Determining mean dates of beginning and end of periods with air temperature above temperature thresholds (5°c, 10°c, 15°c)

Daily/annual fluctuation of air temperature depends on climate characteristics of the given area. Thus we have early or late crossing of air temperature thresholds.

 Temperature thresholds are very important for active life of plants: 0°C, 5°C, 10°C and 15°C. At 0°C, the active life of plants shuts down, above 5°C grasses and true grasses of moderate zone begin vegetating, sub-tropical plants begin vegetating above 10°C, and tropical plants above 20°C.

Mean air temperature above 5°C represents a biological zero for the majority of plants - it is the temperature at which they begin and end their vegetation cycle. Early or late ending of their vegetation cycle is strongly affected by zonality and altitudinal distribution, and with increased latitude and altitude - the quantity of heat reduces.

For the purpose of this climate atlas, we have processed and analysed the mean beginning date, end date, and mean duration of the period with mean daytime temperature ≥ 5°C, 10°C, and 15°C taken at weather stations in the Federation of Bosnia and Herzegovina in the period 1961-1990.

The mean beginning date, end date, and mean duration of the period of these typical threshold temperatures, were determined using methods based on graphs and calculations.

 To determine the beginning/end date using such methods, one must have an overview of the annual temperature changes for the given location, and use it to calculate typical temperatures.

Calculation method is based on the fact that the slope of the upward and downward sections of the annual temperature curve is rather linear.

 The upward section of the annual temperature curve is calculated using the following equation:

$$d_+=D\frac{P-t_b}{t_a-t_b}$$

For the downward section of the curve:

$$d_-=D\frac{t_a-P}{t_a-t_b}$$

Meaning of the symbols:

  • P temperature threshold (5°C, 10°C, 15°C)
  • d+  difference in days between the mean date of the month above the threshold temperature and the date on which the threshold temperature P for the upward section of the curve occurs
  • d-  difference in days between the mean date of the month below the threshold temperature and the date on which the threshold temperature P for the downward section of the curve occurs
  • D difference in days between the mean dates of the month and the mean monthly temperatures or
  • ta mean monthly temperature above the threshold P
  • tb mean monthly temperatures below the threshold P

Analysis of the years of data from the period 1961 -1990 has shown an evident rule concerning horizontal and vertical distribution of stations. The beginning of the vegetation period is the date on which the mean daytime air temperature exceeds 5°C, when the majority of plants enter their growth and development stage. Areas with the earliest beginning date for this period match the areas of the latest end dates for the period and vice versa.

Station

Threshold 5°C

Threshold 10°C

Threshold 15°C

 

Beginning of the period

End of the period

Duration of the period (in days)

Beginning of the period

End of the period

Duration of the period (in days)

Beginning of the period

End of the period

Duration of the period (in days)

BIHAĆ

7 March

24 November

262

10 April

23 October

196

14 May

21 September

130

BJELAšNICA

26 May

28 September

125

19 July

15 August

27

19 July

15 August

27

BUGOJNO

19 March

12 November

238

22 April

12 October

173

1 June

8 September

99

ČAPLJINA

16 January

16 December

334

20 March

14 November

239

28 April

11 October

166

GORAŽDE

10 March

15 November

250

14 April

17 October

186

20 May

17 September

120

GRADAČAC

6 March

23 November

262

7 April

24 October

200

9 May

26 September

140

IVAN-SEDLO

4 April

5 November

215

6 May

4 October

151

25 June

25 August

61

JAJCE

12 March

19 November

252

14 April

20 October

189

20 May

18 September

121

LIVNO

22 March

14 November

237

26 April

12 October

169

4 June

8 September

96

MOSTAR

18 January

16 December

332

19 March

16 November

242

26 April

17 October

174

SANSKI MOST

10 March

20 November

255

12 April

19 October

190

17 May

18 September

124

SARAJEVO

15 March

17 November

247

19 April

17 October

181

25 May

16 September

114

TUZLA

11 March

19 November

253

12 April

19 October

190

16 May

17 September

124

ZENICA

9 March

17 November

253

11 April

20 October

192

15 May

19 September

127

Period with temperatures above 5.0°C in lowlands of the northern Bosnia begins, on average, in the first decade of March, and in the far north-west, during the first and second decade of March. As the altitude increases, dates on which the temperature exceeds 5°C are increasingly postponed in the central parts of the country as well, and occur during the second and third decade of March, and in the mountains, in the first decade of April. (Table 1)

In the south of the country, vegetation begins in late January/early February; in some coastal locations, it lasts all year long.

Vegetation period in lower parts of northern Bosnia usually ends in the second and third decade of November, and in the southern parts of the country, in the second decade of December. In the mountains, vegetation ends much earlier, on average - in the third decade of October.

The average duration of vegetation period in the lowlands is about 259 days, in the central basin area about 247, and in the south of the country, about 326 days. As the altitude increases, duration of vegetation is shorter; above 1000 meters, its average duration is about 195 days, while at heights above 2000 meters, average duration of vegetation is merely 125 days.

Distribution of beginning dates and end dates with temperatures above 10°C in horizontal and vertical direction is quite similar as for the 5.0°C threshold. In the northern part of the country, this period, on average, begins in the first or the second decade of April, in central parts of the country in the third decade, and in the highlands - in the first decade of May. The end of this period in northern parts of the country commences in the second decade of October, while in the mountains, in late September or early October.

In the southern parts of the country, this period starts earlier, in the third decade of March and first decade of April. The period with temperatures above 10°C ends in the first and second decade of November. Periods with mean daytime temperature above 15°C in the south of the country on average begin in late April and early May, and end in the second decade of October. In the lower parts of the country, this period begins in the first decade of May, and ends in the third decade of September. As the altitude increases, the date of beginning of this period is significantly delayed - it occurs in the second or third decade of June. At altitudes above 1300

m, due to a short period with air temperatures above 15°C, determining of this threshold is not of any major practical use.