DOI: 10.25919/5sgf-5g09
title: 9 arcsecond gridded HCAS 2.4 (2001-2018) base model estimation of habitat condition, 18-year epochs including updated NCI v2.0, annual epochs 2001 to 2021, and trends for continental Australia (with caveats)

description: Caveat: this dataset extends the annual epochs used in the HCAS v2.1 data collection but may not represent an improvement in the regional accuracy of condition assessments. Please read the accompanying technical report for method details. This dataset has a limited distribution because it is under revision and will be superseded by HCAS v3.0 with anticipated publication in mid-2024.

This data collection comprises, for continental Australia, the 9-arcsecond gridded Habitat Condition Assessment System (HCAS) version 2.4 (2001-2018) base model (HCAS v2.4) estimation of habitat condition for terrestrial biodiversity, a series of 18-year epochs (including updated NCI v2.0), annual epochs between 2001 and 2021 derived from the base model, and a series of trend analyses derived from the annual epochs. Several other datasets support use and interpretation of the base model, epochs and trends. 

The core collection in the HCAS v2.4 product suite comprises 32 datasets (four 18-year epochs, 21 annual epochs, seven trends), and a larger number of input and supporting datasets to inform use and interpretation, including four corresponding 18-year epochs of the NCI v2.0. The majority are raster datasets in GeoTIFF format (*.tif) at 0.0025° resolution (approx. 250 m grids), Geographic Datum of Australia (GDA) 1994 (EPSG:4283). All GeoTIFFs are also provided as Cloud Optimised GeoTIFFs (COGs) in relevant subfolders labelled ‘COG’. COGs are regular GeoTIFF files with an internal organisation to enable HTTP GET range requests to ask for just the needed parts of a file.

The HCAS v2.4 base model and epochs datasets are habitat condition indices that vary continuously from a theoretical minimum of 0.0 (ecosystem integrity removed) to a maximum of 1.0 (ecosystem integrity in reference condition). The index represents the contribution that a given site (grid cell) makes to the effective area of ecosystem integrity remaining within any given spatial reporting unit, expressed as a proportion of the contribution made by a site in reference condition.

This HCAS v2.4 product suite was developed to extend the annual epochs through to 2021, using remote sensing generated from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite. The MODIS satellite is reaching its end of life and future HCAS updates will be developed using Landsat satellite imagery, as well as other satellite inputs. The MODIS satellite will continue to operate, in a declining orbit, through to December 2025. 

Note: The remote sensing data originally derived for these analyses included the calendar year 2022. However, investigations into reasons for a downward trend in the continental average of the 2022 condition epoch compared with the 2021 epoch, led to the discovery of a data download error in the remote sensing imagery. Missing tiles across some regions of Australia led to erroneous habitat condition estimates using the 2022 data. This affected the 2022 annual epoch, and the 2005–22 and 2001–2022 long-term epochs). The effect is muted in the continental average of the long-term epochs but obvious in analyses using the annual epoch. Therefore, results using the 2022 data were removed from this data collection. Because the analyses using these data for the EN01 measure in the DCCEEW 2022-23 Annual Report were presented as continental and land zonal averages, the data bias error in 2022 does not alter that overall result.

Technical report: Williams KJ, Valavi R, Lehmann EA, Van Niel T, Harwood T, Newnham G, Paget M, Donohue R, Giljohann KM, Liu N, Lyon P, Pinner L, Malley C, Deb D and Ferrier S (2023) Habitat Condition Assessment System (HCAS): developing HCAS v2.4 with annual epochs updated to 2021. Publication number EP2023-4902. CSIRO, Canberra, Australia. https://publications.csiro.au/publications/publication/PIcsiro:EP2023-4902. 

Details are summarised in the product brief provided with this data collection.