FACTSHEET

Useful tools to remotely assess soil water content and vegetation condition Michael Cashen Agricultural Climatologist, Wagga Wagga

When planning next season’s cropping program it is important to know how much water is in the soil. Rainfall totals disguise; rainfall intensity, infiltration into the soil, soil storage capacity, or the agronomical timeliness of the rain event, all affect its usefulness. Recent technological advances in remote sensing and computer modelling offer significant insights into remotely determining soil water content, and related vegetation extent and condition.

Australian Water Availability Project The Australian Water Availability project, developed by CSIRO, monitors and models soil water content across the continent.

The model determines past and present soil water content and changes due to rainfall, plant transpiration, soil evaporation, surface run-off and drainage

Data can be displayed as either a weekly or monthly summary of soil water content in either physical units or as a percentile relative to the same time of year in the period 1961-90.

The image shows monthly soil water content of the upper soil layer as a fraction of total soil water holding capacity. Soils which are close to field capacity would have a value of 1. As water is lost values will decrease toward 0.

This image shows monthly soil water content of the upper soil layer relative to the average of the same month 1961-90. Blue shades indicate wetter conditions than the 1961-90 baseline.

August 2011, www.dpi.nsw.gov.au/publications for updates Primefact 1115 first edition

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Analysis is available for both topsoil (0-0.2mt depth) and subsoil (0.02-1.5mt depth) layers. Surface soil water content is closely linked to short term weather patterns. Subsoil conditions act as a larger deeper store of moisture and tend to reflect accumulated longer term trends as indicated in the monthly percentile maps below.

These two images highlight the difference between soil water content for top and sub soils

To access output from the Australian Water Availability project go to www.csiro.au/awap

Normalised Difference Vegetation Index Normalised Difference Vegetation Index (NDVI) maps are derived from instruments aboard the National Oceanic and Atmospheric Administration (NOAA) satellites. These maps provide an objective index of vegetation volume and growth.

Live green vegetation absorbs visible light as part of the photosynthetic process At the same time plants scatter light in the near infrared spectrum. These differences in absorption are unique and provide a measure of greenness and green cover.

NDVI Values are between -1 and +1. In Australia typical values are between 0.1 and 0.7. Higher values are associated with higher density and greenness, values decrease with water stress, disease or death. Bare soil and snow have values close to 0 and water bodies have negative values.

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You can look at maps showing actual greenness levels (average NDVI) or anomaly levels. Anomalies are variations from the longer term mean values. Selecting the anomaly image allows you to compare current vegetation estimates with the same period in previous years (current baseline period 1992-2008) as illustrated in the images below.

Comparison of average monthly NDVI and NDVI anomaly maps for NSW.

To access the product follow the link to www.bom.gov.au/jsp/awap/ndvi/index.jsp

© State of New South Wales through NSW Department of Primary Industries 2011. You may copy, distribute and otherwise freely deal with this publication for any purpose, provided that you attribute Department of Primary Industries as the owner.

ISSN 1832-6668

Disclaimer: The information contained in this publication is based on knowledge and understanding at the time of writing (May 2011). However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of Department of Primary Industries or the user’s independent adviser.

INT11/49868

Useful tools to remotely assess soil water content and vegetation condition p 3