Between a reef and a hard place: capacity to map the next coral reef catastrophe

Increasing sea surface temperature and extreme heat events pose the greatest threat to coral reefs globally, with trends exceeding previous norms. The resultant mass bleaching events, such as those evidenced on the Great Barrier Reef in 2016, 2017, and 2020 have substantial ecological costs in addition to economic and social costs. Advancing remote (nanosatellites, rapid revisit traditional satellites) and in-field (drones) technological capabilities, cloud data processing, and analysis, coupled with existing infrastructure and in-field monitoring programs, have the potential to provide cost-effective and timely information to managers allowing them to better understand changes on reefs and apply effective remediation. Within a risk management framework for monitoring coral bleaching, we present an overview of how remote sensing can be used throughout the whole risk management cycle and highlight the role technological advancement has in earth observations of coral reefs for bleaching events

A new ecohydraulic management paradigm for salt affected ecosystems and wetlands in low-gradient semi-arid environments

Land clearing for dryland agriculture has altered landscape water balance and is associated with severe valley-floor secondary dryland salinity within parts of Australia, South-East Asia, Africa, North and South America. The pervasive hydrologic process-response model is termed the “hillslope recharge-discharge model” (HRD Model), and attributes salinisation to increased hillslope recharge and rising groundwater tables resulting from reduced evapotranspiration potential following land clearing. New research suggests that internal redistribution of surface water from moderately-sloped hillslopes onto low-gradient broad valley floors, termed the “shedding-receiving model”, may be a significant additional salinisation mechanism and alternative management strategies may be required. A meso-scale surface water gauging network and four valley floor surface water-groundwater interaction sites were established in the Toolibin Lake catchment in southwestern Australia. Based on two years of data, we confirm that the shedding-receiving model holds in this landscape, operating in combination with the pervasive HRD model. There is significant rainfall runoff from moderately sloped uplands, onto low gradient valley floors and high transmission losses result from top-down preferential pathway recharge after the break of season. A new management paradigm was proposed to address the internal runoff redistribution and salt exfiltration mechanisms caused by the shedding receiving behaviour. A lowgradient, broad-based channel, approximately 25m wide, 0.4m deep and running at the valley floor gradient (~0.0003 – 0.0015) was designed to carry a 1:3yr flow. Insights gained from this study of the hydrodynamics suggests that this new approach offers significant opportunity to improve local and downstream resource condition

Energy balance and snowmelt drivers of a marginal subalpine snowpack

Snowmelt from the seasonal snowpack in the Australian Alps is a significant source of water for irrigated agriculture, electricity generation, and environmental flows in the Murray–Darling Basin. Previous studies have reported negative decadal to multidecadal trends in maximum snow depth, snow season duration, and snow-covered area. Here, we characterise the energy balance of this marginal maritime snowpack for the first time. Turbulent fluxes measured using the eddy covariance and bulk aerodynamic methods are compared; discrepancies are attributed to the differing assumptions of the methods and characteristics of the measurement site. We examine the variability of the individual energy balance components and the drivers of snowmelt, and we find that incoming longwave radiation is the dominant control on snowmelt, providing more than 80% of the total energy to the snowpack over the season. During a midwinter rain-on-snow event, the advected rain heat flux provided 8% of the daily total, with the incoming longwave flux still accounting for almost 80%. The ground heat flux contributes a small proportion of the seasonal total but increases in patchy or intermittent snow cover. Comparing these results with those of studies in other maritime locations, we find that the turbulent fluxes are likely to make a proportionally higher contribution to the energy balance due to the short Australian snow season, underpinning the sensitivity of this environment to climate variability and change. These results extend the limited body of knowledge on highly marginal snowpacks and may be relevant to other regions with no direct measurements of the energy balance

How does modifying a DEM to reflect known hydrology affect subsequent terrain analysis?

Many digital elevation models (DEMs) have difficulty replicating hydrological patterns in flat landscapes. Efforts to improve DEM performance in replicating known hydrology have included a variety of soft (i.e. algorithm-based approaches) and hard techniques, such as Stream burning or surface reconditioning (e.g. Agree or ANUDEM). Using a representation of the known stream network, these methods trench or mathematically warp the original DEM to improve how accurately stream position, stream length and catchment boundaries replicate known hydrological conditions. However, these techniques permanently alter the DEM and may affect further analyses (e.g. slope). This paper explores the impact that commonly used hydrological correction methods (Stream burning, Agree.aml and ANUDEM v4.6.3 and ANUDEM v5.1) have on the overall nature of a DEM, finding that different methods produce non-convergent outcomes for catchment parameters (such as catchment boundaries, stream position and length), and differentially compromise secondary terrain analysis. All hydrological correction methods successfully improved calculation of catchment area, stream position and length as compared to using the DEM without any modification, but they all increased catchment slope. No single method performing best across all categories. Different hydrological correction methods changed elevation and slope in different spatial patterns and magnitudes, compromising the ability to derive catchment parameters and conduct secondary terrain analysis from a single DEM. Modification of a DEM to better reflect known hydrology can be useful, however knowledge of the magnitude and spatial pattern of the changes are required before using a DEM for subsequent analyses

Evaluation of multiple satellite altimetry data for studying inland water bodies and river floods

Satellite altimeters have been launched with the objective to monitor changes in sea level and glacial ice sheet topography. More recently, their potential to monitor inland water bodies such as lakes, rivers and wetlands has been recognised. The objective of this study was to assess the accuracy of measuring surface water elevation changes of large multi-channel inland river systems using data from multiple altimetry satellite sensors and different retracking methods. We initially validated satellite altimetry data with in situ gauge data on Lake Argyle and Lake Eildon (Australia), and then investigated data of the only presently operational altimeter, Jason-2/Ocean Surface Topography Mission (OSTM), data at six locations on large inland rivers where temporary gauges were installed during 2011-2012 floods.Our analysis on Lake Argyle showed that the application of an alternative retracking algorithm significantly improved the agreement of altimeter and gauge data. We also found that the altimeter with the smallest footprint (50-90. m) and the highest along-track resolution (40. Hz, ~170. m), ICESat, provided more accurate lake water surface elevation measurements (mean. = 0.00. m, RMSE. = 0.04. m) than other altimeters, Jason-2 (mean. = -0.04. m, RMSE. = 0.28. m), Envisat (mean. = 0.25. m, RMSE. = 0.42. m), Jason-1 (mean. = -0.04. m, RMSE. = 1.07. m), GFO (mean. = 0.5. m, RMSE. = 0.89. m) and T/P (mean. = 0.77. m, RMSE. = 1.5. m).This study also investigated altimetry satellite data accuracy at six Jason-2/OSTM ground track sites crossing the Cooper/Diamantina Rivers where water level loggers were installed to collect data during the 2011-2012 floods (N.B. ICESat ceased operations in 2009). It is shown that satellite altimetry data is able to simulate moderate to major flood events in these large multi-channel inland river systems (R=0.90-0.98). Altimetry data further revealed a variation of water height in the channels across the river system. The general usefulness of satellite altimetry in hydrological applications in remote data sparse regions is confirmed, more specifically to study large multi-channel anabranching river systems such as the Cooper/Diamantina Rivers of the Lake Eyre Basin in Australia and similar systems worldwide where conventional gauging methods are difficult to use. This study also highlights the potential operational applications for monitoring inland flood wave characteristics and hydrodynamic behaviour of remote and multi-channel floodplain systems particularly using the still-operational Jason-2 platform

Evidence of wet-dry cycles and mega-droughts in the Eemian climate of southeast Australia

Understanding past climate variability is critical to informing debate of likely impacts of global warming on weather and climate, and water resources. Here we present a near annual resolution reconstruction of climate developed from a speleothem that spans the Eemian [Marine Isotope Stage 5e (MIS 5e)] from 117,500 to 123,500 years BP—the most recent period in the Earth’s history when temperatures were similar to those of today. Using\ua025\ua0Mg,\ua088Sr, and\ua0137Ba as proxies, we show the first indication of solar and teleconnection cyclic forcing of Eemian climate in southeast Australia, a region at present often affected by severe drought and bushfires. We find evidence for multi-centennial dry periods interpreted as mega-droughts, and highlight the importance of understanding the causes of these in the context of a rapidly warming world, where temperatures are now, or projected to exceed those of the Eemian

Revealing Sediment Transport Pathways and Geomorphic Change in Washover Fans by Combining Drone-Derived Digital Elevation Models and Single Grain Luminescence Data

Chronostratigraphic investigations on coastal sedimentary records such as washover fans or beach-ridge sequences may be used to reconstruct storm chronologies on centennial to millennial time scales. However, modern analogs are pivotal in interpreting depositional processes and reducing uncertainty in evaluating the complex chronostratigraphic architecture of these landforms. Such a modern analog was provided by category 3 tropical cyclone (TC) Olwyn in 2015, which caused a significant storm surge in the Exmouth Gulf (Western Australia). Pre- and post-TC Olwyn geomorphological surveys and high-resolution drone-derived topographical data of a large washover fan document a detailed history of erosion and deposition during the event. The modern analog deposits provided an excellent opportunity to evaluate the use of luminescence-based proxies (luminescence inventories) for tracing event-related sediment source environments and understanding transport processes. Sediments deposited during Olwyn show a systematic relationship between luminescence characteristics and washover fan position. Seaward and central washover sections are indicated by well-bleached deposits due to the beach as the dominant source and/or long transport distances. Lateral washover deposits are characterized by rather local source areas and short transport distances, resulting in higher remnant ages of 70–140 a. Our data show that the combination of sediment source environments and sediment transport length across the fan represents the main control in resetting the luminescence signal and enabling reliable depositional ages to be calculated. It documents the benefit of investigating luminescence inventories when establishing chronologies from complex sedimentary records, thereby demanding a careful consideration of local processes and source areas when interpreting sedimentary TC records

Global warming in the context of 2000 years of Australian alpine temperature and snow cover

Annual resolution reconstructions of alpine temperatures are rare, particularly for the Southern Hemisphere, while no snow cover reconstructions exist. These records are essential to place in context the impact of anthropogenic global warming against historical major natural climate events such as the Roman Warm Period (RWP), Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Here we show for a marginal alpine region of Australia using a carbon isotope speleothem reconstruction, warming over the past five decades has experienced equivalent magnitude of temperature change and snow cover decline to the RWP and MCA. The current rate of warming is unmatched for the past 2000 years and seasonal snow cover is at a minimum. On scales of several decades, mean maximum temperatures have undergone considerable change ≈ ± 0.8 °C highlighting local scale susceptibility to rapid temperature change, evidence of which is often masked in regional to hemisphere scale temperature reconstructions

An Automated Plot Heater for Field Frost Research in Cereals

Frost research to improve genetics or management solutions requires a robust experimental design that minimizes the effects of all other variables that can cause plant damage except for the treatment (frost). Controlled environment facilities cannot faithfully replicate field radiative frost processes, but field studies are limited by the reliability of field methods to exclude frost. An effective field frost exclusion method needs to prevent frost damage while not impacting growing microclimate or yield, and be automatic, modular, mobile, and affordable. In this study, we designed an effective prototype treatment with these features for field frost research that uses diesel heating. The effectiveness of the plot heater to provide an unfrosted control is evaluated by monitoring canopy temperature (CT) and air temperature during frost events, showing that these remain above zero in the heated plots when ambient temperature drops below zero. We find that the plot heater method can prevent potential frost damage at the plot-scale, while not appearing to have an impact on either plant development or yield components. This offers a potential new tool for frost field crop researchers to incorporate a plot-scale control into their experimental design

Chronostratigraphy and geomorphology of washover fans in the Exmouth Gulf (NW Australia) - A record of tropical cyclone activity during the late Holocene

Washover fans typically form due to barrier overwash or breaching and coastal inundation and generally represent geomorphological and depositional evidence of intense storms. Few studies have investigated the chronostratigraphy of washover fans in order to infer magnitude frequency patterns of extreme wave events over longer time scales. Here we present new data on the chronostratigraphy of late Holocene washover fans in the Exmouth Gulf (Western Australia) by using ground penetrating radar and unmanned aerial vehicle (UAV) survey techniques, as well as geomorphological, sedimentological and chronological investigations. This study aims to (i) provide a detailed characterization of the washover fans' geomorphology and stratigraphical architecture; (ii) document depositional processes involved in their formation; (iii) establish a chronostratigraphy based on optically stimulated luminescence (OSL); and (iv) understand the significance of the washover fans for recording past tropical cyclone (TC) activity. The fans consist of multiple sequences of sand, shell debris and coral rubble comprising depositional units related to TC-induced inundation. The units are separated by palaeosurfaces with incipient soil formation, formed during periods of reduced depositional activity. In combination with the interpretation of a UAV-based high-resolution digital surface model, multiple phases of reactivation are inferred. OSL results allow the establishment of a local long-term TC record and suggest storm-induced deposition at similar to 170, similar to 360, similar to 850 and similar to 1300 years ago. Further units were dated to similar to 1950, similar to 2300, and similar to 2850 years ago. The chronology of TC events is consistent with other work relating TC activity with El Nino Southern Oscillation (ENSO) and sea surface temperature (SST) patterns, corroborating the regional palaeotempestological relevance of this unique geomorphological record. (C) 2017 Elsevier Ltd. All rights reserved