HGS RESEARCH HIGHLIGHT – Monetizing the role of water in sustaining watershed ecosystem services using a fully integrated subsurface–surface water model
Aziz, T., Frey, S. K., Lapen, D. R., Preston, S., Russell, H. A. J., Khader, O., Erler, A. R., & Sudicky, E. A. (2023). Monetizing the role of water in sustaining watershed ecosystem services using a fully integrated subsurface–surface water model. https://doi.org/10.5194/hess-2023-25
“Because HydroGeoSphere (HGS) is an integrated subsurface-surface model, it can be used to dynamically integrate key components of the terrestrial hydrologic cycle such as evaporation from bare soil and water bodies, vegetation dependent transpiration with root uptake, snowmelt and soil freeze/thaw dynamics.”
Fig. 2. Key components of terrestrial hydrological cycle mapped by the HGS model. However, it should be noted that the integrity of the HGS outputs are also dependent on the model scale, in that, for example, a model of a 150,000 km2 river basin is best suited to answer big picture questions (i.e., basin water balance, climate change impacts, regional groundwater), while a model built for the SNW can be used to address questions pertaining to localized processes (i.e., individual wetland influences, groundwater recharge and discharge patterns, flood extent, local aquifer conditions, local soil moisture conditions).
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This research, co-authored by David R. Lapen, Susan Preston, Tariq Aziz, and Steven K. Frey, highlights the role of subsurface water in sustaining ecosystem services during droughts. Using HydroGeoSphere (HGS), the team analyzed the South Nation Watershed (SNW) in eastern Ontario, emphasizing how subsurface water supports evapotranspiration in agricultural landscapes.
Subsurface water, encompassing groundwater and soil moisture, is critical for sustaining vegetation and supporting ecosystem services, yet it is often overlooked in water resource valuation. This study emphasizes the significance of subsurface water during periods of water scarcity, particularly for its role in providing green water—water used by plants for evapotranspiration. Using HydroGeoSphere (HGS), a sophisticated modelling platform known for its ability to simulate coupled surface and subsurface hydrological processes, the research examines the interactions between subsurface water, evapotranspiration, and economic productivity in agricultural ecosystems.
The study employs numerical modelling with HGS to simulate 18 years (2000–2017) of hydrological dynamics in the watershed, enabling a detailed evaluation of how subsurface and surface water contribute to evapotranspiration. During extreme droughts, such as the one in 2012, the findings show that subsurface water provided 72% of the green water, valued at $743 million, highlighting its pivotal role in maintaining ecosystem functions when surface water is scarce. Subsurface water contributions were found to be particularly critical during dry periods, demonstrating its resilience and reliability compared to surface water sources.
The research also monetizes the role of water in sustaining ecosystem services, calculating that each cubic meter of green water contributes $0.45 to agricultural productivity and associated ecological benefits. By providing this economic valuation, the study underscores the importance of subsurface water for both ecological and economic resilience in the face of climate variability.
By leveraging HGS, the researchers were able to quantify the hydrological processes driving water availability and evaluate their economic implications. This study offers actionable insights for watershed managers and policymakers, advocating for sustainable subsurface water management practices to enhance resilience against drought and ensure the continued provision of essential ecosystem services. The integration of hydrological modelling and economic valuation highlights a novel approach to understanding and optimizing water resource management in agricultural landscapes.
Abstract:
Water is essential for all ecosystem services, yet a comprehensive assessment of total (overall) water contributions to ecosystem services production has never been attempted. Quantification of the many ecosystem services impacted by water demands integrated hydrological simulations that implicitly characterize subsurface and surface water exchange. In this study, we use a fully integrated hydrological model—HydroGeoSphere (HGS)—to capture changes in subsurface water, surface water, and evapotranspiration (green water) combined with the economic valuation approach to assess ecosystem services over an 18-year period (2000–2017) in a mixed-use but predominantly agricultural watershed in eastern Ontario, Canada. Using the green water volumes and ecosystem services values as inputs, we calculate the marginal productivity of water, which is $0.45 per m3 (in 2022 Canadian dollars). The valuation results show that maximum green water is used during the dry years, with a value of $1.16 billion during a severe drought that struck in 2012. The average product of water for ecosystem services declines during the dry years. Because subsurface water is a major contributor to the green water supply, it plays a critical role in sustaining ecosystem services during drought conditions. For instance, during the 2012 drought, the subsurface water contribution to green water was estimated at $743 million, making up 72 % of the total value of green water used in that year. Conversely, the surface water contributions in green water provision over the modelling period are comparatively miniscule. This study informs watershed management on the sustainable use of subsurface water during droughts and provides an improved methodology for watershed-based integrated management of ecosystem services.