Supplementary material to "Characterization of event water fractions and transit times under typhoon rainstorms in fractured mountainous catchments: Implications for time-variant parameterization"

Abstract

Discerning the rainfall spatial heterogeneity is an important issue as using the water isotopic tracer for transit time evaluation, particularly in meso-scale catchments. Here, we checked the rainfall spatial heterogeneity of event 2 and event 3 in terms of the rainfall amount and its isotopic composition. The spatial distribution of rainfall amount of each storm was interpolated via inverse distance weighted method (power parameter is 2) by 4 CWB rain gauges (see Fig. 1 in main text). The relative difference (RD) and the coefficient of variation (CV) are calculated for illustrating the spatial heterogeneity (Fig. S1 and Table S1). Note that RD is defined as the rainfall minus the average rainfall of a specific cell divided by the mean rainfall of the entire catchment. In this figure, the CVs of the total rainfall are 16% and 10%, respectively, for event 2 and 3 (Fig. S1(a) and Fig. S1(b)). Such low CVs indicated that the variation were much less than the mean, showing the rainfall spatial pattern is relatively homogeneous. Additionally, the distribution of RD shows that the western part receives more rainfall and the RD has a variation of approx. ±40% of the average. In sum, the both indicator showed that the typhoon-induced rainfall is short-lived, intense, but its rainfall spatial heterogeneity in meso-scale catchments is not pretty large. Fig. S1. Rainfall spatial heterogeneity of event 2 (a) and event 3 (b). The black points are rainwater sampling sites with δ 18 O value in parentheses.