GHCN Population: Green Acres is the place for me …
Similar to the previous post, its time to review a previous thread, GHCNv2 and GRUMP Rural and Urban Extents, in regard to the GPWv3 GRUMP data for rural/urban extants in the context of the GHCN rural/smalltown/urban (R/S/U) classification.
Population. Examining the station location on an ONC would determine whether the station was in a rural or urban area. If it was an urban area, the population of the city was determined from a variety of sources. We have three population classifications: rural, not associated with a town larger than 10 000 people; small town, located in a town with 10 000 to 50 000 inhabitants; and urban, a city of more than 50 000. In addition to this general classification, for small towns and cities, the approximate population is provided.
These population metadata represent a valuable tool for climate analysis; however, the user must bear in mind the limitations of these metadata. While we used the most recent ONC available, in some cases the charts or the information used to create the charts were compiled a decade ago or even earlier. In such cases the urban boundaries in rapidly growing areas were no longer accurate. The same is true for the urban populations. Wherever possible, we used population data from the then-current United Nations Demographic Yearbook (United Nations 1993). Unfortunately, onlycities of 100 000 or more inhabitants were listed in the yearbook. For smaller cities we used population data from several recent atlases. Again, although the atlases were recent, we do not know the date of source of the data that went into creating the atlases. Additionally, this represents only one moment in time; an urban station of today may have been on a farm 50 years ago, though it is probably valid to assume that if a station is designated rural now, it was most likely rural 50 years ago. Knowing the importance of avoiding the effect of urban warming by preferring rural stations in climate analysis, these population metadata have been used as one of the criteria in the initial selection of the Global Climate Observing System (GCOS) Surface Network (Peterson et al. 1997a).
GPW GRUMP Rural/Urban Extents
Resolution is 30 second. Values are 0=undef, 1=rural, 2=urban. The downloaded ASCII files are converted to GeoTiff with gdal_translaate. Data is located here:
There are 3912 rural stations, 1409 suburban stations, and 1959 urban stations in the GHCN station inventory. I use the term ‘suburban’ as a synomyn for ‘small town.’
GHCN-GRUMP Rural-Rural matches: 3061 / 3912 => 78% Urban-Urban matches: 1695 / 1959 => 87%
GPW GRUMP Population
Resolution is 30 seconds. Values are for the population count in the grid cell. Coverages is from 84N to 56S. The range of population in the GeoTiff is from 0-xxxx The range of the population in the station inventory is from 0-24187. There are 42 stations that have ‘na’ (-9), most of these are in Antarctica, outside the coverage, but there are three other cases: ”Abbaissia/Cairo HQ’, Dhaka’, and ‘Royal Observa’. There is no obvious method for comparing the gridded population with the GHCN ‘population of nearest town.’
GPW GRUMP Population Density
Resolution is 30 second. Could not be processed due to formatting errors:
Format error in the GRUMP Population Density ascii file:
gdal_translate -ot Int32 -of GTiff gluds00ag_alpha1.asc gluds00ag_alpha1.tiff Input file size is 43200, 16800 0...10...20...30...40...50...60.ERROR 3: Token too long at scanline 10763. ERROR 1: IReadBlock failed at X offset 0, Y offset 10763 ERROR 1: GetBlockRef failed at X block offset 0, Y block offset 10763
Small Town / Suburban
Moving to a binary Rural / Urban designations loses the “Small Town” or “Suburban” designation. Is there a way to retreive it?
I looked at the population histograms for Rural and Urban stations that were previously Suburban but did not note a good break point between the two. Examining the brightness data for R and U stations that were previously Suburban, the vast majority of bright suburban stations are designated urban and the majority of the dark suburban stations are designated rural and there are relatively few remaining ‘mixed’ stations. So the answer seems to be ‘no,’ there is no obvious method to ‘rescue’ suburban stations.
|-GHCN Small Town ||-My Rural / Urban |||-My Brightness ||| |-count SRC _85 SRB _91 SRA 184 SUC 723 SUB 260 SUA _66
I was able to extract data from the GRUMP population density ASCII files earlier through the use of a special Perl data reader that I had written. That method is abandoned here due in favor of using a common GeoTiffDataReader for all the GHCN station metadata (with the exception of the Olsen vegetative data).
The GPWv3 population and population density files will be presented separately from the GRUMP population data used in this GHCN station inventory metadata reconstruction.
Center for International Earth Science Information Network (CIESIN), Columbia University; International Food Policy Research Institute (IFPRI); The World Bank; and Centro Internacional de Agricultura Tropical (CIAT). 2004. Global Rural-Urban Mapping Project (GRUMP), Alpha Version: Population Grids, Population Density Grids. Palisades, NY: Socioeconomic Data and Applications Center (SEDAC), Columbia University. Available at http://sedac.ciesin.columbia.edu/gpw.