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What’s happening early this season?

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Following a dry start to winter in the wheatbelt, the recent rainfall has made a big difference to the amount of water available in the soil profile. According to the Bureau of Meteorology’s (BoM )Australian Landscape Water Balance modelling, the June relative root-zone soil moisture for about a third of the Avon River Basin is at average levels, while the rest of the catchment is experiencing below average levels. This may sound a bit depressing but compared to the same time last year where large areas of the catchment had the lowest 1% of soil moisture on record, things are looking quite positive (Figure 1).


Figure 1. The modelled AWRA-L relative root-zone soil moisture for the south-west of WA for June 2017 (left) compared to June 2018 (right) with the Avon River Basin indicated in grey. Source: Bureau of Meteorology 17/07/2018.


How this rainfall has influenced feed and crop vigour can be seen using satellite image analysis. The NDIV is a vegetation index that estimates plant vigour and can highlight areas of poor or good plant growth. Using the Decipher biomass tool (based on NDVI as an indicator of feed and crop condition) at Muresk Institute in Northam as an example, we see that plant biomas for the first half of 2017 was higher than 2018 but since the rain in June, biomass has caught up to last year’s density and looks likely to go higher (Figure 2).



Figure 2. Spatial comparison of June biomass for 2017 (left) compared to 2018 (right) (red = low; blue = high) and a mid-slope point comparison of biomass through time (bottom) at Muresk Institute, Northam. Source: Decipher 17/07/2018.


For more on the Australian Landscape Water Balance see the recording of BOM Webinar: Get near real-time soil moisture estimates for your location or catchment or the Decipher tool go here.