HOW SOIL TEMPERATURE REGIMES CHANGE
AS THE CLIMATE WARMS
– SHORT COMMUNICATION
DOI:10.30825/5.EJPAU.184.2020.23.1

Juha Karvonen
Department of Agricultural Sciences, Faculty of Agriculture and Forestry, University of Helsinki, Finland

ABSTRACT

Finnish soil temperature regimes have been pergelic, cryic, and frigid, where pergelic is coldest and unsuitable for agricultural use. The study monitored soil temperatures at a soil depth of 50 cm in 2010, 2013, 2016 and 2019 to look at how the soil temperature regimes have changed. Probably, as a result of climate warming the soil temperature regimes in Southern Finland in the Helsinki region at a latitude of 60–61°N have raised from cryic and pergelic to warmer mesic over a period of ten years.

Key words: soil temperature regimes, climate warming, temperature zones, Baltic countries.

INTRODUCTION

The two criteria that define soil temperature regimes are the mean annual soil temperature and temperature difference, which are mean summer soil temperatures of June, July, and August compared with the mean winter soil temperatures of December, January, and February. In the cryic soil temperature regime, the mean annual soil temperature at a depth of 50 cm from the soil surface is higher than 0°C but lower than 8°C, and the average summer temperature rises to 15°C [4]. There is also an average annual temperature of up to 8°C in the frigid soil temperature regime, but the difference between the mean summer, and the mean winter soil temperatures is more than 6°C, and the average summer temperature is at least 15°C. In the mesic soil temperature regime, the mean annual soil temperature is 8°C or higher but it remains lower than 15°C, and the difference between the mean summer and mean winter soil temperatures is more than 6°C [2]. If the mean summer air temperature in Finland increases by 1–2°C, it shifts many soils from cryic or frigid to mesic. In the coming decades, global warming will shift the soil temperature zones in Europe to higher northern latitudes.

MATERIAL AND METHODS

The soil temperatures were recorded year-round using waterproof temperature and humidity loggers (Thermo Button 21G, Proges-Plus, France). The loggers at a depth of 50 cm measured soil temperatures at four-hour intervals, which they recorded into the memory; from there the, the data were transferred for analysis.

RESULTS AND DISCUSSION

Besides mountainous areas, a large part of European soil has had the mesic temperature regime, whose northern border runs along the latitude of 58–59°N in the Baltic Countries and the southern part of the Scandinavian Peninsula (Tab. 1). Previously, Yli-Halla and Mokma [3] have estimated soil temperatures at a depth of 50 cm in Southern Finland in the Jokioinen and Anjala areas at the latitudes of 60–61°N based on the average annual air temperatures. The average soil temperature in Jokioinen was 5.9°C in 1958–1970, and Anjala, it was 6.4°C in 1982–1990. Correspondly, the average annual air temperatures were 3.6°C in Jokioinen and 4.2°C in Anjala, and the average soil temperatures in the summer months were 13.7°C in Jokioinen and 12.7°C in Anjala.

According to results of Yli-Halla and Mokma [3], on the northern coast of the Gulf of Finland at a latitude of 60–61°N opposite Estonia, Southern Finland has had the colder cryic or frigid soil temperature regimes. In 2010–2019, the average air temperature in Southern Finland was 6.9 ± 0.7°C, and it was 7°C or higher seven times. In 2017, the highest air temperature average was 7.8°C [4]. As the climate temperature has risen at least 2°C compared to the 1958–1970 and 1982–1990 averages, the soil temperature regimes of the coastal areas of Southern Finland have moved toward the warmer mesic soil temperature regimes (Tab. 2).

In the same climate and at the same latitude, soil temperatures at 50 cm depth varies relatively little from year to year at the same latitude. Therefore, in the Tuusula in the Helsinki region, the mesic soil temperature regimes that appeared in 2016 and 2019 resulted from global warming, which has also caused a significant increase in soil temperatures compared to the previous 20–40 years [3]. Changes in the soil temperatures in the Helsinki region will continue to be monitored.

CONCLUSION

As the climate temperature rises, soil temperatures will also rise, and the soil temperature regimes of the coastal areas of the Gulf of Finland should be reassessed over the coming decades.

Received: 15.01.2020
Reviewed: 27.01.2020
Accepted: 1.02.2020

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