Wind, storms and fire
Wind
The Paterson district receives quite a lot of windy days, an important factor to be considered when planning agricultural enterprises. This first graph below shows that the strongest winds occur between June and September. Winds coming from the north-west or west in September and October are beginning to warm up, and can quickly 'burn off' the spring flush of white clover. This important pasture legume is an important feed source in summer, but can almost disappear in the face of these hot north-westerlies.
Graph showing average monthly wind speed
It is also important to look at the direction that wind comes from and the number of windy days in the year. Westerly winds blow at Tocal from May to September and easterly winds prevail during the rest of the year. Winds bringing rain are mostly from the south and east from over the ocean. West winds are usually very dry by the time they reach Tocal as they have lost any moisture they may have had in crossing the Great Dividing Range. In summer, a sea breeze often reaches the area by mid to late afternoon.
The following graphs, described as wind 'roses' are representative of the wind occurrences recorded automatically by the Bureau of Meteorology. Note that they do not represent the strength of the wind, but the number of times wind came from that direction. So, for example, in March, the wind came from a south-easterly direction on about thirty occasions. Only two representative samples of months have been noted here because they illustrate the change in wind direction through the year.
Wind roses for March and August
The general pattern for the year is as follows, in June, July and August the wind comes mainly from the west and north-west, with few exceptions. By September, the wind has varied to almost equal occurrences from the north-west and south-east. This pattern is repeated in October. By November the main winds are from the SSE and SE, and this is similar in December, January and March. By April the winds are variable, with the SE only slightly dominant over north and south winds. Winds in May vary from south, SW and west until they return in June to the pattern similar to July but with a greater dominance of westerlies.
Thunderstorms
Thunder occurs about 30 times per year at Tocal and hail occurs on average about once or twice a year; this is less than the number of occurrences on the tablelands and western slopes and usually storms in our region do not cause any damage. Notable severe storms recently occurred on 9 December 1985, 27 November 1988, 20 November 1992 and 4 December 2002.
A particularly strong thunderstorm swept through a narrow band of the Hunter Valley on 4 December, 2002. It originated near Muswellbrook and Scone and moved rapidly down the valley in a swathe that followed Webbers Creek. It hit Tocal in two distinct waves: first as driving rain, hail and wind at 12.30pm, followed 15 minutes later as a wind gale gusting up to 135 km/hr (anemometer readings). Hundreds of tiles from College buildings were peeled off in the north-westerly blast, causing damage estimated at $30,000. Trees on the college were broken off and uprooted, and at the Homestead, the renewed galvanised roof on the Slaughterhouse was blown away and a chimney on the Barracks was broken off.
While storm damage is rare on Tocal it is important in some areas that plans are in place for minimising storm damage, whether for shelter for stock or planning of crops around storm seasons.
Storm damage to the campus and landscape on 4 December 2002
Bushfires
The Australian bush is susceptible, and adapted, to fire. Humans and their structures are not. When high temperatures are combined with low humidity and strong winds, there is always a danger of bushfires if there is sufficient fuel-load to support the spread of fire.
Over the history of Tocal bushfires have ravaged the district on many occasions. Tocal has been seriously affected by fires on a number of occasions because much of the Tocal property is heavily timbered by dry eucalypt forest that is very exposed to bushfires. Most bushfires burn in the dry season, which at Tocal is in spring or early summer. The chance of a bushfire becoming established depends on the amount of fuel available, the number of days since previous rain, the humidity, the air temperature and the windspeed. Wind accelerates the drying of bushfire fuel, supplies the oxygen which promotes combustion, bends the flames over so that they radiate heat to nearby vegetation and carries burning embers away to set fire to timber ahead.
On Tocal fires generally come from the west, though a fire in 1905 also moved north towards Paterson and in 1939 and 1944 fires with narrow fronts kept going across the river to the east. While the property remains at risk through every hot dry summer period, the wetlands and lagoons around Tocal Homestead have provided some protection to the Homestead site from major devastation.
After a fire has started, its behaviour depends on the moisture and the amount of combustible vegetation, the slope of the land, the atmospheric humidity and the wind. Bushfires tend to burn uphill but the direction of the bushfire’s advance can change suddenly as the result of the onset of a sea breeze, or downdraughts from nearby thunderstorms. This can increase the risk to firefighters. Their task is often simply to protect particular places, leaving the main conflagration to be doused by the next rainfall or to burn out by consuming the available fuel.
The impacts of fire can be significant on farm operations. Apart from the potential for loss of infrastructure, stock or crops, it can be a costly and time consuming exercise to return the farm to a situation similar to that before the fire. Fences on Tocal have been burnt three times during the first half of the 20th century.