Recording autumn phenology: An analysis of 2019 records

Summary

Overall autumn 2019 was wet and slightly warmer than average.* There was no overall pattern to the dates in 2019; some species and events were earlier than the benchmark year, whereas others were later. Generally most of the tree events (leaf tinting, first leaf fall, full autumn tinting and bare tree) occurred slightly later or on the average date.

*Compared with the benchmark year of 2007 (chosen because the mean monthly temperatures during that year were similar to the 1961-90 averages).

Analysis of the 2019 records was included in the State of the UK Climate 2019 report, which further highlighted how climate change is having an increasing impact on UK weather. 

The weather of Autumn 2019

The timing of natural events is linked to the weather, so to thoroughly understand  phenology, we must also look at the corresponding weather at that time.

Temperature

• Average monthly temperatures in July, August, September and December were above the Central England Temperature** 30-year average (1961-90).
• October was near average temperatures for the majority of the time, with cold snaps at the very beginning and end of the month.

Rainfall

• Rainfall totals for all months were greater than the 30-year averages.
• There were notable regional differences in rainfall.

**Central England Temperature dataset is a record from a roughly triangular area of the UK, enclosed by Bristol, Lancashire and London.

Autumn leaf tinting

First tinting of trees and shrubs is recorded when the first leaf is spotted changing colour. Leaf tinting begins around this time of year because of reduced sunlight and cooler night time temperatures. 

In 2019 the average first tinting of all trees and shrubs occurred in the last weeks of September to first week of October (aside from horse chestnut*). All species were on or later than the benchmark year average. Elder and rowan were the first to begin tinting (average for both 20 September) with both species of oak being the last (pedunculate: 6 October; sessile: 5 October).

Full tint averages follow a similar pattern, with elder (14 October) and rowan (17 October) leading the way and both oak species not showing average full tint until early November (pedunculate: 6 November; sessile: 2 November). As with first tinting the average full colours were also later than the benchmark year. The greatest difference was with rowan and hawthorn, both being 8 days later than the 2007 benchmark.

*A note on horse chestnut records:

Horse chestnut was the earliest species to reach full autumn tinting (8 October) with an average first tint just less than a month earlier (9 September). This follows a pattern seen over recent years, as the trees change colour earlier due to the presence of the horse chestnut leaf miner. Leaf miner is now present across most of south-central England, East Anglia and the Midlands. An infestation results in the horse chestnut leaves becoming brown and crispy and may also lead to earlier leaf loss. This change in leaf colour occurs earlier than it would otherwise and is likely recorded as so by citizen scientists in these areas.

Find out more about horse chestnut leaf miner and how we're training volunteers to spot pests and diseases with our Observatree project.

Leaf fall and bare trees

Overall the average leaf fall dates for all trees were very close to the benchmark year. Three species (ash, beech, elder) were marginally early, four species (hawthorn, hazel, field maple and sycamore) were the same as their benchmark year averages and the remainder were slightly late. The average first leaf fall dates for all species occurred in October, except for pedunculate oak which was 1 November.

Similarly the average bare tree dates for all species occurred in November, except for pedunculate oak which was exactly one month after the average first leaf fall on 1 December. Records reveal that for all species it takes about a month from the first leaf fall until it is recorded as ‘bare’. Weather will significantly influence both events, with rainfall (both drought condition and heavy rainfall), wind and freezing temperatures all encouraging leaves to drop.

Bird migration

Swifts are always the first of the African migrants to return to their warmer over wintering grounds. In 2019 the average date for last-seen swift was 10 August, 3 days earlier than the benchmark year. Last seen house martins (18 September) and swallows (17 September) were both two days earlier than the benchmark year.

In contrast, at the end of autumn redwings and fieldfares return to the UK from colder climes such as Scandinavia and Iceland. The average date to first see redwing was 1 November and 2 November for fieldfare, both roughly a week later than the benchmark year.

Take a look at our bird pages for more information on recording bird migration this year.

Thank you

Thank you for adding Nature’s Calendar records this year. We really appreciate your support, especially under such unusual circumstances. Your records have given us an indication of how the timing of natural events unfolds across the UK and that’s really important to help us understand the impact of weather and climate on our wildlife. We couldn’t do it without you.

Tell us what's happening near you this autumn. Autumn is a ‘forgotten season’ in terms of recording phenology. Spring events are much more popular to record and we’re calling for your help to make sure our autumn records match up, so that we can keep contributing to important research like the State of the UK Climate report.

New to Nature’s Calendar or want a quick reminder on recording Autumn?

For a little more information and inspiration, take a look at our Autumn watch video on tracking and recording signs of the changing season.