A STORM Brewing: Climatic Change and its Impact on Heritage in 2020 – Manchester and Mellor Conditions

The Ironbridge at Ironbridge, early March 2020.

The weather in 2020 has felt extreme in the Manchester area, with flash floods threatening to swamp homes and archaeology sites, and then a drought leading to moorland fires and threats to upland prehistoric sites: all within just a few weeks of each other. Since 2016 I’ve been working with the Mellor Archaeological Trust on a research project, STORM, designed to help local archaeological organisations that ran historic sites cope with the heritage threats posed by climate change. Studies by Historic England and Historic Environment Scotland have shown that these threats include sea level changes, flooding events, droughts, and vegetation changes, all of which can lead to damage, erosion, and the undermining of archaeological sites.

The impact of sudden weather events on heritage was again evident in February 2020 when two powerful cyclones crossed Ireland, Britain, and mainland Europe just a week apart: storms Ciara and Dennis. The heritage impact was felt at a variety of sites. The Ironbridge Gorge suffered two flooding events with homes, shops, and internationally important industrial archaeology sites flooded as the River Severn burst its banks. Burgh le Marsh windmill in Lincolnshire had its sails ripped off. Elsewhere, homes and shops at Appleby in the Eden Valley in Cumbria were flooded, the waters lapping around the graveyard boundary of the medieval parish church and threatening to overtop the historic stone bridge across the river. Two historic watermills also reported damage due to floods: Daniels Mill near Bridgnorth in Shropshire, Heron Mill in the Eden Valley in Cumbria. Subsequently, the CHERISH research project, which is looking at the impact of coastal erosion on archaeological sites in the Irish Sea zone, has been out recording damage to sites along the eastern Irish and Welsh coasts.

Such storm events are not uncommon, but weather threats include not just sudden events like these but also long-term threats from subtler changes. The STORM project was funded through the European Union’s Horizon 2020 research programme and ran from 2016 to 2019 and was designed to look at the impact of both sudden and long-term climate threats to heritage. Now a second phase is beginning with the Mellor Archaeological Trust monitoring trends in the climate and their potential impact on local heritage sites whilst using the hazard system developed by the two dozen STORM project partners and tested at five pilot sites around the Mediterranean, western, and northern Europe (see elsewhere on this blog).

The remains of Oldknow’s Mill, Mellor

Mellor was the only pilot site within the STORM project where there were multi-period below-ground archaeological remains in an upland context at three separate locations. Thus, Oldknow’s Mill lies in a valley location at c. 90m above sea level. The Iron Age hillfort at the Mellor Old Vicarage sits at c. 220m on the western end of a prominent ridge. Finally, the Bronze Age burial site of Shaw Cairn lies on the south-west edge of Mellor Moor, an area of upland peat and heathland, at c. 324m. All three sites lie within a 2km radius of each other.

The STORM project analysis of the current climate at Mellor is based upon observations from the Met Office Ringway weather station (centred SJ 844 814) on the boarder of Manchester and northern Cheshire, lying c. 15km west of the pilot site. This provides a run of weather data parameters from 1946 to 2004 and climate indices were determined for the period 1971 to 2000 based upon these observations.

Of particular relevance to the recent stormy winter and dry spring in the Manchester area is the rainfall pattern observed in the period 1971 to 2000, a period characterized by mild winters with average mean temperatures around 5°C, and relatively cool summers with mean temperatures around 16C. The total yearly precipitation sum in this period averages approximately 800mm. The precipitation amounts, as well as the occurrence of wet days, are distributed relatively evenly throughout the year, with precipitation totals ranging between 165mm in spring (March, April, May) to 240mm in autumn (September, October, November) with between 10 and 14 wet days per month. On average, there were around 20 heavy precipitation days (days with a minimum of 10mm precipitation) and three very heavy precipitation days (days with a minimum of 20 mm precipitation) occurring each year during the baseline period. Furthermore, there were around 10 consecutive wet days and 20 consecutive dry days on average each year. For the full 1971-2000 baseline period, the longest consecutive wet day period was 16 days, and the longest consecutive dry day period was observed to be 30 days.

An initial analysis of weather data from a weather station at Rostherne, near Ringway, <a href=’https://www.worldweatheronline.com/&#8217; title=’Historical average weather’>Data provided by WorldWeatherOnline.com</a> and from the Mellor weather stations for 2020 indicates how unpredictable the weather pattern has been in the region.

At Mellor Mill data shows that February 2020 was the wettest for that month since the STORM project began in 2016 and that April was the driest for that month since the project began in 2016. Not perhaps surprising given the short run of data that the Mellor project has recorded, nor statistically significant. However, February 2020 and May 2020 were amongst the wettest months (February with 138mm) and driest months (May with 12.2mm) since 1970 in the Manchester area, using the data from Rostherne and comparing it with the average data for those months from Ringway for the period 1971 to 2000.

These events increase the impact of both the acute and long-term hazards brought about by climate change on heritage sites. In Mellor there were several periods in February and March of more than 10 consecutive wet days. Fortunately, both Storm Ciara and Storm Dennis only brought down a few branches around the Mellor Mill and Old Vicarage sites, neither of which sustained significant damaged. Nor did the excessive rainfall lead to any major flooding along this part of the River Goyt, which passes the Mellor Mill site.

The dry months of April and May 2020 (24.5mm and 12.2mm respectively), each with more than 20 consecutive dry days, saw moorland fires on the moors to the north-east of Manchester around Saddleworth and on the moorlands to the east of Mellor in the northern peak district. Fortunately, Shaw Cairn was not affected by the fires, although the moorland smoke clouds were once again visible from the site as they had been during the moorland fires of the summer of 2018. The smoke, though, drifted across south Manchester along with smell of peat burning.

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