Preprints
https://doi.org/10.5194/gmd-2022-161
https://doi.org/10.5194/gmd-2022-161
Submitted as: development and technical paper
23 Jun 2022
Submitted as: development and technical paper | 23 Jun 2022
Status: this preprint is currently under review for the journal GMD.

Coupling a large-scale hydrological model (CWatM) with a high-resolution groundwater flow model to assess the impact of irrigation at regional scale

Luca Guillaumot1, Mikhail Smilovic1, Peter Burek1, Jens de Bruijn1,2, Peter Greve1, Taher Kahil1, and Yoshihide Wada1 Luca Guillaumot et al.
  • 1Water Security Research Group, Biodiversity and Natural Resources Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria
  • 2Institute for Environmental Studies, VU University, De Boelelaan 1087, 1081HV, Amsterdam, The Netherlands

Abstract. In the context of changing climate and increasing water demand, large-scale hydrological models are helpful for understanding and projecting future water resources across scales. Groundwater is a critical freshwater resource and strongly controls river flow throughout the year. It is also essential for ecosystems and contributes to evapotranspiration, resulting in climate feedback. However, groundwater systems worldwide are quite diverse, including thick multi-layer aquifers and thin heterogeneous aquifers. Recently, efforts have been made to improve the representation of groundwater systems in large-scale hydrological models. The evaluation of the accuracy of these model outputs is challenging because: (1) they are applied at much coarser resolutions than hillslope scale, (2) they simplify geological structures generally known at local scale, and (3) they do not adequately include local water management practices (mainly groundwater pumping). Here, we apply a large-scale hydrological model (CWatM), coupled with the groundwater flow model MODFLOW, in two different climatic, geological, and socioeconomic regions, the Seewinkel area (Austria) and the Bhima basin (India). The coupled model enables simulation of the impact of the water table on groundwater-soils and groundwater-rivers exchanges, groundwater recharge through leaking canals, and groundwater pumping. This regional scale analysis enables assessment of the model’s ability to simulate water tables at fine spatial resolutions (1 km for CWatM, 100–250 m for MODFLOW) and when groundwater pumping is well estimated. Evaluating large-scale models remains challenging, but the results show that the reproduction of (1) average water table fluctuations and (2) water table depths without bias can be a benchmark objective of such models. We found that subgrid resolution (river incision) is the main factor that affects water table depth bias, while pumping affects time fluctuations. Finally, we use the model to assess the impact of groundwater-based irrigation pumping on evapotranspiration, groundwater recharge, and water table observations from boreholes.

Luca Guillaumot et al.

Status: open (until 18 Aug 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on gmd-2022-161', Astrid Kerkweg, 23 Jun 2022 reply

Luca Guillaumot et al.

Luca Guillaumot et al.

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Short summary
We apply for the first-time a large-scale hydrological model at regional scale with a very high spatial resolution and including a water management and groundwater flow model. The model is used to infer the impact of irrigation on evapotranspiration and groundwater recharge in both irrigated and non-irrigated areas. Water table time-fluctuations recorded in boreholes are well reproduced; however, reproducing water table depth would require finer resolution (<100 m).