angeles, m. et al - prediction of future climate change in the caribbean region using global general...

8/3/2019 Angeles, M. Et Al - Prediction of Future Climate Change in the Caribbean Region Using Global General Circulation M

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INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. (in press)Published online in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/joc.1416

Predictions of future climate change in the caribbean regionusing global general circulation models

Moises E. Angeles,a,* Jorge E. Gonzalez,b David J. Erickson IIIc and Jose L. Hernandezca Mechanical Engineering Department, University of Puerto Rico-Mayaguez, Mayaguez, PR

b Mechanical Engineering Department, Santa Clara University, Santa Clara, CAc Oak Ridge National Laboratory, Oak Ridge, TN

Abstract:

Since the 1800s the global average CO2 mixing ratio has increased and has been related to increases in surface air

temperature (0.6 0.2 C) and variations in precipitation patterns among other weather and climatic variables. The Small

Island Developing States (SIDS), according to the 2001 report of the Intergovernmental Panel on Climate Change (IPCC),

are likely to be among the most seriously impacted regions on Earth by global climate changes. In this work, three

climate change scenarios are investigated using the Parallel Climate Model (PCM) to study the impact of the global

anthropogenic CO2 concentration increases on the Caribbean climate. A climatological analysis of the Caribbean seasonal

climate variation was conducted employing the National Center for Environmental Prediction (NCEP) reanalysis data, the

XieArkin precipitation and the ReynoldsSmith Sea Surface Temperature (SST) observed data. The PCM is first evaluated

to determine its ability to predict the present time Caribbean climatology. The PCM tends to under predict the SSTs, which

along with the cold advection controls the rainfall variability. This seems to be a main source of bias considering the

low model performance to predict rainfall activity over the Central and southern Caribbean. Future predictions indicate

that feedback processes involving evolution of SST, cloud formation, and solar radiative interactions affect the rainfall

annual variability simulated by PCM from 1996 to 2098. At the same time two large-scale indices, the Southern Oscillation

Index (SOI) and the North Atlantic Oscillation (NAO) are strongly related with this rainfall annual variability. A future

climatology from 2041 to 2058 is selected to observe the future Caribbean condition simulated by the PCM. It shows,

during this climatology range, a future warming of approximately 1 C (SSTs) along with an increase in the rain production

during the Caribbean wet seasons (early and late rainfall seasons). Although the vertical wind shear is strengthened, ittypically remains lower than 8 m/s, which along with SST > 26.5 C provides favorable conditions for possible future

increases in tropical storm frequency. Copyright 2006 Royal Meteorological Society

KEY WORDS IPCC; ERS; LRS; PCM; current Caribbean climate; future Caribbean climate; SSTs; VWS

Received 15 November 2005; Revised 17 July 2006; Accepted 23 July 2006

INTRODUCTION

The Caribbean rainfall season has a bimodal nature,

where the initial peak of this season, called early rain-

fall season (ERS), begins in May and it extends until

July, with a brief dry period in July (Taylor et al., 2002).The second half of the overall rainy season or late rainfall

season (LRS) spans from August to November. During

the LRS, after the Northern Tropical Atlantic (NTA) sea

surface temperature (SST) exceeds the threshold of con-

vection (26.5 C), the atmosphere becomes the principal

modulator of the thermal convection by means of the

vertical wind shear (VWS) (Taylor et al., 2002). Giannini

et al. (2001a), Chen and Taylor (2002), and Kingtse et al.

(2001) define the VWS as the difference between the hor-

izontal wind speed in the upper troposphere at 200 mb

* Correspondence to: Moises E. Angeles, Mechanical EngineeringDepartment, University of Puerto Rico-Mayaguez, Mayaguez, PR.E-mail: [email protected]

and wind speed in the lower troposphere at 850 mb.

According to Arkin (1998), Bell and Halpert (1998), and

Gerald et al. (1999), the weakening of the VWS (8 m/s)

causes an increase in the rainfall over the Caribbean

basin, especially when the NTA and the main develop-

ment region (MDR) have SSTs > 26.5 C. The MDR is alatitudinal band along 5 N and 10 N where the easterly

waves are developing during the NTA rainy season (Tay-

lor et al., 2002). Taylor, Chen and Taylor (2002), Knaff

(1997, 1998), indicated that once the NTA SST is above

the threshold for convection, the principal factors that

enhance Caribbean rainfall and the hurricane develop-

ment are: low surface pressure, low VWS, lower convec-

tive stability, and warmer NTA. Knaff (1997) established

that a sea level pressure (SLP) increase causes a vertical

temperature profile of 0.5 C in the middle level, lead-

ing to a more stable atmosphere and consequently less

deep convection is supported. Folkins and Braun (2003)observed, using statistical analysis, that the rainfall as

a function of the SSTs has a small variability to SSTs

Copyright 2006 Royal Meteorological Society


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M. E. ANGELES ET AL.

below 26.5 C, increasing rapidly from 26.5 C to 29.5 C

and decreasing again with greater values.

Short time-scale climate changes in the Caribbean

region caused by global scale effects such as El Nino

and La Nina events were investigated by Taylor (1999)

and Giannini et al. (2000) who showed that a strong

relationship exists between the ERS and the El Ninoevents. Chen et al. (1997) and Taylor et al. (2002) have

established that a strong La Nina event generally leads to

a drier than normal ERS. In addition, Enfield and Alfaro

(1999) showed that a warm tropical Atlantic combined

with a cool tropical Pacific scenario has a tendency to

enhance the rainfall amount over the Caribbean basin

and Central America. Malmgren et al. (1998) claim that

the Caribbean mean air temperature is influenced by

the El Nino event while the rainfall is correlated with

the NAO.

Very little work has been reported to determine the pos-

sible impacts of global climate changes in the Caribbean

region. Goldenberg et al. (2001) have studied the Atlantic

hurricane activity during the past century. They estab-

lished that multidecadal-scale VWS and SST change and

an additional SST increase due to anthropogenic global

warming could generate the exceptional hurricane activ-

ity since 1995. In a workshop held in Kingston, Jamaica

in January 2001, daily data for the Caribbean region were

analyzed. These data were digitized and used to calculate

several maximum and minimum air temperature indexes,

heavy rainfall events, maximum consecutive dry days

among other indexes (Peterson et al., 2002). This work-

shop concluded that the Caribbean climate is changing

and the atmospheric alterations are following the globalclimate change trends. In a global scale the surface tem-

perature of the Earth has increased by 0.6 0.2 C, while

the annual precipitation in middle latitudes of the North-

ern Hemisphere has been increasing by approximately

0.5% per decade. In contrast, the precipitation in the sub-

tropics (from 10 N to 30 N) has decreased on average

by 0.3% per decade (Intergovernmental Panel on Cli-

mate Change, 2001). These facts motivated the IPCC

to conduct a study of technical, scientific, and socioe-

conomic information to determine the risk of climate

changes generated by human activity (Intergovernmental

Panel on Climate Change, 2000). Under this proposal,the IPCC issued in 1992 the IS92 scenarios, where the

IS92a scenario was called the Business as Usual Sce-

nario (BAUS). In addition, small islands, according to

the 2001 Report of the IPCC, have a high vulnerabil-

ity and a low adaptive capacity, therefore likely to be

the most seriously impacted pieces of land by global cli-

mate changes. Changes in the Caribbean climate patterns

can cause significant damages to property, the economy,

and may result in loss of lives (Caribbean Environmental

Health Institute, 2002).

General Circulation Models (GCMs) are commonly

used to predict impacts of climate change from variousstandard IPCC scenarios. GCMs are physical representa-

tions of atmospheric and oceanic dynamics that have in

general coarse horizontal resolutions around a few hun-

dred kilometers (T42 with 250 km). Rainfall in GCMs

is calculated taking into account the water and ice mixing

ratio and cloud cover in the microphysics parameteriza-

tion. Von Salzen and McFarlane (2002) suggested that

often most of the convective activity in GCMS occurs in

an area and penetration height much smaller than the hor-izontal and vertical resolutions resulting in cumuliform

clouds smaller than the horizontal grid size and strati-

form clouds smaller than the grid vertical resolution. Von

Salzen and McFarlane (2002) and Collins et al. (2004)

point out that the different clouds in GCMs are repre-

sented by a bulk cloud in the mass flux approach based

on the entraining plume model. McGuffie and Henderson

(1997) indicate that the deep convection produces more

cloudiness, decreasing the surface net upward radiation

and increasing the SST and precipitation. This is referred

to as positive feedback. At the same time, the bulk cloud

must generate a negative feedback (increase the earths

albedo and decrease the SSTs along with the precipita-

tion) to represent correctly the cloud cover behavior in

GCMs. The greater cloud amounts result in increases of

the earths albedo when stratus clouds have formed, and

therefore less solar radiation is absorbed by the earth.

The Ocean component from the Parallel Climate Model

(PCM) is initialized with SSTs for the year of 1995 from

the assimilated Ocean data instead of standard initial-

ization (Dai et al., 2004). When simulated atmospheric

field was compared using the approaches of SST initial-

ization, negligible differences were found, but the new

approach uses less computational resources. In addition,

PCM takes into account the Greenhouse gases by meansof the time-variant boundary data set for tracer emis-

sions (Buja and Craig, 2002). The BAUS from IPCC are

ingested into PCM in this way and the long wave parame-

terization computes the radiative flux for CO2, CH4, NO2,

and H2O. Dai et al. (2001), assessed PCM to reproduce

the East summer monsoon rainfall (ESMR) and to pre-

dict the climate change of the Yangtze River for the 21st

century using the BAUS. The model predicts a surface

warming of 2 C and a surface evaporation increase of

approximately 7% over the Yangtze River in the 21st

century during JJA. Washington et al. (2000) carried out

PCM simulations for global and regional areas. Theircontrol run showed a slight global average temperature

increase of 0.0174 C per century for the present. When

the transient CO2 concentration increase of 1% per year

reaches its doubling point, a global warming of 1.27 C is

obtained. At regional areas, the long-term Gulf of Mex-

ico, the east Greenland and Labrador Current systems are

well depicted. There are no PCM or other reported GCM

simulations for the Caribbean basin. In this work we will

investigate the climatological trends and possible future

climate changes for the Caribbean region using PCM.

The analysis will use the observed Caribbean data

and simulated information from GCMs. We selectedPCM because it offers high-resolution integrations and

more realistic representation of surface and atmospheric

Copyright 2006 Royal Meteorological Society Int. J. Climatol. (in press)

DOI: 10.1002/joc


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PREDICTIONS OF FUTURE CLIMATE CHANGE IN THE CARIBBEAN REGION

physical processes (Washington et al., 2000) along with

a lower use of computational resources.

The remaining part of this paper is organized as

follows: The description of the PCM atmospheric model

is presented in the second section. The third section

describes our methodology. The fourth section shows

the climatological Caribbean conditions. The fifth sectionexplains the current climate simulated by PCM. The

sixth and seventh section describes the long-term and

future Caribbean climate. The eighth and ninth sections

present the climatological monthly variability and future

Caribbean climate change. The last section presents

concluding remarks.

GLOBAL CIRCULATION MODEL

In this research, the PCM model version 1 is used.

The PCM is composed of the NCAR Community Cli-

mate Model version 3 (CCM3) with a T42 resolution(2.8 latitude and longitude) and 18 hybrid sigma ver-

tical levels, the Los Alamos National Laboratory Parallel

Ocean Program (POP), whose resolution on average is 0.5

degrees near the Equator and 0.6 degrees in the remain-

ing areas. The sea ice model from the Naval Postgraduate

School is another PCM component and it has 25 25 km

resolution over the artic ocean. The land surface bio-

physics component runs with T42 resolution (Dai et al.,

2004; Washington et al., 2000; Weatherly and Arblaster,

2000). A semianalytic dipole grid is constructed where

the northern pole is in North America and the south-

ern hemisphere is a Mercator grid with a pole exactly

over the South Pole (Smith and Gent, 2002). Usuallythe GCMs perform history runs to initialize their Ocean

model component (standard initialization). The history

run corresponds to previous runs from the preindustrial

time to the present to generate the initial conditions. PCM

makes use of a new approach to initialize the Ocean

model, it uses observed data conditions from 1995 (Dai

et al., 2004; Barnett et al., 2004).

METHODOLOGY

In this work the current climate conditions are evaluated

from PCM numerical results and it is defined as theaverage of the atmospheric variables between the years

1996 and 2010, while the future climate predictions are

based on years 2041 2055. Because of this possible

future global climate change, the question of how the

climatological characteristics of the Caribbean region

will be affected as a consequence of a future global

climate change owing to an increase in atmospheric CO2concentrations. This paper attempts to answer the query

and to understand this issue.

One possible approach is to use regional models, which

are able to simulate mesoscale phenomena implying a

range of 1100 km and days to week. However, our goalis to study the long-term present and future Caribbean

climatology, and thus the GCMs are the best selection

for long-term simulation and when considering the IPCC

scenarios.

The Caribbean region (8.75 N25.25 N and

88.75 W58.75 W) is divided into three periods: the dry

season (DS), which corresponds to DecemberApril, the

ERS, and the LRS (Taylor et al., 2002; Giannini et al.,

2001a; Taylor, 1999). The National Center for Envi-ronmental Prediction (NCEP) reanalysis data with 2.5

degrees of resolution and the Climate Prediction Cen-

ter (CPC) XieArkin data, which uses gauge observa-

tions and satellite estimations are used to calculate the

climatological conditions of the Caribbean region. The

moisture/dry advection at the 850 mb of level is calcu-

lated using the dot product between the moist-air mass

mixing ratio (wv) gradient and the wind velocity field

(

V). The equation where this dot product is present iswvt

+

V

wv =N

n=1 Rn, where Rn is the source/sink

yields of moist air. The ReynoldsSmith observed SSTs

are interpolated to 1-degree resolution using the nearestmethod. The PCM output with T42 resolution is interpo-

lated from the hybrid sigma-pressure 18 vertical levels

to the standard 17 levels. The SSTs from the POP model

is interpolated from an orthogonal curvilinear coordinate

to a regular grid of 1 degree resolution. The synoptic

indices, Southern Oscillation Index (SOI) and the North

Atlantic Oscillation (NAO), were calculated from 1996 to

2098. SOI was calculated following the National Oceanic

and Atmospheric Administration methodology (NOAA-

Climate Prediction Center, 2003), while the NAO takes

into account the seasonal variation of the polar low and

the subtropical high. To consider the seasonal variabil-

ity of the low and high systems, two regions are located

following the methodology suggested by Oman (2004).

Region 1 covers the area from 70 W to 10 W and 55 N

to 70 N and region 2, the area from 70 W to 10 W and

35 N to 45 N. The SLP climatology from PCM is aver-

aged over these areas, and then it is subtracted from the

monthly data to obtain the anomalies. Finally the SLP

anomalies difference between region 1 and region 2 is

estimated as the NAO.

CLIMATOLOGICAL CONDITIONS IN THE

CARIBBEAN BASINThe Caribbean basin has small land areas where the

easterly wind flows almost constantly and in a well-

defined trajectory. According to Waliser et al. (1993),

the convection intensity has little sensitivity to changes

in SSTs below 26.5 C, but it increases rapidly as SSTs

increase from 26.5 to 29 C. At higher SSTs the deep

convection decreases again. The value of 26.5 C is called

the threshold for convection, while 29.5 C is the upper

limit of the Tropical SSTs.

During the first season, what is considered as the DS,

the climatological conditions are characterized by SSTs

well below the convection threshold in almost the entireNTA. Only the western Caribbean is able to support

convective activity, where the SST > 26.5 C line barely


DOI: 10.1002/joc


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reaches the Caribbean Leeward Greater Antilles. The

warm pool in the NTA spreads gradually eastward and

in the next season (ERS) reaches the Windward Greater

Antilles with SSTs between 27.5 and 28 C. The SSTs

with values that develop deep convection and close to

the SST upper limit encompasses the entire Caribbean

basin and the MDR during the LRS. Figure 1(a), (b),and (c) shows the warm pool climatological evolution

on the NTA and the MDR. In addition to the nonlinear

correlation of the rainfall with the SSTs (Folkins and

Braun, 2003), the rainfall is a function of the spatial and

time dimension. The areas over the Caribbean Sea along

the MDR are dry regions during the DS with accumulated

precipitation as low as 10 mm. The rainfall increases

noticeably in the ERS generating intense precipitation in

the western Caribbean Sea (between 120 and 200 mm).

The intense precipitation area spreads up to the Leeward

Greater Antilles in the LRS, following the spread of theSSTs (Figure 1(d), (e), and (f)).

The three Caribbean rainfall seasons are characterized

by cold advection in the Eastern Caribbean and a warm

advection toward the Western Caribbean and the Central

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(c) (f)

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Figure 1. Observed climatological SSTs from ReynoldsSmith for (a) DS, (b) ERS, and (c) LRS. The blue color depicts SST < 26.5 C, while

the red color SST > 26.5 C. Observed climatological accumulated precipitation from CPC-merged analysis for (d) DS, (e) ERS, and (f) LRS


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American coast, helping to maintain the areas with lower

or greater rainfall, respectively (Figure 2(a), (b), and (c)).

The weak vertical wind shear in the Central and southern

Caribbean basin (


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which imply that the dry advection effect is cut off by

the SST above the threshold for convection, warm advec-

tion, VWS < 12 m/s and orographic expansional cooling.

In the rainy season a weaker dry advection zone contin-

ues over the Central Caribbean and Central American

coastline (not shown here).

CURRENT CLIMATOLOGY SIMULATED BY PCM

PCM outputs were averaged from 1996 to 2010 to

assess the ability of the model to predict the Caribbean

climatology. The simulated Caribbean basins atmo-

sphere under the BAUS by PCM shows easterly wind

flows very close to the observed climatology, with devi-

ations in the wind direction during the LRS. Figure 3(a),

(b), and (c) shows the warm pool climatological evolu-

tion on the NTA and MDR. The first Caribbean season

is characterized by SSTs well below the observed datain the entire NTA (between 23 and 25 C) generating a

very weak vertical convection. The warm pool in the

NTA appears for the first time in the next season (ERS)

where SSTs between 26.5 and 27 C reach the Wind-

ward Greater Antilles in clear contrast with the actual

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Figure 3. Current climatological SSTs from PCM (19962010) for (a) DS, (b) ERS, and (c) LRS. The blue color depicts SST < 26.5 C, while

the red color SST > 26.5 C. Climatological accumulated precipitation from PCM is calculated for (d) DS, (e) ERS, and (f) LRS


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climatology. The SSTs with values that develop deep

convection and close to the SST upper limit, encom-

passes the northern boundary of the Caribbean region

and the eastern MDR in the LRS (between 27 and

28.5 C), which approaches the observed climatological

SSTs. Following the observed climatological behavior,

the southern Caribbean Sea is a drier region duringthe DS (accumulated precipitation as low as 10 mm).

The rainfall increases noticeably in the ERS and LRS

resulting in intense precipitation in the boundaries of the

Caribbean basin (between 80 and 200 mm). During the

ERS and LRS, the southern Caribbean area, including the

South AmericanCaribbean coast, receives low rainfall

amount, which is opposite to the observed climatolog-

ical rainfall increase (Figure 3(d), (e), and (f)). During

the three seasons, a permanent cold and warm advec-

tion is always present on the Caribbean basin. A warm

advection is located in the northwestern Caribbean basin

increasing the air temperature in the low atmosphere turn-ing the atmosphere more unstable. The cold advection

has an opposite effect and it is present over the east-

ern and central Caribbean Sea (Figure 4(a), (b), and (c)).

It ensures a less unstable atmosphere and the genera-

tion of lower rainfall amount. The vertical wind shear is

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10

1614 18 20 2322 24.2 25 26 26.5 27 29 8 6 3 2 0 84 12 16 20 24 28 3228

Figure 4. Current Caribbean climatology (1996 2010) predicted by PCM for the air temperature at 1000 mb level and easterlies to see thewarm/cold advection for (a) DS, (b) ERS, and (c) LRS, the VWS for (d) DS, (e) ERS, and (f) LRS. The blue color depicts air temperature


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in very good agreement with the observed climatology.

A VWS < 8 m/s is located in the Central and southern

Caribbean basin during the DS with a weak vertical con-

vection generated by very low SSTs. In the ERS and LRS,

a VWS of


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2000 2010 2020 2030 2040 2050 2060 2070 2080 20900.072

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erfraction

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2000 2010 2020 2030 2040 2050 2060 2070 2080 2090690

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Figure 5. PCM time series from 1996 to 2098, averaged over the Caribbean basin for (a) Cloud Cover, (b) Solar flux at the surface, (c) SSTs,

and (d) Accumulated precipitation

current climate. The SSTs in the Caribbean region begin

to increase in the DS reaching SST differences (SSTDs)

between 0.6 and 0.8 C, decreasing in the ERS (between

0.4 and 0.5 C) and reaching the maximum SSTDs of

1 C in the LRS (northern Caribbean sea), where the

future warmer Caribbean is clearly shown (Figure 7(a),

(b), and (c)). Because the air-mixing layer is in permanent

contact with the ocean surface, the air temperature at

the 1000 mb level has a continued future air temperature

increase from one season to another.

The future climatology has a wetter northwesternCaribbean and Greater Antilles during the DS, obtaining

rainfall differences (RDs) between the future and current

climatology as high as 10 mm in the Greater Antilles.

In this season the RDs are close to zero in the southern

and eastern Caribbean. The ERS shows a future tendency

to increase rainfall when a RD of approximately 5 mm

is located over the Western Caribbean, but the rainfall

decreases in all Caribbean boundaries, as opposed to

the LRS when the RDs are greater than zero in the

entire Caribbean and MDR with RDs as high as 20 mm

(Figure 7(d), (e), and (f)). Over the areas where positive

RDs are present, positive SSTDs are also present. Duringthe ERS the SSTDs decrease with respect to the DS and

simultaneously small values of RDs are present, while in

the LRS the SSTDs increase corresponds to more intense

RDs with respect to the ERS. The influence of the SSTs

over the convection intensity causes those areas where

SSTDs have values around 0.6 C and SSTs between 29

and 30 C to have more rainfall than areas where the

SSTDs have values around 0.8 C and SSTs between 27

and 28 C. Thus, the seasonal increase or decrease of the

SSTDs causes seasonal rainfall variability while the SSTs

spatial distribution affects the rainfall spatial distribution.

Similar to the current climatology, cold advection is

present in the Caribbean Sea, ensuring a dry middle andsouthern Caribbean region in the three Caribbean seasons

(Figure 8(a), (b), and (c)). The future VWS reinforces

slightly during the three seasons, but it continues within

the ranges to generate lower rainfall in the DS (>8 m/s)

and more intense rainfall in the ERS and LRS (


10/15


2000 2010 2020 2030 2040 2050 2060 2070 2080 2090

3

2

1

0

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I

2000 2010 2020 2030 2040 2050 2060 2070 2080 209020

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NA

O

(b)(a)

Figure 6. PCM time series from 1996 to 2098, averaged over the Caribbean basin for (a) SOI and (b) NAO

The future moisture and dry advection intensification(difference between the future and current climate) helps

to produce positive and negative RD, respectively, during

the three Caribbean seasons (not shown here).

MONTHLY VARIABILITY AND INTERACTIONS

BETWEEN THE ATMOSPHERIC VARIABLES AND

SSTs

The variability of the vertical wind shear, the mois-

ture/dry advection, the SSTs, and the rainfall amount

from the climatological observed data and PCM are aver-

aged over the Caribbean basin. In the DS and ERS theobserved climatological temporal variability of the verti-

cal wind shear (in absolute values) along with the SSTs

indicates the influence of these variables over the pre-

cipitation temporal evolution. Strong VWS during the

DS followed by a weakening in the ERS is in clear

inverse relation with the rainfall when it decreases slowly

from January to March and enhances rapidly up to May.

This inverse relation is again observed during the LRS

(Figure 9(a)). The ocean component of PCM simulates

a climatological seasonal SST variation in direct relation

with the rainfall such as the observed Caribbean clima-

tology. The VWS shear in the PCM current Caribbean

climate has an inverse relation with the Caribbean rainfallcorresponding to the observed climatology. In addition,

two deviations are observed in the climatological monthly

VWS. They are weak in the month of March and an

increase in absolute value in the month of September

causing a rainfall decrease (Figure 9(b)). The SST and

the VWS appear to drive the simulated rainfall tem-

poral variability in the three Caribbean seasons and as

a consequence, the rainfall follows the tendency of the

observed climatology with some bias. A shift is present

in the PCM current climatology when the slight decrease

in rainfall in July (bimodal nature), observed in the actual

climatology, is shifted toward the month of September byPCM just when VWS increases (Figure 9(a) and (b)). The

deviations observed in the atmospheric variables produce

the rainfall bimodal behavior shift toward the month ofSeptember, but PCM is able to capture this event. Thus,

the Caribbean rainfall characteristics and tendencies are

detected.

THE FUTURE CARIBBEAN CLIMATE CHANGE

In the future Caribbean climate, the seasonal variability

of the SSTs, the air temperature at 1000 mb, the rainfall,

the dry/moisture advection, and the VWS are similar to

the current climate (Figure 10) showing an intensification

of these variables. The combination of SSTs increase

and lower VWS (below 8 m/s) with similar seasonalvariations to the current climate are favorable conditions

for greater tropical storms frequency mainly because

the VWS prevents the axisymmetric organization of

deep convention (Goldenberg et al. 2001) causing lower

ventilation of the warm core of the initial vortex of

tropical cyclones.

Figure 11(a) and (b) shows a future warmer and wet-

ter Caribbean region, with the same seasonal variation

for the SSTs and the precipitation as the current climate.

The future maximum SSTs and air temperature aver-

aged over the Caribbean basin were above the current

climate in 0.7 and 0.75 C, respectively, in the month

of October. The Caribbean rainfall increases during theLRS as seen in Figure 11(b). The DS also presents a

future rainfall increase, but in the month of March,

while in the ERS, rainfall is below the current clima-

tology. The future precipitation increase is confirmed

when the annual accumulated rainfall shows a future

wetter western and northwestern Caribbean basin with

20 and 100 mm, respectively, above the current cli-

mate (Figure 11(c)). Over the western Caribbean region,

a future wind magnitude increase of the easterlies is

observed (not shown here) along with a solar flux increase

when the current and future PCM climatology are com-

pared. The future solar flux decreases for all the otherareas, including the Greater and Lesser Antilles (see

Figure 11(d)). The changes in these parameters present


DOI: 10.1002/joc


11/15


30N

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Figure 7. Future Caribbean climatology (20412055) predicted by PCM for the SSTs for (a) DS, (b) ERS, and (c) LRS. The contour lines

represent the SST in the future climate and the color background the difference between predicted future and present climates. Climatologically

accumulated precipitation predicted by PCM for (d) DS, (e) ERS, and (f) LRS. The contour lines represent the differences between the future

and current climate

a likely Caribbean climate change under the BAUS for

the years 20412055.

SUMMARY AND CONCLUSIONS

The observed climatological behavior of the Caribbean

rainfall is supported by the SSTs, the VWS and thewarm/cold advection. The moisture advection has no

relevance in the spatial variability of the rainfall in

the ERS and LRS. The less important effect of the

moisture/dry advection is explained due to the high water

vapor content in the Caribbean atmosphere. VWS of


12/15


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Figure 8. Future Caribbean climatology (20412055) predicted by PCM for the air temperature at 1000 mb level and easterlies to see the

warm/cold advection for (a) DS, (b) ERS, (c) LRS, VWS for (d) DS, (e) ERS, and (f) LRS. The pink color depicts weak VWS (less than8 m/s), while the purple color stronger VWS. The contour lines represent the difference of the VWS absolute values between future and current

climatology. Positive differences imply a stronger future VWS, while negative values a weaker VWS

observed rainfall variability with an underestimation of

the SSTs and rainfall values. The moisture/dry advection

has a better agreement with the observed climatology

in the DS and LRS. The cold advection and the VWS

over the Caribbean Sea help maintain a permanent lower

rainfall in this region. A future (20412055) Caribbean

climate change is observed, with a warmer NTA, a higher

air temperature, and a wetter Caribbean region. Although

the VWS is strengthened, it continues within the rangesto allow for more intense rainfall in the ERS and LRS

(


13/15


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Figure 9. Climatological monthly variation of the atmospheric and oceanic variables for (a) Observed data and (b) Current climatology from

PCM. The values are arranged following the legend next to Figure 10


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pcp mm

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water vapor mixing105 kg/kg

Figure 10. Monthly variability of the PCM atmospheric and oceanic variables for the future climatology. The values are arranged following the

legend next to the figure

along with probable more intense tropical storms sea-

son, depicting future climate change. The future increases

over the annual average of the climatological wind speed

of the easterlies, the solar flux at the surface and theannual accumulated rainfall as established in this work is

an earmark of future Caribbean climate change.

ACKNOWLEDGEMENTS

This work was sponsored by the NASA-EPSCOR grant

#NCC5-595. The simulations were conducted at the High

Performance Computing Facilities at UPR Rio Piedras.The authors acknowledge the Oak Ridge National Labo-

ratory, the Computer Science and Mathematics Division


DOI: 10.1002/joc


14/15


JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

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Current Climate PCM

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Rainfall mm

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3

Figure 11. Comparison of the atmospheric and oceanic variables between the future and present PCM climatologies for (a) the SSTs and

(b) Accumulated rainfall. The future climatology is shown for annual (c) Accumulated rainfall and (d) Surface solar flux. The contour lines

depict the rainfall difference between the future and present climatologies, while the solar flux has a contour interval of 1 W/m 2

for the assistance and invaluable support in providing the

appropriate PCM outputs.

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