The River Murray in November and spring 2015

In the first weekly report of each month, our river operators look back at the month that came before so here’s our rundown on the River Murray in November and also Spring 2015.

Interested also in our look back on the 2014-15 water year? See our blog post.

Looking for detailed rainfall, inflows, storage and operations for the river week ending 2 December 2015? Have a read of our weekly report.

Our look back

This is an excerpt from our weekly report of river operations on the Murray for the river week ending 2 December 2015.

November 2015 saw wetter conditions than the long-term average across the majority of the Basin (see below map). The Bureau of Meteorology (BoM) has reported that overall rainfall for the Basin in November was 21 per cent above the long-term mean, with an area-averaged total of 48.4 millimetres—the 49th lowest (of 116) November rainfall on record. In contrast, BoM also reports that spring area-average rainfall for the Murray–Darling Basin was 30 per cent below the mean, and was 35th lowest on record due to the very dry conditions seen in September and October.

Murray Darling Basin rainfall deciles for November 2015 (Source: Bureau of Meteorology).

Temperatures for November were above average across almost all of Australia, including the Murray–Darling Basin (see below map). In particular, minimum temperatures were the equal highest on record across Australia. Queensland recorded their second highest mean and minimum temperature anomaly (+1.96 °C and 1.87 °C, respectively), and third highest maximum temperature anomaly (+2.06 °C). NSW, Victoria and South Australia had maximum temperatures anomalies greater than 2 °C above the long-term average, which ranked in the top 20 warmest on record.

Spring 2015 was the second warmest spring on record for Australia with a maximum temperature anomaly of +2.08 °C (compared with the record in 2014 of +2.32 °C). All Basin states recorded temperature anomalies in the top 10 highest on record. Victoria recorded their second highest maximum temperature anomaly in spring (+2.99 °C) while NSW and South Australia recorded their fourth highest (+2.86 °C and +2.71 °C, respectively).

Murray Darling Basin mean temperature anomaly for November 2015 (Source: Bureau of Meteorology).

Despite the higher rainfall throughout November, the warm temperatures and dry catchments resulted in inflows staying relatively stable. Monthly inflows (excluding Snowy, Darling, IVT and environmental inflows) increased slightly from around 245 gigalitres in October to around 250 gigalitres during November. Based on historic data, this volume would be exceeded in November in 85 out of 100 years.

Estimated evaporation losses from MDBA storages for November 2015 are reported in the below table. Evaporation is estimated by multiplying the surface area of the storage by the net evaporation. Net evaporation is derived by subtracting the rainfall recorded at the storage from the calculated evaporation. Compared to last year, evaporation for November 2015 was significantly lower at both Dartmouth and Hume. This can be attributed to the lower temperatures and higher rainfall in the south-eastern regions of the Basin, as well as the lower volumes of water in storage (hence smaller wetted surface areas). At Menindee Lakes and Lake Victoria, evaporative losses were more consistent with those from last year.

Table 1: Monthly evaporation figures for MDBA storages

**Evaporative loss from storage = surface area of the storage x net evaporation. Net evaporation = measured evaporation (using a ‘pan’ instrument) – rainfall.

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Follow the link to see previous monthly updates from the last six months.