ACTA UNIVERSITATIS LODZIENSIS THE EXTREME PRECIPITATION CONDITIONS IN ŁÓDŹ IN THE PERIOD

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1 ACTA UNVERSTATS LDZENSS FLA GEGRAPHCA PHYSCA 3, 1998 Joanna Wibig, Krzysztof Fortuniak THE EXTREME PRECPTATN CNDTNS N ŁÓDŹ N THE PERD EKSTREMALNE WARUNK PADWE W ŁDZ W KRESE Reord of daily preipitation totals from Łódź from the period has been analysed. The annual ourses of frequenies of days without preipitation and with preipitation in partiular ranges were presented. t was shown that ourrene of preipitation is stronger related to the harater of irulation than to diretion of air mass advetion. Long-term variability of frequenies of days without preipitation, days with totals exeeding 10 mm/day and long-term variability of the highest daily total during the year were analysed. t was shown that the highest daily totals our in day with irulation of type Eo. NTRDUC'N AND DATA The aim of the paper was to analyse the interannual and long-term variability of daily preipitation in Łódź with speial attention on extreme events. The reord of daily preipitation totals from meteorologial station Łódź-Lublinek was used. The station is loated at airport on south-west from the ity (ep = 51 44'N,.A. = 19 24'E, h = 184 m). The reord began on 1st May There were few gaps in the reord: in the seond half of 1939 (from August to Deember), in 1945 and in January They all were onneted with beginning and ending of Seond World War. To ompare the highest preipitation totals with the extreme preipitation events in July 1997 the daily totals from this month were also used (Codzienny Biuletyn..., 1997). Cirulation was desribed by s u h o w s k a - K l e i n (1978, 1991) lassifiation. [241]

2 242 J. Wibig, K. Fortuniak a) Ul " '" 0.5 " Q :J rr i..:..: "3 Ól li t :> es '" '" :J o '" :::E «..., :J..., u.. :::E..., «o z (f) o o " 0.6 Ci Ul 0.4 " '" Q \ :J rr i..:..: "3 Ól li t :> es '" :::E '" «:::E '" :J..., :J o..., u....., «o z (f) o b) < r o;; < r < ;; r < 5.0 n/h!s. o;; r < 10.0 li!:!!!::!!!!:!!! 10.0 ;; r Fig. 1. Relative frequenies of days without preipitation (a) and days with preipitation seleted limits (b) within Rys. 1. Częstość dni bez opadu (a) i dni z opadem w wybranyh przedziałah (b)

3 The extreme preipitation onditions in Łódź lnterannual VARABLTY The relative frequeny of dry days (Fig. 1) shows the maximum during late summer and early autumn (from August to tober) and minimum in winter (Deember-February). Reversal ourse is for frequeny of days with preipitation. For all values below 5 mm per day the probability of preipitation ourrene is the greatest during winter and the lowest in summer. n the ase of daily totals higher than 5 mm per day the maximum falls in summer and the minimum in winter. t was found that harater of irulation (ylonal or antiylonal) is of a ruial importane for ourrene of preipitation (Fig. 3), whereas the diretion of air mass advetion (western or eastern) onstitutes only a seond - rate fator. Vl 0.7 <ts " 0.6 " Q 0.5 () 004 D l 0.3 T D 0.2 > 0.1 a) 0.0..i...: j "'5 i> li t :> ej <ts <ts D --, «--, U. --, l l D «z D (J) Vl 0.7 <ts 0.6 " Q 004 () D l 0.3 T 0.2 D > b) =A l.o ;;j Ci ::; i> li t> :> o <ts D «l --, l D --, u. --, «(J) z Fig. 2. Relative frequeny of dry days in relation to irulation lasses: western (W) or eastern (E) types (a) and antiyloni (A) or yloni (C) types (b) Rys. 2. Częstość dni bez opadu w zależnośi od typu yrkulaji: typy zahodnie (W) i wshodnie (E) (a) oraz typy antyyklonalne (A) i yklonalne (C) (b)

4 244 J. Wibig, K. Fortuniak LNG-TERM VARABLTY The long-term variability of frequeny of dry days was also investigated. This frequeny dereases (Fig. 3) during warm season (from April to tober) as well as during' old one (November-Marh) and of ourse also in a year as a whole. nly the last two tr,ends are statistially signifiant at 5% level. 160 ell ' ' 120 () (]) ::J ' J l, ---, ,, B , m ', r , - 'a = -0,194', ' --r () (]) ::J 40 ',, 20---_+.l,.-ł -t-_+-+ t ell ' ' () 150 (]) ::J 125 ' Fig. 3. Frequeny of dry days during warm season, from April to tober (A), old season, from November to Marh (8), and during hydrologial year, from November to tober (C). The trend line (dashed one) and the slope "a" are given Rys. 3. Lizba dni bez opadu w sezonie iepłym, od kwietnia do października (A), hłodnym, od listopada do mara (8) i w roku hydrologiznym, od listopada do października (C). Linia przerywana przedstawia trend, podano współzynnik nahylenia "a" A

5 The extreme preipitation onditions in Łódź E E. 75 o 'Ci. 50 U D Q Fig. 4. The highest daily totals in partiular year with its trend (dashed line) Rys. 4. Najwyższe rozne sumy dobowe z zaznazoną linią trendu (krzywa przerywana) A reord of the highest daily totals in partiular year was also looked into (Fig. 4). There is slightly dereasing tendeny, but below the level of statistial signifiane. Also the sequene of annual frequenies of days with totals exeeding 10 mm per day (Fig. 5) did not show any trend , ,------r---, , Cl) " 15 () H-J.-l-l---łlJ----\-f-Hl Hl ł-JH--ł----1 o-.& o i Fig. 5. Relative frequeny of days with preipitation higher than l mm per day with trend (dashed line) Rys. 5. Częstość dni z opadem dobowym przekrazająym 10 mm, zaznazono linię trendu (krzywa przerywana)

246 J. Wibig, K. Fortuniak DRY AND WET SPELLS A dry spell was defined as a sequene of days ompletely without preipitation. The distributions of suh spells aording to their lenght is shown at Fig. 6.

6 246 J. Wibig, K. Fortuniak DRY AND WET SPELLS A dry spell was defined as a sequene of days ompletely without preipitation. The distributions of suh spells aording to their lenght is shown at Fig. 6. nly spells equal or longer than five days were taken into onsideration. The longest one lasted 45 days. A wet spell was defined as a sequene of days with preipitation even if its amount was unmeasureable (Le. lower than 0.1 mm). Their distribution (Fig. 7) indiates that the longest one persisted 34 days. EXTREME PRECPTATN EVENTS Twenty the longest daily totals in Łódź in analysed period were hosen. Most of them fell in July (Fig. 8) and during days with north-eastern and eastern yloni irulation (type Eo in suhowska-klein lassifiation). The highest daily total in Łódź reahed mm and the twentieth one was 39.8 mm. During extremely high preipitation events in July 1997 two daily sums fell into this range (62 mm on 6th and 44 mm on 7th July). There were also in Łódź 22 ases of short wet spells with totals exeeding 50 mm. All days within these spells were analysed. Most of them were in July (Fig. 9), but they were found even in November. They usually ourred during days with north-eastern and eastern yloni irulation. The highest preipitation sum during these periods was mm. During extremely high preipitation events in July 1997 were two suh spells with sums 168 mm (from 5th to 9th July) and 60 mm (from 19th to 23rd July). n reorded history there were three other ases of suh two-spell lusters (fab. 1). The one in July 1997 had the highest total. Tablei Charateristi of preipitation during four the most extensive lusters of wet spells (in m 1) Charakterystyka opadu podzas ztereh najintensywniejszyh podwójnyh okresów opadw),h (w mm) Year First spell Seond spell Total preipitation Jul. (95.3) 31 Jul... {)3 Aug. (90.6) Jul. (115.9) Jul. (74.6) May--02 Jun. (65.0) Jun. (117.0) Jul. (168.0) Jul. (60.0) 228.0

7 The extreme preipitation onditions in Łódź Ql en - Q u Ql :;:) ty length of dry period (n days) Fig. 6. Frequeny of dry spells longer than 4 days during analysed period Rys. 6. Lizba okresów bezopadowyh dłuższyh niż 4 dni w analizowanym okresie Ql en 120 3= Q 100 u 80 Ql :;:) ty :::: :::; :m length of wet period (in days) Fig. 7. Frequeny of wet spells longer than 4 days during analysed period Rys. 7. Lizba okresów opadowyh dłuższyh niż 4 dni w analizowanym okresie

8 12 a) b) 10 g- 8 7 l1:l U l1:l Cl 6 u Qi Cl 5.Q E :::J.Q 4 4 E :::J "5 i> E- '?5. CD ::s w CD l1:l..., :::J..., :::J o C\J «(fj z u o U l1:l U U :::> u w (fj l1:l (fj Z W Z Z Fig. 8. The distribution of twenty the highest daily preipitation totals aording to month of ourrene (a) and irulation type (b) Rys. 8. Rozkład 20 dni z najwyższymi dobowymi sumami opadu w zależnośi od miesiąa, w którym wystąpiły (a) i panująego typu yrkulaji (b) 40 a) b) l1:l u Cl l1:l 20 U.Q Cl E 15 Qi :::J.Q E :::J 10 5 itl "5 i> E- t :> o w CD?5. LL..., :::J..., :::J o w «(fj z l1:l u u Z u u W l1:l (fj u :::> z w w (fj w (fj z z w Fig. 9. The distribution of days within the 22 spells with preipitation sums exeeding Smm aording to month of ourrene (a) and irulation type (b) Rys. 9. Rozkład dni z 22 okresów opadowyh o sumah przekrazająyh Smm w zależnośi od miesiąa, w którym wystąpiły (a) i panująego typu yrkulaji (b)

9 The extreme preipitation onditions in Łódź Authors wish to aknowledge the nstitute of Meteorology and Water Management for provision of dat REFERENCES Codzienny biuletyn meteorologizny, lipie 1997, MGW, Warszawa suhowska-klein B., 1978, Kiltalog typów yrkulaji atmosferyznej, WKiŁ, Warszawa suhowska-klein B., 1991, Katalog typów yrkulaji atmosferyznej ( ), MGW, Warszawa Department of Meteorology and Climatology University of Łódź STRESZCZENE W opraowaniu analizowano szereg dobowyh sum opadu z Łodzi z okresu Przedstawiono rozny bieg zęstośi występowania dni bez opadu i z opadem w poszzególnyh przedziałah wartośi. Stwierdzono, że pojawienie się opadu zależy w większym stopniu od harakteru yrkulaji niż od kierunku napływu mas. Badano długoletnią zmienność zęstośi dni bez opadu, dni z sumą opadu powyżej 10 mm i największej dobowej sumy opadu w roku. Pokazano, że najwyższe dobowe sumy opadu pojawiają się w dniah o yrkulaji Eo.

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