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The climatic and agroclimatic characterization of autumn 

on the territory of Moldova

 

From meteorological point of view the beginning of the autumn season   is considered along with the stable transition of the average daily air temperature through +15C  towards its decrease. On the territory of the Republic of Moldova autumn starts in average between 12 (Briceni) and 23 September (Cahul), and its length is in average 80 days. Nevertheless, in the last years, depending on the synoptic processes particularities, the start date of autumn may deviate from the average. So, since the beginning of observations the earliest autumn was recorded on 23 August 1980, and the latest on 16 October 1896. Autumn season ends along with the stable transition of the average daily air temperature through 0C towards its decrease, that is usually recorded in the first decade of December.

The average air temperature in autumn oscillates between +8,3..+10,6C. The coldest autumn was registered in 1988,  with the  average  air  temperature of +6..+8C,  that  is 2-2,5C lower that the norm. The warmest autumn was recorded in 1923, when the average air temperature during the mentioned season constituted +13..+14C, that is 3-3,5C above the norm. Since the beginning of observations the lowest autumn temperature was recorded on 29 November 1892 -21,7C (Chişinău), and the highest +37,3C (9 September, 1946, Chişinău).

The first frosts on the soil surface are noticed in average on the territory of the republic in the first half of October, and in the air, generally, in the second half of the same month. Still, in some years, the surface soil frosts may occur even in the first decade of September - 8 September, 1953, (Camenca, Rîbniţa, Bravicea, Corneşti, Comrat) with the intensity of 0ºC, and in the air in the second decade of September (17 September, 1952, Briceni, Bălţi, Tiraspol, Leova) with intensity up to -2,5ºC.

The quantity of fallen precipitations during the autumn season on the territory of the country is in average 100-135 mm, or circa 20% of the annual norm. The driest was the autumn of 1963, when the registered quantity of precipitations constituted 8-36 mm, or 7-27% of the norm.  During the 1996 autumn, there has happened the vice versa the quantity of fallen precipitations exceeded the norm 2-3 times and reached the value 240-345 mm. In the last years the precipitations daily maximum during the season reached the value 153 mm (September, 2001, Leova).

For the autumn season it is specific the increase of the number of days with fog (in average from 1-2 days in September to 5-9 days in November). In some years, by the end of September there may fall the first snow, and in November there may be recorded ice and frost deposits, as well as snow storms. Still, the probability of these events is very low. Amongst the dangerous meteorological phenomena there may be noticed the early frosts, that may occur in September in average once in 7 years, and in October almost yearly. The probability of heavy rains reduces in average to once in 2 years in September and once in 8 years in October.

The temperature regime during the autumn season on the territory of the republic fully insures the ripeness of the autumn crops.

According to long term average data, in the first half of September the full maturity of maize beans (5-17 September), the ripeness of the late apple and pear varieties (7-12 September) is recorded. This period represents the optimal term for autumn wheat seeding in the majority of the districts of the country.The   long term average productive humidity reserves in the arable soil layer constitute 20 -25 mm.

In the second half of September, after 11-14 days since the seeding, the autumn wheat rise phase is noticed.

Along with the stable transition of the daily average temperature through +15ºC towards its decrease, the favorable conditions for the development and growth of the grapes are finishing.  

At the end of September the sugar beet harvesting begins.

According to long term average data, until 10 October the seeding of the autumn wheat finishes. The autumn wheat seeded after this term ends the autumn vegetation period without reaching the twinning phase and has a poorly developed root system not resilient to the winter frost.     

The autumn wheat, seeded in optimal terms, namely in the first decade of October, registers the appearance of the third leaf and in the second decade the mass twinning.

By the end of October the defoliation of the fruit trees begins.

According to the long term average data, in the second decade of October (the stable transition of the average daily air temperature through +10º) the active vegetation of the crops ends. In this period the sugar beet, potato, fruits and late vegetables harvesting is finalized.

The early autumn frosts reduce the vegetation period of the grapes. Besides this, the wood ripeness process (accumulation of reserve and protection substances against the winter frosts) is disturbed. The most dangerous are the early autumn frosts with the intensity-6 and lower, because they damage the formed buds.

During the stable transition of the daily average air temperature through +5º towards its decrease (in average in the first decade of November) the vegetation period of the crops finishes. In this period (in average on 11-14 November) the apples, plums, apricots, somewhere the cherries, sour cherries and pears finalize their defoliation phase. In November, all the agricultural works end.

During the stable transition of the daily average air temperature through +3º towards its decrease (in average on 21-26 November) the autumn crops vegetation period interrupts. In this period they are passing the twinning phase.  

In September and October there are favorable conditions for the agricultural activities. In November the number of favorable days for these activities gradually reduces.

 

Chief MCMC                   T. Bugaeva   

Chief AFC                      T. Mironova