Rainfall rates estimated from polarimetric weather radar measurements
of a convective rainstorm are used as input to a two-dimensional physi
cally based rainfall-runoff model. The correlation length of the input
rainfall field L(S) is 2.3 km. Runoff simulations are performed on tw
o semi-arid watersheds covering 32 km2 and 121 km2 at basin data grid
sizes L(M) of 125 m and 200 m, respectively. The characteristic basin
length scale L(W) is taken as the square root of the watershed area. R
ainfall data at resolutions L(R) of 1, 2, 3, 4, 6 and 8 km serve as mo
del input to determine the effect of precipitation data spatial resolu
tion on computed outflow hydrographs. Two dimensionless length paramet
ers are identified which describe the similarity of the effect of rain
fall data aggregation on both basins. The first parameter, L(R)/L(S),
describes 'storm smearing', and the second parameter, L(R)/L(W), descr
ibes 'watershed smearing'. Results from simulations without infiltrati
on show storm smearing occurring as L(R) --> L(S). Watershed smearing
causes more significant deviations from simulations using the finest-r
esolution data when L(R)/L(W) exceeds 0.4. Results with infiltration r
eveal that excess rainfall volumes decrease with increasing L(R)/L(W).
Additionally, excess rainfall volumes do not converge as L(R)/L(W) is
decreased to the practical lower limit provided by contemporary weath
er radars, which is of the order of 1 km.