Coupling a large-scale hydrological model (CWatM v1.1) with a high-resolution groundwater flow model (MODFLOW 6) to assess the impact of irrigation at regional scale

Abstract

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 multilayer 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–soil and groundwater–river 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 grid resolution is the main factor that affects water table depth bias because it smooths river incision, 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.

Supposed Effects of Wetland Restoration on Hydrological Conditions and the Provisioning Ecosystem Services—A Model-Based Case Study at a Hungarian Lowland Catchment

“…To put our results into context, hydrological modelling of drained lowland catchments is a challenging and complex task [69,[76][77][78][79][80][81]. In general, calibration can be carried out for several hydrological variables; however, it is also limited by several factors which justify the relatively lower model accuracy.…”

The use of GRDC gauging stations for calibrating large-scale hydrological models

“…For regional studies (Hanasaki et al, 2022;Guillaumot et al, 2022), the resolution is already 1 km or below. Approaches to upscaling to coarser resolutions are mainly based on comparing the reported UPA and the UPA calculated from the river network (Fekete and Vörösmarty, 1999;Zhao et al, 2017).…”

MODFLOW as a Configurable Multi‐Model Hydrologic Simulator

“…Applications include Fienen et al (2021Fienen et al ( , 2022aFienen et al ( , 2022b Interoperability GWF, GWT External programs can control and interact with MODFLOW during execution (Hughes et al 2022). Applications include Guillaumot et al (2022) and White et al (2023) full Python support for all MODFLOW 6 models and packages. We welcome input from the community through our public software repository.…”