Title

NSW Aridity Index - High resolution (30 meter)

Show on SEED Web Map

Name: Show on SEED Web Map

Protocol: WWW:DOWNLOAD-1.0-http--download

Description:

Display dataset on SEED map viewer

Function: download

Data Quality Statement

Name: Data Quality Statement

Protocol: WWW:DOWNLOAD-1.0-http--download

Description:

Data quality statement for NSW Aridity Index - High resolution (30 meter)

Function: download

Download Package

Name: Download Package

Protocol: WWW:DOWNLOAD-1.0-http--download

Description:

Data (GeoTIFF)

Function: download

ArcGIS REST Services Directory - NSW Aridity Index - High resolution (30 meter)

Name: ArcGIS REST Services Directory - NSW Aridity Index - High resolution (30 meter)

Protocol: WWW:DOWNLOAD-1.0-http--download

Description:

An ArcGIS Server web service represents a GIS resource such as a map, locator, or image that is located on an ArcGIS Server site and is made available to client applications. Depending on the layers enabled, this web service allows a user to query its features and/or visualise the dataset. This service is aimed at advanced geographical information users, and will require access to geographical information system (GIS) software such as ArcGIS/ArcMap.

Function: download

Code

1ee4c0a1-d576-44ae-8b6f-b5215e6325ba

Name

ISO 19115

Edition

2016

Code identifying the spatial reference system

4283

Topic category

climatologyMeteorologyAtmosphere

environment

Title

ANZLIC Search Words

Reference date

2008-05-16

Coordinate reference system

Authority code

urn:ogc:def:cs:EPSG::

Code identifying the coordinate reference system

5711

End position

N/A

Contact info

Contact position

Data Broker

Organisation name

NSW Department of Climate Change, Energy, the Environment and Water

Full postal address

NSW

Australia

data.broker@environment.nsw.gov.au

Telephone number

131555

Email address

data.broker@environment.nsw.gov.au

Web address

https://www.nsw.gov.au/departments-and-agencies/dcceew

Responsible party role

pointOfContact

Lineage

1 Introduction Aridity index or radiative index of dryness (AIB) is a non-dimensional measure of the long-term balance between rainfall and net radiation. Landscape aridity can be calculated from the annual sum of net radiation, Rn (MJ/m2/day) and precipitation, P through the following ratio Equation 1 AIB = Rn / λP
where P is the average daily rainfall (m/day) and λ is the latent heat of vaporisation (MJ/m3) which is a function of topographic adjusted surface temperature, TD (°K): Equation 2 λ = (3.146 – 0.002361TD) x 1000 And TD is a function of air temperature Ta (°C), the change of temperature with elevation Tlapse , The topographic downscaling factor STD, Z is the elevation of each 30 m cell, Zb is the average elevation of 5 km tile, and the leaf area index, LAI by the following equation: Equation 3 TD (°C) = Ta – ((Tlapse*(z-zb)) / 1000) + k (STD – 1/STD) x (1 – LAI / LAImax) Equation 4 TD (°K) = TD (°C) + 273
Where k = 1 and the standard lapse rate will typically decrease at a rate of roughly 9.8 degrees Celsius per thousand meter, Tlapse = 9.8.

2 Layers implemented in the model 2.1 Net Radiation (Rn) Mean monthly solar radiation was modelled across Australia using topography from the 1 arcsecond resolution SRTM-derived DEM-S and climatic and land surface data. The twelve SRAD modelled net radiation layers (MJ/m2/day) were used to calculate the net radiation layer. The 1 arcsecond tiled SRAD net radiation .tif files can be found here: https://data.csiro.au/collection/csiro:18670?q=net%20radiation&_st=keyword&_str=47&_si=1

.tif files were opened in ArcGIS Pro, projected, extracted to the area of interest, and averaged over the twelve months.

2.2 Average daily rainfall (P) Annual daily rainfall NetCDF files for thirty years from 1992 to 2021 were downloaded from Australian climate data SILO website. The NetCDF files can be found in here: https://www.longpaddock.qld.gov.au/silo/gridded-data/ By using Python code in each individual year, the mean rainfall in each year was calculated, consecutively the mean rainfall over the 30 years were calculated. After exporting the final .tif file and opening it into ArcGIS Pro, projected and extracting the area of interest, the pixel values divided by 1000 to convert the rainfall unit from mm to m. Finally, the layer was resampled to 30 m to have the same pixel size as net radiation layer.

2.3 Surface temperature (Ta) The maximum and minimum surface temperature NetCDF files for thirty years from 1992 to 2021 were also downloaded from Australian climate data SILO website. The NetCDF files can be found in here: https://www.longpaddock.qld.gov.au/silo/gridded-data/

In ArcGIS Pro, the average surface temperate for each year was calculated by the following equation: Equation 5 (Tmax + Tmin) / 2 The exported .tif file were projected and extracted to the area of interest and resampled to 30 m.

2.4 Digital elevation model (DEM) from SRTM The SRTM .tif files were downloaded from the SEED website: https://datasets.seed.nsw.gov.au/dataset/srtm18 The raster file was projected and extracted to the area of interest and snapped to the surface temperature layer.

2.5 Lapse rate temperature (Tlapse) Lapse rate standard was mentioned in the introduction section.

2.6 Topographic downscaling factor (STD) Topographic downscaling factor was calculated based on the modelled mean monthly shortwave radiation ratio. Mean monthly shortwave radiation ratio was modelled across Australia using topography from the 1 arcsecond resolution SRTM-derived DEM-S and climatic and land surface data. The twelve SRAD modelled short wave ratio layers were used to calculate the mean short ware ratio layer. The 1 arcsecond mosaic SRAD short wave ratio .tif files can be found here: https://data.csiro.au/collection/18731v002

Tif files were opened in ArcGIS Pro, projected and snapped to surface temperature (Ta), extracted to the area of interest, and averaged over the twelve months.

2.7 Leaf area index (LAI) Bands 4, 5 and 6 of the Landsat 8 scenes to cover the area of interest were downloaded and mosaiced. By the equation 6, leaf area index was calculated. Equation 6 Band 5 / (Band 4 + Band 6) The Landsat 8 scenes can be found here: https://earthexplorer.usgs.gov/ The final mosaic raster file was projected and snapped to surface temperature (Ta) and extracted to the area of interest.

2.8 Maximum leaf area index (LAImax) The leaf area index layer with 30 m pixel size In ArcGIS Pro was aggregated with max aggregation technique to 5000 m. By applying this step, we will have the maximum LAI value in each 5 km which is required in Equation 3.

2.9 Topographic adjusted surface temperature (TD ) In Python by using equation 3, topographic adjusted surface temperature (TD) can be calculated.

2.10 Latent heat of vaporisation (λ) In Python by using Equation 2, latent heat of vaporisation (λ) can be calculated.

References: Nyman et al., 2014. Aust. Met. and Ocean. Journal 64 109–122.

Use constraints

This data is provided under a Creative Commons Attribution 4.0 licence http://creativecommons.org/licenses/by/4.0. Attribute 'NSW Department of Climate Change, Energy, the Environment and Water' in publications using this data.

Limitations on public access

Contact position

Data Broker

Organisation name

NSW Department of Climate Change, Energy, the Environment and Water

Full postal address

NSW

Australia

data.broker@environment.nsw.gov.au

Telephone number

131555

Email address

data.broker@environment.nsw.gov.au

Web address

https://www.nsw.gov.au/departments-and-agencies/dcceew

Responsible party role

pointOfContact

Contact position

Data Broker

Organisation name

NSW Department of Climate Change, Energy, the Environment and Water

Full postal address

NSW

Australia

data.broker@environment.nsw.gov.au

Telephone number

131555

Email address

data.broker@environment.nsw.gov.au

Web address

https://www.nsw.gov.au/departments-and-agencies/dcceew

Responsible party role

pointOfContact