Areal Precipitation

Question 1

Definition

Answer 1

Areal precipitation: Precipitation in a specific area expressed as an average depth of liquid water over the area

Estimation can be made direct from point observations or in two steps, first interpolating point rainfall on a raster and then taking the average over all raster cells within the considered region.

Interpolation of precipitation for unknown point u0 fromweighted sum with weights wi of neighbouring points ui:

[equation page 8]

Question 2

Methods:

Answer 2

 Arithmetic mean: w = 1/n

 Thiessen-Polygons method: w = 1, (nearest neighbour)

 Inverse-Distance method: w ~ 1/d2

 Isohyetal method: w = f (isohyetal areas)

 Geostatistical methods: w = f (variogram)