J. N. Callow

The effect of farm dams and constructed banks on hydrologic connectivity and runoff estimation in agricultural landscapes

System coupling and landscape connectivity control the flow of water and sediment through landscapes. Although coupling is well known to control long-term landscape development and shorter-term sensitivity to disturbance, the anthropogenic influences on coupling are seldom considered in hydrologic investigations. In particular, the building of small-scale water diversion (earth banks) and collection (farm dams) infrastructure on hillslopes in dryland agricultural areas may significantly alter hillslope-channel coupling. Twelve sub-catchment basins in a dryland agricultural region were investigated under their natural (ignoring infrastructure) and modified (including infrastructure) conditions to investigate the influence of water collection infrastructure on hydrologic connectivity, and whether manual modification of a Digital Elevation Model (DEM) could account for the impact of these factors in hydrologic simulation of hydrologic and geomorphic processes. Dam numbers and density have both increased over the period of available aerial photography (1965-1999), resulting in an average 39.5% reduction (range 4.3-86.7%) in the area retaining hydrologic connectivity with the basin outlet. Analysis of basins dominated by either banks or dams, and with combinations of both was performed using the Cumulative Area Distribution (CAD), Hypsometric Curve (HC), Simplified Width Function (SWF) and Instantaneous Unit Hydrograph (IUH). The geomorphic descriptors (CAD and HC) showed little change in basin structure as a result of farm dam and bank construction, but hydrologic descriptors (SWF and IUH) indicate that hillslope processes are significantly altered by farm dams and banks. Because runoff models are sensitive to catchment area, incorporating hillslope water capture and diversion infrastructure into the base data sets may offer a solution to improved parameterisation of spatial models of hydrology, particularly in dryland agricultural regions.

Blending landsat and MODIS data to generate multispectral indices: A comparison of "index-then-blend" and "Blend-Then-Index" approaches

The objective of this paper was to evaluate the accuracy of two advanced blending algorithms, Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM) and Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model (ESTARFM) to downscale Moderate Resolution Imaging Spectroradiometer (MODIS) indices to the spatial resolution of Landsat. We tested two approaches: (i) “Index-then-Blend” (IB); and (ii) “Blend-then-Index” (BI) when simulating nine indices, which are widely used for vegetation studies, environmental moisture assessment and standing water identification. Landsat-like indices, generated using both IB and BI, were simulated on 45 dates in total from three sites. The outputs were then compared with indices calculated from observed Landsat data and pixel-to-pixel accuracy of each simulation was assessed by calculating the: (i) bias; (ii) R2; and (iii) Root Mean Square Deviation (RMSD). The IB approach produced higher accuracies than the BI approach for both blending algorithms for all nine indices at all three sites. We also found that the relative performance of the STARFM and ESTARFM algorithms depended on the spatial and temporal variances of the Landsat-MODIS input indices. Our study suggests that the IB approach should be implemented for blending of environmental indices, as it was: (i) less computationally expensive due to blending single indices rather than multiple bands; (ii) more accurate due to less error propagation; and (iii) less sensitive to the choice of algorithm.

A multimethod approach to inform epikarst drip discharge modelling: Implications for palaeo-climate reconstruction

Resolving the hydrological processes that form speleothems and the palaeo-climate archives that they contain is difficult. Typical approaches to hydrological investigation are not suited to karst landscapes, geophysics are seldom applied, drip monitoring and modelling have limitations, and ignoring potential hydrological impacts can result in a proxy record that does not reflect the external environment. We aim to understand the processes and controls that have created a palaeo-climate proxy record preserved in a speleothem (JC001) in the “Grotto of Oddities”, part of the Jersey Cave at the Yarrangobilly Caves, Australia, to infer the likely nature and resolution of this record. Electrical Resistivity Tomography (ERT), traditional surveying, and drip discharge monitoring (April 2013 to February 2015) were used to investigate the structure and hydrology of the epikarst overlying the “Grotto of Oddities”. Data collected through these methods were then used to construct a physically informed and parsimonious drip hydrology model. Geophysics showed that changes in hillslope above the “Grotto of Oddities” are collocated with a region of low resistivity which forms an epikarstic reservoir acting to supply enhanced discharge to the speleothem. Drip monitoring showed hysteretic behaviour with a distinct threshold response, and a simple drip classification indicated that the speleothem associated with the drip has the potential to record palaeo-seasonality or an annual-decadal signal. Discharge modelling indicated discharge was comprised of quick and slow flow, and that discharge is probably perennial. These multi-method results together indicate that the speleothem likely represents a palaeo-climate record of a length and resolution unprecedented for non-glacial areas of the Southern Hemisphere and for Australia in particular, and will significantly enhance current knowledge of the climate of southeast Australia. While ERT methods have previously been applied in the karst landscape, to our knowledge, this represents the first application of these multiple methods in combination as an approach to assess the fidelity of a speleothem, based on an understanding of the hydrological processes for palaeo-climate reconstruction.

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.

A method for extensive spatiotemporal assessment of soil temperatures during an experimental fire using distributed temperature sensing in optical fibre

The use of distributed temperature sensing (DTS) for ecological applications has increased rapidly in the last 6 years. Here we demonstrate the first use of DTS to measure soil temperatures during a fuel reduction burn – in an urban grassy Tuart–Banksia woodland remnant near Perth, Western Australia. Optical fibre with an acrylate material coating (diameter 242μm), but no other jacketing or cabling, was buried in the soil at depths between 0 and 5cm. Measurements were recorded over 316m of optical fibre using a DTS measurement unit, providing data over a 5.5-h period at 20-s intervals; resulting in 1243 temporal measurements at 60-cm spatial resolution. Soil temperatures were calibrated to an error of±6.8% at 250°C. Methods for installation, calibration and data visualisation are presented. Issues associated with assessment of DTS data in a fire ecology context are discussed.

Co-authorship analysis of the speleothem proxy-climate community: working together to tackle the big problems

Understanding the environmental context of speleothem palaeo-climate proxies is fundamental to their interpretation. We analyse four methodological approaches to accomplish this: stalactite discharge analysis, proxy/process tracer studies, discharge modelling, and geophysics. Datamining produced citation data sets that reflected these methodological subdisciplines. Social network analysis is used to examine co-authorship within and between these sub-disciplines, and between the joint methodological community and the broader speleothem proxy climate community. Members of the sub-disciplines have become more connected to one another over time, and to members of the other sub-disciplines. High degrees of connectivity between and within communities allows for the rapid and efficient adoption of new ideas and methods, and will enable the community to effectively tackle emerging complex problems.

Drone photogrammetry and KMeans point cloud filtering to create high resolution topographic and inundation models of coastal sediment archives: Drone photogrammetry point cloud filtering

Coastal areas are vulnerable to the impacts of tropical cyclones (TC), tsunamis and other water super-elevation events, but the frequency of these events is often poorly represented by conventional records. Coastal overwash deposits (including washover fans) can provide a longer-term archive of event frequency. Because of their low-gradient geomorphic form, washover fans require high accuracy (centimetre-resolution) topographic models to understand patterns of connectivity and dynamics that control archive formation. Using images collected by a remotely piloted aircraft system (RPAS, or ‘drone’) and Structure-from-Motion (SfM) photogrammetry techniques, we apply a novel point-cloud filtering technique based on KMeans classification of the R-G-B colour of each X-Y-Z point to remove vegetation and create a centimetre-resolution and accuracy bare-earth digital terrain model (DTM) of a washover fan in Exmouth Gulf (Western Australia). Using the RPAS-SfM orphophoto and DEM data, supported by ground-penetrating radar (GPR) and field stratigraphic analysis, we show how this approach can be applied to understand dynamics controlling low-gradient geomorphic landforms, using an example of a washover fan sedimentary archive in northwestern Australia created by extreme overwash events. Our approach reveals the likely role of backflooding and terrestrial runoff in creating backwater environment for sub-aqueous deposition and good sediment preservation and identifies key areas to target for detailed dating and stratigraphic analysis of a potentially decadal to sub-millennial resolution sediment archive of TC activity. Copyright