Home > GHCN > GHCN Land Cover: Steamed Veggies

GHCN Land Cover: Steamed Veggies

2010 April 25

Introduction

The GHCN station inventory includes two vegetative descriptions. The first is a two character marker stveg which is described as “general vegetation near the station based on Operational Navigation Charts; MA marsh; FO forested; IC ice; DE desert; CL clear or open;”. The second is grveg which is described as “gridded vegetation for the 0.5×0.5 degree grid point closest to the station from a gridded vegetation data base.” The gridded vegetation is derived directly from the Olson World Ecosystem Complexes data.

I looked at the Olson gridded vegetation in a previous post Olson Ecosystem Complex: Grilled Veggies. In this post, I am looking at how various “Land Cover” data sets match up with the GHCN ONC ‘stveg’ data field.

GHCN Vegetation

Peterson and Vose 1997 describe the GHCN vegetation fields as follows:

Vegetation. If the station is rural, the vegetation for that location is documented. The classifications used on the ONC are forested, clear or open, marsh, ice, and desert. Not all ONC had complete vegetation data, so these metadata are not available for all stations. An additional source of vegetation data is included in GHCN metadata: the vegetation listed at the nearest grid point to each station in a 0.5° ´ 0.5° gridded vegetation dataset (Olson et al. 1983). This vegetation database creates a global vegetation map of 44 different land ecosystem complexes comprising seven broad groups. These metadata do not indicate the exact vegetation type at the station location, but they do provide useful information. In particular, an ecosystem classification can be used to some degree as a surrogate for climate regions since vegetation classes depend, to a large extent, on climate.

And the GHCN v2 fortran reader comments:

c stveg=general vegetation near the station based on Operational
c Navigation Charts; MA marsh; FO forested; IC ice; DE desert;
c CL clear or open;
c not all stations have this information in which case: xx.

In fact, there are no stations labeled “CL” in the GHCN v2 station inventory file (v2.temperature.inv) and less than 10% of the stations have any ONC vegetation label. As far as a ‘reconstruction’ of the station inventory goes, I can achieve a 91% match rate by simply marking all stations with an ‘xx’ category.

Nevertheless, let’s briefly survey some of the land cover data sets available that seem appropriate to objective of describing the vegetation near the reporting station.

World Wildlife Global Lakes and Wetlands

WWF Wetlands

Prepared by the spatial-analyst.net site with it’s original source at: http://www.worldwildlife.org/science/data/item1877.html. See glwd31.

Cat       0 : other classes
Cat       1 : Lake
Cat       2 : Reservoir
Cat       3 : River
Cat       4 : Freshwater Marsh, Floodplain
Cat       5 : Swamp Forest, Flooded Forest
Cat       6 : Coastal Wetland
Cat       7 : Pan, Brackish/Saline Wetland
Cat       8 : Bog, Fen, Mire (Peatland)
Cat       9 : Intermittent Wetland/Lake
Cat      10 : 50-100% Wetland
Cat      11 : 25-50% Wetland
Cat      12 : Wetland Complex (0-25% Wetland)

In the GHCN station inventory, there are only 70 stations explicitly flagged as marsh (MA). From these 70, 29 were identified as a “MA” (category 4 or greater) in the WWF Lakes and Wetlands glwd31.tif data file – a match rate of only 41%.

FAO (2001): Global Ecological Zoning for the Global Forest Resources Assessment 2000. FAO, Rome

FAO Global Ecological Zones
Prepared by the spatial-analyst.net site with it’s original source at: http://cdiac.ornl.gov/ftp/global_carbon/. See ecoflor.

Cat       1 : Boreal coniferous forest
Cat       2 : Boreal mountain system
Cat       3 : Boreal tundra woodland
Cat       4 : No data
Cat       5 : Polar
Cat       6 : Subtropical desert
Cat       7 : Subtropical dry forest
Cat       8 : Subtropical humid forest
Cat       9 : Subtropical mountain system
Cat      10 : Subtropical steppe
Cat      11 : Temperate continental forest
Cat      12 : Temperate desert
Cat      13 : Temperate mountain system
Cat      14 : Temperate oceanic forest
Cat      15 : Temperate steppe
Cat      16 : Tropical desert
Cat      17 : Tropical dry forest
Cat      18 : Tropical moist deciduous forest
Cat      19 : Tropical mountain system
Cat      20 : Tropical rainforest
Cat      21 : Tropical shrubland
Cat      22 : Water

Number of stations marked with listed vegetation type:

Match GHCN ...... EcoFlor
60% . 0456 desert 0274 (cat 6,12,16,21)
86% . 0079 forest 0068 (cat 1,2,3,7,8,11,14,17,18,19,20)
01% . 0070 marsh. 0001 (cat 22)
36% . 0039 ice... 0014 (cat 5)

The match rate is good for the ‘forest’ category which is the main thrust of this data set and fair for ‘desert.’

Land Cover Type Yearly Climate Modeling Grid (CMG) (MODIS)

USGS MOD12c12

Prepared by the spatial-analyst.net site with it’s original source at: https://lpdaac.usgs.gov/lpdaac/products/modis_products_table/land_cover/yearly_l3_global_0_05deg_cmg/mod12c1 See IGBP.

Cat       0 : Water
Cat       1 : Evergreen Needleleaf forest
Cat       2 : Evergreen Broadleaf forest
Cat       3 : Deciduous Needleleaf forest
Cat       4 : Deciduous Broadleaf forest
Cat       5 : Mixed forest
Cat       6 : Closed shrublands
Cat       7 : Open shrublands
Cat       8 : Woody savannas
Cat       9 : Savannas
Cat      10 : Grasslands
Cat      11 : Permanent wetlands
Cat      12 : Croplands
Cat      13 : Urban and built-up
Cat      14 : Cropland/Natural vegetation mosaic
Cat      15 : Snow and ice
Cat      16 : Barren or sparsely vegetated
Cat     254 : Unclassified
Cat     255 : Fill Value

Number of stations marked with listed vegetation type:

Match GHCN ...... IGBP
64% . 0456 desert 0294 (cat 7,16)
53% . 0079 forest 0042 (cat 1,2,3,4,5)
03% . 0070 marsh. 0002 (cat 11)
58% . 0039 ice... 0021 (cat 15)

This Land Cover data set reduces the forest match rate developed with the previous data set but is an improvement in GHCN matching in the other categories.

NASA Earth Observations: Land Cover Classification (1 year – Terra/MODIS)

NEO LC

Available on the NASA Earth Observations site. Select the GeoTIFF option from the right hand corner. This data set uses the same IGBP land classification categories listed in the IGBP section immediately above.

Number of stations marked with listed vegetation type:

Match GHCN ...... IGBP
68% . 0456 desert 0312 (cat 7,16)
53% . 0079 forest 0042 (cat 1,2,3,4,5)
06% . 0070 marsh. 0004 (cat 11)
62% . 0039 ice... 0024 (cat 15)

The NEO LandCover GeoTIFF offers modest improvements in GHCN matching over the previous USGS LC data set.

Discussion

The ‘stveg’ is the leading example of useless information included in the GHCN v2 station inventory. With less than 10% of the stations categorized and only 5 categories (one unused), it offers a very incomplete picture of the vegetation at the station location.

It is an interesting historical note that both vegetation fields in the inventory are derived from ‘traditional mapping’ as opposed to satellite mapping. ONC for the stveg. Olson for the grveg. Since 1997, numerous satellite based products have been developed – mostly based on either MODIS or its predecessor AVRHH.

Ecosystem categorization can get much more complex than limited IGBP set used above. The World Wildlife Foundation Ecosystem data set has 827 categories listed.

Resources

Peterson and Vose, 1997 An Overview of the Global Historical Climatology Network Temperature Database
http://spatial-analyst.net
NASA Earth Observations

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  1. 2010 April 30 at 1:40 pm

    Hi Ron,

    If you can’t get all your links up at stoat, I’ll read them if posted here.

    Paul

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