Scaling and regionalization of flood flows in British Columbia, Canada

A regionalization of flood data in British Columbia reveals a common scaling with drainage area over the range 0.5 x 10(2) < A(d) < 10(4) km(2). This scaling is not a function of flood return period, which implies that simple scaling-consistent with a snowmelt-dominated flow regime-applies to the province. The observed scale relation takes the form Q infinity A(d)(0.75), similar to values reported in previous studies. The scaling relation identified was used to define the regional pattern of hydroclimatic variability for flood flows in British Columbia after discounting the effect of drainage area. The pattern was determined by kriging a scale-independent runoff factor k for the mean annual flood, 5 year flood and 20 year flood. The analysis permits quantification of uncertainty of the estimates, which can be used in conjunction with the mapped k-fields to calculate a mean and range for floods with the identified return period for ungauged basins. Owing to the sparsity of data, the precision is relatively poor. The standard error is generally less than 75% of the estimate in the southern half of the province, whereas in the northern half it is often between 75 and 100%. Examination of the relative increase in flood magnitude with increasing return period reveals spatially consistent but statistically insignificant differences. Flood magnitude tends to increase more rapidly in the western regions, where rain events may contribute to flood generation. The relative increase in flood magnitude with return period is consistently lower in the eastern mountain ranges, where snowmelt dominates the flood flow regime. Copyright (C) 2002 John Wiley Sons, Ltd.