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The length of the annual growing season is the period between the day when the average daily air temperature in spring exceeds the temperature threshold of 5 °C and the day when it drops below this value in autumn.

Air temperature at 5 °C is generally recognised as the lower temperature threshold for plant vegetation, while the period with average air temperatures exceeding the temperature threshold denotes the length of annual cycle of vegetation. The temperature threshold so determined is used as one of the conditions for the classification of agri-ecological zones.


Charts

Figure PS06-1: Average annual growing season length in individual places throughout Slovenia in reference periods 1961-1990 and 1991-2007
Sources: 

Archive of Meteorological Data, Environmental Agency of the Republic of Slovenia, 2008

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Ljubljana Novo mesto Bilje Slap pri Vipavi Murska Sobota Maribor Rateče
1961-1990 number of days 243 238 278 276 237 243 187
1991-2007 number of days 255 251 281 286 240 247 197
Figure PS06-2: Changes in the average annual growing season length in Ljubljana
Sources: 

Archive of Meteorological Data, Environmental Agency of the Republic of Slovenia, 2008

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1961 1962 1963 1964 1965 1966 1967 1968 1969 1970
growing season number of days 279 227 249 256 243 226 268 243 235 234
1971 1972 1973 1974 1975 1976 1977 1978 1979 1980
growing season number of days 247 270 216 226 265 239 278 255 246 222
1981 1982 1983 1984 1985 1986 1987 1988 1989 1990
growing season number of days 246 222 237 235 210 243 224 228 252 260
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
growing season number of days 237 284 222 275 231 246 249 230 261 284
2001 2002 2003 2004 2005 2006 2007
growing season number of days 246 280 237 269 249 273 266

Goals

The length of annual growing season as one of environmental change indicators, together with its changes in time and space, allows for an assessment of the impact that the changing climate has on the development of plants and their environment. This indicator can also prove helpful in the preparation of adjustment procedures for the newly arising conditions and mitigation of possible adverse effects (National Environmental Action Programme).


The rise in average air temperatures and the increased frequency of days with temperatures exceeding the vegetation threshold influence the prolongation in the length of annual cycle of vegetation. The latter has a non-homogeneous character, with appreciable deviations within the period in question (i.e. 1961-2007). The 5-year running average indicates a slight cyclic oscillation. The last cycle of 5-year running average values indicates the prolongation in the length of annual cycle of vegetation since the 1990’s, which is also made strikingly evident by the comparison of average values for the periods 1961-1990 and 1991-2007.

The adjustments to the changed length of cycle of vegetation are expressed as gradual changes in agricultural technology, which, owing to the nature of agricultural production, is a lengthy process. In introducing new technologies into agricultural practice, special account is to be taken of environmental factors, the laws of environmental protection and supporting information systems (agri-meteorological data). In accordance with the National Environmental Action Programme, reduction of the burden caused by the changing length of cycle of vegetation (introduction of new varieties) will require upgrading of existing legal and economic instruments for environmental protection (biodiversity, sustainable development), acting in line with the adopted international conventions (Framework Convention of the United Nations on Climate Change, United Nations Convention to Combat Desertification, Convention on Bilogical Diversity), strengthening supervision over sources of environmental hazards, heightening environmental awareness, enhancing the knowledge on environmental issues, and encouraging sustainable forms of agricultural production.


The source of the original database is the Archive of meteorological data, Environmental Agency of the Republic of Slovenia.

For the illustration of the length of annual growing season in Slovenia, an analysis was made of daily air temperatures at 7 meteorological stations for the period 1961-2007 (meteorological stations: Rateče, Bilje, Slap pri Vipavi, Ljubljana, Novo mesto, Maribor, Murska Sobota).
Criteria for the calculation of the length annual growing season are taken from the CCL/CLIVAR (Working group on Climate change Detection, European Climate Assessment & Datasets), which labels the length of annual growing season as an indicator of climate changes No 143 (www.knmi.nl/samenw/eca). The annual growing season length presents the number of days between the first occurance of at least six censecutive days with the daily mean air temperature above 5 °C and the first occurence after July 1 of at least six consecutive days with daily mean temperature below 5 °C. In relation to the climate situation in Slovenia, the spring condition has been changed in such a way that the spring temperature threshold occurs after the last series of six or more consecutive spring days with the temperature above 5 °C, thereby excluding at least six-day long early winter warmings.


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