CLIMATE

Data collected, by the Bureau of Meteorology from various localities within the region, as climate averages, are presented in Appendix I. For ease of analysis and presentation the data have been reduced to an index, the Australian Smart Dry Climate Index (Smart and Dry, 1980) given as Table 3. This index uses the following parameters to assess climate:

• Temperature is characterised by both, the Mean January daily temperature, or MJT, and by the difference between January and July mean daily temperatures, known as the Mean Annual Range or MAR.
• Sunshine is characterised as mean daily hours of bright sunshine for a standard growing season, October to March. The only data available for the region are from the Nowra RAN base.
• Rainfall is summed over the full year and also over the standard growing season (October – March).
• Relative humidity, or RH, is expressed as the mean 9.00am value for January.

Data generated by the Index are given below for major centres in the proposed region (see Locality Map). Note that no data are available for Ulladulla, the most southerly town in the region. For the sake of completion the data from Point Perpendicular Lighthouse, located 40 Km northeast of Ulladulla, in Jervis Bay, and the Pilot Station at Moruya, 60Km south of Ulladulla, are included as alternates for Ulladulla.

REGIONAL CLIMATIC DATA IN SMART DRY INDEX FORMAT

Discussion of Climatic Data

Temperature expressed as the mean January temperature (MJT) and calculated by taking the average of the mean daily maximum and the mean daily minimum (see raw data Appendix II) has a very limited range from 19.900C (Moruya Heads) to 21.650C (Wollongong University). The mean annual range (MAR) has an equally limited range from 8.900 to 9.850C.

Rainfall data show two generalised populations, one ranging approximately 850mm and 950mm annually with growing season totals in the range 480 to 530mm, the other with annual totals above 1000mm and growing season totals in the range 650 to 800mm. The higher rainfall population, represented here by the Nowra RAN Airbase, is representative of localities close to the major escarpment which lies 10 to 35 Km west of the coast (see the Section 5.4, Physiography, below). Areas immediately west of the escarpment have significantly higher rainfall than the coastal area (see the comparison with the Southern Highlands region below) due to orographic rainfall on the western slopes of the Great Divide that face easterly-moving weather systems. Some orographic rain spreads across the escarpment to fall on its immediate eastern side. This orographic rain rarely reaches the coast.

The major rainfall on the coastal fringe is not orographic precipitation but is from the periodic presence of low-pressure cells in the Tasman Sea that brings general rain to the area.

This generalised pattern of rainfall distribution is represented very well in the area of greatest concentration of wine grape growing – the area between Nowra and Gerringong. Vineyards close to the town of Berry and the escarpment (for example Cambewarra Estate, Bundewallah) have up to 50% more rain (1450mm versus 950mm) than vineyards on the coast such as Coolangatta Estate and Seven Mile Vineyard.

The other major climatic feature that has common expression throughout the area is relative humidity. The mean 9am data for January show uniformly high relative humidity (mostly above 70%) throughout the region.

The dominant coastal setting of the region leads to low sunshine hours, sunshine hours being here given as annual average hours per day. In common with many coastal localities cloud cover is common throughout the proposed region.

The relatively high MJT data classify the region as being a “Warm” wine producing area. Similarly the low MAR values, together with the low sunshine hours and high relative humidity, classify the climate of the region as maritime.

By contrast, as shown in Table 4, the nearest adjacent wine producing region, Southern Highlands, has a climate characterised by similar rainfall patterns (including a marked east – west variability) but lower temperatures leading to a “cool climate” classification. The comparative data for Robertson (in the east of the region, close to the escarpment) and Bowral (in the west, away from the escarpment) have been used and compared to Nowra town area (on the coast) and Nowra RAN Air Base, which is to the west, close to the Great Dividing Range.

As can be seen from the data, localities close to the escarpment (RAN Air base, Robertson) have higher rainfall (orographic) than areas away from the escarpment. The Southern Highlands also has lower average temperatures (particularly evident in the mean annual range).

COMPARATIVE REGIONAL CLIMATIC DATA IN SMART DRY INDEX FORMAT