increases on average, and expands over larger areas, as the grid cell size increases. 

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Related key publications 
  • Rouholahnejad Freund, M. Zappa, J. W. Kirchner, Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model, Hydrol. Earth Syst. Sci., 24, 5015–5025, 2020. [pdf].
  • E. Rouholahnejad Freund, Y. Fan, J. W. Kirchner, Global assessment of how averaging over heterogeneity of precipitation and potential evapotranspiration affects modeled evapotranspiration rates, Hydrol. Earth Syst. Sci. Discuss.,, 2019 [pdf].

  • Fan, Y., M. Clark, D. M. Lawrence, S. Swenson, L. E. Band, S. L. Brantley, P. D. Brooks, W. E. Dietrich, A. Flores, G. Grant, J. W. Kirchner, D. S. Mackay, J. J. McDonnell, P. C. D. Milly, P. L. Sullivan, C. Tague, H. Ajami, N. Chaney, A. Hartmann, P. Hazenberg, J. McNamara,  J. Pelletier, J. Perket, E. Rouholahnejad‐Freund, T. Wagener, X. Zeng, E. Beighley, J. Buzan, M. Huang, B. Livneh, B. P. Mohanty, B. Nijssen, M. Safeeq, C. Shen, W. van Verseveld, J. Volk, D. Yamazaki, Hillslope hydrology in global change research and Earth system modeling, Water Resources Research, 55, doi:10.1029/2018WR023903, 2019 [pdf].

  • E. Rouholahnejad Freund, J. Kirchner, A Budyko framework for estimating how spatial heterogeneity and lateral moisture redistribution affect average evapotranspiration rates as seen from the atmosphere, HESS, 21, 217-233, 2017 [pdf]. 

@ EAWAG/ETH Zurich (Aug 09 - Jun 14)
GENESIS EU project (Grant  226536)

Hydrology of continental Europe in an era of change

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A combination of driving forces are increasing pressure on local, national, and regional water supplies needed for irrigation, energy production, industrial uses, domestic purposes, and the environment. In many parts of Europe groundwater quantity, and in particular quality, have come under sever degradation and water levels have decreased resulting in negative environmental impacts. Rapid improvements in the economy of the eastern European block of countries and uncertainties with regard to freshwater availability create challenges for water managers. At the same time, climate change adds a new level of uncertainty with regard to freshwater supplies. In this research we build and calibrate an integrated hydrological model of Europe using the Soil and Water Assessment Tool (SWAT) program. The water resources are quantified at subbasin level with monthly time intervals. We also disentangled issues with data availability, calibration of large-scale distributed models, and outline procedures for model calibration and uncertainty analysis. The calibrated model and results provide the basis for further assessment of the impact of climate change on water availability and quality.

Related key publications 
  • K. C. Abbaspour, E. Rouholahnejad, S. Vaghefi, R. Srinivasan, H. Yang, and B. Klöve, European Continent Scale Hydrology and water quality model: Calibration and Uncertainty of a high-resolution large-scale SWAT model, J. of Hydrology, 524, 733–752, 2015 [pdf]. 
@ EAWAG/ETH Zurich (Aug 09 - Jun 14)
enviroGRIDS EU project (Grant  226740)

Water resources of Black Sea basin in a changing climate

The Black Sea Basin (BSB), in particular, suffers from ecological unsustainability and inadequate resource management leading to severe environmental, social, and economical problems. To better tackle the future challenges, we used the Soil and Water Assessment Tool (SWAT) to model the hydrology of the BSB coupling water quantity, water quality, and crop yield components. In this PhD. I assessed the impacts of land use and climate change on water resources of BSB at high spatial and temporal resolution. To attain this goal, the specific objectives of this PhD project were: i) to build a high-resolution hydrologic model of the Basin using the Soil Water Assessment Tool (SWAT), ii) design a parallel processing scheme that makes the calibration of such high-resolution model possible,  iii) analyze the historic spatio-temporal availability of water resources components, mainly blue water flow, green water flow, and green water storage; iv) assess the severity of impacts of land use change on water balance components using historical information, and v) assess the impact of combined climate and land use changes on future water resources of the BSB.


PhD Thesis 
Modeling the hydrology of the Black Sea Basin and assessing the impacts of climate change and land use change on water resources, Elham Rouholahnejad, Diss., Eidgenössische Technische Hochschule ETH Zürich, Nr. 21603, 2013 [pdf].
Related key publications 
  • Rouholahnejad Freund, E., Abbaspour, K. C., Lehmann, A. Water Resources of the Black Sea Catchment under Future Climate and Landuse Change Projections, J. of Water, 9(8), 598, 2017 [pdf].
  • A. Lehmann, Y. Guigoz, N. Ray, E. Mancosu, K. C. Abbaspour, E. Rouholahnejad Freund, K. Allenbach, A. De Bono, M. Fasel, A. Gago da Silva, R. Baer, P. Lacroix, G. Giuliani, A regional platform from past to future land use, climate, demography, hydrology and beaches on the Black Sea catchment, Nature Scientific Data, 4, 170087, 2017 [pdf].
  • R. Bär, E. Rouholahnejad, K. Rahman, K. Abbaspour, A. Lehmann, Climate Change and Agricultural Water Resources: A vulnerability assessment of the Black Sea catchment, Environmental Science and Policy, 46, 57-69, 2015 [pdf].

  • E. Rouholahnejad, K. Abbaspour, R. Srinivasan, V. Bacu, A. Lehmann, Water resources of the Black Sea Basin at high spatial and temporal resolution, WRR, 50 (7), 5866, 2014 [pdf]. 

  • E. Rouholahnejad, K. Abbaspour, M. Vejdani, R. Srinivasan, R. Schulin, A. Lehmann, A parallelization framework for Calibration of hydrological models, Environment Modelling and Software, 31, 28-26, 2012 [pdf].

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