The seasonal distribution of atmospheric precipitations in the Khabarovsk territory in connection with forest fires

THE SEASONAL DISTRIBUTION OF ATMOSPHERIC PRECIPITATIONS IN THE KHABAROVSK TERRITORY IN CONNECTION WITH FOREST FIRES

Telitsyn G.P. (Bolshekhekhtsyrski State Nature Reserve, Khabarovsk, RF)

Our analysis of the relationship between sums of summer precipitations and sums of winter precipitations based on the data of three weather stations in the Khabarovsk territory for the years of 1974-2008 demonstrated that in 80 % of cases low sums (lower than the yearly average) of winter precipitations were followed by low sums of precipitations of the posterior summer, and vice versa.

Seasonal distribution (winter vs. summer) of atmospheric precipitation data of three weather stations of the Khabarovsk territory for the years of 1974 - 2007 were analyzed to reveal the conjectured relationships between sums of winter precipitations and precipitation sums of posterior summers, and vice versa: between sums of summer precipitations and those of the posterior winters. It was presumed that if such relationships exist, they could be used for forecasting sums of precipitations of the posterior season based on that of the preceding one. Would the analysis result in revealing the presumable relationships, the latter could be useful as the key for selection of the analogous year to copy its weather scenario on the coming year to foresee weather cataclysms, as well as those tied with them (forest fires, floods, etc.).

Initial data and treatment procedure

Precipitations of November, December, January, February and March were summed for winter periods, and for posterior summer periods precipitations were summed for April, May, June, July, August, September and October. The corresponding weather data were found in Weather Annual Collections [1] for three weather stations: Khabarovsk, Georgievka and Komsomolsk situated in the vicinity of the corresponding towns in the Khabarovsk territory (province). Procedure of forming the weather data for the analysis is illustrated in the Table (fragment) below. Computer software Excel was used for determination of correlation ties, drafting equations and trends between winter precipitations and those of the posterior summers, and vice versa: between the summers precipitations and that of the posterior winters.

Consideration of results

Our analysis of the data illustrated in the fragment Table below resulted in the following:

• When the total winter precipitations (November, December, January, February and March) exceed or are equal to its annual average, the summer total precipitations can be either higher or lower its annual average, but those higher are more probable than those lower (62 % and 38 %, correspondingly).

• When the total winter precipitations (Novembr - March) are lower than its annual average, the total precipitations of the posterior summer (April - October) are lower its annual average in 80 % of the analyzed years.

Also, certain coincides are revealed between the years of higher both winter and yearly precipitations and the years of maximum activity of the Sun. For example, in the southern part of the Khabarovsk territory during years of maximum Sun activity (1971, 1981, 1991, 2000), forest fire seasons were not severe in these very years, particularly in 1981, when both winter and year precipitation totals were twice as much as those of annual averages, and, accordingly, the seasonal fire number was twice less the annual average.

In contrary, during the years of Sun activity minimums (1976, 1986, 1998, 2008) in the southern part of Khabarovsk territory totals of winter and summer precipitations were much lower then the annual averages, and this phenomenon coincides with high numbers of seasonal forest fires in these years.

However, this pattern was marked only for the southern part of the Khabarovsk territory. It was not confirmed for the northern half, where maximums of forest fire season severity coincided with the maximums of activity of the Sun.

Table (abridged). Yearly totals of winter and summer precipitations and there&s ratio in 1974 - 2008 according to the data of weather stations in Khabarovsk, Georgievka and Komsomolsk._

Totals of precipitations by winter and summer seasons in Averaged for 3 weather

Year 1974-2008 by the data of 3 weather stations, mm stations

(for winter season (November summer season (April Win- Sum- ratio

sum- through March) through October) ter, mer, W/S

mer Khab. Geor. Koms. Khab. Geor. Koms. mm mm

seasons) (W) (S)

Yearly 91 89 87 521 583 454 85 563 6.6

average:

The average ratio between summer precipitation and that of preceding winter is 6.6, namely for Khabarovsk 6.9, Georgievka - 6.5 and for Komsomolsk - 6.0. Decreasing of the ratio from the south to the north evidences of the increasing of the continental factor in this direction, which is fairly corresponding with assessments of this factor calculated by [4, p. 102} based on the special method.

Yearly distribution of winter precipitations for 1974 - 2008 (Table) shows that in the years of maximum fire weather danger in the south of Khabarovsk territory and, correspondingly, of maximum seasonal fire numbers, the totals of winter precipitations were much lower than their yearly average (81 mm) and were, e.g., 75 mm in 1998, and 50 mm in 2003. And contrary, in the years of rainy summers, and, correspondingly, in the years of minimum forest fire season severity, totals of winter precipitations were much higher, than their yearly average, e.g. 116 mm in 1991, 118 mm in 1994, 120 mm in 1997, and 112 mm in 2002.

The correlation between winter and posterior summer precipitations was found to be positive and rather tight. The common (for the three weather stations) correlation coefficient was calculated as 0.27 (Fig. 1), and the linear relationship was found to be as follows:

Y = 2 X + 400 (r = 0,27 ± 0,02) mm, (1)

where X is the sum of winter precipitation, mm; Y - sum of summer precipitations, mm; r - correlation coefficient.

Winter precipitations, mm

Fig. 1. Positive correlation between winter precipitations and these of posterior summers

This correlation relationship makes possible to forecast, more or less accurately, the precipitation sum for the posterior summer period, based on that of the preceding winter. Accordingly, it would be possible to anticipate the corresponding nature events, such as floods or forest fires as far as they are resulted from the level of summer precipitations.

Another question arises: does the reverse relationship exist - that between summer precipitations and that of the posterior winter? Our analysis revealed that such a relationship does not exist - correlation coefficient is -0,09 (Fig. 2). So, the pattern of distribution of yearly precipitations between winter and summer is shifted during the winter months. Consequently, it is impossible to forecast sums of winter precipitations based on that of the preceding summer.

Fig. 2. The correlation between summer precipitations and those of the posterior winter periods is negligible (correlation coefficient -0,09)

Conclusions:

References