Unraveling Long-Term Flood Risk Dynamics Across the Murray-Darling Basin Using a Large-Scale Hydraulic Model and Satellite Data

River floods are one of the most devastating extreme hydrological events, with oftentimes remarkably negative effects for human society and the environment. Economic losses and social consequences, in terms of affected people and human fatalities, are increasing worldwide due to climate change and urbanization processes. Long-term dynamics of flood risk are intimately driven by the temporal evolution of hazard, exposure and vulnerability. Although needed for effective flood risk management, a comprehensive long-term analysis of all these components is not straightforward, mostly due to a lack of hydrological data, exposure information, and large computational resources required for 2-D flood model simulations at adequately high resolution over large spatial scales. This study tries to overcome these limitations and attempts to investigate the dynamics of different flood risk components in the Murray-Darling basin (MDB, Australia) in the period 1973–2014. To this aim, the LISFLOOD-FP model, i.e., a large-scale 2-D hydrodynamic model, and satellite-derived built-up data are employed. Results show that the maximum extension of flooded areas decreases in time, without revealing any significant geographical transfer of inundated areas across the study period. Despite this, a remarkable increment of built-up areas characterizes MDB, with larger annual increments across not-flooded locations compared to flooded areas. When combining flood hazard and exposure, we find that the overall extension of areas exposed to high flood risk more than doubled within the study period, thus highlighting the need for improving flood risk awareness and flood mitigation strategies in the near future.

Murray-Darling Basin Plan: Case Study in Market-Based Approach to Water Sharing in Australia

The Murray-Darling Basin (MDB) is an area in southeastern Australia that has the largest and most regulated river system in the country. Historically, it has been an area of conflict over water resources, with efforts to bring the different states together to negotiate water sharing since the early 1900s. In the 20th century, the focus of water policy was predominantly on water supply infrastructure: building large-scale dam storages, weirs, and other irrigation region infrastructure. However, increasing problems with both water quality and quantity from the 1970s onwards—such as acid sulphate soils, salinity, declines in vegetation health, and species loss—meant that more attention was turned to water demand management options. These included establishing formal water markets, trade liberalization, and water extraction caps. The National Water Initiative (2004) and the Water Act (2007) laid the groundwork in unbundling water and land ownership and created the Murray-Darling Basin Authority (MDBA). The MDBA was tasked with developing the MDB Plan (Basin Plan 2012) to readjust the balance between consumptive water use and the environment. The Basin Plan when implemented in 2012 aimed to return up to one third of consumptive water extraction to environmental use, making it one of the biggest reallocations of water to the environment in the world. It has predominantly used market-based approaches to do so. However, conflict over water sharing has remained a dominant feature of MDB water reform. Self-interest among states and irrigation interests have impacted environmental water recovery methods, resource expenditure, and allocation—subsequently weakening both the Basin Plan and water policy in general. Given current policy developments, there is real danger of targets not being met, and environmental sustainability being continually compromised. The ongoing issues of drought, climate change, and readdressing First Nations access to—and ownership of—water have emphasized distributional issues in water sharing. It is clear also that the Basin Plan has been wrongly blamed and misattributed for ongoing rural community declines, with current amendments and reductions in water reallocation targets a result of this. What is clear is that the Basin Plan is currently not the fully sustainable solution for water sharing that it set out to be. It will need to continually evolve, along with various institutions to support water governance and rural community economic development in general, to address existing overallocation and future climate challenges. The challenges of equity, rural community development, and distributional fairness lie firmly in the sphere of strong governance, high-quality data, and first-best economic and scientific policies.

Mind the Gap! Reconciling Environmental Water Requirements with Scarcity in the Murray–Darling Basin, Australia

The Murray–Darling Basin Plan is a $AU 13 billion program to return water from irrigation use to the environment. Central to the success of the Plan, commenced in 2012, is the implementation of an Environmentally Sustainable Level of Take (ESLT) and a Sustainable Diversion Limit (SDL) on the volume of water that can be taken for consumptive use. Under the enabling legislation, the Water Act (2007), the ESLT and SDL must be set by the “best available science.” In 2009, the volume of water to maintain wetlands and rivers of the Basin was estimated at 3000–7600 GL per year. Since then, there has been a steady step-down in this volume to 2075 GL year due to repeated policy adjustments, including “supply measures projects,” building of infrastructure to obtain the same environmental outcomes with less water. Since implementation of the Plan, return of water to the environment is falling far short of targets. The gap between the volume required to maintain wetlands and rivers and what is available is increasing with climate change and other risks, but the Plan makes no direct allowance for climate change. We present policy options that address the need to adapt to less water and re-frame the decision context from contestation between water for irrigation versus the environment. Options include best use of water for adaptation and structural adjustment packages for irrigation communities integrated with environmental triage of those wetlands likely to transition to dryland ecosystems under climate change.

A geophysical analysis of Aboriginal earth mounds in the Murray River Valley, South Australia

Earth mounds are common archaeological features in some regions of Australia, particularly within the Murray-Darling Basin. These features are generally considered to have formed via the repeated use of earth oven cookery methods employed by Aboriginal people during the mid- to late-Holocene. This study assesses the relative effectiveness of key geophysical methods including magnetometry, groundpenetrating radar (GPR) and electrical resistivity tomography (ERT) in mapping, and determining the stratigraphy of earth mound sites. Three earth mounds adjacent to Hunchee Creek, on Calperum Station in South Australia's Riverland region, were chosen to conduct a comparative trial of these methods. This research demonstrated that geophysics can be used to both locate mounds and provide information as to deposit thickness and size. Individual ovens within mounds can also be located. This suggests a greater potential role for geophysics in understanding the Holocene archaeological record in Australia.

Shifting Goalposts: Setting Restoration Targets for Waterbirds in the Murray-Darling Basin Under Climate Change

The Murray-Darling Basin (the Basin) is the largest river system in Australia, supplying about 40% of the country’s irrigated agricultural output. Associated water resource development has come with a heavy price for the Basin’s freshwater ecosystems degrading them over decades. Australian governments are attempting to achieve environmental sustainability by returning water to the environment through buy-back of irrigation licences and improved water efficiencies. To determine effectiveness, basin-wide management objectives were established for key indicators, including waterbird populations and life histories which can effectively indicate ecosystem function and condition, driven by flow and flooding regimes. Ongoing monitoring of waterbird numbers indicates continued declines. We evaluated the feasibility of meeting established waterbird objectives under existing and predicted climates. We modelled long-term waterbird numbers using one of the world’s largest ongoing waterbird surveys (1983–2020), covering about 13.5% of the area of the entire Basin. Our findings suggest that under near future climate change projections, waterbird numbers will likely continue to decline, and remain below restoration targets set for the Basin. We discuss the current policy settings for using environmental water to support waterbird populations, recommending adjustments to restore the Basin’s waterbird populations and their wetlands in order to meet Australia’s conservation targets in relation to the ongoing global crisis of biodiversity loss.