Seasonal climate comparison 2024 update
The climatic data of the current growing season in comparison to the previous seasons across WA’s 9 wine regions has been summarised by DPIRD technical officer Yu-Yi Liao.
This analysis offers wine producers insights into the similarities and differences between the current and previous growing seasons.
The graphs below illustrate monthly rainfall and accumulated rainfall from June 2021 to April 2024, followed by a comparison of accumulated growing degree days (GDD), average monthly temperature between the last 3 growing seasons, and daily rainfall for the current season.
This summer marked the warmest on record in WA since 1910 (BOM, 2024). Across all regions, there has been a substantial increase in accumulated GDD units compared to previous seasons, particularly attributed to above-average spring temperatures.
Reviewing the 3-year rainfall data, all regions experienced lower accumulated rainfall in 2023-24 compared to the previous 2 seasons. This is primarily due to the low rainfall recorded in October, March and April in 2023-24.
Growing degree day (GDD) unit calculation: the average daily temperature minus 10 when it is higher than 10°C; temperature lower than 10°C is counted as 0.
Accumulated GDD is the accumulation of GDD units from 1 October to 30 April.
Swan District
Figure 1 and 2 show data collected from the BoM Millendon weather station (site number 9281) representing the Swan District wine region.
Swan District recorded the lowest accumulated rainfall among the 9 regions during the current season.
The 2023-24 season rainfall started high in June, then gradually declined throughout summer except for a slightly higher amount in September than the previous 2 seasons; overall, the current season finished 165 mm lower than the previous season.
Unseasonal heat in October and November resulted in an early acceleration of accumulation of GDD in the 2023-24 growing season, totalling 2,977 units, exceeding the previous season’s accumulation by 505 units.
Perth Hills
Two stations were used to represent the Perth Hills, BoM station Bickley (site number 9240) and DPIRD station Glen Eagle in figure 3 and 4.
Winter rainfall in the current season was notably lower (by 110 mm) than in the previous 2 seasons.
Interestingly, January 2024 recorded 26 mm of rain, contrary to the typically dry summer conditions observed in most other regions.
Perth Hills experienced a similar trend of GDD accumulation with slightly cooler temperatures compared to Swan District.
By the end of April 2024, accumulated GDD marked 2,656 units, which is 550 units higher than the previous season.
Peel
Peel’s data in figure 5 and 6 is sourced from BoM Dwellingup weather station (site number 9538). Both 2022-23 and 2023-24 experienced a dry spring (137 mm and 155 mm respectively) compared to 2021-22 (303mm rainfall). Meanwhile, the 2023-24 season saw notably lower rainfall during November, December, March and April.
The accumulated GDD for the current season reached 2,401 units, which is 496 units higher than the 2022-23 season. There was also a noteworthy 36mm rainfall event on 17 January, similar to that observed in the Perth Hills region.
Geographe
DPIRD’s weather stations' Capel, Donnybrook and Dardanup 2 were compiled to represent Geographe in figures 7 and 8.
The low rainfall experienced in July 2023 impacted total winter rainfall for the season and from October 2023 little rainfall was experienced as illustrated by the plateauing trend line in figure 7.
Accumulated GDD totalled 2,494 units by the end of the 2023-24 growing season, which is 516 units higher than the previous season and 376 units higher than 2021-22.
Margaret River
Figure 9 and 10 illustrate Margaret River’s seasonal data from DPIRD’s Vasse, Wilyabrup, Margaret River, Rosa Brook and Karridale weather stations.
The winter rainfall pattern in the 2023-24 season mirrored that of the previous 2 seasons.
October rainfall across the 3 seasons showed 2023-24 to be significantly lower and this trend continued throughout the following months.
The accumulated GDD reached 2,158 units by the end of 2023-24.
The warm conditions during spring significantly affected early accumulated GDD, and this trend continued throughout the rest of the season.
Blackwood Valley
Data derived from BoM Bridgetown weather station (number 9617), DBCA station Styles Tower and DPIRD station Nannup are shown in figures 11 and 12.
In contrast to all other regions, accumulated rainfall from June 2023 to February 2024 followed a similar trend to the previous 2 seasons.
March and April in 2024 were unseasonably dry but overall, the total rainfall for 2023-24 was not all that dissimilar to the previous 2 seasons.
Figure 12 shows the 2023-24 season recorded a higher accumulated GDD (2,269 units) than the previous 2 seasons
October and November of 2023 were particularly warm, and few rainfall events occurred from December 2023 until the end of the growing season.
Manjimup
The BoM weather station at Manjimup (site number 9573) and DPIRD’s Manjimup HRS station provided data to represent Manjimup's growing season in figures 13 and 14.
Winter rainfall remained relatively consistent across the 3 seasons. The main variation occurred in spring, where the 2023-24 season experienced around 23% less rainfall than the previous 2 seasons. Additionally, March and April 2024 saw significantly less rainfall than previous seasons.
The 2023-24 season accumulated 2,055 GDD units, which is 441 units higher than the previous season and 294 units higher than 2021-22 season.
Pemberton
The DPIRD Pemberton weather station was the only station used in figures 15 and 16.
Pemberton enjoyed high rainfall in June 2023 but showed a drying trend from October 2023.
The region tends to experience rainfall above 100 mm in April but received only 7.2 mm in 2024.
As with all other wine regions, Pemberton also experienced a warmer 2023-24 season, accumulating 2,010 units of GDD by the end of April 2024. This total is 445 units higher than the previous vintage (1,566 units) and 285 units higher than the 2021-22 season (1,726 units).
Great Southern
Weather stations from the sub-regions of the Great Southern wine region were combined to produce figures 17 and 18.
The 2023-24 winter rainfall pattern was similar to 2021-22 and wetter than 2022-23; however, from October 2023, the current season rainfall trend was most similar to 2022-23 except for the low rainfall recorded in March and April 2024.
Comparing data across all 9 WA wine regions, the Great Southern region had the least difference in accumulated GDD between the 3 seasons.
Accumulated GDD marked 1,876 units by the end of the 2023-24 season and is 194 units higher than the previous vintage and 421 units higher than the 2021-22 season.
Summary of extreme heat days and heat waves over the past 3 seasons
The number of extreme heat days (defined for this article as 38°C and above) across the past 3 seasons is summarised in table 1; the data shows fewer extreme heat days in the 2022-23 season than in the other 2 seasons.
| Wine region | 2021-22 growing season | 2022-23 growing season | 2023-24 growing season |
|---|---|---|---|
| Swan District | 26 | 9 | 26 |
| Perth Hills | 19 | 3 | 18 |
| Peel | 11 | 1 | 12 |
| Geographe | 13 | 2 | 13 |
| Margaret River | 4 | 0 | 4 |
| Blackwood Valley | 7 | 0 | 13 |
| Manjimup | 6 | 0 | 7 |
| Pemberton | 6 | 0 | 3 |
| Great Southern | 2 | 0 | 3 |
Additionally, table 2 summarises the occurrences of heat waves, defined as 5 or more consecutive days with a maximum temperature of 35°C and above.
Interestingly, there are similar numbers of heatwave occurrences in seasons 2021-22 and 2023-24.
Worth noting, the Swan District wine region recorded a 10-day heatwave from 13 to 22 February 2022 and a 9-day heatwave from 7 to 15 February 2024.
| Wine region | 2021-22 growing season | 2022-23 growing season | 2023-24 growing season |
|---|---|---|---|
| Swan District | 3 | 3 | 4 |
| Perth Hills | 3 | 1 | 3 |
| Peel | 3 | 1 | 2 |
| Geographe | 2 | 0 | 1 |
| Margaret River | 1 | 0 | 0 |
| Blackwood Valley | 2 | 0 | 1 |
| Manjimup | 1 | 0 | 0 |
| Pemberton | 1 | 0 | 0 |
| Great Southern | 0 | 0 | 0 |
For further information on the data presented, contact Yu-Yi Liao.