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Wet and dry spells in the Rio Santa Basin, Tropical Andes of PeruFabien Maussion, Maria Siller, Miriam Schlumpberger, Max Hartmann, and Wolfgang GurgiserDepartment of Atmospheric and Cryospheric Sciences, University of Innsbruck, Austria – [email protected]
Context
The Rio Santa basin in Peru (Ancash region):• Strong west – east contrasts (dry→ wet)• Rainy season: ≈ October to March, mostly (deep) convection• Subsidence agriculture (rainfed)• → Vulnerable to climate variability and change
80W 70W 60W 50W 40W
20S
10S
Eq.
10N
1000 km
RIO SANTABASIN
PACIFIC
ATLANTIC
VENEZUELA
COLOMBIA
EQU.
PERU BRAZIL
BOLIVIA
PARAGUAY
AMAZONIANBASIN
ALTIP
LAN
O
78.5W 78.0W 77.5W 77.0W
10.5S
10.0S
9.5S
9.0S
8.5S
100 km
HUARAZ
HUASCARAN6768 m
0
1000
2000
3000
4000
5000
Alti
tude
(m
)
Figure 1: Overview of the study area with a close up of the Rio Santa basin
Motivation
• Precipitation variability strongly correlated to 200hPa zonal wind(Bolivian high)
• Conceptual framework formulated by Garreaud et al. (2003) forthe Altiplano but never tested at such low latitudes
• Does the framework apply to the Rio Santa region as well?• Is moisture availability really the only driver for wet & dry spells?
Figure 2: Seasonally averaged (1979–2016) horizontal wind streamlines and geopotential height at200hPa from ERA-Interim data
Figure 3: Conceptual framework for rainy and dry episodes over the Altiplano (Garreaud et al., 2003)
Definition of Wet and Dry spells
• Daily precipitation from 16 stations (1979–2016, variable quality)• Wet spell: 50% of stations exceed the 70th percentile of daily
rainfall amount for at least three consecutive days• Dry spell: 50% of stations inferior to the 30th percentile of daily
rainfall amount for at least five consecutive days• Average of 3.3 wet spells per rainy season (duration 8 days)• Average of 2.3 dry spells per rainy season (duration 10.8 days)
Teleconnections: synoptic composite analysis (ERA-Interim)
Figure 4: Composite analysis during wet and dry spells. Top: 200hPa winds and geopotential.Middle: 200hPa wind and temperature anomalies (95% confidence). Bottom: 500hPa windcomposite and specific humidity anomalies.
Figure 5: Cross section at 9.75°S. Top: wind. Bottom: wind and specific humidity anomalies.
Case study: WRF simulations
302010
0102030
ER
A-I
nte
rim
zonal w
ind s
peed
at
20
0 h
Pa (
m s−
1)
EASTERLIES
WESTERLIES
DRYcase
WETcase
0
2
4
6
8
10
GPM
pre
cipit
ati
on
(mm
day−
1)
P70
P30
Dec Jan Feb Mar Apr2014 2015 2015 2015 2015
stati
on
dry
/wet
spells
Figure 6: Selection of the simulation periods.
-80W -70W -60W -50W -40W
-20S
-10S
Eq.
10N D01 (WRF25)
D02 (WRF5)
D03 (WRF1)
Figure 7: WRF model domains.
79W 78W 77W 76W 75W 74W
10S
9S
WET pblACM
0
2
5
10
20
50
80
120
3 da
ys p
reci
pita
tion
(mm
)
79W 78W 77W 76W 75W 74W
10S
9S
DRY pblACM
0
2
5
10
20
50
80
120
3 da
ys p
reci
pita
tion
(mm
)
Figure 8: Simulated 3-day accumulated precipitation in the wet and dry cases (WRF 1km).
78 77 76 75longitude (deg W)
0
1
2
3
4
5
6
7
alt
itude (
km a
sl)
Huaraz
EP AB
WET: Day 1, 15:00 LT
75
80
85
90
95
rela
tive h
um
idit
y (
%)
78 77 76 75longitude (deg W)
0
1
2
3
4
5
6
7
alt
itude (
km a
sl)
Huaraz
EP AB
DRY: Day 2, 15:00 LT
75
80
85
90
95
rela
tive h
um
idit
y (
%)
78 77 76 75longitude (deg W)
0
1
2
3
4
5
6
7
alt
itude (
km a
sl)
Huaraz
EP AB
quiverbckg5 m s−1WET: Day 1, 15:00 LT
8
4
0
4
8
meri
dio
nal w
ind s
peed (
m s−
1)
78 77 76 75longitude (deg W)
0
1
2
3
4
5
6
7
alt
itude (
km a
sl)
Huaraz
EP AB
quiverbckg5 m s−1DRY: Day 2, 15:00 LT
8
4
0
4
8
meri
dio
nal w
ind s
peed (
m s−
1)
Figure 9: Cross section at 9.75°S. Top: relative humidity. Bottom: zonal and meridional wind.
Conclusions
• synoptic composite analysis roughly confirms previousconceptual framework – albeit coarse and qualitative
• detailed WRF modelling provides a much more nuanced picture• ingredients for convection need to be studied in more detail!
References:Garreaud, R. D., Vuille, M., and Clement, A. C. (2003). The climate of the Alti-plano: observed current conditions and mechanisms of past changes. Palaeo-geography, Palaeoclimatology, PalaeoecologySchlumpberger (2017) & Siller (2017), Master Theses:http://diglib.uibk.ac.at/urn:nbn:at:at-ubi:1-6985
http://diglib.uibk.ac.at/urn:nbn:at:at-ubi:1-7816
Acknowledgements:This study relies heavily on the two Master Theses listed above.The WRF simulations were run on the HPC infrastructure of the U. of Innsbruck.