Measurement of Convective Mean Rainfall over Small Areas using High-Density Raingages and Radar

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  • 1 Illinois State Water Survey, Urbana, IL 61801
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Abstract

Techniques of measuring area-mean convective rainfall over small areas (<2000 km2) are investigated using data from several gage-radar rainfall measurement studies. These data suggest that for low gage densities (≲1 gage per 250–300 km2) and for some climates (e.g., Illinois) that gage-radar area-mean convective rainfall measurements may be more accurate than gage-only measurements. The same result was not supported by data from another climate, suggesting that changes in raincell size and rain evaporation rate may affect the results. Further studies are needed to verify these suggestions. The data indicate that radar adds little to gage measurement of mean areal convective rainfall for gage densities of ≳1 gage per 100–200 km2.

Use of a space-variable gage adjustment of radar data is seen to be preferable to use of an averaged single adjustment factor, except in cases involving extrapolations of the space-variable adjustment factor. For such cases, e.g., over large lakes or outside of gage networks, use of the averaged single adjustment factor may be preferable.

Abstract

Techniques of measuring area-mean convective rainfall over small areas (<2000 km2) are investigated using data from several gage-radar rainfall measurement studies. These data suggest that for low gage densities (≲1 gage per 250–300 km2) and for some climates (e.g., Illinois) that gage-radar area-mean convective rainfall measurements may be more accurate than gage-only measurements. The same result was not supported by data from another climate, suggesting that changes in raincell size and rain evaporation rate may affect the results. Further studies are needed to verify these suggestions. The data indicate that radar adds little to gage measurement of mean areal convective rainfall for gage densities of ≳1 gage per 100–200 km2.

Use of a space-variable gage adjustment of radar data is seen to be preferable to use of an averaged single adjustment factor, except in cases involving extrapolations of the space-variable adjustment factor. For such cases, e.g., over large lakes or outside of gage networks, use of the averaged single adjustment factor may be preferable.

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