Against the background of climate change and the increasing demand for water, there is an urgent need for tools to adequately model water availability. In a new study, researchers applied a large-scale model linking surface water to groundwater, which can be used to estimate water resources with high spatial accuracy.
Groundwater – water found in porous and fractured rock underground – is the largest source of fresh water on Earth apart from ice caps and glaciers. It feeds rivers, lakes, and other bodies of water and is essential to ecosystems. In addition, groundwater systems are an integral part of agricultural irrigation, especially in areas with scarce surface water resources.
Existing large-scale models tend to oversimplify groundwater flow, often do not adequately integrate human water management, and operate with less precision than is required to model small-scale hydrological processes. In a new study in geological model development, A team of IIASA researchers has linked the Community Water Model (CWatM) (Burek et al., 2020) with the MODFLOW groundwater flow model, allowing water tables to be reproduced with very fine spatial resolution. The integrated model simulates the hydrological processes that occur in soil and surface water bodies on the ridge slope scale, with reticulum cells smaller than 1 km. It can be used to model water cycles at different geographic scales, from small basins to entire countries.
By comparing the Austrian Seewinkel region and the Indian Bhima Basin, spanning 573 and 46,000 square kilometers respectively, the researchers tested the model’s ability to adequately reproduce the groundwater table under different climatic, geological and socioeconomic conditions. The simulated results were validated using water level depths and fluctuations over a period of 35 years at Seewinkel and 16 years at Bhima.
“These biophysical models are important because water cycles need to be quantified for sound water management. We can study how local and regional water processes interact by linking models at different scales. In particular, a model such as CWatM-MODFLOW is a useful tool for mapping the impact of water management plans. future, land cover changes, or climate change,” says Luca Guillot, lead author of the study and a researcher with the IIASA Water Security Research Group (currently at the French Center for Weather Research – CNRM).
Furthermore, the authors used the model to assess the impact of groundwater-based irrigation on the water cycle in the two regions under study. They found that irrigation increases the amount of water that moves into the atmosphere through evaporation from the soil and transpiration through plant tissues, but reduces groundwater support to rivers and wetlands, especially during dry seasons. The results also indicate that the groundwater table is deeper in areas with intensive irrigation pumping.
Despite ongoing challenges in reproducing groundwater depth patterns and calibrating the model as accurately as possible (~100 m), the study represents a significant improvement in large-scale hydrologic modeling.
“Humans are transforming the planet’s water systems. IIASA water models can answer important questions about how we affect regional and global water systems at different spatial and temporal scales. Regional stakeholders, including policy makers, can use this information to create realistic scenarios for managing water,” concludes study co-author and director of the Biodiversity and Natural Resources Program Yoshihide Wada IIASA.