Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012
www.na -haza ds-ea h-sys -sci.ne /12/715/2012/
doi:10.5194/nhess-12-715-2012
© Au ho (s) 2012. CC A ibu ion 3.0 License.
Na u al Haza ds
and Ea h
Sys em Sciences
The 20 Feb ua y 2010 Madei a lash- loods: synop ic analysis and
ex eme ain all assessmen
M. F agoso1, R. M. T igo2, J. G. Pin o3, S. Lopes1,4, A. Lopes1, S. Ulb ich3, and C. Mag o4
1IGOT, Uni e si y o Lisbon, Po ugal
2IDL, Facul y o Sciences, Uni e si y o Lisbon, Po ugal
3Ins i u e o Geophysics and Me eo ology, Uni e si y o Cologne, Ge many
4Labo a ´
o io Regional de Engenha ia Ci il, R.A. Madei a, Po ugal
Co espondence o: M. F agoso ([email p o ec ed])
Recei ed: 9 May 2011 – Re ised: 26 Sep embe 2011 – Accep ed: 31 Janua y 2012 – Published: 23 Ma ch 2012
Abs ac . This s udy aims o cha ac e ise he ain all ex-
cep ionali y and he me eo ological con ex o he 20 Feb u-
a y 2010 lash- loods in Madei a (Po ugal). Daily and
hou ly p ecipi a ion eco ds om he a ailable ain-gauge
s a ion ne wo ks a e e alua ed in o de o econs i u e he
empo al e olu ion o he ains o m, as i s geog aphic inci-
dence, con ibu ing o unde s and he lash- lood dynamics
and he ype and spa ial dis ibu ion o he associa ed im-
pac s. The excep ionali y o he ains o m is u he con-
i med by he e u n pe iod associa ed wi h he daily p ecip-
i a ion egis e ed a he wo long- e m eco d s a ions, wi h
146.9mm obse ed in he ci y o Funchal and 333.8mm on
he moun ain op, co esponding o an es ima ed e u n pe-
iod o app oxima ely 290y and 90y , espec i ely. Fu he -
mo e, he synop ic associa ed si ua ion esponsible o he
lash- loods is analysed using di e en sou ces o in o ma-
ion, e.g., wea he cha s, eanalysis da a, Me eosa images
and adiosounding da a, wi h he ocus on wo main issues:
(1) he dynamical condi ions ha p omo ed such anomalous
humidi y a ailabili y o e he Madei a egion on 20 Feb u-
a y 2010 and (2) he upli mechanism ha induced deep con-
ec ion ac i i y.
1 In oduc ion
On he 20 Feb ua y 2010 he island o Madei a was hi by
o en ial ain all ha igge ed ca as ophic lash- loods, ac-
coun ing o a dea h oll o 45, wi h oughly hal o he ic-
ims (22) alone occu ing in he capi al ci y o Funchal, while
6 o he pe sons we e decla ed missing. I was he deadlies
hyd o-me eo ological ca as ophe in he Po uguese e i o y
in he las ou decades and he economic damage cos s we e
es ima ed o be US$1.9 billion (EM-DAT CRED, 2010). The
island o Madei a is qui e densely popula ed, pa icula ly in
i s sou he n coas , wi h ci ca 267000 inhabi an s in 2011
census, wi h 150000 (app oxima ely 40%) li ing in he Fun-
chal dis ic , one o he ea lies ou ism ho spo s in Eu ope,
cu en ly wi h app oxima ely 30000 ho el beds. In 2009, he
a chipelago ecei ed 1 million gues s; his co esponds o an
income o mo e han 255 Million Eu o (INE-Ins i u o Na-
cional de Es a ´
ıs ica, h p://www.ine.p ).
Madei a is a moun ainous island wi h 740.7km2, loca ed
in he eas e n sub opical a ea o he No h A lan ic Ocean
(Fig. 1a); I s o og aphy (Fig. 1.b) is domina ed by a igo -
ous olcanic landscape, wi h deep alleys, s eeped slopes
and sca ps, exhibi ing i s highes ele a ions along a E–W
o ien ed ba ie , whe e he maximum al i ude is achie ed
a he op o he eas e n moun ain ange (1861m a Pico
Rui o). Loca edbe ween he 30◦and 33◦la i ude N,Madei a
has a Medi e anean ype clima e mode a ed by he A lan ic
Ocean, and since he island o og aphic ba ie (E–W) has
an almos pe pendicula o ien a ion wi h he p e ailing wind
di ec ion (NE), empe a u e and ain all a y ema kably be-
ween he no he n and sou he n slopes. The no he n slopes
a e mo e humid han he sou he n coun e pa s a he same
al i ude, while he amoun o ain all inc eases wi h al i ude
on bo h slopes (P ada e al., 2009). The mean annual p e-
cipi a ion a ies be ween 600mm in he Funchal dis ic o
close o 3000mm a he op o he eas e n moun ain ange
(s a ions 43 and 25 in Fig. 1, espec i ely).
Rele an ain-induced na u al haza ds in Madei a a e
lash- loods, landslides, deb is lows and less equen ly -
sunamis, which can be caused by coas al ock slides (Ro-
d igues and Ayala-Ca cedo, 2003). Unlike he Azo es and
Cana y Islands, Madei a lacks majo olcanic ac i i y and
is p one only o ela i ely modes ea hquake e en s. Flash-
loods cons i u e p obably he mos dange ous na u al haza d
Published by Cope nicus Publica ions on behal o he Eu opean Geosciences Union.
716 M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods
Figu es
(a)
(b)
Fig. 1. Loca ion (a) and elie (b) o he island o Madei a (Po ugal). Do s a e loca ions o he ain-
gauge s a ions used in his s udy (names and desc ip ion in Table 1). Limi s o he d ainage basins
a ec ed by he 20 Feb ua y lash- loods and landslides a e also shown (names and desc ip ion in he
ex ).
Fig. 1. Loca ion (a) and elie (b) o he island o Madei a (Po ugal). Do s a e loca ions o he ain-gauge s a ions used in his s udy (names
and desc ip ion in Table 1). Limi s o he d ainage basins a ec ed by he 20 Feb ua y lash- loods and landslides a e also shown (names and
desc ip ion in he ex ).
Table 1. Main lash- lood e en s in Madei a be ween 1800 and 2010 (SRES, 2010).
Da e Mos a ec ed a eas Casual ies and damage
9 Oc obe 1803 Funchal 800–1000 casual ies
6 Ma ch 1929 S. Vicen e 40 casual ies, 11 houses des oyed
30 Decembe 1939 Madalena do Ma 4 casual ies
21 Sep embe 1972 San o An ´
onio 2 casual ies
20 Decembe 1977 Es ei o de Cˆ
ama a de Lobos 2 casual ies and 45 dislodged
23 and 24 Janua y 1979 Machico, Po o da C uz, Camacha, 14 casual ies
Canhas, Calhe a and Faj˜
a do Penedo
29 Oc obe 1993 All he island 4 casual ies, 4 missed people, 306 dislodged,
27 inju ed people, 76 houses des oyed
5 and 6 Ma ch 2001 Cu al das F ei as and S. Vicen e 4 casual ies and 120 dislodged people
22 Decembe 2009 Madalena do Ma and S. Vicen e Houses and oads des oyed
20 Feb ua y 2010 Funchal and Ribei a B a a 45 casual ies, 6 missed people
in Madei a, whe e he phenomenon has he common name o
“alu i˜
ao”, e e ing o lash- loods a ec ing s eams whose
discha ges and ene gy inc ease d ama ically a e in ense
ain all episodes, d agging mud, blocks and deb is, and p o-
ducing a powe ul and des uc i e cu en (Ribei o, 1985).
An in en o y o lash- loods esponsible o human casual ies
o se e e damage compiled by Quin al (1999) e e s 30 lash-
lood e en s a e he his o ical ca as ophe o 9 Oc obe 1803
– when mo e han 800 people we e killed, mos ly in Funchal
– un il he end o 1998. Taking in o conside a ion he numbe
o casual ies o damage, a mo e ecen compila ion (SRES,
2010), indica es 9 main e en s o disas ous lash- loods o e
he 1800–2009 pe iod (Table 1). Simila o he occu ence
in Oc obe 1803, he damage su e ed du ing he 20 Feb u-
a y 2010 e en was pa icula ly ha m ul in he sou he n slope
o he island, mainly in he Funchal ci y dis ic . Examples
o damages and des uc ion associa ed wi h he lash- loods
in he down own a ea o Funchal and Ribei a B a a, wo o
he mos a ec ed a eas, a e shown in Fig. 2. An ex ao di-
na y olume o solid ma e ial – deb is and huge blocks – was
d agged and deposi ed by he o en ial lows. A sys ema ic
su ey o he landslides p oduced in 20 Feb ua y 2010 based
Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012 www.na -haza ds-ea h-sys -sci.ne /12/715/2012/
M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods 717
a)
(b)
c)
Fig. 2. Pho os showing he des uc i e e ec s o he 20 Feb ua y 2010 lash- loods and landslides in:
(a) down own and (b) uplands; (c) Se a de Água, Ribei a B a a.
Fig. 2. Pho os showing he des uc i e e ec s o he 20 Feb ua y 2010 lash- loods and landslides in: (a) down own and (b) uplands; (c) Se a
de ´
Agua, Ribei a B a a.
on emo e-sensing analysis and alida ed by ield da a collec-
ion allowed he iden i ica ion o 3291 landslides in Funchal
d ainage basins and 5172 landslides in he Ribei a B a a sec-
o (SRES, 2010). Acco ding o he same epo , as a esul
o his la ge numbe o landslides, i was es ima ed ha a ol-
ume o a leas 250000m3o solid ma e ial was deposi ed in
he Funchal u ban a eas.
The hyd ological and geomo phological impac s ela ed
o his ex eme e en we e concen a ed o e i e d ainage
basins (limi s shown in Fig. 1) belonging o he sou h-
e n lank o he island, h ee o hem loca ed in he Fun-
chal egion (Ribei a de S˜
ao Jo˜
ao, Ribei a de San a Luzia
and Ribei a de Jo˜
ao Gomes) while he emaining belong o
he Ribei a B a a sec o (Ribei a da Tabua, Ribei a B a a).
These d ainage basins a e e y small (wi h a eas a ying be-
ween 8.8km2and 15km2), and hei shape is elonga ed,
excep in he case o Ribei a B a a basin, he la ge one, wi h
40.9km2and exhibi ing a unnel shape. The i e d ainage
basins a e also cha ac e ised by he dominance o s eep
slopes (mean slopes a ying be ween 28 and 37 %, wi h some
a eas wi h slopes o e 50%) and sho imes o concen a-
ion (in e io o 3.3h in all cases, es ima ions made using
he Temez me hod, SRES 2010). These wo pa ame e s a e
ele an ea u es o lash- looding p oduc ion. Acco ding
o SRES (2010), he es ima ed peak low o he 20 Feb u-
a y 2010 e en eached 234m3s−1in he Ribei a de Jo˜
ao
Gomes, close o 300m3s−1in S˜
ao Jo˜
ao and San a Luzia
s eams and 663m3s−1in Ribei a B a a.
The complexi y o he phenomenon s udied he e and he
ex eme se e i y o i s impac s, esul ed om he combi-
na ion o deb is- lows, landslides and lash- looding, ig-
ge ed and p oduced in a sho ime lapse as a consequence
www.na -haza ds-ea h-sys -sci.ne /12/715/2012/ Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012
718 M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods
o an in ense p ecipi a ion episode ( he “pa oxysm”, in
20 Feb ua y 2010), bu also con olled by an eceden and
longe du a ion ain alls, p o iding c ucial p e-exis ing con-
di ions o he disas e ( he anomalous we 2010 win e in
Madei a). In ac , he in ense ain all e en esponsible o
he 20 Feb ua y 2010 lash- loods in Madei a occu ed du -
ing a pa icula ly anomalous we win e a ec ing mos sec-
o s o sou he n Ibe ian Peninsula (And ade e al., 2011; Ball,
2011; Vicen e-Se ano e al., 2011), and also he Madei a
a chipelago. As desc ibed in de ail below, se e al s a ions
egis e ed mo e han he iple o he a e age p ecipi a ion
du ing he win e (DJF) mon hs. Mo eo e , he ex eme ain-
all e en o he 20 Feb ua y was p eceded by e y high
p ecipi a ion du ing he p e ious mon hs and, among o he s,
an in ense p ecipi a ion episode occu ed h ee weeks ea lie
(2 Feb ua y), a ec ing mos ly he cen al moun ain ange
wi h se e e looding impac s being el in a s eam o he
no he n coas (Faial). Undoub edly, he accumula ed p e-
cipi a ion egis e ed h oughou he win e con ibu ed o sa -
u a e soils, inducing a ou able condi ions o inc ease and
accele a e su ace uno , agg a a ing lash- lood suscep i-
bili y in he Madei a d ainage basins (SRES, 2010). The e-
o e, he excep ionali y o he 20 Feb ua y ains o m episode
should be analysed wi hin he con ex o he whole win e , as
he impac s obse ed du ing he e en we e clea ly ampli ied
by he con inuous moun ing o hese p edisposing ac o s o
lash- lood occu ence.
This in es iga ion is ocused on he me eo ological ea-
u es o his ex eme e en , wi h he ollowing main objec-
i es:
1. To p o ide a de ailed spa ial and empo al cha ac e i-
sa ion o he p ecipi a ion obse ed on he 20 Feb u-
a y 2010 ha igge ed he lash- loods and landslides.
Daily and hou ly p ecipi a ion eco ds om he a ail-
able ain-gauge s a ions ne wo k a e e alua ed in o de
o econs i u e he empo al e olu ion o he ains o m,
as well as i s geog aphic incidence, con ibu ing o un-
de s and he lash- lood dynamics and he ype and spa-
ial dis ibu ion o he associa ed impac s.
2. To es ima e he excep ionali y o he ains o m, using
he longes mon hly, daily and sub-daily p ecipi a ion
se ies a ailable o Madei a, wi h a special emphasis
on he compu a ion o es ima es o he e u n pe iods
o daily p ecipi a ion obse ed du ing he 20 Feb u-
a y 2010 e en .
3. To desc ibe he mos ele an a mosphe ic ac o s in-
ol ed in his ex eme ain all e en , iden i ying he
main a mosphe ic synop ic condi ions and also ele an
physical mechanisms ha a ou ed i s de elopmen .
2 Da a and me hods
The p esen esea ch esul s om he collec ion, compila ion
and analysis o di e se ypes o da a, in o ma ion ha can be
conside ed o be included in wo main opics: p ecipi a ion
da a and a mosphe ic da a.
2.1 P ecipi a ion da a
The Island o Madei a is well co e ed by wea he s a-
ions wi h ain-gauges. Un o una ely hese s a ions
a e main ained by h ee di e en o ganiza ions, namely:
(1) IM/Ins i u o de Me eo ologia, (2) IGA/In es imen os e
Ges ˜
ao da ´
Agua and (3) LREC/Labo a ´
o io Regional de En-
genha ia Ci il. Since ou aim is o ob ain de ails on he
ex ension and in ensi y o he e en , a ca e ul p elimina y
wo k o da a assembling was pe o med o e ie e a ho-
mogenous p ecipi a ion da ase , allowing a wide geog aph-
ical co e age o he island and o be su icien ly ep esen a-
i e o i s complex o og aphy. Thus, daily and hou ly p e-
cipi a ion da a om a o al o 47 me eo ological and ain-
gauge s a ions we e ga he ed. Thei loca ion is depic ed in
Fig. 1b and hei main cha ac e is ics a e p esen ed in Ta-
ble 2. We a e con iden ha he aingauge ne wo k densi y
(exceeding 6 s a ions/100km2)is su icien ly ep esen a i e,
in spi e o he s eep o og aphy ha domina es he island land-
scape. The p ecipi a ion da a om hese 47 s a ions was used
o p oduce hou ly and daily p ecipi a ion maps ela i e o he
20 Feb ua y 2010 ollowing he applica ion o app op ia e
geos a is ical echniques. In his ega d, he o dina y k iging
was chosen as in e pola ion me hod, es ima ing speci ic a -
iog am models o each map (e.g., Goo ae s, 1997; Showal-
e , 2010).
In addi ion o hese p ecipi a ion da a, long- e m se ies
o annual maximum daily p ecipi a ion we e collec ed, al-
lowing he e alua ion o he e u n pe iod, i.e., an objec i e
measu e o he long- e m excep ionali y o he 20 Feb u-
a y e en . Un o una ely, only wo se ies wi h app op i-
a e empo al leng h (wi h ongoing obse a ions and a leas
mo e han 60y o eco ds) – Funchal/Obse a ´
o io (no. 43,
Fig. 1b) and A eei o (no. 25, Fig. 1b) – we e a ailable and
used o his analysis. Mo eo e , bo h se ies a e no comple e
and hei quali y was also a ec ed by changes in he ins u-
men s along he o al pe iod o collec ed in o ma ion, s a -
ing in 1936 and ending in 2010. Ne e heless, he numbe
o gaps was 5% (8%) o missing da a o Funchal (A eei o),
which was conside ed o be accep able when compu ing he
e u n pe iod es ima ions.
2.2 Synop ic and a mosphe ic da a
The synop ic con ex o he 20 Feb ua y 2010 ex eme e en
was analysed using di e en sou ces o in o ma ion. Wea he
cha s co e ing he Eas e n A lan ic we e ob ained om he
Ge man Wea he Se ice (Deu sche We e diens ; DWD)
Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012 www.na -haza ds-ea h-sys -sci.ne /12/715/2012/
M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods 719
Table 2. Desc ip ion o me eo ological s a ions and aingauges used in his s udy.
Code Designa ion Longi ude La i ude Al i ude
(see Fig. 1) (W) (N) (m)
1 Seixal (LREC) 17◦0602100 32◦4901200 70
2 S. Vicen e, Pos o Flo es al (LREC) 17◦0201900 32◦4703500 120
3 Pon a do Sol (LREC) 17◦0504400 32◦4005600 130
4 Lombo dos Palhei os (LREC) 16◦5005200 32◦4601800 212
5 S˜
ao Gonc¸alo (LREC) 16◦5202400 32◦3804100 220
6 LREC – EMA (LREC) 16◦5601500 32◦3805300 260
7 Achada do Til (LREC) 17◦0101300 32◦4603900 300
8 Massapez (LREC) 17◦0901700 32◦4204700 300
9 T apiche (LREC) 16◦5603400 32◦4002900 590
10 Faj˜
a Noguei a (LREC) 16◦5400800 32◦4402200 629
11 P aze es (LREC) 17◦1105200 32◦4500100 632
12 Faj˜
a O elha (LREC) 17◦1303800 32◦4602700 635
13 Faj˜
a do Penedo (LREC) 16◦5701900 32◦4701800 637
14 Camacha (LREC) 16◦5003600 32◦4000900 675
15 Po o Moniz, Es . Zoo . – EMA (LREC) 17◦1005200 32◦5002900 675
16 Pinhei o Fo a (LREC) 17◦0702800 32◦4302300 750
17 Cu al das F ei as (LREC) 16◦5702000 32◦4403100 800
18 Casa Velha (P.F.) (LREC) 16◦5001700 32◦4203600 880
19 Pico das Ped as (P.F.) (LREC) 16◦5303700 32◦4602800 920
20 Pico Ve de – EMA (LREC) 17◦1003000 32◦4505400 1020
21 T ompica, Pos o Flo es al (LREC) 17◦0002200 32◦4201500 1188
22 PEF EMA (LREC) 16◦5304800 32◦4105600 1300
23 Pico da U ze (LREC) 17◦0604800 32◦4404600 1365
24 Es anquinhos (LREC) 17◦0401500 32◦4600000 1590
25 A eei o-LREC 16◦5404500 32◦4300000 1590
26 Machico - EMA (LREC) 16◦4602600 32◦4301700 170
27 Meia Se a (IGA) 16◦5200200 32◦4202000 1100
28 ETA Aleg ia (IGA) 16◦5500000 32◦4003900 611
29 Encumeada (IGA) 17◦0101500 32◦4404700 854
30 Bica da Cana (IGA) 17◦0301200 32◦4501000 1585
31 Co a G ande (IGA) 17◦0505000 32◦4401400 1340
32 O il (IGA) 16◦5005600 32◦4202900 1014
33 Ros´
a io, Faj˜
a Rod igues (IGA) 17◦0104800 32◦4503800 575
34 Fon e do Bispo (IGA) 17◦1003500 32◦4701700 1245
35 San o Se a, Lamacei os (IGA) 16◦5002400 32◦4401600 784
36 San o da Se a, Quin a (IGA) 16◦4804600 32◦4302000 660
37 Achada da Madei a (IGA) 16◦5803200 32◦4604100 521
38 Ch˜
ao das Fei ei as (IGA) 16◦5205400 32◦4302900 1180
39 Ch˜
ao dos Lou os (IGA) 17◦0004900 32◦4501100 900
40 Cu al das F ei as ETA (IGA) 16◦5702900 32◦4301200 743
41 Poiso, Pos o Flo es al (IGA) 16◦5205800 32◦4203200 1360
42 Ribei a do Alec im (IGA) 17◦0702200 32◦4405800 1293
43 Funchal/Obs. (IM) 16◦5301800 32◦3803800 58
44 Luga de Baixo (IM) 17◦0501700 32◦4003900 15
45 Pon a do Pa go (IM) 17◦1503100 32◦4803700 312
46 S˜
ao Jo ge (IM) 16◦5400600 32◦4905200 185
47 Funchal/Lido (IM) 16◦5505300 32◦3705800 25
and we e use ul o he ecogni ion o he main ea u es
o he associa ed synop ic a mosphe ic ci cula ion. A -
mosphe ic ields we e ex ac ed om he ERA-In e im e-
analysis (ECWMF) da ase , a ailable on a 1.5◦×1.5◦la -
i ude/longi ude mesh and a e used o analyse he dynami-
cal aspec s o he me eo ological e en . The he modynamic
en i onmen associa ed wi h his e en is cha ac e ised by
wo ins abili y pa ame e s, he Li ed index (LI) and CAPE
(Con ec i e A ailable Po en ial Ene gy). The LI is he em-
pe a u e di e ence be ween an ai pa cel li ed adiaba ically
and he en i onmen empe a u e a 500hPa (e.g., Galway,
1958). Nega i e alues o LI indica e ha he a mosphe e
is uns able. The mo e nega i e alues o LI, he highe
he p obabili y o hunde s o m occu ence. CAPE is he
www.na -haza ds-ea h-sys -sci.ne /12/715/2012/ Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012

720 M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods
Fig. 3. (a)Accumula ed daily p ecipi a ion (ADP) in A eei o (s a ion numbe 25 in Fig. 1) be ween 1 Oc obe 2009 and 28 Feb ua y 2010
(blue line) and compa ison wi h he long- e m median ( ed line) and 95 h pe cen ile (da k line) o he ADP o he same ime span, es ima ed
o e he 1936/37–2008/09 pe iod. Indica ed is he occu ence o h ee e en s (1) 22 Decembe 2009 lash lood (2) 2 Feb ua y 2010 hea y
ain all e en (3) 20 Feb ua y 2010 lash lood. No e: he ep esen ed p ecipi a ion da a we e eco ded in di e en me eo ological s a ions,
howe e , jus sepa a ed by a ew me es and loca ed app oxima ely a he same heigh (20m o di e ence). (b) Hou ly e olu ion o he
20 Feb ua y 2010 ains o m in Madei a, in ou selec ed udog aphic s a ions om he Funchal ci y su oundings. Indica ed hou s in he
abcissae axis a e he ending ime o he co esponding p ecipi a ion amoun . The al i ude (me es) o he ou ain-gauge s a ions is inse ed
in he legend.
amoun o ene gy a pa cel o ai would ha e i li ed e i-
cally h ough he a mosphe e (Monc ie and G een, 1972;
Doswell and Rasmunsen, 1994). Posi i e CAPE indica e
posi i e buoyancy o an ai pa cel being, hus, an indica-
o o a mosphe ic ins abili y. The humidi y anspo as-
socia ed wi h his e en has been calcula ed based on his
da a using 3-D backwa d ajec o ies (Me h en, 1997). This
ool allows he acing o humidi y (o o he a mosphe ic
con en s) o an ai pa cel and has been used, he e o e, in
some s udies (e.g., Me h en e al., 2001). In addi ion, he
diagnos ic o he in ense mid-la i ude cyclone sys em asso-
cia ed o he 20 Feb ua y 2010 lash- loods in Madei a was
also pe o med using app op ia e sequences o Me eosa -9
sa elli e images (in a- ed and wa e apou channels, and
also om he de i ed p oduc Mul i-Senso P ecipi a ion Es-
ima e, a ailable a www.eume sa .in ). Fu he , he e olu-
ion o local condi ions o he oposphe ic column was e-
cons i u ed using da a om he adiosounding s a ion in Fun-
chal. Un o una ely, only one sounding pe day is launched
(a 12:00UTC). Sounding plo s, he modynamic pa ame e s
and s abili y indices we e compu ed using he RAwinsonde
Obse a ion (RAOB) so wa e (Schewchuk, 2002).
3 Rain all analysis
This sec ion is de o ed o he empo al and spa ial cha ac-
e isa ion o he p ecipi a ion associa ed wi h his p ominen
e en . We s a by analysing he p ecipi a ion du ing he
an eceden mon hs leading o he ex eme e en . I mus be
unde lined ha he accumula ed p ecipi a ion in he p e i-
ous mon hs was e y impo an o he phenomenon s udied
he e. The la ge numbe o landslides and deb is lows sud-
denly p oduced in he 20 Feb ua y 2010, a e connec ed wi h
he accumula ed ain all. This ac o agg a a ed he se e -
i y o he impac s o he lash loods, p o iding an eno mous
amoun o ocks, deb is and solid ma e ial o be d agged in o
he alleys. A e wa ds, a de ailed desc ip ion o he spa ial
and empo al e olu ion o he p ecipi a ion e en is p o ided.
Finally, he excep ionali y o he e en is e alua ed wi h long
eco ds ha allow compu ing he e u n pe iods associa ed
wi h he e en .
3.1 The ex emely we 2009–2010 win e in he Madei a
Islands
The analysis o Fig. 3a allows he compa ison o he accu-
mula ed daily p ecipi a ion (ADP) be ween he beginning o
he 2010 hyd ological yea (s a ing 1 Oc obe 2009) and he
end o Feb ua y 2010 (blue line) wi h he long- e m median
( ed line) and 95 h pe cen ile o he ADP (black line) o he
same 72-y long pe iod (i.e., 1937/38–2008/09). The p e-
cipi a ion da a shown in his igu e (A eei o s a ion, no. 25
in Fig. 1b) is ep esen a i e o he p ecipi a ion eco ds in he
uppe pa o he eas e n moun ains o he island, close o one
o i s highes peaks. The win e was ex emely we a A eei o
(abo e 4000mm o ain all be ween 1 Oc obe 2009 and
28 Feb ua y 2010), exceeding mo e han wice he median
Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012 www.na -haza ds-ea h-sys -sci.ne /12/715/2012/
M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods 721
amoun o ADP ob ained be ween 1937 and 2008 o he
same pe iod. Fu he mo e, he accumula ed ADP a he
end o Feb ua y was also signi ican ly highe han he co -
esponding 95 h pe cen ile; in ac , he win e o 2009/2010
was he ainies we season since 1937. Ne e heless, he
ela i e ank o his win e was no cons an h oughou he
empo al window analysed in Fig. 3a, s a ing wi h a we Oc-
obe , he ADP emained sligh ly abo e he median un il mid
Decembe , inc easing o highe pe cen ile only a e wa ds.
In ac , a e he 22 Decembe 2009, he ADP begun o ex-
ceed he 95 h pe cen ile and kep abo e his h eshold un-
il he end o Feb ua y. The e o e, his compa a i e analysis
clea ly demons a es ha he 2009/2010 ainy season was ex-
cep ionally we a he moun ainous egion a ew kilome es
abo e he Funchal bay a ea. In pa icula , hea y p ecipi a-
ion episodes wi h ex emely high amoun s a daily scale oc-
cu ed: 22 Decembe 2009, 2 Feb ua y 2010 and 20 Feb u-
a y 2010 (he e desc ibed). These e en s a e ma ked 1–3 in
Fig. 3a.
In he Funchal a ea, he anomalously we 2010 win e
(DJF) was e en mo e ex eme (in ela i e e ms) han wha
has been desc ibed o he Madei a uplands. The accu-
mula ed p ecipi a ion in 2010 win e was 997mm in Fun-
chal/Obse a o y s a ion (no. 43 in Fig. 1b), la gely exceed-
ing he 95 h pe cen ile o i s his o ical eco ds o his sea-
son, which is close o 700mm. In pa icula , he p ecipi a ion
amoun obse ed a his s a ion du ing Feb ua y – 458.7mm
– co esponds o he new absolu e all- ime eco d since 1865,
i.e., since he beginning o egula obse a ions in he is-
land. We would like o s ess ha his alue exceeds 8 imes
he median alue o Feb ua y p ecipi a ion (ob ained o he
no mal 1971–2000 pe iod). This analysis con i ms ha he
20 Feb ua y 2010 e en was p eceded by an equally ou -
s anding anomalous accumula ed p ecipi a ion, pa icula ly
on he uppe pa s o Eas e n Moun ains, which p obably
lead o inc ease he slope ins abili y a he ups eam sec o s
o he Funchal ca chmen s and, hus, inducing a ou able
condi ions o igge ing landslides. The con ol o ain all
on landslides di e s subs an ially depending upon landslide
dep h and kinema ics and he a ec ed ma e ial. Shallow soil
slips and apid deb is lows a e ypically ac i a ed by a sho
pe iod o e y in ense ain, while deep-sea ed o a ional and
ansla ional slides a e usually associa ed wi h less in ense
ain all occu ing in a pe iod las ing se e al weeks o se e al
mon hs (e.g., Zˆ
eze e e al., 2005).
3.2 Spa ial ea u es and empo al e olu ion o he
20 Feb ua y 2010 ains o m
A syn he ic o e iew o he 20 Feb ua y ain all o selec ed
s a ions is depic ed in Fig. 3b, whe e we can app ecia e he
e olu ion o hou ly p ecipi a ion h oughou he day ela i e
o ou selec ed ain-gauge s a ions placed in he su ounding
a eas o he Funchal u ban dis ic . Among hese ain-gauge
s a ions, S˜
ao Gonc¸alo (220m o al i ude, no. 5 in Fig. 1b)
is he lowes al i ude s a ion and is loca ed eas o Funchal.
T apiche (590m, no. 9 in Fig. 1b) and Camacha (690m,
no. 14 in Fig. 1b) a e ep esen a i e si es om he in e medi-
a e sec o s o he slopes and a e espec i ely loca ed o he
wes and eas o he Funchal ci y a ea. A eei o (1590m,
no. 25 in Fig. 1b) is he mos ele a ed ain-gauge ep esen ed
in Fig. 3b, illus a ing he ains o m on he ups eam sec o o
he d ainage basin ha c oss he Funchal u ban dis ic , and
whe e lash- loods occu ed.
The o al du a ion o he ains o m was qui e unusual
wi h oughly 14 consecu i e hou s o unin e up ed p ecip-
i a ion o e mos o he Island, s a ing a 03:00UTC and
ending only a 17:00UTC. The hou ly p ecipi a ion in en-
si y inc eased g adually du ing he ea ly mo ning hou s o
20 Feb ua y in his sou he n sec o o he Madei a Island.
In e es ingly, he mos in ense and c i ical pe iod o he
s o m hi ini ially he lowe and midway sec o s o he slopes
(Fig. 3b), whe e he hou ly ain all in ensi y eached a leas
60mmh−1be ween 08:00 and 09:00UTC. A his s age, he
p ecipi a ion was much lowe in he uppe sec o s o he
moun ainous a ea, such as he A eei o Peak. Howe e , du -
ing he ollowing hou s, while he p ecipi a ion s a ed o
dec ease a lowe al i udes, an inc ease can be obse ed a
highe le els (e.g., A eei o), wi h a maximum a 11:00UTC,
when landslides and loods we e al eady occu ing and ag-
g a a ing hei impac s e en mo e. A e wa ds, and un-
il 14:00UTC, e y abundan p ecipi a ion was accumula ed
a he ups eam sec o s o he d ainage sys ems, especially
hose ha low in o he Funchal coas al a eas, as i is demon-
s a ed by he hou ly in ensi y a es abo e 30mmh−1in he
A eei o ain-gauge s a ion (Fig. 3b).
In o de o ob ain an app op ia e econs i u ion o he
space- ime a iabili y o he p ecipi a ion associa ed wi h he
20 Feb ua y ains o m in Madei a, hou ly maps we e elabo-
a ed using all a ailable in o ma ion om he 47 ain-gauges
o he island (Fig. 4). These ele en hou ly maps illus a e
he e olu ion o he ains o m be ween 05:00 and 16:00UTC,
hus, allowing a de ailed ep esen a ion o he e en ( he i s
h ee hou s a e omi ed as p ecipi a ion amoun s we e el-
a i ely small). Figu e 4 documen s he ini ial phase o he
e en , when p ecipi a ion began o ba e he sou he n lanks
o he island, especially i s eas e n sec o s, including he Fun-
chal dis ic . F om 08:00 o 09:00UTC, he ain all was
mo e in ense a lowe sec o s o he sou he n slopes, wi h
in ensi ies close o 35mmh−1. In he ollowing wo hou s,
he p ecipi a ion a e inc eased (up o 60 o 80mmh−1) and
was mo e concen a ed o e he in e media e ele a ion sec-
o s a ound he Funchal egion, a slope le els be ween 500
and 1000m o al i ude. The mos in ense co es o se e e
p ecipi a ion a e 10:00UTC mainly a ec ed a eas close o
Funchal o i s su oundings. F om 11:00UTC onwa ds, he
mos in ense p ecipi a ion mo ed no hwa ds and was mos ly
con ined o he uplands and highe peaks o he cen al idge
o he island. Th oughou his pe iod, he spa ial pa e n o
p ecipi a ion dis ibu ion is gene ally ma ked by he majo
www.na -haza ds-ea h-sys -sci.ne /12/715/2012/ Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012
722 M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods
Fig. 4. Hou ly p ecipi a ion in Madei a, 20 Feb ua y 2010, be ween 05:00 UTC and 16:00 UTC. The
maps a e based on da a om he same ain-gauge ne wo k ep esen ed in ig. 1 (loca ions) and lis ed
in Table 2.
Fig. 4. Hou ly p ecipi a ion in Madei a, 20 Feb ua y 2010, be ween 05:00UTC and 16:00UTC. The maps a e based on da a om he same
ain-gauge ne wo k ep esen ed in Fig. 1 (loca ions) and lis ed in Table 2.
opog aphic con as s (depic ed in Fig. 1b), sugges ing ha
he o og aphy played an impo an ole o enhance and ocus
he e en , esul ing in a longe and e en ainie s o m.
The o al daily p ecipi a ion amoun s o he 20 Feb u-
a y 2010 in Madei a a e shown in Fig. 5a. Since no el-
e an showe s occu ed a e i s end 17:00 UTC, he p e-
cipi a ion dis ibu ion is ep esen a i e o he whole e en .
Two majo indings eme ge om he analysis o Fig. 5a:
(a) he la ge a ea o he island (>50%) wi h o al p ecip-
i a ion inside he 250mm isoye h limi s; and (b) he exis-
ence o wo main co es o ex emely abundan p ecipi a-
ion, wi h amoun s a ying be ween 250 and 370mm, one
loca ed o e he uplands and sou he n slopes o he eas e n
moun ains (A eei o pla eau), and ano he one cen ed o e
he cen al pla eau sec o (Pa´
ul da Se a and Encumeada). A
close look a Fig. 5a indica es ha he Funchal a ea was en-
i ely su ounded by he c escen pa e n ha cha ac e ises
he sou heas e n peak o in ense ain alls, which explains he
se e i y o lash- loods, landslides and deb is- lows impac s
on i s d ainage basins (see example in Fig. 2b). On he o he
hand, he second p ecipi a ion peak o e he cen al pla eau
is esponsible o he ca as ophic impac s o loods and land-
slides in he Ribei a B a a a ea, loca ed u he wes in he
sou he n lank o he Island (Fig. 1b). The main co es o
excessi e ain all may be exp essed by mapping he o al
numbe o hou s wi h p ecipi a ion abo e 10mm (Fig. 5b;
SRES, 2010). The pe iod o sus ained in ense p ecipi a ion
was conside ably long, a ying om i e o en consecu i e
hou s o e ex ended a eas, which was, e y p obably, a c i -
ical condi ion o igge he la ge numbe o landslides and
o he complex slope mo emen s obse ed in he wo main
a ec ed sec o s (i.e., Funchal and Ribei a B a a, c . Fig. 5b).
Undoub edly, he e ec s o such a la ge numbe o land-
slides, p o iding an ou s anding olume o solid ma e ial o
be d agged along s eams, accoun ed o agg a a ing lash-
looding impac s, esul ing in he ca as ophic and deadly
e en on he lowe sec o s o he small d ainage basins.
3.3 Assessmen o he p ecipi a ion excep ionali y
The es ima ion o e u n pe iods is a classical app oach in
o de o e alua e he excep ionali y and magni ude o ex-
eme me eo ological e en s. This echnique uses he ex-
eme alues analysis, he b anch o p obabili y and s a is ics
ha is used o make in e ences abou he size and equency
o ex eme e en s (S o ch and Zwie s, 2003). The p op i-
e ies o some o he mos used ex eme alues dis ibu ions
in clima ology and hyd ological sciences we e desc ibed by
Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012 www.na -haza ds-ea h-sys -sci.ne /12/715/2012/
M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods 723
Fig. 5. (a) To al daily p ecipi a ion in Madei a (00:00–24:00UTC),
20 Feb ua y 2010. The map is based on da a om he same ain-
gauge ne wo k ep esen ed in Fig. 1 (s a ion names a e lis ed in Ta-
ble 1). (b) Numbe o hou s wi h p ecipi a ion abo e 10mm and
landslides dis ibu ion on Funchal and Ribei a B a a a eas. This
map is based on a subse o he ne wo k p esen ed in Fig. 1, consis -
ing only in udog aphic s a ions. Sou ce: SRES, 2010.
Gumbel (1958) and ecen e iews documen a la ge num-
be o applica ions (e.g., Coles, 2001; Alexande sson e al.,
2001; S enson and Jones, 2010). The a ailabili y o long-
e m se ies o he pa ame e o be analysed is a manda o y
condi ion o ca y ou his ype o in es iga ion in an app o-
p ia e way, which ep esen s in many cases a signi ican con-
s ain . In he p esen s udy, he sca ce a ailabili y o long-
e m se ies posed a p oblem. Ano he p oblem is ha he
a chi es only con ain he p ecipi a ion accumula ion o ixed
pe iods (e.g., 24h beginning a 09:00UTC), ins ead o accu-
mula ions o e a mo ing window (e.g., 24-h pe iod).
Wi h ega d o he p ecipi a ion se ies o annual max-
ima wi hin 24h, app op ia e long- e m eco ds (1936–2010)
a e only a ailable o wo me eo ological s a ions: A eei o
and Funchal/Obse a o y. A numbe o expe imen s we e
conduc ed in o de o i he mos commonly used ex eme
alue dis ibu ions o he da a. The bes i ing model was
ob ained wi h he GEV dis ibu ion, anking he se o e-
sul s om h ee s anda d es s o e alua e he goodness o i :
Kolgomo o -Smi no , Ande son-Da ling and Chi-squa ed
es s (e.g., Wilks, 2005). Re u n pe iods o he 24h ain-
all obse ed o he 20 Feb ua y 2010 o bo h si es con-
i m he excep ionali y o he ains o m. In he case o
he moun ainous A eei o s a ion, he 24h amoun de ec ed
(333.8mm) co esponds o an es ima ed e u n pe iod o ap-
p oxima ely 90y . In con as , he 24h amoun obse ed in
Funchal/Obse a o y (146.9mm) co esponds o a e u n pe-
iod es ima ed o be in he o de o 290y , hus, an e en less
equen e en .
Cau ion is equi ed when es ima ing such long e u n pe-
iods, as hey a e much longe han he ime se ies used o
compu e hem. In any case his s a is ical app oach clea ly
sugges s ha he 20 Feb ua y2010 ex emee en can be clas-
si ied as excep ional o bo h s a ions, al hough e en mo e
ou s anding in he Funchal a ea han a he op o he Eas -
e n moun ains. Mo eo e , i mus be s essed ha almos
80% o his ex eme daily p ecipi a ion obse ed in he Fun-
chal/Obse a o y occu ed wi hin a six hou s pe iod (08:00
and 14:00UTC). This pe iod o sus ained in ense ain-bu s s
p oduced 114.8mm o accumula ed p ecipi a ion, an imp es-
si e amoun o 6h-du a ion in Funchal, as i was con i med
a e a compa ison wi h p e ious co esponding annual max-
ima o e he 1980–2009 pe iod: This alue exceeds he p e-
ious maximum o his ime leng h (92.6mm, obse ed in
27 Sep embe 1989).
4 Synop ic con ex
This sec ion is de o ed o he discussion o he main aspec s
o he a mosphe ic ci cula ion and associa ed physical mech-
anisms ha we e esponsible o he 20 Feb ua y copious
amoun s o ain all in Madei a Island. I is impo an o ad-
d ess i s he la ge-scale a mosphe ic condi ions associa ed
wi h he p olonged p ecipi a ion anomaly in Madei a du ing
he win e 2010. In ac , his win e was cha ac e ised by
a clea p e alence o he nega i e phase o he No h A -
lan ic Oscilla ion (NAO) (new win e eco d-b eaking, e.g.,
Osbo n, 2011), wi h s ong posi i e SLP anomalies in he
Iceland low a ea and nega i e anomalies in he Azo es high
p essu e egion (And ade e al., 2011; Vicen e-Se ano e al.,
2011). In p e ious wo ks (e.g., Ulb ich e al., 1999; T igo
e al., 2004; San os e al., 2005, 2009) i was demons a ed
ha hese la ge-scale a mosphe ic ci cula ion condi ions as-
socia ed wi h nega i e NAO phases induce an inc ease in he
equency o mid-la i ude cyclones a ec ing he en i e wes -
e n Ibe ian egion and a la ge sec o o he con iguous no h
A lan ic basin, he e o e, a ec ing also he island o Madei a.
This signi ican inc ease (dec ease) o low p essu e sys ems
du ing he nega i e (posi i e) phase o he NAO pa e n is he
mos impo an mechanism con ibu ing o high (low) p e-
cipi a ion amoun s o e wes e n Ibe ia (Ulb ich e al., 1999;
www.na -haza ds-ea h-sys -sci.ne /12/715/2012/ Na . Haza ds Ea h Sys . Sci., 12, 715–730, 2012
730 M. F agoso e al.: The 20 Feb ua y 2010 Madei a lash- loods
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