Effect of subsampling tropical cyclone rainfall on flood hydrograph response in a subtropical mountainous catchment
Journal
Journal of Hydrology
Journal Volume
409
Journal Issue
1-2
Pages
248-261
Date Issued
2011
Author(s)
Abstract
Accurate rainfall input is a prerequisite for simulations that aim to generate accurate hydrographs, which are crucial for flood forecasting, particularly in regions that are prone to frequent typhoon (tropical cyclone) invasions, such as Southern Asia. Few studies have investigated the effect of spatial resolution in typhoon rainfall monitoring on modeled hydrographs. Eight typhoon cases were examined in a mountainous watershed (335km2) featuring hourly radar-based 1.3-km resolution rainfall estimates. Radar-based hourly rainfall was subsampled at various densities in space, and then re-interpolated to full scale for modeling. The highest resolution rainfall datasets were taken as an ideal input in TOPMODEL for calibration and to derive the reference hydrographs, which were further used to examine the response of modeled hydrographs to imperfect rainfall. The correlation between rainfall similarities (compared with radar-based) and corresponding hydrograph similarities (compared with reference) were identified. The two most important findings were as follows: (1) in predicting flood peak timing in mesoscale watershed, high spatial resolution is not required because typhoon-induced rainfall is less variable in space and more concentrated in the temporal scale and (2) satisfactory hydrographs with EC>0.8 were obtained in 96% test cases, indicating that even a totally biased rainfall (in terms of total amount and rainfall field) may produce a plausible hydrograph. Hydrologic models transfer the spatiotemporal rainfall input into time-series discharge, in which the spatial dimension is converted into travel time. Those positive and negative rainfall biases in space may compensate once allocated in the same arrival time frame in the hydrograph. This explains why in many cases sparsely gauged rainfall input also generates promising hydrographs. In other words, as discussing the effect of other distributed factors on simulated hydrographs, the highly accurate rainfall input is an essential prerequisite to prevent the compensation. © 2011 Elsevier B.V.
Type
journal article