A Nonparametric Stochastic Approach for Disaggregation of Daily to Hourly Rainfall Using 3-Day Rainfall Patterns

Heeseong Park,Gunhui Chung

doi:10.3390/w12082306

Abstract

As infrastructure and populations are highly condensed in megacities, urban flood management has become a significant issue because of the potentially severe loss of lives and properties. In the megacities, rainfall from the catchment must be discharged throughout the stormwater pipe networks of which the travel time is less than one hour because of the high impervious rate. For a more accurate calculation of runoff from the urban catchment, hourly or even sub-hourly (minute) rainfall data must be applied. However, the available data often fail to meet the hydrologic system requirements. Many studies have been conducted to disaggregate time-series data while preserving distributional statistics from observed data. The K-nearest neighbor resampling (KNNR) method is a useful application of the nonparametric disaggregation technique. However, it is not easy to apply in the disaggregation of daily rainfall data into hourly while preserving statistical properties and boundary continuity. Therefore, in this study, three-day rainfall patterns were proposed to improve reproducible ability of statistics. Disaggregated rainfall was resampled only from a group having the same three-day rainfall patterns. To show the applicability of the proposed disaggregation method, probability distribution and L-moment statistics were compared. The proposed KNNR method with three-day rainfall patterns reproduced better the characteristics of rainfall event such as event duration, inter-event time, and toral amount of rainfall event. To calculate runoff from urban catchment, rainfall event is more important than hourly rainfall depth itself. Therefore, the proposed stochastic disaggregation method is useful to hydrologic analysis, particularly in rainfall disaggregation.

Highlights

With the urban catchment being paved, rain must be discharged throughout the stormwater pipe networks
It was assumed that boundary continuity is not necessary to be preserved
Disaggregated hourly rainfall data should have similar statistical properties and cross-boundary continuity must be preserved when event duration is longer than a day

Summary

Introduction

With the urban catchment being paved, rain must be discharged throughout the stormwater pipe networks. Many researches have been conducted to disaggregate historical annual flow data to monthly or daily flow data and preserve statistical properties [1,2,3,4,5,6,7]. Replaces the kernel density estimation [9] to avoid the computational inefficiency and the boundary issues This technique was applied to disaggregate yearly flow to monthly [11]. A method of the combination of KNNR method and optimization technique was applied to disaggregate monthly flow data into daily flow [13]. Three-day rainfall patterns were proposed to preserve statistical properties of hourly rainfall continuity across the boundaries. The statistical properties with/without three-day rainfall patterns of disaggregated and observed hourly rainfall were compared

Stochastic Disaggregation Using the KNNR Method

Proposed Three-day Rainfall Patterns

Applied Data

Hourly rainfall distributionininSeoul

Conclusions