Historical trend of hourly extreme rainfall in Peninsular Malaysia

Transcription

1 Theor Appl Climtol (2015) 120: DOI /s ORIGINAL PAPER Historil tren of hourly extreme rinfll in Peninsulr Mlysi A. H. Syfrin & M. D. Zlin & L. Juneng Reeive: 9 My 2013 /Aepte: 27 Mrh 2014 /Pulishe online: 15 My 2014 # The Author(s) This rtile is pulishe with open ess t Springerlink.om Astrt Hourly rinfll t etween the yers 1975 n 2010 ross the Peninsulr Mlysi were nlyze for trens in hourly extreme rinfll events. The nlyses were onute on rinfll ourrenes uring the northest monsoon (Novemer Ferury) known s NEM, the southwest monsoon (My August) known s SWM, n the two inter-monsoon sesons, i.e., Mrh April (MA) n Septemer Otoer (SO). Severl extreme rinfll inies were lulte t the sttion level. The extreme rinfll events in Peninsulr Mlysi showe n inresing tren etween the yers 1975 n The tren nlysis ws onute using liner regression; no seril orreltion ws etete from the Durin- Wtson test. Orinry kriging ws use to etermine the sptil ptterns of trens in sesonl extremes. The totl mount of rinfll reeive uring NEM is higher ompre to rinfll reeive uring inter-monsoon sesons. However, intense rinfll is oserve uring the inter-monsoon seson with higher hourly totl mount of rinfll. The estern prt of peninsulr ws most ffete y strtiform rins, while onvetive rin ontriutes more preipittion to res in the western prt of the peninsulr. From the istriution of sptil pttern of tren, the extreme frequeny inex (Freq >20) gives signifint ontriution to the positive extreme rinfll tren uring the monsoon sesons. Menwhile, oth extreme A. H. Syfrin (*): M. D. Zlin UTM Rzk Shool of Engineering n Avne Tehnology, Universiti Teknologi Mlysi, Jln Semrk, Kul Lumpur, Mlysi e-mil: syfrinhlim@gmil.om M. D. Zlin e-mil: zlin@i.utm.my L. Juneng Shool of Environment Nturl Resoures, Fulty of Siene n Tehnology, Universiti Kengsn Mlysi UKM, Bngi, Selngor, Mlysi e-mil: juneng@ukm.my frequeny n extreme intensity (24-Hr Mx, Freq >95th, Tot >95th, Tot >99th, n Hr Mx) inies give signifint ontriution to the positive extreme rinfll tren uring the inter-monsoon sesons. Most of the signifint extreme inies showe the positive sign of trens. However, negtive tren of extreme rinfll ws foun in the northwest ost ue to the existene of Titiwngs Rnge. The extreme intensity, extreme frequeny, n extreme umultive inies showe inresing trens uring the NEM n MA while extreme intensity n extreme frequeny h similr trens uring the SWM n SO throughout Peninsulr Mlysi. Overll, the hourly extreme rinfll events in Peninsulr Mlysi showe n inresing tren etween the yer 1975 n 2010 with notle inresing trens in short temporl rinfll uring inter-monsoon seson. The result lso proves tht onvetive rin uring this perio ontriutes higher intensity rins whih n only e pture using short urtion rinfll series. 1 Introution Reent inreses in the frequeny n intensity of extreme rinfll events hve rise onern tht humn tivity might hve resulte in n ltertion of the limte system. It is elieve tht rise in oth frequeny n intensity of extreme rinfll events re the mjor impts of glol wrming (Sen Roy 2009; Cheng et l. 2012). Intense rinfll ourrenes in short temporl sles or persistent rinfll over long perio of time often le to mssive floos resulting in hzrous situtions. Peninsulr Mlysi experienes unpreitle rinfll events, whih uses hvo, n fixing them osts millions of Mlysin ringgit. The inrese in mssive floo ses, inluing flsh floo n lnslies in the lst ee, is ue to the inrese in rinfll intensities. Severl ftors suh s urn het isln (UHI) effet n lol temperture hnges ontriute to the extreme rinfll

2 260 A.H. Syfrin et l. events. Lrge-sle limti flututions, suh s the position of the Men-Jullin osilltion (MJO) n the El-Nino southern osilltion (ENSO) phses, my lso moulte the frequeny n mount of preipittion on wet y (Cyn et l. 1999). For instne in Mlysi, the ourrene of the two most extreme ENSOs in 1982/1983 n 1997/1998 were reporte to e the ftor responsile for extreme limte hnges in Peninsulr Mlysi (Zin et l. 2010). However, ue to lol ftors too, extreme rinfll events my present ontrsting ehvior in ifferent regions ross Mlysi. A numer of stuies involving the etermintion of extreme rinfll tren were one using ily rinfll t with ifferent intensity tegories efining extreme rinfll events. For instne, Griffiths et l. (2003) investigte the reltionship etween the South Pifi Convergene Zone n extreme rinfll tren using inies whih onsiere oth extreme frequenies n intensities in the tropil South Pifi. Correltion etween inies n the totl rin ws lso etermine in this stuy. Shmili n Frei (2005) foun inresing trens in hevy preipittion uring utumn n winter in Switzerln over the perio In other region, Hylok n Niholls (2000) foun eresing tren in extreme frequeny n extreme intensity in southwest Western Austrli, while n inresing tren ws foun in extreme preipittion of estern Austrli. These finings gree with severl stuies one throughout the Asin region prtiulrly in Mlysi. Suhil et l. (2010) foun inresing trens in oth the totl mount of rinfll n the frequeny of wet ys uring the northest monsoon, whih give rise to the inresing tren of rinfll intensity for the perio of Similrly, inresing trens in the extreme intensity inies lso were foun y Zin et l. (2010) for the perio of However, oth stuies hve foun signifint erese in the numer of wet ys uring this perio. Besies extreme rinfll trens, extreme temperture n ry spell trens re lso eing stuie in some regions. Alexner n Arlster (2009) foun inresing trens in temperture extremes, prtiulrly signifint inrese in the numer of wrm nights n het wves with muh longer ry spells intersperse with perios of inrese extreme preipittion over Austrli. Stuies in Peninsulr Mlysi foun tht most of the ry spell inies epite ownwr trens uring the northest monsoon over the yers of 1975 to Anlyzing sesonl hourly tren of extreme rinfll events will give etter insight to extreme rinfll ehvior ompre to ily trens. Hylok n Niholls (2000) rgue tht nlysis of extreme rinfll, se on totl ily rinfll is prolemti ue to vrying qulity of the t. In 2009, Sen Roy hs proven tht hourly t inite more etile results, where the tren of mximum hourly rinfll in the estern prt of the Gngeti Plin n Uttrnhl showe n inresing tren uring winter, ry-summer, n wet-summer monsoon seson, whih ontrste n erlier stuy using ily rinfll showing eresing tren of ily extreme rinfll in these sme res (Sen Roy n Blling 2004). Similr stuies on ily rinfll t ws lso onute in Mlysi y Zin et l. (2010). Inresing trens in severl extreme inies were reporte. However, nlyzing hourly rinfll oul give etter inition of the sesonl ontriution to the nnul extreme rinfll s mentione erlier. Hene, this stuy proposes to (1) nlyze the trens of extreme hourly rinfll events ross Peninsulr Mlysi, n (2) esrie the profile of hourly extreme rinfll in Peninsulr Mlysi. The use of hourly rinfll with lrge numer of inies n over long historil perio will proue more urte ount of the sptil istriution n tren of extreme rinfll in Mlysi. 2Dt Peninsulr Mlysi is lote etween 1 n 6 N in the northern ltitue n etween 100 to 103 E longitue. The surfe limte is influene y the NEM etween Novemer n Ferury n y SWM etween My n August. The NEM monsoon is usully ssoite with hevier rinfll with the estern n southern regions eing the most ffete res. In etween these two monsoons re the inter-monsoon sesons ourring in Mrh April (MA) n Septemer Otoer (SO), whih rings intense onvetive rinfll to the western ost of Peninsulr Mlysi. In this stuy, hourly rinfll t were soure from the Mlysi Dringe n Irrigtion Deprtment (DID). The rinfll sttions were selete se on two riteri: (1) equy of t n length of reor n (2) even istriution of rinfll sttions ross Peninsulr Mlysi. Sttions with missing vlues, greter thn 2 % of the totl reor hours within 1 Jnury 1975 to 31 Deemer 2010, were exlue. The verge nerest neighor (ANN) ws use in ensuring the sttions hosen re spre evenly over the Peninsulr Mlysi. The verge nerest neighor rtio is given s follows: ANN ¼ D 0 D E ð1þ where D 0 is the oserve men istne etween eh sttion n their nerest neighor, n D 0 ¼ X i¼1 i n ð2þ n D E is the expete men istne for the sttions given rnom pttern, D E ¼ r 0:5 ffiffiffiffiffiffiffiffiffi. ð3þ n A

3 Historil tren of hourly extreme rinfll 261 i equls the istne etween sttion i n its nerest sttion, n orrespons to the totl numer of fetures, n A is the totl stuy re. The z ANN -sore for the sttisti is lulte s follows: z ANN ¼ D 0 D E SE where SE ¼ r 0:26136 ffiffiffiffiffiffiffiffiffiffiffi n.a 2 ð4þ ð5þ If the z ANN -sore is less thn 1, the sttions re lustere. Otherwise, the sttions re spre evenly. The lulte z ANN - sore is 2, whih flls into tegory of isperse istriution t 99 % level of signifine. Using these riteri, 25 sttions (Tle 1) were selete for this stuy. The istriution of sttions is portrye in Fig. 1. 3Methoology In this stuy, 8 sesonl extreme rinfll inies were exmine se on hourly rinfll t t the 25 selete sttions. The extreme rinfll inies, hosen fter Sen Roy (2009) onsiere oth the intensity n frequeny of extreme rinfll events (Tle 2). A rinfll mount of t lest 0.1 mm is hosen s threshol for hourly rinfll. In this stuy, perentiles were use rther thn fixe threshol s it is more urte mesure n suitle for region like Peninsulr Mlysi whih hs highly vrile rinfll n high sptil rinfll intensity (Hylok n Niholls 2000; Griffiths et l. 2003). The 95th n 99th perentile ws selete s the threshol to represent extreme rinfll events. All preipittion events ove 0.1 mm ourring throughout the entire stuy perio were sorte in sening orer for eh sttion seprtely, in orer to etermine the threshol vlue for the 95th n 99th perentile. Next, the totl mount n frequeny of events ourring eh yer ove the 95th n 99th perentile were lulte. Hours with rinfll exeeing 95th perentile were referre to s very wet n hours with rinfll exeeing 99th perentile s extremely wet. Tle 1 Nme of sttions with longitue n ltitue No. Sttion Nme of sttion Long ( ) Lt ( ) Sek. Men. Bukit Besr, Kot Tinggi Johor Chin Chin (Tepi Jln) Melk Setor JPS Sikmt Seremn Pejt JPS Sungi Mngg Selngor SMK Bnr Tsik Kesum, Semenyih Selngor Pust Kwln P/S Telok Gong Selngor JPS Ampng, Selngor Sek. Ke. Kg. Lui Selngor Rumh Pm JPS Jy Seti Selngor Stor JPS, Tg Krng Selngor Loji Air Kul Kuu Bhru Selngor Iu Bekln Sg. Bernm Selngor Rumh Pm JPS Bngunn Terp, Selngor Pust Kesihtn Keil, Btu Kuru Perk Kg. Keik, Phng Rumh Pm Phng Tu, Pekn Rumh Pm Py Kngsr, Phng JPS Kemmn, Terenggnu Sek. Men. Sultn Omr Dungun, Terenggnu Gu Musng, Kelntn Kg. Menerong, Terenggnu Setor JPS, Kul Terenggnu Lhr Ikn Mti Kepl Bts, Penng Ampng Peu, Keh Png Ktong, Kngr

4 262 A.H. Syfrin et l. Fig. 1 Distriution of sttions use in this stuy THAILAND MALAYSIA SOUTH CHINA SEA STRAITS OF M ALACCA Rinfll sttions The trens for eh of these 32 inies (8 extreme rinfll inies for 4 sesons) were lulte using lest squre liner regression nlysis metho t eh sttion level. For eh sttion, mtrix of 36 rows, 1 for eh yer from 1975 to 2010, n 9 olumns representing the yer n eh of the 8 vriles ws evelope. Simple liner regression (LS) nlysis with the yer of reor serving s inepenent vrile ws estlishetootinthestnrize regression oeffiient, representing the strength n sign of ny tren, for eh of the eight vriles. The signifine of this liner fit ws teste using t test t 5 % level of signifine. Another test to etet the tren within the time series is the nonprmetri Mnn-Kenll (MK) test. The Mnn-Kenll test is se on the sttisti S. Eh pir of oserve vlues y i, y j (i>j) of the rnom vrile is inspete to fin out whether y i >y j or y i <y j. P is the numer of the former type of pirs, n M is the numer of the ltter type of pirs. Then S is efine s follows: S ¼ P M ð6þ For n>10, the smpling istriution of S is s follows. Z follows the stnr norml istriution where 8. pffiffiffiffiffiffiffiffiffiffiffiffiffiffi >< ðs 1Þ VrðSÞ if S > 0; Z ¼ 0. if S ¼ 0; pffiffiffiffiffiffiffiffiffiffiffiffiffiffi >: ðs þ 1Þ VrðSÞ if S < 0 ð7þ

5 Historil tren of hourly extreme rinfll 263 Tle 2 Rinfll inies with efinitions n units Definitions Inex nme Unit Extreme umultive rinfll 1. Lrgest sesonl totl mount of rinfll reore over 24 onseutive hours for eh yer (24) 24-Hr Mx mm/24-h Extreme intensity 2. Annul sesonl hourly mximum mount of rinfll the sesonl hourly mximum mounts Hr Mx mm/hr of rinfll were etermine seprtely for eh yer. 3. Lrgest sesonl totl mount of rinfll reore over five onseutive hours for eh yer 5-Hr Mx mm/5-h 4. Totl mount of rinfll exeeing 95th perentile for eh yer Tot>99th mm/hr 5. Totl mount of rinfll exeeing 99th perentile for eh yer Tot>95th mm/hr Extreme frequeny 6. Frequeny of sesonl rinfll events greter thn 20 mm within 1 h for eh yer Freq>20 hr 7. Frequeny of rinfll exeeing 95th perentile within 1 h for eh yer Freq>95th hr 8. Frequeny of rinfll exeeing 99th perentile within 1 h for eh yer Freq>99th hr There is orretion for ties when y i =y j. The null hypothesis of no tren is rejete when the ompute Z vlue is greter thn z α in solute vlue. These were one seprtely oring to four ifferent sesons of Peninsulr Mlysi. After tht, the fiel signifine test for eh extreme inex is teste using the regionl verge Mnn-Kenll test (RAMK) s suggeste y Yue et l. (2002). No orreltion exist in the rinfll t, hene the regionl MK test without sptil n temporl orreltion ws use in the stuy. The sum of MK m sttistis of m inepenent sites is given y S SUM ¼ Sk. k¼1 The stnrize RAMK sttisti S is 8. r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi S 1 Vr S if S > 0; >< Z ¼ 0 if S ¼ 0;. r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi >: S þ 1 Vr S if S < 0 ð8þ where S¼ S SUM =m is normlly istriute n n e represente y S e N 1 m m m μk ; σ 2 k. The smple k¼1 k¼1 men n vrine of the RAMK sttisti re E S ¼ 0 n m Vr S ¼ 1 Vr ð Sk Þ. Next, orinry kriging metho m 2 k¼1 ws employe to etermine the sptil ptterns of trens in sesonl extremes. Furthermore, the utoorreltion in the rinfll t ws lso teste using the Durin-Wtson (DW) test where H 0 :ρ=0 vs. H 1 :ρ>0. The test sttisti is ¼ n ðe i e i 1 Þ 2 i¼2 n ei 2 where e i ¼ y i y i n y i n y i re the oserve n preite vlues of the response vrile for iniviul i. The DWsttisti for the t ws foun to e pproximtely 2, whih i¼1 inites tht there is no utoorreltion in the rinfll t t the 5 % level of signifine. 4 Results n isussion This setion will isuss the sptil profile of extreme rinfll inies s well s the sptil trens of sesonl extreme rinfll inies for the whole of Peninsulr Mlysi. 4.1 Sptil profile of extreme rinfll inies As for the extreme intensity n extreme umultive inies, it is interesting to note tht the sptil pttern of rinfll tivities over the inter-monsoon seson, notly MA, shows onsistent pttern of higher inies in the western region (Figs. 2, 3, 4, 5, n 6). The Hr-Mx reore higher vlue in this seson ompre to other sesons with mount of rinfll rehing up to mm. This is in greement to the generl ssumption tht onvetive rin ourring uring the intermonsoon perio hs higher intensities ompre to strtiform rin whih our uring the monsoon seson sine the mximum rinfll epits higher vlue in reltively short time (i.e., hourly) n suh results nnot e pture using ily t s portrye y the results of Zin et l. (2010), in whih the highest extreme intensities ourre uring NEM seson. The sptil pttern of the 5 Hr-Mx n 24 Hr-Mx follows the sme pttern. However, the Hr-Mx presents ifferent pttern with higher hourly mximums in the western region initing tht the NEM rings strtiform rin whih re long urtion hevy rins. The western regions re ffete y the NEM ut to lesser egree. Hene immense floos usully our in the estern regions uring the NEM. The northern prt of the peninsulr reeives little rin uring the NEM ue to the existene of Titiwngs Rnge (Bnjrn Titiwngs) whih loks the region from reeiving the rin rought on the

6 264 A.H. Syfrin et l Fig. 2 Sptil istriution of Hr Mx inex for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

7 Historil tren of hourly extreme rinfll Fig. 3 Sptil istriution of 5-Hr Mx inex for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

8 266 A.H. Syfrin et l Fig. 4 Sptil istriution of 24-Hr Mx inex for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

9 Historil tren of hourly extreme rinfll Fig. 5 Sptil istriution of totl mount for Tot >95th inex, for northest monsoon seson (NEM), southwest monsoon seson (SWM), intermonsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

10 268 A.H. Syfrin et l Fig. 6 Sptil istriution of totl mount for Tot >99th inex for northest monsoon seson (NEM), southwest monsoon seson (SWM), intermonsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

11 Historil tren of hourly extreme rinfll Fig. 7 Sptil istriution of Freq >20 inex for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

12 270 A.H. Syfrin et l Fig. 8 Sptil istriution of totl mount for Freq >95th inex for northest monsoon seson (NEM), southwest monsoon seson (SWM), intermonsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

13 Historil tren of hourly extreme rinfll Fig. 9 Sptil istriution of totl mount for Freq >99th inex for northest monsoon seson (NEM), southwest monsoon seson (SWM), intermonsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

14 272 A.H. Syfrin et l Fig. 10 Sptil pttern of trens for Hr Mx for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

15 Historil tren of hourly extreme rinfll Fig. 11 Sptil pttern of trens for 5-Hr Mx for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

16 274 A.H. Syfrin et l Fig. 12 Sptil pttern of trens for 24-Hr Mx for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

17 Historil tren of hourly extreme rinfll Fig. 13 Sptil pttern of trens for Tot >95th for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

18 276 A.H. Syfrin et l Fig. 14 Sptil pttern of trens for Tot >99th for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

19 Historil tren of hourly extreme rinfll Fig. 15 Sptil pttern of trens for Freq >20 for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

20 278 A.H. Syfrin et l Fig. 16 Sptil pttern of trens for Freq >95th for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

21 Historil tren of hourly extreme rinfll Fig. 17 Sptil pttern of trens for Freq >99th for northest monsoon seson (NEM), southwest monsoon seson (SWM), inter-monsoon seson (MA), n inter-monsoon seson (SO) over 36 yers ( )

22 280 A.H. Syfrin et l. north esterly wins. By ompring Hr Mx n 24-Hr Mx inies, it is shown tht the western region experienes short urtion extreme rinfll (Hr Mx) uring the NEM n MA ut the estern inluing some res in the northwestern region experiene long urtion extreme rinfll (24-Hr Mx) uring the sme sesons. Suh results explin the ourrenes of flsh floos whih frequently hppen in urn res (i.e., west ost) s well s mssive floos in nonurn res (i.e., est n northwest osts). It is lso shown tht the northern region experienes oth short n long perio of extreme rinfll uring the SWM n SO. As for the Tot >95th n Tot >99th, NEM reore the highest mount of rinfll tht exees the 95th n 99th perentile throughout the 36 yers followe y SWM n the inter-monsoon sesons. Monsoon sesons umulte higher totl mount of rinfll thn inter-monsoon sesons ue to monsoon sesons omprising of 4 months while intermonsoon sesons omprising of 3 months. Similrly, the estern region reeives highest rinfll uring the NEM while the western region reeives highest rinfll uring the MA. Furthermore, the northern region reeives highest rinfll uring the remining sesons, SWM n SO. In reltion to tht, s the numers of ys for the four sesons re not the sme, the extreme frequeny inies will e ompre etween monsoon n inter-monsoon sesons (Figs. 7, 8, n 9). During the monsoon sesons, the extreme rinfll events frequently ourre uring the NEM where the estern region reore the highest totl mount of rinfll for the 95th n 99th perentile with mount of rinfll rehing up to n mm, respetively. During the inter-monsoon sesons, the extreme rinfll events frequently ourre uring the SO where the northern region reore the highest totl mount of rinfll for the 95th n 99th perentile with mount of rinfll rehing up to n mm, Tle 3 Signifint hourly extreme inies for eh sttion uring NEM Sttion Hr Mx 5-Hr Mx 24-Hr Mx Freq> 20 Freq> 95 th Tot> 95 th Freq> 99 th Tot> 99 th * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * represents positive tren, represents negtive tren where rkene ox represents signifint tren for LS test, n * represents positive signifint tren for MK test *

23 Historil tren of hourly extreme rinfll 281 respetively. As for the Freq >20, the frequeny of rinfll events greter thn 20 mm within 1 h is foun to e higher uring the NEM n MA for the eh monsoon n intermonsoon sesons. 4.2 Tren nlysis of extreme rinfll inies Figures 10, 11, 12, 13, n 14 illustrte the sptil pttern of trens for ll extreme intensity inies for eh seson. The vlues represent the oeffiient of trens of whih positive sign inites upwr tren, wheres negtive sign inites ownwr tren. All the extreme intensity inies show similr pttern of tren where lmost ll regions show inresing trens uring ll sesons. The trens re more pronoune towrs the southern prt of peninsulr. Negtive trens re mostly in the northern region of the peninsulr. Similrly, the extreme frequeny inies (Figs. 15, 16, n17) revel upwr trens in lmost ll regions uring ll sesons. Suh trens re lso more signifint towrs the southern prt of peninsulr uring these sesons. The highest vlue of positive tren oeffiient for Hr Mx is oserve for the MA (highest vlue of 0.6) while NEM hs the lowest. In ontrst, NEM hs the highest vlue of positive oeffiients of Freq >20, Freq >95th, n Tot >95th while SO hs the lowest. Besies, SWM hs the highest vlue of positive oeffiients of Freq >99th n Tot >99th wheres SO hs the lowest. As for the 5-Hr Mx n 24-Hr Mx, the highest vlue of positive oeffiients re shown uring MA n the NEM, respetively, of whih oth inies hs the lowest positive vlue of oeffiients uring SO. Agin y ompring Hr Mx n 24-Hr Mx, the short urtion of extreme rinfll epits n upwr tren uring MA while the long urtion of extreme rinfll epits Tle 4 Signifint hourly extreme inies for eh sttion uring SWM Sttion Hr Mx 5-Hr Mx 24-Hr Mx Freq> 20 Freq> 95 th Tot> 95 th Freq> 99 th Tot> 99 th * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * represents positive tren, represents negtive tren where rkene ox represents signifint tren for LS test, n * represents positive signifint tren for MK test *

24 282 A.H. Syfrin et l. the sme tren uring NEM over the yers Most of the extreme inies (totl of six out of eight inies) hs higher vlue of positive oeffiients uring the NEM n hs the lowest uring SO. Thus, it n e onlue tht the positive tren of extreme rinfll over the yers is stronger uring the NEM. This shows tht the NEM rings inresing mount of rinfll ompre to other sesons, hene the min ontriuting ftor to the rinfll in Mlysi is the northesterly wins over the South Chin Se whih is relte to ol surges. The extreme rinfll in the west ost is lso use y strong pulses of west win ssoite with the MJO, s it psses through the mritime ontinent (Slhuin n Curtis 2011). In ition, six inies hve shown higher vlue of positive oeffiients uring the monsoon sesons. This lso proves tht the positive tren of extreme rinfll is stronger uring the monsoon sesons ompre to the intermonsoon sesons etween the yers 1975 n The signifint ontriution of extreme inies to Mlysi s extreme rinfll Tles 3, 4, 5, n 6 revel the signifint hourly extreme inies of eh rinfll sttion using LS n MK test. In generl, lrge numer of signifint hnges in extreme inies re foun uring the monsoon sesons tht re the NEM n SWM, n this supports the finings isusse in Setion 4.2. The nlysis from MK test showe tht ll the signifint extreme oeffiients revele upwr trens. However, the results otine etween LS n MK tests re slightly ifferent ue to ifferent pprohes employe y oth methos in nlyzing the trens (Zin et l. 2010). Figure 18 epits the signifint trens of extreme rinfll inies for ll sesons where the lrgest irle/tringle represents the lrgest ontriution of extreme rinfll inies to the extreme rinfll trens. It shows tht positive trens re more ovious uring Tle 5 Signifint hourly extreme inies for eh sttion uring MA Sttion Hr Mx 5-Hr Mx 24-Hr Mx Freq> 20 Freq> 95 th Tot> 95 th Freq> 99 th Tot> 99 th * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * represents positive tren, represents negtive tren where rkene ox represents signifint tren for LS test, n * represents positive signifint tren for MK test

25 Historil tren of hourly extreme rinfll 283 Tle 6 Signifint hourly extreme inies for eh sttion uring SO Sttion Hr Mx 5-Hr Mx 24-Hr Mx Freq> 20 Freq> 95 th Tot> 95 th Freq> 99 th Tot> 99 th * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * represents positive tren, represents negtive tren where rkene ox represents signifint tren for LS test, n * represents positive signifint tren for MK test the NEM while negtive trens re more ovious uring the SWM. The western region s well s the mile prt of the peninsulr experiene more positive trens uring the NEM, SWM, n MA while the northern region experienes more negtive trens uring the sme sesons. Eighty perent of the signifint extreme rinfll trens ome from the monsoon sesons, i.e., NEM n SWM. In ft, 33 % reltes to the NEM n SWM, while the rest 22 n 12 % re relte to MA n SO, respetively. In generl, 65 % of the inies show positive tren of whih 14 % re signifint while the rest 35 % of the inies showe negtive tren of whih only 4 % re signifint. The fiel signifine test showe tht ll extreme intensity, extreme umultive, n extreme frequeny inies revele positive trens uring the NEM n MA throughout Peninsulr Mlysi over the yers However, only extreme intensity n extreme frequeny revele the sme trens uring the SWM n SO. In prtiulr, Hr Mx, Tot >95th, Tot >99th, Freq >99th, n 5-Hr Mx showe upwr trens uring the SWM while other inies remin unhnge. Menwhile, Hr Mx, Tot >99th, n Freq >99th epite the similr trens uring the SO while other inies remin unhnge. 5 Conlusion Anlysis of extreme intensity inies shows higher vlues in the estern region uring the NEM while the western region epits higher inies uring MA. For the northern region, high inies were oserve uring the SWM n SO. However, short extreme intense rinfll (Hr Mx) ws oserve minly t sttions lote on the west ost where the hourly mximum ws reore uring the inter-monsoon seson while in ontrst, extreme umultive rinfll (24-Hr Mx)

26 284 A.H. Syfrin et l Fig. 18 Signifint trens of extreme rinfll inies uring northest monsoon seson (NEM), southwest monsoon seson (SWM), intermonsoon seson (MA), n inter-monsoon seson (SO) (lrger irle/ tringle inites lrger numer of signifint extreme rinfll inies where irle represents signifint positive tren, tringle represents signifint negtive tren)

27 Historil tren of hourly extreme rinfll 285 ws oserve t sttions lote on the estern region where the highest vlue ws reore uring the monsoon seson. This shows tht hourly t gives etter inition of the sesonl ontriution to the nnul extreme rinfll ompre to ily t. It gives etter profile of the extreme inies with regrs to short n long urtion rinflls. From the sptil pttern of tren nlysis, sttions lote on the western n southern streth whih omprises of mostly urn res epit n inrese in numer of very wet n extremely wet hours. This explins the inrese in the frequeny of flsh floos ourrenes in these regions. Suh nlyses lso onlue tht the 95th perentile threshol is onsistent with the 99th perentile threshol. However, northwest region experienes erese in numer of very wet n extremely wet hours. Thus, negtive tren of extreme rinfll ws foun in the northwest region n n e onsiere s rier re. In ition to tht, the extreme frequeny inex (Freq >20) gives more signifint ontriution to the positive extreme rinfll tren uring the monsoon sesons. Menwhile, oth extreme frequeny n extreme intensity (24-Hr Mx, Freq >95th, Tot >95th, Tot >99th, n Hr Mx) inies give more signifint ontriution to the positive extreme rinfll tren uring the inter-monsoon sesons. It is lso foun tht the highest numer of very wet hours n extremely wet hours our uring the NEM whih y lrge re proue y strtiform rin. In summry, the fiel signifine test prove tht most of the signifint extreme inies showe the positive sign of trens throughout Peninsulr Mlysi minly uring the NEM n MA. Speifilly, the extreme intensity, extreme frequeny, n extreme umultive inies showe inresing trens uring the NEM n MA while extreme intensity n extreme frequeny h similr trens uring the SWM n SO. Overll, the hourly extreme rinfll events in Peninsulr Mlysi showe n inresing tren etween the yers 1975 n 2010 with notle inresing trens in short temporl rinfll ws oserve uring inter-monsoon seson. Suh result lso shows tht onvetive rin uring this perio ontriutes higher intensity rins whih n only e pture using short urtion rinfll series. Aknowlegments This work ws supporte y the Dringe n Irrigtion Deprtment in proviing the hourly rinfll t. This reserh ws fune y the Ministry of Eution Funmentl Reserh Grnt (FRGS vote 4 F120), sponsorship from the Interntionl Islmi University of Mlysi n Ministry of Higher Eution, Mlysi. Open Aess This rtile is istriute uner the terms of the Cretive Commons Attriution Liense whih permits ny use, istriution, n reproution in ny meium, provie the originl uthor(s) n the soure re reite. Referenes Alexner LV, Arlster JM (2009) Assessing trens in oserve n moelle limte extremes over Austrli in reltion to future projetions. Int J Climtol 29(3): Cyn DR, Remon KT, Rile LG (1999) ENSO n hyrologi extremes in the western Unite Sttes. J Clim 12(12):3516 Cheng CS, Aul H, Li Q, Li G (2012) Possile impts of limte hnge on extreme wether events t lol sle in south-entrl Cn. Clim Chng 112: Griffiths GM, Slinger MJ, Leleu I (2003) Trens in extreme ily rinfll ross the South Pifi n reltionship to the South Pifi Convergene Zone. Int J Climtol 23(8): Hylok M, Niholls N (2000) Trens in extreme rinfll inies for n upte high qulity t set for Austrli, Int J Climtol 20(13): Slhuin A, Curtis S (2011) Climte extremes in Mlysi n the equtoril South Chin Se. Glol Plnet Chng 78(3 4):83 91 Shmili J, Frei C (2005) Trens of hevy preipittion n wet n ry spells in Switzerln uring the 20th entury. Int J Climtol 25(6): Sen Roy S (2009) A sptil nlysis of extreme hourly preipittion ptterns in Ini. Int J Climtol 29(3): Sen Roy S, Blling RC (2004) Trens in extreme ily preipittion inies in Ini. Int J Climtol 24(4): Suhil J, Deni SM, Zin WZW, Jemin AA (2010) Trens in Peninsulr Mlysi rinfll t uring the Southwest Monsoon n Northest Monsoon sesons: Sins Mlys 39(4): Yue S, Chun, Wng Y (2002) Regionl stremflow tren etetion with onsiertion of oth temporl n sptil orreltion. Int J Climtol 22: Zin WZW, Jmluin S, Deni SM, Jemin AA (2010) Reent hnges in extreme rinfll events in Peninsulr Mlysi: Theor Appl Climtol 99(3 4):