International Workshop on Climate Downscaling Studies at Tsukuba,
October 4, 2017

Climate of the Philippines and the sea
surface temperature effect on summer
monsoon rainfall in the Philippines
Jun Matsumoto*, **, Hiroshi TAKAHASHI*,** , DADO Julie Mae Borejon*,
Dzung Nguyen-Le***, and Marcelino Villafuerte II***** Department of Geography, Tokyo Metropolitan University (TMU)** Japan Agency for Marine-Earth Science Technology (JAMSTEC)*** Hokkaido University**** Philippine Atmospheric, Geophysical and Astronomical Services
Administration (PAGASA)
Mt Pinatubo Lahar and Mt. Arayat on the way from Manila to Baguio, March 2012

1.
2.
3.

Outline of this talkClimatic seasonal changes of regional rainfall andwind at 850 hPa in the Philippines by 5-day mean
TRMM and ERA_Interim data, respectively.
The effect of spatial resolution on simulated
rainfall over the western Philippines
The potential impact of sea surface temperatureon rainfall over the western Philippines

For items 2&3: Using WRF-ARW v3.6.1 Model

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2. Effect of spatial resolution on
simulated rainfall over the westernPhilippines
What resolution can RCMs reproduce
summer monsoon rainfall on thenorthwestern coast of the Philippines?
Dado, J.M. & Takahashi, H.G. 2017. Effect of spatial resolution on
simulated rainfall over western Philippines, Geogr. Reps. Tokyo
Metrop. Univ. 52: 1-9.
8

WPH
14–19 oN
119.5–121oE•>50–70 % of annual rainfall
occurs in June-August
during Southwest
Monsoon Season (SWM)

9Model &experimental setup
WRF-ARW v3.6.1

Domains
1. D01 – 25km
2. D01 – 12.5km
3. D02 – 8km, nested in
40km
4. D02 – 5km, nested in
25km

21

D01

25km

D01

12.5km3

D01

40km

D028kmSimulation Period
June to August
1982-2012

4D02

D01

5km

25km

10Model &experimental setup
WRF-ARW v3.6.1
Boundary Conditions

21

D01

25km

D01

12.5kmAtmospheric --- ERAInterim

3

SST --- NOAA monthly
OISSTv2
Parameterization
Microphysics --- WSM 6classgraupel
-D01

40km

D02

8km

Planetary boundary layer --4Mellor-Yamada-Janjic

Land surface --- Unified
NOAH

No cumulus convective
parameterization

D02

D01

5km

25km

11Data for evaluation of monthly rainfall
1. APHRODITEAsian Precipitation Highly-Resolved Observational Data
Integration Towards Evaluation of Water Resources (Yatagai et al.
2012)- Daily rainfall from 1982–2007- 0.25deg resolution

2. Seven (7) stations from PAGASA
Philippine Atmospheric Geophysical and Astronomical Services
Administration- Daily rainfall amount, 1982-2012- Stations span the WPH region.

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Monthly rainfall amountWRF model vs APHRODITE 1982-2007

Rainfall amountimproved in thehigher resolution
models.

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Model performance in terms of spatial
distribution of monthly rainfall
Location of the 7 PAGASA stations

Climatological mean(1982-2012 mean)
rainfallper STATION
for every monthJune , July , August

Grids are for visualization purposes only, not the actual model grids

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JUNEJULY

AUGUST12.5 km has the closest distribution to PAGASA
in terms of climatological rainfall distribution
5km is better than 25km
downscaling improves model’s spatial variation of rainfall thru
minimizing RMS difference153. Potential impact of sea surface
temperature on rainfall over thewestern Philippines
What is the impact of local SST west of thePhilippines on the summer monsoon
rainfall on the northwestern coast of thePhilippines?
Dado, J.M. & Takahashi, H.G. 2017. Potential impact of sea surface
temperature on rainfall over the western Philippines, Progress inEarth and Planetary Science , 4:23, DOI 10.1186/s40645-017-0137-6.
16

Can SST affect rainfall west of the Philippines?
850 mb winds (vectors) + SST (shaded contours)
[oC]

m/s

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Model & experimental setup
Boundary Conditions
Atmospheric:ERA Interim
Sea surface temperature:
NOAA monthly OISSTv2
Parameterization
Microphysics:
WSM 6-class graupel
Planetary boundary layer:
Mellor-Yamada-Janjic
Land surface:
Unified NOAH
No cumulus convectiveparameterization (CCP)

D02
D01

5km

25km

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WRF-ARW v3.6.1-- Simulation Period: June to August, 1982-2012-- Resolution analysis: 5km, nested within 25km
domain-- ERA Interim atmospheric boundary condition-- NOAH Land Surface Model-- No cumulus convective parameterization(CCP)CTL experiment

CLM experiment

w/ monthly mean SST data
fromNOAA OISST v2

w/ monthly climatological SST(1982-2012) from NOAAOISST v2

Compare CTL and CLM results
Determine the sensitivity of rainfall
to the variations of SST19SST impact
For each year,CTL

CLMSENSITIVITY /ANOMALY

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SST impact

WPH

WSSTWPH
14–19 oN
119.5–121oE
WSST
12–18 oN
115–120oE
21Spatial distribution of monthly rainfall

1. Results

vs TRMM-PR 1998-2012

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SST impact on rainfall
REGRESSION ANALYSIS
relationship between rainfall sensitivity to SST anomaly in WSST region
200Regression coefficient
Slope ->
rate of change ofrainfall per 1K SST
warmingPctl-clim (mm)1000Theil-Sen method
Estimate trend using
median slope among alllines through all pairs ofpoints-100-200-300-1-0.5

00.51

SST anomaly (K)

1.5

223

SST impact on rainfall
SPATIAL MAP of the regression coefficient

regression coefficient of the rainfall
sensitivity to the SST anomaly in theWSST region

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SST impact on rainfall“+” - significant values at the 90% significance level determined by correlation coefficients based on 29 degrees of freedom.

• Positive rainfall sensitivity to 1-K SST warming over the domain.
• Higher and statistically significant sensitivity was observed for oceanic
rainfall near the WSST region.
• Rainfall in the WPH increased by ~100 mm K-1 SST warming in theWSST25

Conclusions

1. Onset of southwest monsoon is very abrupt in mid-May,
while it retreats gradually from the north in midSeptember, and fully retreat in late October.
2. Best RCM resolutions reproducing summer monsoon
rainfall on the northwestern coast of the Philippines:

12.5km for spatial distribution of climatologicalmonthly rainfall, 5km for interannual monthly rainfall
amount.

3. Positive SST anomalies in WSST region induce positive
rainfall anomalies in the WPH region.
– Based on regression analysis, WPH rainfall ismodulated by interannual variation in WSST by~100mm per 1K SST warming.

The END
Thank you!
.

Sunset in the Manila Bay on March 27, 2007