Projected changes in thermal seasons and the growing season in Finland

Abstract

ABSTRACT:The durations of the thermal seasons and the growing season till the end of this century are inferred from projected monthly mean temperatures, separately for the SRES A2 and B1 scenarios. For the baseline period 1971-2000, we use a high-resolution observational data set covering Finland, and an average of the temperature responses simulated by 19 global climate models (GCMs) is added to the observed temperatures to obtain projections for the future. Daily climatological temperatures, needed for the determination of the onset and end dates of the seasons and the effective temperature sum, are derived from the monthly means employing a Fourier algorithm that can reproduce monthly mean temperatures perfectly.Under baseline conditions, there are four thermal seasons everywhere in Finland apart from the elevated area in northwestern Lapland. Under the A2 scenario, thermal winter will disappear in the South-western part of the country by the period 2070-2099. Elsewhere winter shortens by 2-4 months. Summer lengthens by slightly over 1 month. Intermediate seasons become longer everywhere except in northernmost Lapland. The thermal growing season lengthens in inland areas by 40-50 days, on the south-western coast even more. The effective temperature sum doubles in the north and increases 1.5-fold in the south. Conditions in Lapland would thus resemble those currently prevailing in southern Finland. Under the B1 scenario the change is smaller, especially in the second half of the century.The robustness of the findings was assessed by considering the differences between the temperature change projections of the various models. The uncertainty in the onset and termination dates was typically of the order of ±2 weeks. Regional downscaling based on regional climate model (RCM) data did not alter the main conclusions.

The thermal seasons variability in Poland, 1951–2010

“…Such results confirm the thesis presented by Menzel (2000), Ruosteenoja et al (2010) and others for various parts of Europe. Autumn is the season with the highest tendency toward later onset, and it starts, on average, later by 0.14 days/year in Poland.…”

“…Many papers considered eight thermal seasons in relation to phenological conditions (Piotrowicz 2010), four seasons while referring to astronomical or meteorological criteria (Pielke et al, 1987;Rapp and Schoenwiese 1994;Tveito et al 2000;Ruosteenoja et al 2010), and six seasons according to original attempts at disambiguation (Jaagus et al 2003;Czernecki and Miętus 2010).…”

“…In a temperate climate zone, increases in mean air temperature usually induce an earlier onset and a lengthening of the growing seasons (Carter 1998;Menzel 2003;Kożuchowski and Degirmendžić 2005;Song et al 2009;Irannezhad and Kløve 2015), described as any period with a daily mean temperature above 5°C. An earlier onset is also typical for spring and summer, while autumn and winter begin later (Ruosteenoja et al 2010).…”

“…As presented in some papers (Rapp and Schoenwiese 1994;Jaagus et al 2003;Kożuchowski and Degirmendžić 2005;Ruosteenoja et al 2010), the sensitivity of the thermal seasons' occurrence may vary depending on the region and may have different impact on the environment, its adaptive capabilities, including further agricultural and food production problems (Kramer et al 2000;Lobel and Field 2007). This fact causes an increase of interest in thermal seasons' variability as an additional index of climate changes, which follow the direct perception of humans (Rebetez 1996).…”

Optimal Regulation of the Balance between Productivity and Overwintering of Perennial Grasses in a Warmer Climate

“…In addition to this direct effect of temperature and CO 2 concentration, cool regions with non-productive winters are likely to have longer thermal growing seasons (often defined as the part of the year when the daily mean temperature exceeds 5 • C), with earlier springs and later autumns. For example, in Finland, where the annual mean temperature has most likely increased by at least 2 • C during the last 150 years [3], the thermal growing season was predicted to become one to three months longer by the end of the century as compared to the period 1971-2000 [4]. Such extended growing seasons are expected to contribute to the increase in annual grassland yields in temperate climates [5][6][7][8][9].…”