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Elham Rouholahnejad Freund
Laboratory of Hydrology and Water Management, Ghent University, Ghent, Belgium

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Preprint content
Published: 04 March 2021
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Land surface models are highly uncertain in estimating evapotranspiration (ET) fluxes, and differ substantially in their projections of how ET will evolve in the future. Biases in estimated ET fluxes will affect the partitioning between sensible and latent heat, and thus alter simulated temperatures and model predictions of droughts and heatwaves. One potential source of bias is the "aggregation bias" that arises whenever nonlinear processes, such as those that regulate ET fluxes, are modeled using averages of heterogeneous inputs. Here we demonstrate that this aggregation bias leads to substantial overestimates in ET fluxes in a typical large-scale land surface model. The proposed methodology can be used to correct for aggregation biases in ET estimates by quantifying the effects of finer-resolution spatiotemporal variability in ET drivers at each modeling time step, without explicitly representing sub-grid heterogeneities in large-scale land surface models. 

ACS Style

Elham Rouholahnejad Freund; Massimiliano Zappa; Kirchner James. Aggregating over land surface heterogeneity systematically biases evapotranspiration estimates in large-scale evaporation models. 2021, 1 .

AMA Style

Elham Rouholahnejad Freund, Massimiliano Zappa, Kirchner James. Aggregating over land surface heterogeneity systematically biases evapotranspiration estimates in large-scale evaporation models. . 2021; ():1.

Chicago/Turabian Style

Elham Rouholahnejad Freund; Massimiliano Zappa; Kirchner James. 2021. "Aggregating over land surface heterogeneity systematically biases evapotranspiration estimates in large-scale evaporation models." , no. : 1.

Journal article
Published: 28 October 2020 in Hydrology and Earth System Sciences
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Evapotranspiration (ET) influences land–climate interactions, regulates the hydrological cycle, and contributes to the Earth's energy balance. Due to its feedback to large-scale 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. One potential source of bias is the so-called “aggregation bias” that arises whenever nonlinear processes, such as those that regulate ET fluxes, are modeled using averages of heterogeneous inputs. Here we demonstrate a general mathematical approach to quantifying and correcting for this aggregation bias, using the GLEAM land evaporation model as a relatively simple example. We demonstrate that this aggregation bias can lead to substantial overestimates in ET fluxes in a typical large-scale land surface model when sub-grid heterogeneities in land surface properties are averaged out. Using Switzerland as a test case, we examine the scale dependence of this aggregation bias and show that it can lead to an average overestimation of daily ET fluxes by as much as 10 % across the whole country (calculated as the median of the daily bias over the growing season). We show how our approach can be used to identify the dominant drivers of aggregation bias and to estimate sub-grid closure relationships that can correct for aggregation biases in ET estimates, without explicitly representing sub-grid heterogeneities in large-scale land surface models.

ACS Style

Elham Rouholahnejad Freund; Massimiliano Zappa; James W. Kirchner. Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model. Hydrology and Earth System Sciences 2020, 24, 5015 -5025.

AMA Style

Elham Rouholahnejad Freund, Massimiliano Zappa, James W. Kirchner. Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model. Hydrology and Earth System Sciences. 2020; 24 (10):5015-5025.

Chicago/Turabian Style

Elham Rouholahnejad Freund; Massimiliano Zappa; James W. Kirchner. 2020. "Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model." Hydrology and Earth System Sciences 24, no. 10: 5015-5025.

Journal article
Published: 16 April 2020 in Hydrology and Earth System Sciences
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Accurately estimating large-scale evapotranspiration (ET) rates is essential to understanding and predicting global change. Evapotranspiration models that are applied at a continental scale typically operate on relatively large spatial grids, with the result that the heterogeneity in land surface properties and processes at smaller spatial scales cannot be explicitly represented. Averaging over this spatial heterogeneity may lead to biased estimates of energy and water fluxes. Here we estimate how averaging over spatial heterogeneity in precipitation (P) and potential evapotranspiration (PET) may affect grid-cell-averaged evapotranspiration rates, as seen from the atmosphere over heterogeneous landscapes across the globe. Our goal is to identify where, under what conditions, and at what scales this “heterogeneity bias” could be most important but not to quantify its absolute magnitude. We use Budyko curves as simple functions that relate ET to precipitation and potential evapotranspiration. Because the relationships driving ET are nonlinear, averaging over subgrid heterogeneity in P and PET will lead to biased estimates of average ET. We examine the global distribution of this bias, its scale dependence, and its sensitivity to variations in P vs. PET. 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.

ACS Style

Elham Rouholahnejad Freund; Ying Fan; James W. Kirchner. Global assessment of how averaging over spatial heterogeneity in precipitation and potential evapotranspiration affects modeled evapotranspiration rates. Hydrology and Earth System Sciences 2020, 24, 1927 -1938.

AMA Style

Elham Rouholahnejad Freund, Ying Fan, James W. Kirchner. Global assessment of how averaging over spatial heterogeneity in precipitation and potential evapotranspiration affects modeled evapotranspiration rates. Hydrology and Earth System Sciences. 2020; 24 (4):1927-1938.

Chicago/Turabian Style

Elham Rouholahnejad Freund; Ying Fan; James W. Kirchner. 2020. "Global assessment of how averaging over spatial heterogeneity in precipitation and potential evapotranspiration affects modeled evapotranspiration rates." Hydrology and Earth System Sciences 24, no. 4: 1927-1938.

Preprint content
Published: 12 February 2020
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Evapotranspiration (ET) influences land-climate interactions, regulates the hydrological cycle, and contributes to the Earth's energy balance. Due to its feedbacks to large-scale hydrological processes and its impact on atmospheric dynamics, ET is a key driver 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. One potential source of bias is the so-called aggregation bias that arises whenever nonlinear processes, such as those that regulate ET fluxes, are modeled using averages of heterogeneous inputs. Here we demonstrate a general mathematical approach to quantifying and correcting for this aggregation bias, using the GLEAM land evaporation model as a relatively simple example. We demonstrate that this aggregation bias can lead to substantial overestimates in ET fluxes in a typical large-scale land surface model when sub-grid heterogeneities in land surface properties are averaged out. Using Switzerland as a test case, we examine the scale-dependence of this aggregation bias and show that it can lead to overestimation of daily ET fluxes by as much as 21 % averaged over the whole country. We show how our approach can be used to identify the dominant drivers of aggregation bias, and to estimate sub-grid closure relationships that can correct for aggregation biases in ET estimates, without explicitly representing sub-grid heterogeneities in large-scale land surface models.

ACS Style

Elham Rouholahnejad Freund; Massimiliano Zappa; James W. Kirchner. Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model. 2020, 2020, 1 -18.

AMA Style

Elham Rouholahnejad Freund, Massimiliano Zappa, James W. Kirchner. Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model. . 2020; 2020 ():1-18.

Chicago/Turabian Style

Elham Rouholahnejad Freund; Massimiliano Zappa; James W. Kirchner. 2020. "Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model." 2020, no. : 1-18.

Preprint content
Published: 12 February 2020
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ACS Style

Elham Rouholahnejad Freund; Massimiliano Zappa; James W. Kirchner. Supplementary material to "Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model". 2020, 1 .

AMA Style

Elham Rouholahnejad Freund, Massimiliano Zappa, James W. Kirchner. Supplementary material to "Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model". . 2020; ():1.

Chicago/Turabian Style

Elham Rouholahnejad Freund; Massimiliano Zappa; James W. Kirchner. 2020. "Supplementary material to "Averaging over spatiotemporal heterogeneity substantially biases evapotranspiration rates in a mechanistic large-scale land evaporation model"." , no. : 1.

Preprint content
Published: 17 June 2019
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ACS Style

Elham Rouholahnejad Freund. Response to reviewer#2. 2019, 1 .

AMA Style

Elham Rouholahnejad Freund. Response to reviewer#2. . 2019; ():1.

Chicago/Turabian Style

Elham Rouholahnejad Freund. 2019. "Response to reviewer#2." , no. : 1.

Preprint content
Published: 03 May 2019
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ACS Style

Elham Rouholahnejad Freund. Response to Reviewer #1 comments. 2019, 1 .

AMA Style

Elham Rouholahnejad Freund. Response to Reviewer #1 comments. . 2019; ():1.

Chicago/Turabian Style

Elham Rouholahnejad Freund. 2019. "Response to Reviewer #1 comments." , no. : 1.

Preprint content
Published: 15 March 2019 in Hydrology and Earth System Sciences Discussions
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The major goal of large-scale Earth System Models (ESMs) is to understand and predict global change. However, computational constraints require ESMs to operate on relatively large spatial grids (typically ~1 degree or ~100 km in size) with the result that the heterogeneity in land surface properties and processes at smaller spatial scales cannot be explicitly represented. Averaging over this spatial heterogeneity may lead to biased estimates of energy and water fluxes in ESMs. For example, evapotranspiration rates and the properties that regulate them are spatially heterogeneous at scales orders of magnitude smaller than typical ESM grid cells. Here we quantify the effects of spatial heterogeneity on grid-cell-averaged evapotranspiration (ET) rates, as seen from the atmosphere over heterogeneous landscapes across the globe. In an earlier study, we used a Budyko framework to functionally relate ET to precipitation (P) and potential evapotranspiration (PET), and used a sub-grid closure relation to quantify the effects of sub-grid heterogeneity on average ET at 1° by 1° grid cells- the scale of typical ESM. We showed that because the relationships driving ET are nonlinear, averaging over sub-grid heterogeneity in P and PET leads to overestimation of average ET. In this study, we extend that work to the globe and examine the global distribution of this bias, its scale dependence, and the underlying mechanisms. Our analysis shows that this heterogeneity bias is more pronounced in mountainous terrain, in landscapes where P is inversely correlated with PET, and in regions with temperate climates and dry summers. We also show that the magnitude of this heterogeneity bias grows on average, and expands over larger areas, as the size of the grid cell increases. Correcting for this overestimation of ET in ESMs is important for modeling the water cycle, as well as for future temperature predictions, since current overestimations of ET rates imply smaller sensible heat fluxes, and potential underestimation of dry and warm conditions in the context of climate change. Our work provides a basis for translating the heterogeneity bias into correction factors in large-scale ESMs, and highlights the regions where more detailed mechanistic modeling is needed.

ACS Style

Elham Rouholahnejad Freund; Ying Fan; James W. Kirchner. Global assessment of how averaging over land-surface heterogeneity affects modeled evapotranspiration rates. Hydrology and Earth System Sciences Discussions 2019, 2019, 1 -19.

AMA Style

Elham Rouholahnejad Freund, Ying Fan, James W. Kirchner. Global assessment of how averaging over land-surface heterogeneity affects modeled evapotranspiration rates. Hydrology and Earth System Sciences Discussions. 2019; 2019 ():1-19.

Chicago/Turabian Style

Elham Rouholahnejad Freund; Ying Fan; James W. Kirchner. 2019. "Global assessment of how averaging over land-surface heterogeneity affects modeled evapotranspiration rates." Hydrology and Earth System Sciences Discussions 2019, no. : 1-19.

Commissioned manuscript
Published: 27 February 2019 in Water Resources Research
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Earth System Models (ESMs) are essential tools for understanding and predicting global change, but they cannot explicitly resolve hillslope‐scale terrain structures that fundamentally organize water, energy, and biogeochemical stores and fluxes at subgrid scales. Here we bring together hydrologists, Critical Zone scientists, and ESM developers, to explore how hillslope structures may modulate ESM grid‐level water, energy, and biogeochemical fluxes. In contrast to the one‐dimensional (1‐D), 2‐ to 3‐m deep, and free‐draining soil hydrology in most ESM land models, we hypothesize that 3‐D, lateral ridge‐to‐valley flow through shallow and deep paths and insolation contrasts between sunny and shady slopes are the top two globally quantifiable organizers of water and energy (and vegetation) within an ESM grid cell. We hypothesize that these two processes are likely to impact ESM predictions where (and when) water and/or energy are limiting. We further hypothesize that, if implemented in ESM land models, these processes will increase simulated continental water storage and residence time, buffering terrestrial ecosystems against seasonal and interannual droughts. We explore efficient ways to capture these mechanisms in ESMs and identify critical knowledge gaps preventing us from scaling up hillslope to global processes. One such gap is our extremely limited knowledge of the subsurface, where water is stored (supporting vegetation) and released to stream baseflow (supporting aquatic ecosystems). We conclude with a set of organizing hypotheses and a call for global syntheses activities and model experiments to assess the impact of hillslope hydrology on global change predictions.

ACS Style

Y. Fan; 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; Dai Yamazaki. Hillslope Hydrology in Global Change Research and Earth System Modeling. Water Resources Research 2019, 55, 1737 -1772.

AMA Style

Y. Fan, 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, Dai Yamazaki. Hillslope Hydrology in Global Change Research and Earth System Modeling. Water Resources Research. 2019; 55 (2):1737-1772.

Chicago/Turabian Style

Y. Fan; 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; Dai Yamazaki. 2019. "Hillslope Hydrology in Global Change Research and Earth System Modeling." Water Resources Research 55, no. 2: 1737-1772.

Journal article
Published: 12 August 2017 in Water
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As water resources become further stressed due to increasing levels of societal demand, understanding the effect of climate and landuse change on various components of the water cycle is of strategic importance. In this study we used a previously developed hydrologic model of the Black Sea Catchment (BSC) to assess the impact of potential climate and landuse changes on the fresh water availability. The BSC model was built, calibrated, and validated against observed daily river discharge for the period of 1973–2006 using the Soil and Water Assessment Tool (SWAT) as the modeling tool. We employed the A2 and B2 scenarios of 2017–2050 generated by the Danish Regional Climate Model (HIRHAM), and four potential future landuse scenarios based on the Intergovernmental Panel of Climate Change (IPCC)’s special report on emissions scenarios (SRES) storylines, to analyze the impact of climate change and landuse change on the water resources of the BSC. The detailed modeling and the ensemble of the scenarios showed that a substantial part of the catchment will likely experience a decrease in freshwater resources by 30 to 50%.

ACS Style

Elham Rouholahnejad Freund; Karim C. Abbaspour; Anthony Lehmann. Water Resources of the Black Sea Catchment under Future Climate and Landuse Change Projections. Water 2017, 9, 598 .

AMA Style

Elham Rouholahnejad Freund, Karim C. Abbaspour, Anthony Lehmann. Water Resources of the Black Sea Catchment under Future Climate and Landuse Change Projections. Water. 2017; 9 (8):598.

Chicago/Turabian Style

Elham Rouholahnejad Freund; Karim C. Abbaspour; Anthony Lehmann. 2017. "Water Resources of the Black Sea Catchment under Future Climate and Landuse Change Projections." Water 9, no. 8: 598.

Journal article
Published: 11 January 2017 in Hydrology and Earth System Sciences
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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. Our approach uses Budyko curves, as a simple model of ET as a function of atmospheric forcing by P and PET. From these Budyko curves, we derive a simple sub-grid closure relation that quantifies how spatial heterogeneity affects average ET as seen from the atmosphere. We show that averaging over sub-grid heterogeneity in P and PET, as typical Earth system models do, leads to overestimations of average ET. For a sample high-relief grid cell in the Himalayas, this overestimation bias is shown to be roughly 12 %; for adjacent lower-relief grid cells, it is substantially smaller. We use a similar approach to derive sub-grid closure relations that quantify how lateral redistribution of water could alter average ET as seen from the atmosphere. We derive expressions for the maximum possible effect of lateral redistribution on average ET, and the amount of lateral redistribution required to achieve this effect, using only estimates of P and PET in possible source and recipient locations as inputs. We show that where the aridity index P/PET increases with altitude, gravitationally driven lateral redistribution will increase average ET (and models that overlook lateral redistribution will underestimate average ET). Conversely, where the aridity index P/PET decreases with altitude, gravitationally driven lateral redistribution will decrease average ET. The effects of both sub-grid heterogeneity and lateral redistribution will be most pronounced where P is inversely correlated with PET across the landscape. Our analysis provides first-order estimates of the magnitudes of these sub-grid effects, as a guide for more detailed modeling and analysis.

ACS Style

Elham Rouholahnejad Freund; James W. Kirchner. A Budyko framework for estimating how spatial heterogeneity and lateral moisture redistribution affect average evapotranspiration rates as seen from the atmosphere. Hydrology and Earth System Sciences 2017, 21, 217 -233.

AMA Style

Elham Rouholahnejad Freund, James W. Kirchner. A Budyko framework for estimating how spatial heterogeneity and lateral moisture redistribution affect average evapotranspiration rates as seen from the atmosphere. Hydrology and Earth System Sciences. 2017; 21 (1):217-233.

Chicago/Turabian Style

Elham Rouholahnejad Freund; James W. Kirchner. 2017. "A Budyko framework for estimating how spatial heterogeneity and lateral moisture redistribution affect average evapotranspiration rates as seen from the atmosphere." Hydrology and Earth System Sciences 21, no. 1: 217-233.

Journal article
Published: 01 December 2016 in Environmental Science & Policy
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Large-scale water scarcity indicators have been widely used to map and inform decision makers and the public about the use of river flows, a vital and limited renewable resource. However, spatiotemporal interrelations among users and administrative entities are still lacking in most large-scale studies. Water scarcity and interrelations are at the core of the water-ecosystem-energy-food nexus. In this paper, we balance water availability in the Black Sea catchment with requirements and consumptive use of key water users, i.e., municipalities, power plants, manufacturing, irrigation and livestock breeding, accounting for evaporation from major reservoirs as well as environmental flow requirements. We use graph theory to highlight interrelations between users and countries along the hydrological network. The results show that water scarcity occurs mainly in the summer due to higher demand for irrigation and reservoir evaporation in conjunction with relatively lower water resources, and in the fall-winter period due to lower water resources and the relatively high demand for preserving ecosystems and from sectors other than irrigation. Cooling power plants and the demands of urban areas cause scarcity in many isolated locations in the winter and, to a far greater spatial extent, in the summer with the demands for irrigation. Interrelations in water scarcity-prone areas are mainly between relatively small, intra-national rivers, for which the underlying national and regional governments act as key players in mitigating water scarcity within the catchment. However, many interrelations exist for larger rivers, highlighting the need for international cooperation that could be achieved through a water-ecosystem-energy-food nexus

ACS Style

M. Fasel; C. Bréthaut; E. Rouholahnejad; M.A. Lacayo-Emery; A. Lehmann. Blue water scarcity in the Black Sea catchment: Identifying key actors in the water-ecosystem-energy-food nexus. Environmental Science & Policy 2016, 66, 140 -150.

AMA Style

M. Fasel, C. Bréthaut, E. Rouholahnejad, M.A. Lacayo-Emery, A. Lehmann. Blue water scarcity in the Black Sea catchment: Identifying key actors in the water-ecosystem-energy-food nexus. Environmental Science & Policy. 2016; 66 ():140-150.

Chicago/Turabian Style

M. Fasel; C. Bréthaut; E. Rouholahnejad; M.A. Lacayo-Emery; A. Lehmann. 2016. "Blue water scarcity in the Black Sea catchment: Identifying key actors in the water-ecosystem-energy-food nexus." Environmental Science & Policy 66, no. : 140-150.

Preprint content
Published: 31 August 2016 in Hydrology and Earth System Sciences
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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. Our approach uses Budyko curves, as a simple model of ET as a function of atmospheric forcing by P and PET. From these Budyko curves, we derive a simple sub-grid closure relation that quantifies how spatial heterogeneity affects average ET as seen from the atmosphere. We show that averaging over sub-grid heterogeneity in P and PET, as typical earth system models do, leads to overestimates of average ET. For a sample high-relief grid cell in the Himalaya, this overestimation bias is shown to be roughly 12 %; for adjacent lower-relief grid cells it is substantially smaller. We use a similar approach to derive sub-grid closure relations that quantify how lateral redistribution of water could alter average ET as seen from the atmosphere. We derive expressions for the maximum possible effect of lateral redistribution on average ET, and the amount of lateral redistribution required to achieve this effect, using only estimates of P and PET in possible source and recipient locations as inputs. We show that where the aridity index P/PET increases with altitude, gravitationally driven lateral redistribution will increase average ET (and models that overlook lateral redistribution will underestimate average ET). Conversely, where the aridity index P/PET decreases with altitude, gravitationally driven lateral redistribution will decrease average ET. The effects of both sub-grid heterogeneity and lateral redistribution will be most pronounced where P is inversely correlated with PET across the landscape. Our analysis provides first-order estimates of the magnitudes of these sub-grid effects, as a guide for more detailed modeling and analysis.

ACS Style

Elham Rouholahnejad; James W. Kirchner. A Budyko framework for estimating how spatial heterogeneity and lateral moisture redistribution affect average evapotranspiration rates as seen from the atmosphere. Hydrology and Earth System Sciences 2016, 21, 217 -233.

AMA Style

Elham Rouholahnejad, James W. Kirchner. A Budyko framework for estimating how spatial heterogeneity and lateral moisture redistribution affect average evapotranspiration rates as seen from the atmosphere. Hydrology and Earth System Sciences. 2016; 21 (1):217-233.

Chicago/Turabian Style

Elham Rouholahnejad; James W. Kirchner. 2016. "A Budyko framework for estimating how spatial heterogeneity and lateral moisture redistribution affect average evapotranspiration rates as seen from the atmosphere." Hydrology and Earth System Sciences 21, no. 1: 217-233.

Journal article
Published: 28 August 2016 in Transactions in GIS
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This article presents SCOPED, an innovative approach for extracting environmental data using OGC services. In the field of water resource management, SCOPED-W (‘W’ for ‘Water’) is a method that was developed in the framework of EU/FP7 IASON and EOPOWER projects. This platform supports the collection of data required to build a Soil and Water Assessment Tool (SWAT) model and the uptake, spatialization and dissemination of raw data generated from the outputs of different SWAT models for the Black Sea region. Scientists are documenting the data served by the platform in ISO standardized metadata to support informed use. SCOPED-W primarily targets the community of SWAT users in the Black Sea region but it can easily be replicated in other geographical areas. Additionally, the SCOPED approach is based on data interoperability that makes it fully compatible with other domains of application as demonstrated here with three original use cases. The article also highlights the benefits of the approach for the GEO community and discusses future improvements for supporting integration with other platforms such as UNEP Live.

ACS Style

Yaniss Guigoz; Pierre Lacroix; Elham Rouholahnejad; Nicolas Ray; Gregory Giuliani. SCOPED-W: SCalable Online Platform for extracting Environmental Data and Water-related model outputs. Transactions in GIS 2016, 21, 748 -763.

AMA Style

Yaniss Guigoz, Pierre Lacroix, Elham Rouholahnejad, Nicolas Ray, Gregory Giuliani. SCOPED-W: SCalable Online Platform for extracting Environmental Data and Water-related model outputs. Transactions in GIS. 2016; 21 (4):748-763.

Chicago/Turabian Style

Yaniss Guigoz; Pierre Lacroix; Elham Rouholahnejad; Nicolas Ray; Gregory Giuliani. 2016. "SCOPED-W: SCalable Online Platform for extracting Environmental Data and Water-related model outputs." Transactions in GIS 21, no. 4: 748-763.

Journal article
Published: 01 May 2015 in Journal of Hydrology
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SummaryA 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. Different components of water resources are simulated and crop yield and water quality are considered at the Hydrological Response Unit (HRU) level. The water resources are quantified at subbasin level with monthly time intervals. Leaching of nitrate into groundwater is also simulated at a finer spatial level (HRU). The use of large-scale, high-resolution water resources models enables consistent and comprehensive examination of integrated system behavior through physically-based, data-driven simulation. In this article we discuss 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 information support to the European Water Framework Directive and lay the basis for further assessment of the impact of climate change on water availability and quality. The approach and methods developed are general and can be applied to any large region around the world

ACS Style

K.C. Abbaspour; E. Rouholahnejad; Seyed Saeid Ashraf Vaghefi; Raghavan Srinivasan; H. Yang; Björn Klöve. A continental-scale hydrology and water quality model for Europe: Calibration and uncertainty of a high-resolution large-scale SWAT model. Journal of Hydrology 2015, 524, 733 -752.

AMA Style

K.C. Abbaspour, E. Rouholahnejad, Seyed Saeid Ashraf Vaghefi, Raghavan Srinivasan, H. Yang, Björn Klöve. A continental-scale hydrology and water quality model for Europe: Calibration and uncertainty of a high-resolution large-scale SWAT model. Journal of Hydrology. 2015; 524 ():733-752.

Chicago/Turabian Style

K.C. Abbaspour; E. Rouholahnejad; Seyed Saeid Ashraf Vaghefi; Raghavan Srinivasan; H. Yang; Björn Klöve. 2015. "A continental-scale hydrology and water quality model for Europe: Calibration and uncertainty of a high-resolution large-scale SWAT model." Journal of Hydrology 524, no. : 733-752.

Journal article
Published: 01 February 2015 in Environmental Science & Policy
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Agriculture in the Black Sea catchment is responsible for a considerable share of the area's total water withdrawal and the majority of its total water consumption. It therefore plays a key role in sustainable water resources management. However, in the future water resources will be exposed to climate change. This assessment aims at identifying the most vulnerable regions and to explain the reasons of this vulnerability. It is based on a combination of the well-known Driver–Pressure–State–Impact–Response framework (DPSIR) and the vulnerability concept as defined by the Intergovernmental Panel on Climate Change (IPCC). Three distinctive climate change scenarios are used to assess their impacts on water resources for agriculture: (1) an increase in temperature; (2) a decrease in precipitation; and (3) a combination of the first and second scenarios. The data for this assessment is derived from a SWAT model (Soil and Water Assessment Tool). The results show that the regions of the Black Sea catchment are impacted by climate change differently. Some countries benefit from climate change (e.g., Turkey, Ukraine, Romania, Moldova, Hungary, Bulgaria) while others will encounter considerably worse agro-climatic conditions in the future (e.g., Montenegro, Austria, Bosnia–Herzegovina). Additionally, natural plant growth conditions mostly improve due to more suitable temperature conditions. In contrast, the deteriorating agricultural conditions mainly result from a diminishing irrigation potential that is caused by reduced precipitation. The conclusion emphasises the important role of the legal framework as well as more sustainable agronomic practices and proposes improvements for future assessment methods in this research field

ACS Style

Roger Bär; E. Rouholahnejad; K. Rahman; K.C. Abbaspour; A. Lehmann. Climate change and agricultural water resources: A vulnerability assessment of the Black Sea catchment. Environmental Science & Policy 2015, 46, 57 -69.

AMA Style

Roger Bär, E. Rouholahnejad, K. Rahman, K.C. Abbaspour, A. Lehmann. Climate change and agricultural water resources: A vulnerability assessment of the Black Sea catchment. Environmental Science & Policy. 2015; 46 ():57-69.

Chicago/Turabian Style

Roger Bär; E. Rouholahnejad; K. Rahman; K.C. Abbaspour; A. Lehmann. 2015. "Climate change and agricultural water resources: A vulnerability assessment of the Black Sea catchment." Environmental Science & Policy 46, no. : 57-69.

Journal article
Published: 16 July 2014 in Water Resources Research
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The pressure on water resources, deteriorating water quality, and uncertainties associated with the climate change create an environment of conflict in large and complex river system. 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. The hydrological model of the BSB was calibrated and validated considering sensitivity and uncertainty analysis. River discharges, nitrate loads, and crop yields were used to calibrate the model. Employing grid technology improved calibration computation time by more than an order of magnitude. We calculated components of water resources such as river discharge, infiltration, aquifer recharge, soil moisture, and actual and potential evapotranspiration. Furthermore, available water resources were calculated at subbasin spatial and monthly temporal levels. Within this framework, a comprehensive database of the BSB was created to fill the existing gaps in water resources data in the region. In this paper, we discuss the challenges of building a large‐scale model in fine spatial and temporal detail. This study provides the basis for further research on the impacts of climate and land use change on water resources in the BSB.

ACS Style

Elham Rouholahnejad; Karim C. Abbaspour; Raghavan Srinivasan; Victor Bacu; Anthony Lehmann. Water resources of the Black Sea Basin at high spatial and temporal resolution. Water Resources Research 2014, 50, 5866 -5885.

AMA Style

Elham Rouholahnejad, Karim C. Abbaspour, Raghavan Srinivasan, Victor Bacu, Anthony Lehmann. Water resources of the Black Sea Basin at high spatial and temporal resolution. Water Resources Research. 2014; 50 (7):5866-5885.

Chicago/Turabian Style

Elham Rouholahnejad; Karim C. Abbaspour; Raghavan Srinivasan; Victor Bacu; Anthony Lehmann. 2014. "Water resources of the Black Sea Basin at high spatial and temporal resolution." Water Resources Research 50, no. 7: 5866-5885.

Book chapter
Published: 01 January 2013 in Advances in Intelligent Systems and Computing
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The continuous expansion of distributed hydrological models applied on different geographical regions in order to solve and predict water resource problems raised multiple issues related to the model calibration and execution processes. The calibration process was performed on SWAT (Soil and Water Assessment Tool) hydrological model that could be used to predict the impact of land management practices on water, sediment and agricultural chemical yields in complex watersheds. This paper presents methods, algorithms, data access issues and human-computer interaction techniques used in developing a Web application for the Grid based SWAT model execution and calibration, called gSWAT. The SWAT model calibration process is time consuming (e.g. in some situations its execution could reach hours or even days in length). The Grid is the platform that integrates the gSWAT application, due to its parallel and distributed characteristics, offering high computation and storage capabilities in response to the calibration process requirements.

ACS Style

Danut Mihon; Victor Bacu; Denisa Rodila; Teodor Stefanut; Karim Abbaspour; Elham Rouholahnejad; Dorian Gorgan. Grid Based Hydrologic Model Calibration and Execution. Advances in Intelligent Systems and Computing 2013, 187, 279 -293.

AMA Style

Danut Mihon, Victor Bacu, Denisa Rodila, Teodor Stefanut, Karim Abbaspour, Elham Rouholahnejad, Dorian Gorgan. Grid Based Hydrologic Model Calibration and Execution. Advances in Intelligent Systems and Computing. 2013; 187 ():279-293.

Chicago/Turabian Style

Danut Mihon; Victor Bacu; Denisa Rodila; Teodor Stefanut; Karim Abbaspour; Elham Rouholahnejad; Dorian Gorgan. 2013. "Grid Based Hydrologic Model Calibration and Execution." Advances in Intelligent Systems and Computing 187, no. : 279-293.

Journal article
Published: 31 July 2012 in Natural Hazards and Earth System Sciences
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The calibration and execution of large hydrological models, such as SWAT (soil and water assessment tool), developed for large areas, high resolution, and huge input data, need not only quite a long execution time but also high computation resources. SWAT hydrological model supports studies and predictions of the impact of land management practices on water, sediment, and agricultural chemical yields in complex watersheds. The paper presents the gSWAT application as a web practical solution for environmental specialists to calibrate extensive hydrological models and to run scenarios, by hiding the complex control of processes and heterogeneous resources across the grid based high computation infrastructure. The paper highlights the basic functionalities of the gSWAT platform, and the features of the graphical user interface. The presentation is concerned with the development of working sessions, interactive control of calibration, direct and basic editing of parameters, process monitoring, and graphical and interactive visualization of the results. The experiments performed on different SWAT models and the obtained results argue the benefits brought by the grid parallel and distributed environment as a solution for the processing platform. All the instances of SWAT models used in the reported experiments have been developed through the enviroGRIDS project, targeting the Black Sea catchment area.

ACS Style

D. Gorgan; V. Bacu; D. Mihon; D. Rodila; K. Abbaspour; E. Rouholahnejad. Grid based calibration of SWAT hydrological models. Natural Hazards and Earth System Sciences 2012, 12, 2411 -2423.

AMA Style

D. Gorgan, V. Bacu, D. Mihon, D. Rodila, K. Abbaspour, E. Rouholahnejad. Grid based calibration of SWAT hydrological models. Natural Hazards and Earth System Sciences. 2012; 12 (7):2411-2423.

Chicago/Turabian Style

D. Gorgan; V. Bacu; D. Mihon; D. Rodila; K. Abbaspour; E. Rouholahnejad. 2012. "Grid based calibration of SWAT hydrological models." Natural Hazards and Earth System Sciences 12, no. 7: 2411-2423.

Journal article
Published: 01 May 2012 in Environmental Modelling & Software
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ACS Style

E. Rouholahnejad; K.C. Abbaspour; M. Vejdani; Raghavan Srinivasan; R. Schulin; Anthony Lehmann. A parallelization framework for calibration of hydrological models. Environmental Modelling & Software 2012, 31, 28 -36.

AMA Style

E. Rouholahnejad, K.C. Abbaspour, M. Vejdani, Raghavan Srinivasan, R. Schulin, Anthony Lehmann. A parallelization framework for calibration of hydrological models. Environmental Modelling & Software. 2012; 31 ():28-36.

Chicago/Turabian Style

E. Rouholahnejad; K.C. Abbaspour; M. Vejdani; Raghavan Srinivasan; R. Schulin; Anthony Lehmann. 2012. "A parallelization framework for calibration of hydrological models." Environmental Modelling & Software 31, no. : 28-36.