Mapping groundwater-dependent ecosystems using a high-resolution global groundwater model

Global population growth, economic growth, and climate change have led to a decline in groundwater resources, which are essential for sustaining groundwater-dependent ecosystems (GDEs). To understand their spatial and temporal dependency on groundwater, we developed a framework for mapping GDEs at a large scale, using results from a high-resolution global groundwater model. To evaluate the proposed framework, we focus on the Australian continent because of the abundance of groundwater depth observations and the presence of a GDE atlas. We first classify GDEs into three categories: Aquatic (focusing on rivers), wetland (inland wetlands), and terrestrial (phreatophyte) GDEs. We then define a set of rules for identifying these different ecosystems based on, among others, groundwater levels and groundwater discharge. We run the groundwater model in both steady-state and transient mode (period of 1979-2019) and apply the set of rules to map the different types of GDEs using model outputs. For the steady-state mode, we map the presence and absence of GDEs, and we evaluate results against the Australian GDE atlas using a critical success index derived from hit rate, false alarm rate, and missing rate. Results show a hit rate and a critical success index (CSI) above 80 % for each of the three GDE types. From transient runs, we analyse the changes in groundwater dependency between two time periods, 1979-1999 and 1999-2019, and observe a decline in the average number of months that GDEs receive groundwater, pointing at an increasing threat to these ecosystems. The proposed framework and methodology provide a first step towards analysing how global climate change and water use may affect GDE extent and health.