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

Recent area change among 5 Köppen climate types

By Beck et. al (2005)

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

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

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

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

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

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.

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)

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.

Annual precipitation in dry areas

Precipitation over central Australian regions is more than the other dry regions.

New criteria for desert

Desert climate: Annual precipitation is less than 240 mm even if originally assign to desert climate as 10(t+α).

Verification of modified and original classification（１）

Modified KöppenOriginal Köppen Vegetation

Better correspondence with observed vegetation

Modified

Verification of modified and original classification （２）

Original Vegetation

Trend of annual precipitation

One of the regions with the most increasing precipitation for 1901-2005 as well as for 1979-2005

IPCC 2006

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.

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.

Marginal precipitation for vegetation growth

Arid climate condition:

Precipitation-10(Temperature+α)<0

Time evolution of this quantity

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)

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.

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.