Second Inwma!iml Coufemnce
"%pica1 Climafoto~Me8clcomlom mid H~mIogy"
Procacdingsedited by
G.D e m d e , M. DCDapper. J. Alurandre
pp. 2740 (2004)
?
$
L
1 ,
i
'
Preliminary Results of a Reduced-gravity Mode1 of
the Wind-induced Oscillations of the Thermocline
in Lake Tanganyika
Jaya N m * ,Eric D E L E B R S ~ W * ,
Pierre-Denis PUSERER
**, *** & S6bastien LERAND*. ***'
t
i
- Lake Tanganyika ; Therm~cliie;Internal Sdche ; Reduced-
Kaywoms.
gravity Model.
S m w . - A two-dimensional, reducd-pvity m d e l is established to
study the wind-induced oscillations of the thermocline of Lake Tanganyika. An
analytical solution is obtained for a sirapIified, one-dimensional, linearized set of
equations, which suggests that the first mode of oscillation - exhibiting one
node only
should be dominant. The sensitivity to the wind stress, the stratification and the unperhubed thermoche depth of the amplitude and period of
the linear solution is analysed. Numerical soIutions of the complete, non I'>near,
two-dimensional reduced-pvity model are compared cursorily with fieId data
and are seen lo exhibit properties that are rather similar to those of the idealized,
ondmensional model.
-
t
-
1. Introduction
Lake Tanganyika is one of the deepest freshwater lakes in the world
with a maximum depth of about 1,470 m. The lake is situated from
* M t u t d9Ash-onomiect de Wopbysiqut G.Lemdtrc, Universitt Catholicpc de
LouMin, 2 Chemin du Cyclotron,B-1348 Louvaio-la-Neuve (Belgmm).
** Geology and Minera1og)r Deparbnent, Royal Museum for Cenhal Africa,
13 Leuvensesteenweg, B-3080,Tenwren (Belgium).
*** Lahratoire d'Ecologie des E a u Deuces, FacuI& Universitaires NotsefDame dc
la Paix, 61 rue de BruxeIlan, B-5000Namur (Belgium).
**** *Centre for Systems Engineering and Applied Mechanics, Uniwit6 Catholique
de Lourain, 4 Avenue G.Lemaitre, B-1348Lonvain-la-Neuvt (Belgium).
THE WIND-INDUCED OSCULATIONS OF l733 THERM-
29
siond model of the lake hydrodynamics and ecology. The hrst stage of
this undmhking is concerned with the study of one of the most striking
features of the lake hydrodynamics, i.e. the tiIting of themocline occurring during the dry season and the associated Iarge-amplitude internal
seiches (COULER& S H G1991,
~ CHT-WA
1999, PWs~rnet al.
1999,PLENER& C O E2001).
~ These phenomena, which are believed to
be induced by the wind forcing, are studied herein by means of a reducedgravity model.
In the next section, the equations and the surface forcing of the
reduced-gravity model are established. Then, this model is simplified to
a one-dimensional, hear model, of which an analytical solution is
derived and anaIysed. FinalIy, numerical results of the complete reducedgravity model a ~ eobtained, and compared cursorily with field data and
one-dimensional,analytical solutions.
W'E
Fig. I.
31%
-Map of Lake Tanganyika
3'20' S to 8'45' S, and 29'05' E to 3 1°15' E (fig. 1). On average, its
length and width are of the order of 650 h and 50 h,
r e e v e l y . The
lake is a significant source of food for the countries sharing it, Le. DR
Congo, Burundi, Tanzania and Zambia. The region undergoes two main
seasons, the &y season and the wet season. The dry season, approximately from May to September, is characterized by smng southeasterly
winds,the trade winds, whereas during the wet season the winds are generally naaheastdy and weaker {COULTER
& SPIGEL
19911,though same
short, strong wind events can occur during this season. For the dty seasons of E N S 0 years. preliminary data suggest that the air temperature is
higher and the wind weaker. This seems to cause variability in catches of
several species of pelagic fisbes, affecting the economy and the food
stock of the neighbouring populations (htsm1997, WSNIER
et al.
2000). Furthermore, over recent years, the Iake hydrodynamics has been
seen to exhibit variability related to climate change (RJSNIER
1997,
2000).
Understanding the Iake hydrodynamics and its variability is important
for the management of its resources, as well as undemtanding limnologica1comditioils in the framework of paleochtic studies such as the ongoing CLlMLAXCE project (DESCY et al. 2002). h this respect, numerical
modelling is an ~ d u a b l tool.
e Our objective is to build a zhree-hen-
2. The Reduced-gravity Model
Tbe thermocline is present all year round over a large fraction of the
lake. This is the main reason why a two-layer mode1 is believed to be a
relevant tool for representing the motions of the tbermocline in an idealized manner. In such a model,the prognostic variables related to each
layer are assumed to be vertically homogeneous.If the subscripts "l'"and
"2" are asscciated with the top and the bottom layer, respectively, h. W
and n (i = 1,2)denote, for tbe i-th layer, the unperhubed depth, the component of the horizontal velocity along the x-axis and the component of
the horizontal veIocity along the y-axis, x and y being Cartesian horizontal coordinates as tlIustrated in figure 2. Let 11 and f represent the upward
displacement of the lake surface and the downward displacement of the
thennoclhe, respectively, which is assumed to be impermeable (fig. 3). If
the pycnocIine and bottom stresses are neglected,the continuity and horizontal momentum equations read :
where t is time ;U,= we, + v~e,is the velocity vector h the i-th layer ; p;
and e, are the horizontal unit vectors associated with the X and y coordinate axes, while e, = ex X e, is the vertical unit vector, pointing upward ;
f is the Coriolis factor - which is relativeIy small and negative in the
domain of interest -and g is the gravitational acceleration 9.8 m sj).
(5
In the governing equations above, the vector is the wind W s , which
is evaluated by means of the S m & BANKE(1975) pararneterihw,
t = p. 10.63 x 10.' + 0.066 X 1D'lv.l) 1v.l v,,
(3
where p. (= 1 kg m') is the air density and v. is the wind velocity,
expressed in m S ' , The actual height of each water layer is d u a t e d as
H,= h) -t1 + E and Hz= hl - E. The dissipative terms are expressed as
D,= v (Aflvu,)+ V W v ) (i = 1,2),
(6)
where R, and A, are the horizontal eddy viscosities, which are taken to be
differeat in the X- and y-directions because the ''width" of the lake is
much smalIer than its "length". If the constant p, (i = 1,2)represents the
water density in the i-th Iayer, the relative density difference e is defined
to be
E = l c P L ,
(7)
P*
The density is computed from the UNESCO (1981) equation of state
of the water, in which the salinity is set to zero wide the pressure is assumed to be equd to one amosphere as density variations m mainly
due to temperature variations in Lake Tanganyika. Given the range of the
avaiIable in sihr tempem&re profiles, E is likely to be smaller than l W.
The displacement of the lake surface is assumed to be much smaller
than that of the pycnacline. Therefore, by virtue of continuity equations
(I) and (31, the layer heights and tmspom satisfy aHllat = aH,lat =
-P
(fiu,) = V (H2u2).
Thus, the order of magnitude of the top Iayer
t~ansport,H1ar,
is equal to that of the bottom layer, H1u2,
implying that
the order of magnitude of the left-hand side of momentum equation (2) is
equivalent to that of the lefi-hand side of (4). As the thickness of the
hypolimnion ranges from about 100 m to over 1,000 m while the depth
of the e p i h d o n rarely exceeds 50 to 100 m, the ratio HII Hzis generally much smaller than unity. Therefwe, the contributions to the pressure
force prevailing in the hypoZimnon are likely to be the only dominant
terms in (4), i.e. -gHzv(q - = 0. By virtue of continuity equations (1)
and (31, the lake-averaged values of and 5 must be constants, which are
m
bottom
L
@+X
Fig.
2. Bathymetry
(in
metres) of L&
Fig. 3. - The main p m e h r s and variables of a two-layer
Tanganyika.
model of the l&, which upon assuming that h, c< h, pives rise to
a d u d - g r a v i ty model.
-
assumed to be zera in all applications considered below. As a resuIf. the
displacement of the lake surface and that of the thermocline satisfy
approximateIy the following relation
-
Substituting (8) into the pressure force in the right-band side of (Z),
neglecting relative to 5, dropping the subscripts "l", it is readily seen
that the equations governing the dynamics of the epilimnion cm be
approximated by
..
$+$*4:4>
with H = h + 5. The latter equations are similar to those of a one-layer,
deptfi-inregrated model, except for the reduction of the gravitational
acceleration by the small dimensionless factor E. Hence, they make up a
modd usually referred to as "reduced-gravity model". Models of this
type have demonstrated their ability to represent the displacement of a
pycnocline in many applications.
,k,,$3.*
,p,:>'
.
J
,
L
-
3. The Linearized, Onedimensional Mode1
According to
et al. (2002), a suitable idealized wind forcing
is as follows : during the wet season the wind stress is zero,and during
the dry season the wind is assumed to blow at a constant velocity from
the southern end of the lake toward the northern one. Let Td and denote
the duration of the dry season and that of the wet season, respectively, sa
that one year is T = + T. Then, if time is prescribed to be zero at the
beginning of a dry season, the wind stress can be written as 5 = z,(t)e,
with
.
nature.
kl I
1
n+rw
I--?-
c
>,
'
O
N OFS THE - l x E l I M m
33
Assuming that the t h e m l i n e displacement remains small compared
with the thiclmess of the epibnion, neglecting the CorioIis force and the
advective part of the acceleration, integrating governing equations (9)(10) over the width of the lake and parameterizing the dissipative terms
as Newtonian friction
for physical reasons and for the sake of simplicity, as well -, the following linearized, one-dimensional model
focused on along-lake variations is obtained :
-
L
A''
' :,
,
.>,
~
,
where y is the relevant Newzonian friction coefficient At the initial
instant the themwline displacement and the veIocity are assumed to be
zero.The impermeability of the lake ends requires that the velocity be
pregcribed to be zero at any h e at both ends of the lake, i.e. v (t, y = 0)
= 0 = v(t, y) = L,where L = 650 km is the length of the lake.
The steady-state response of the thennodine to the dry season wind
stress PT is a linear function of the distance y to the southenunost end of
the lake, with the thermoctine being shallower in the south and deeper in
the north, i.e.
where pz is a positive commit representing the dry season wind stress,
which is to be estimated by means of parameterization (3,howing the
order of magnitude of the wind speed ;X is the Heaviside step function,
i.e. a function which is equal to 1, lD, or 0,according to whether its argument is > 0,= 0,< 0.The surface forcing (1 1) (fig. 4) is used te obrain all
of the results presented herein, be they of an analytical or a numerical
wind Ness: tpV)
+*4
L
THE INDUCED O
The associated along-lake velociv is obviously zero. This solution is
incompatible with the initial conditions and, hence, cannot set in abruptly. For this reason, a transient regime develops, in which oscillations of
the thermocline are superimposed on the steady-state solution. The
response to a Heavlsidetype wind forcing s t d n g at t = 0 reads
P :d m a b M & y -
P=
vH(t,y) = 2 V"@ sin(w,t) sin (ka]
,
nml
time r
to
t-0
l-T
with
1-TtG
Fig. 4. -Schematic representation of the annual cycIe of the wind stress /I1).
'
4t
E. = and
€gm2
va=- 4~
mk '
(16)
..,
EX$
.,l
.
,
-.
-i....$$*r.,,.. ,
e?.:). ,
.
'.
,<".:L
,
where the damping coefficient, the angular frequency and the wave
number of the n-th mode are p = y / 2,W. = (egWI,Z p)'"and k.= (2n
1)nlL,respectively.As the model is hear and the surface wind stress is
a sum of Heaviside functions, the adutions of (1I)-(13)may be expressed
as a sum of appropriately-delayed responses to a single Heaviside-type
forcing, Le.
-
-
r:
fr;
F,m;
:
1
v
9
!
i;
r
.
I
The oscillations of the thermoche may be seen as standing waves, of
which the n-th mode exhibits 2n - 1 nodes. As E. / E , ' = (2n - I)-l, the
arnpIitudesE. of the oscillation modes decrease quickly as n increases, so
that only the first mode contributes significantly to the oscillations, as is
illustrated in figure 5. In 0th words, the present sirnpIlfied model suggests that the thermmline osciUations are likely to exhibit only one node,
in the centre of the lake, and two maxima, at the ends of the lake.
W',.
r
I
1
A
.',,
..
Furthermore, according to the idealized solution above, the amplitude
md period of thermochne oscillations should depend on the wind stress,
the density difference -or stratification-and the unperturbed depth of
the thermocline as indicated in table 1, and exhibit values of the order of
those dispIayed in figure 6.The latter suggests that the period of the oscillations is much less sensitive than the amplitude of the thermoche
motions to the variations of the model parameters and forcing,
QualitativeilIusmtion of the sensitivity of the ampliiude and period of Ulmoclinc .
oscillations to model parameters or forcing, in accordance with the Iinearized,
me-dimensionalmodel solution
Faiod
AmpIitude
t
Wind velocity : v. t
L
&
Stratification : E T
.l
Unperturbed depth of the thwmocline : A t
L
. . . .
:
!
.
I
10
-
Fig. 5. The first thee modes (n = 1,2,3) of the thamocline oscinations, as
in expressions /l$) and (17).
35
THB m W D U C E D OSCILLATIONS OF THE THWMOCIDE
h
.
/
.
.
. .
.
*
pm-.
.I
amplitude: 4 = 20 f l I metres
.. ..p
20
30
40
amplitude (metres)
I
50
60
Fig. 6. -Values of the amplitude E, and period 2 n I W, of the first -and only significant -mode of thermocline oscillations obtained by varying the wind velacity v, the
relative density difference E and the unperturbed depth of the W r m ~ : I i n he in the intervals 3 5 v. 5 7 (m a-'), 0.5 X l@'5 E e 1I[r and 30 s h 5 70 (m),which rue believed to
represent the mge of the admissiblevalues of these p m e t e r s . The damping coeficient
p i s set to 2 year.', a value which has a minor impact on the amplitude and period of h
oscillations
but seems te be ~ppropriatein view of the numerical results discussed
below. The mean and standard deviation of amplitude E, md period 2 a l w, are indicated.
-
THE WINI]-INDUCEDOSCLUTIONS OF THE THEKMdCLTNE
4, NnmerieaI Results from the Complete Reduced-gravityModel
I..
Eg.7. -Evolution dmhg the second year of simuIation of the downwad d q b
mmt of the thermache at the northern (solid curve) and southern (dashed curve) ends of
the lake, as evaluated by means of the complete, seduced-gravitymodel. The unperturbed
depth ofthe thermoche, the dry season duration, the wind spead, and the relative density
d i m c e are h = 50 m. X, = 4 months, v. = 5 m s',and E = 6.3 x 10-1.respectively.
(BAWO 1998)is implemented, consisting in setting to zero the water
fluxes crossing the boundaries of every grid box in which the actual water
coIumn depth wouId become
after one-time step - smaIler than a
critical value, which is taken to be 5 ni herein.
A series of numerical experiments is conducted, with different values
of the model parameters, the results of which are in agreement with table
1. A detailed discussion of this work may be found in NAIM et al.
(20021, along with an in-depth comparison with €heavailable field data,
which includes the identification of the main timescales of the themocline displacement by means of wavelet analysis. 7)pical numerical
results are displayed in figure 7. The latter is qualitatively and - to a
large extent -quantitatively similar to the analytical solution of the hear model presented in figure 8, indicating the relevance of the analytical
solution (18). The tilting of the rhermocline induced by the dry season
wind stress -from day 1 to day 120 in figures 7 and 8 -, and the oscillations of the thermdine may be found in all availabIe field data, as may
be seen in, for instance, COULTER
& SPIGEL
(1 99 1). NAITHANI
et al. (2002)
-
The equations (9)-(10)of the complete reduced-gravity model are discretized on an Plrakawa C-grid,and solved by means of a finite-volume
scheme including a forward-backwud time stepping similar to that
described h BECK ER^ & DEL~~RSNUDER
(1993).The "width" of the lake
being much smaller than its "length",the grid size in the X-directionis set
to be smaller than that associated with the y-direction, Le. Ax = 3 h and
Ay = I0 km. To ensure numerical stability, the time increment At must be
such as that (BECKERS
&DELEERS~
1993).
ER
It is readily seen that setting At = 5 minutes is appropriate for most
relevant values of the model parameters. For numerical reasons,the horizontal viscasities are given values satisfying A, J k = A y / M . A series
of numerical experiments suggests that the suitable order of rnagitude of
A, is 3 m2S.'.
In certain model runs, the upward dispIacernent of the themocline can
be equivalent to the unperturbed depth of the thermocline. To prevent the
themocline from outcropping, an elementary wemg-drymg algorithm
37
and figure 9.
fig. 8. -Evolution during the second year of calculation of the downward dispiacement of the themocbne at the northern (solid curve) and southern (dashed curve) ends of
the lake, as obtained from the analytical solution (1 8) of the simplified, linearized model.
The model parameters listed in the caption to figure 7 are equal to those selected to obtain
the present results. I n addition, the friction parametery is set to 4 year1.
'EL9-S99 : TOT
Jo Jonor Lpa~mrO- -@S
p v
p~!Bqmoarqq1nXo8
8Elp XRJlllS EX aylJ0 U O g E Y A 'EL61 ' E ) 'mtWa 'a 'S 'KuvuS
:(g) 6 Xydv~80aBo!gp v rlsqoq pqof3 - -EJV31kyas
pomu pm a n q 3 uo paseq s~llprreq-gprn
E :smalsilsosa u i 3 3 ~
'a
lUT3-
'&-I8p
~smm 0 s JO ~13edq
2
'a N' -I
p 'S '
m ~ "a-3
s 'msnd
'96.E8 'dd
' S ~ W 'ktr%W
~ B
P Q V R 'qa~P00d:h O T 9 ) PlmM ?P30 5-7
,
1m5a u
'l~prhm
: f f~f - ~@ne8m~
qq ssnopnpn~
p @ o ~ o n m n prim panadmp P PW 'TOOZ 'a '-Q
-BI 'a-"dmm
'cm
'8s-SP :LOP '9t80141401NH
suog~ls a a q iv suollanl3nl~: ~tlapaqa
a p k :,nW ~3!80toUtU!~'6661 '3 'ElM!03
- .8q_rllmStrq,aqg j o
\
-@@qd mOIJ
~m
'@
*'I;
W n d
'h"ommmowq '-g
'nom8nrs~ S n h '*a
'EWZ-OL~Z:LZ "~~~
.u?ara~. ~ n r u a w' t p a ~
* e q ~ K r n Z u qa, m tq sa3mq3 L 3 o l o u q pm al~tmpxna3ea "0002'a-a -'
'dd OS ' I Q F U C L L - M W I L W ~ ~
2V-I ua sauaqsg
am 30 inama9ette~atp JOJ y3leasaa v-0~~
- 'qLm%ne~
..am 30 saSw1crq3 s a p q s g pm 6801omrr11 'awu.q3 '~661'wd ' m n d
'6E-EZ : E ' # 3 ~ l l ~ # ~
~ n l dp~uwruar!~zug
- q i l w l a~ y g JO s u o g ~ p s oaqmuuaqr
q '8' m m s m a m ~'-1' m ~
pa3np~pu$
p0 s ! s L p v ' z ~'a-a
z
- p'dd~' s a q q m!& IW q r JOJ"
~
3 p u o3~ ~ a ~n 3r z3 l 0 w q n g - '(-3)
~ T ~ 3~
v-1
~ w ,
n! Wm hr[!qw~
a ~ ~ r n 'z
r mz
u 'MA
-'
'aS-'
"3 " a a o m m ~
"3 L m b w
"'W 'mq "1 Kww.uv~'-1
'mdw
'-7'm
'-7a
' xw "a-a 'EUNSIW';I-'[ 'msaa
'Q.-6p 'dd ' S W h v ~ y pJO3xo
~ n 987 SJ! Pm Z T ~ ~ am
W '('m
'M '9'mc7nO3 : U[
'S3pIEndperpL~'1661: 'W"8"mras 'q 'M 'f)'-03
'H-65 : m ' m B q q q W ~ ' q 6 n e Z q aye? JO W E M e m o 3 ~
p sarlem pwu! pm aogeaggeas 'smmaolaw '6667 'H'g'a ' ~ m e a m m
' P O I - ~: (1
~ 1 801: '~3!~Kqd
~ m e m ~ n d t l l$o03pu.tnof - .spu%
m d s snopn uo sanem iCl~nefa~ p u mm-~owqs
!
30 uope8edmd aqr M,
panda2 maw sxw v 30 hq~qas'€661'a "as-a
7
l
-
-
S w a m JO uog~ptysp p m u m$ spotpaw 30
uogvnpng '3661 'V ' 0
m-
X ~ P A [ W 'Q
pm s!oj?~, a ' ~ J I ~ F J Sy! ~ p;nqapv are u o y m n ~
6E
~~m do s~om-rmsomnm-m
>
1
-
I
*I
d:
?
,I
,,
A-,
-
.i
'.aV' MEIM-
.
-1apom
pgolo3a m q l ~ mpqdnor, aq n ! m[
~ a u 'amaqas amso13 a3napq
-m r! S p n l 3 q ~apour3 ~ p o r p L q' p n o ! s u a q - q B bq army
m u av m passarppe aq m m pm ' y m q v!m ~p~sasppom
p
aw dq
-sarda~Ion SE a3uapqm ponpv-p- 03 anp 3a a -1C1ahggadsa~
'swam $0 m maj B pm FM p oi E $0 mpm a q j a apwgdum ne pm
poyzd r?m B aheq pm 'qv[ a q $0 a p p F ar.p j o pooqmoqq%taaatp F
apon ano Xpo Sqyqgxa apom a q ~6q palmpop 1Cla8nq are 'pmm maX
p ~nasardam y q m 'aqmraratp a g $0 srrup~fl[l3soa q pm ap
jo md maqvon a q n! ladaap 3 ~ a m[
q
ag
aqmmraq ayr 30
3ugp noseas-XTp a q Zynpo~darJQ a[qede~m laponr &!~&-pa3np
'ala[dmoa a g jo wpsaz p y m u arfl put! noynlos pyA@ue a u
A,
w m w o v a mag -P =U = W Epm on 'OOZ*OS[ brl: '06
'OL '& 'OE '5 '1 mdap a¶ W puod-03 1I 011s=qimn a a ~.n8unlnd~
.
p Bprpv ayr
m sqldap s n o w %1-E66t n!pamgrnur m a d m aw 30 s a w amL -6
-
~~~p
UNBSCO 1981. Tenth Report of the Joint Panel on Oceanographic Tables and
Standads. UNESCO Technical Papers in Marine Sciences, 36.
-
CL:'.'
4
- 7'?
h
,J
i :,,
,
:
1 :
L
?
Second lnlemalfuna~Caflfir*rce
i
n Mecreamlom and HydmbgyY
Fmesdings edited by
Relationship between the Zonal: Circulation over the
Equatorial Indian and hcific Oceans and the East
African Lakes : Victoria, Tanganyika and
Nyassa-Malawi Level Fluctuations
\' '
Laurent B w c o m * & Yves RCHARD
**
Kmmms. - East African Lakes ; Lake Level Fluctuations ;Hydrological
Varinbility ; Atmosphereocean Interaction ;Telmnnection ;Indian Ocean ;El
Nifio Southern Oscillation ;Zonal Circulation.
SUMMARY. The analyses of the Great East African Lakes, qctoria,
Tanganyika, and Nyassa-Malawi Ievel records show synchronisrns. which can
only be accounted for large-scale mechanisms.The relations between lake-level
variations and atmospheric circulation indexes are studied. This way, for the period 1946-2000, fow indexes are selected to characterjze the bond autumn zonal
circulation ~ v e the
r Pacific and Indian Oceans, Over the Indian Ocean two surface Zonal Wind Index (ZWI calculated for October to December) are used. For
the Pacific the Southern OscilIation Index (SOU and the Niiio 3 index (during the
same quarter) are held to account for the El Nfia Southern Oscillation (!ZNSO).
This exploration shows that overall negative correlations between lwel fluctuations (especially for Vjctwia and Tanganyika) are sdy obtained with Indian
Ocean circulation indexes. If ZWI are highly correlated with ENSO indexes,
except a positive correlation with Nyassa-Malawi, no correlations with ENSO
events m show. It seems tempting to consider that, for the 1946-2000period,
the autumn zonal circulation cell over the Indian Ocean may play a role in the
equatorial lake level anomalies.Intense ZWI (abnormally smng western wind)
is associated with deficient auhunn rainfall followed by lower l& rise. On the
-
* FRE[=NRS 2566 "ORSA-,
cedex prance).
B i t 504, Universitk Paris-Sud. 914U5 Orsay
** UMR-CNRS 5080, Centre de Recherchex de Climatologie, UniversitE de
Bourgogne, 21004 Dijon d e x (Fhnce).
Second International Conference on
TROPICAL CLIMATOLOGY,
IMEmOROLOGY AND HYDROLOGY
Climate-related Risk Analysis and Sustainable Development
in Tropical cl as
Bmssels, 13-14 December, 2001
Royd Academy
of Ovmeas Sciences
Royal Meteorological Institute
of Belgium
Guest Editam :G. D e m d e , M.De Dapper, J. AJexandre
2004
CONTENTS
Foreword .........................................................................
Opening Speech ..................................... ............................
Tropical Meteorology
R. W ,Variability and Rends of the Summer Monsoon Rainfall in
Bangladesh ................................................................
I. N m , E. DEUERSNIJDER,
P,-D. PLISMER & S. L m , Pfeliminq
Results of a Reduced-gravity Model of the Wind-induced
Oscillations of the Thmocline in Lake Tanganyika ..................
L.B m m m & Y. R-,
Rela?ionshjpbetween the Zonal Circulation
ovw the Equatorid Indian and Pacific Oceans and the East African
Lakes :Victoria, Tanganyika and Nyassa-Malawi Level Fluctuations.
ROYAL~ R O L O O I C A LINSNS'ITIUTE
OF BELGIUM
ROYAL A c A n m
OFOYERSEAS SC~ENCFS
av. Circulake / Ringlaan 3
B-ll80 B ~ u s s m(BeIgium)
Tel. : 02.373.05.08
Fax : 02.373.05.28
E-mail : nni_mfo@oma.be
Web : www.meteo.beJlW-KM
me Defacqzslmat l/3
B-1000B~ussas(BeIgium)
TeI. : 02.538.02.1 1
Fax : 02.539.23,53
E-maiI :kaowmom@skynetbe
Web : http//www.kaowarsom.be
ISBN 90-75652-36-4
D/2004/0149/5
J. Moeuwso~s,I. N Y S SJ.~DECKERS,
,
H. hfmm & 1. P O E S ~ The
,
Climatic Significance of Late-Pleistmene and Early- to MiddleHolocene Mass Movements and their Aesent-day Remobiization in
Rwanda and Ethiopia .....................................................
J. Hus, Magnetic Susceptibility : a Proxy of the Palaeoenvironrnent and
Palamclimate in Sediments ..............................................
J. NYSSEN,
3. P o ~ m ,H. Vm-,
J. MOEYERSONS,
J. DECKERS,
H,M m & C. S-,
Spatial Variability of Rain and its Erosivity
in a Tropical Mountain Catchment :Tigray, Northern Ethiopia ......
Agricdtum, Food and Weather Prediction
F.LW, M. COWLI & E.F.LAMBIN*
Monitoring Natural Disasters and
''Hot Spots" of h d - c o v e r Change with SPOT4 Vegetation to
Assess Region at Risk.................................................... 123
E. C.KIPKoRIR, S.M.G A ~I. MUKABANA
,
!t% D.h,
Evaluation of the
Onset of the Growing Season for Various Climatic Zones in Kenya
by means of a Soil Water Balance Method for DifferentSoiI Types. I37
C.B.S.h,
L.P.S ~ O N D &
S T. R WHEELER,
Modelling the Partitioning
of Solar Radiation Caphue and Evapotranspiration in Intercropping
Systems ................................................................... 15 1
M.F.NARANJO,
Change in the Wydrologicd Management of the Mexican
Basin during the 16th Century ........................................... 175
G. l? &m,
M.&m, F.BAEDB,T.Mmm, P,D.JONES
& T.TSUKAHARA,
-1872
Extension of the Japanese hstnunental MetewoIogicaI
Observation Series Back to 1819 h.....................................,.
187
A. GIODA,J. ROWWL, Y.L'Hm & B. PCIUYAUD,
Analyse at variabilig
ternporelle d'lme longue S& de pIuies des Andes en relatim avec
1'DscillationAustrala (La Paz, 3 658 m 1891-2000) ................. 199
A. D m s , Early Weather Obsemtions in Olukonda,Namibia, 1905-1%?6.. 219
V,THANH
TAM,
E DESW
& 0.BMEUAN,Estimation of Underground
Rivers in a Tropical Kam Area by way of a Multithematic Study ... 231
G.R DEWXE, Intensity-Dwrion-Frequency (IDF') Curves for Yangam-
bi, Congo, based upon Long-term High-fiquwcy Precipitation
Data Set (Part 9 ........................................................... 245
B. Monmom & G.R. ~ M A R E R , The Est&lisbment of IntensityDuration-Frequency Curves far Precipitation in Yangmbi, Congo
(Part IX) .................................................................... 253
Y. S ~ E ~ HDesign
I,
Rood Estimation under Inadeguate Data - a Case
Study ....................................................................... 267
M. MUCHINDA,
Drought Incidence in Zambia over the Thirty-year Period
1970/1971 - 1999(2000...................................................
J, C. MOIJBABANW, C~assficationdes rtgimes pluviom&Eiques en
Rkpublique ~ m r a t i q u du
e Cmgo et rn Angola ....................
B. NEPLWA,Long-term........................................................
Temperature and hecigitatim Variability and
Trends in Kuwait..
P.&ER, B. TYCHON,
A. OER & R. PAUL,L'enseignement en gestion des
risques naturels ............................................................
P,O m ,Can Dust Variability be a Regional Indicator of L4tnd Degradation
Trend in Arid and Semi-arid Areas 7 Analysis in the Sahel ...........
S. S- & P. 0- Are the 1 9 9 and 2000 Urban Floods in Senegal due to
Exceptional Rainfall Events ? ...........................................
E.v S O K O L ~ ~ NN.
A ,N.SOKOLIHWA
& E. K. S-W,
The Assessment
of the Connection between the Atmospheric Circulation and the Sea
Surface Temperature (SST)of the Quatwial Pacific for Synoptic
Scale Processes using B e Singular Value Decomposition Methd
( S W ) ......................................................................
28 1
295
3M
321
331
345
353