HCAS 3.1 (1988-2022) base model estimate of habitat condition (90m grid) and National Connectivity Index (NCI) 2.0, annual epochs of HCAS from 1990 to 2022 for continental Australia with uncertainty

Brief description

Citation: Valavi R, Lehmann EA, Liu N, Levick S, Giljohann KM, Williams KJ, Johnson S, Botha EJ, Munroe SEM, Collings S, Searle R, Van Niel TG, Newnham G, Paget M, Joehnk K, Hosack GR, Harwood TD, Malley C, Gunawardana D, Sivanandam P, Richards AE, Tetreault Campbell S and Ferrier S (2025) HCAS 3.1 (1988-2022) base model estimate of habitat condition (90m grid) and National Connectivity Index (NCI) 2.0, annual epochs of HCAS from 1990 to 2022 for continental Australia with uncertainty. Updated data collection 63571. CSIRO, Canberra, Australia. DOI: https://data.csiro.au/collection/csiro:63571.

This updated HCAS v3.1 data collection derives in part from Geoscience Australia’s archive of Landsat Earth observation Collection 3 Analysis Ready Data (Commonwealth of Australia, 2021) Derivative Products version 3.1.0 (Geoscience Australia, 2022) and version 3.0.0 (Lymburner, 2022) between 1988 and 2022, and comprises for continental Australia:
• the 90 m gridded (Australian Albers projection, EPSG 3577, Geographic Datum of Australia 1994) Habitat Condition Assessment System version 3.1 (1988-2022) base model (HCAS v3.1) estimation of habitat condition for terrestrial biodiversity
• 33 annual short-term epochs of HCAS from 1990 to 2022, formed using 3-year antecedent rolling averages of remotely sensed variables.
• model-based uncertainty quantification as 95% confidence interval limits for the estimates of habitat condition for the long-term epoch (1988-2022) and selected short-term epochs (Lehmann et al., 2025)
• a classification of long- and short-term epochs of habitat condition into six modification levels based on experts’ best estimate of condition for each category of the Vegetation Assets, States and Transitions (VAST) narrative framework (Thackway and Lesslie, 2006; 2008)
• updated National Connectivity Index (NCI) v2.0 (Giljohann et al., 2022) for the long-term epoch using the HCAS v3.1 base model
• long-term epoch of connectivity-adjusted condition (NCIC) derived from the geometric mean of the corresponding NCI and HCAS outputs (1988-2022)
• several other datasets to support use and interpretation of the long- and short-term epochs of HCAS habitat condition products and derivatives, including reference sites and remote sensing inputs.

The HCAS v3.1 short-term epochs derive from the base model. The NCI and NCIC are developed by DCCEEW and published in this HCAS data collection, for the convenience of end users.

The majority are raster datasets in GeoTIFF format (*.tif) at 90 m grid resolution, Geographic Datum of Australia (GDA) 1994 (Australian Albers, EPSG:3577). All GeoTIFFs are provided as Cloud Optimised GeoTIFFs (COGs). In most cases, a corresponding *.png map image is also provided for quick views. Example summary tables by IBRA bioregions are also provided.

The HCAS v3.1 base model and epoch habitat condition data varies 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.

Data extent is defined by any data pixel that intersected a coastline polygon as defined by the land fraction dataset (Liu 2024). The data and no-data extent of each grid layer encompasses the area within the Australian Continental Exclusive Economic Zone (EEZ) (Alcock et al., 2020), excluding territories of Cocos, Christmas, Norfolk, Macquarie, Heard, and McDonald Islands, as well as Antarctica (Liu and Newnham, 2024).

Data are described in "Habitat Condition Assessment System (HCAS) version 3.1: A guide to the 90-metre data collection with uncertainty. Technical report EP2025-1549" (published in 2025, available from CSIRO's publication repository, see related links).
Lineage: The HCAS v3.1 product suite was developed at 90 m grid resolution in Australian Albers projection (GDA94) using a combination of:
• 14 annualised time series of remotely sensed ecosystem characteristic variables, 1988 to 2022 (Levick et al., 2025), sourced from the Digital Earth Australia Surface Reflectance NBART Landsat Analysis Ready Data Collection 3 (Commonwealth of Australia, 2021) derivative products v3.1.0 (Geoscience Australia, 2022) and v3.0.0 (Lymburner, 2022)
• 58 environmental covariates selected from more than 120 'non-anthropogenic' candidates largely sourced from the Terrestrial Ecosystem Research Network (TERN) compilation (Malone et al., 2025; Searle, 2023) with additional custom variables developed by Liu et al. (2025);
• spatially inferred reference sites as training data (Giljohann et al., 2025), sampled to represent the most intact remaining examples of Australia’s varied ecosystems and their environments (Valavi et al., 2025a)
• spatially inferred reference sites as benchmark data (Giljohann et al., 2025), sampled to represent both remotely sensed ecosystem characteristic variables and their environments from among the most intact remaining examples of Australia’s ecosystems (Valavi et al., 2025a).

The HCAS v3.1 reference ecosystem model (REM) was developed using a generalised additive model (GAM) with 488,619 reference sites as training data, 46 environmental covariates (selected from 58), and 14 remotely sensed ecosystem characteristic variables summarised over 35 years (1988 to 2022). The REM was used in the HCAS v3.1 base model with the 1988 to 2022 long-term epoch and 544,668 benchmark reference sites. Short-term epochs for each of the 14 remotely sensed ecosystem characteristic variables were derived as 3-year antecedent rolling averages (the target year and the two prior years), 1990 to 2022 (33 epochs). These processing steps are detailed in (Valavi et al., 2025a).

Model-based uncertainty estimates were derived from 100 bootstrap runs applied to the sample of training and benchmark reference sites to derive 95% confidence interval limits (upper 97.5th percentile of condition estimate, lower 2.5th percentile of condition estimate, and the resulting 95% confidence interval width) for each 90x90m pixel of the long-term epoch (1988-2022) and nine selected short-term epochs ending: 1990, 1995,

All data products were derived using a 90 m spatial grid in Australian Albers (GDA94 / Australian Albers).

The core collection in the HCAS v3.1 product suite comprises 34 datasets of habitat condition (the base model long-term epoch and 33 short-term epochs) with uncertainty quantification, and other input, derived and supporting datasets to inform use and interpretation, including the long-term epoch (1988-2022) of the NCI (v2.0 method) and the derived connectivity-adjusted condition, NCIC.

The "Habitat Condition Assessment System (HCAS) version 3.1: A guide to the 90-metre data collection with uncertainty" (updated and republished in 2025 as EP2025-1549) documentation, accompanying this data collection (see related links), outlines how the HCAS v3.1 differs from the HCAS v3.0 (Valavi et al. 2024; Williams et al. 2024) and HCAS v2.3 (Harwood et al., 2023; Williams et al., 2023a) data products. The updated product guide describes the uncertainty quantification products and provides further detail about limitations of particular note.

This data collection also includes an update to the National Connectivity Index version 2.0 (NCI v2) base model using the corresponding HCAS v3.1 inputs. The NCI v2.0 method (Giljohann et al. 2022) has not changed, only the input condition data.

Technical reports (in preparation) provide details about the inputs, processing methods, outputs and uncertainty quantification applied in developing HCAS version series 3. For the latest publications see: https://research.csiro.au/biodiversity-knowledge/projects/hcas/. Contact us at hcas@csiro.au or geospatial@dcceew.gov.au.