climate classification using reanalysis data
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Climate Classification Using Reanalysis Data
Nobuo Yamazaki1, Kentaro Suzuki2, KiyotoshiTakahashi3, Masaru Chiba3 and Hirotaka Kamahori4
1 Meteorological College, Japan Meteorological Agency2 Saga Local Meteorological Observatory, Japan Meteorological Agency3 Meteorological Research Institute, Japan Meteorological Agency4 Climate Prediction Division, Japan Meteorological Agency
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Recent area change among 5 Köppen climate types
By Beck et. al (2005)
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ContentsValidation of 4 major reanalysis dataset by making Köppen classification mapsHow well Köppen climate classification corresponds to actual vegetation ?--> Improve by modifying criterionTime evolution of thresholds defining Köppen classification
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Data used
Monthly temperature and precipitation :JRA-25, ERA-40, NCEP-R1 and NCEP-R2 1979-2002Global precipitation datasets :CMAP standard and GPCP version2 1979-2002Land cover data derived from NDVI by Defries and Townsend(1994) -->Vegetation CRU TS2 Temperature and precipitation, 1951-2002
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Köppen climate classification
Rainfirest
Monsoon
Savanna
Step
Tem
perate
Tem
perate
Desert
Cool W
in
Cool Sum
Tem
perate
Ice Cap
Tudra
Cool m
oist
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0
5
10
15
20
25
30
35
40
CMAP JRA ERA40 NCEP R-1 NCEP R-2
Rat
io o
f in
consi
stent
grid
poin
ts (%)
Global
Land
Ocean
Validation of reanalysis precipitation Reference map: GPCP+Mean Temp.
Smaller is better
1979-2002
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Land cover distribution
Water
Broadleaf evergreen
High lat. deciduous
Confrerousevergreen
Tudra
Mixed coniferious
Grassland
Wooded grass
N/A
Broadleaf deciduous
Cultivated crops
Shrubs and bare ground
Bare ground
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Comparison around Australia
Original Köppen Vegetation
Bare ground is much smaller than Desert area.
Most of the central Australia is classified to desert, while observed vegetation show shrub and bare ground, suggesting not desert but step climate.
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Arid climate
Arid climate(B) is classified r<20(t+α),r:Annual precipitation(mm),t:Annual mean temperature(℃)
α:0 or 7 or 14 depending on ratio of summer or winter precipitation to annual precipitation.Desert(BW) r<10(t+α)
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Modification of threshold for desert climate
Most of the central Australia is classified to desert, while observed vegetation show shrub, suggesting not desert but step climate. In the dry areas evapo-transpiration is nearly equal to precipitation. So try to change threshold of precipitation.
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Annual precipitation in dry areas
Precipitation over central Australian regions is more than the other dry regions.
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New criteria for desert
Desert climate: Annual precipitation is less than 240 mm even if originally assign to desert climate as 10(t+α).
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Verification of modified and original classification(1)
Modified KöppenOriginal Köppen Vegetation
Better correspondence with observed vegetation
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Modified
Verification of modified and original classification (2)
Original Vegetation
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Trend of annual precipitation
One of the regions with the most increasing precipitation for 1901-2005 as well as for 1979-2005
IPCC 2006
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Change in beginning of warm season
Köppen’s classification uses warm and cold seasons.
Warm season:the Six warmest months.
Period is 6 months fixed, but timing may shift.
Definition of beginning of warm season: 1st month in the consecutive 6 warmest months.
1 2 3 4 5 6 7 8 9 10 11 12May warmest-->April is the first.
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Change: Beginning of warm season. Northern Hemisphere
Earlier ‘Spring’
Later ‘Spring’
Tropics: Rainy season affects warm season.
Continental climate: Spring warming is larger than fall warming.
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Marginal precipitation for vegetation growth
Arid climate condition:
Precipitation-10(Temperature+α)<0
Time evolution of this quantity
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At the end of 20th century, drying tendency is observed except temperate climates.
Temperature as well as precipitation contributes to this.
Anomaly of limit precipitation for vegetation
PrecipitationPrecipitation-10*(Temp.-a)
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Summary 1Kõppen’s classification generally corresponds to to estimated vegetation, with some exception around Australia. Minor modification of precipitation criterion for desert climate improves the correspondence in some other arid region as well as around Australia. As validation of precipitation from different reanalysis data-sets, Kõppen’s classification map is used, showing JRA-25 and ERA-40 are better.
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Summary 2Over land:(1)Warm season begins earlier in the extratropics and later in the tropics.(2)Except temperate, tendency for drier climate: Temperature increase is more than precipitation increase.