3.21 VARIATION IN ANNUAL RAINFALL - GRID

Data ID

Description:

Rainfall variation calculated as the standard deviation of annual totals as a percentage of average annual rainfall

Chapter:

3 Climate

File name:

Cov

File type:

ArcView grid

Geographical area:

Namibia

Keywords:

rainfall

variation

annual

Notes on data, analysis and

Rainfall variation calculated as the standard deviation of annual totals as a percentage of average annual rainfall. To

compilation:

illustrate the co-efficient of variation, consider the following example: Take a location (station) with an average rainfall

of 400 mm per year and a co-efficient of variation of 40%. A value of 40% means that the standard deviation is 160

mm (40% = (160/400)*100), and that area would see annual rainfall totals of between 240 and 540 mm in two-thirds of

all years. In the remaining third of all years, annual rainfall totals would be below 240 or above 540 mm.

An interpolated grid was created from point data using a kriging interpolator in Arcview. Grid cell size = 5km. This grid

file was created from data for almost 300 stations and came from the following report:

Namibia Resource Consultants. 1999. Rainfall distribution in Namibia: Data analysis and mapping of spatial, temporal,

and Southern Oscillation Index aspects. Windhoek: Ministry of Agriculture, Water and Rural Development.

For incorporation in the atlas, the grid dataset was converted to the projection parameters used in the atlas and masked

to the country borders. Map units of the grid are in m. See Fig 3.18 Average and Median annual rainfall for source data.

Data quality and organisation

Positional Accuracy:

interpolation of points - accuracy will be reasonable in areas with clusters of stations and low in areas with few stations

Vector/Raster:

Raster

Spatial reference

Projection:

Albers Conical Equal Area

Spheroid

Bessel

Standard parallel1

-27

Standard parallel2

-19

Longitude of central meridian

18.5

Latitude of projection origin

-27

Fields

Field name

Field description

Value

COV (%)

Count

Number of cells with the same value

Source/Distribution

Data Source:

Namibia Resource Consultants. 1999. Rainfall distribution in Namibia: Data analysis and mapping of spatial, temporal,

and Southern Oscillation Index aspects. Windhoek: Ministry of Agriculture, Water and Rural Development.

Distribution notes:

Unrestricted