# Identifying the Minimum Number of Flood Events for Reasonable Flood Peak Prediction of Ungauged Forested Catchments in South Korea

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Study Areas

#### 2.2. Identifying Flood Peaks

#### 2.3. Flood Predictive Model

#### 2.3.1. Random Forest

#### 2.3.2. Streamflow and Meteorological Dataset

^{−2}day

^{−1}), G is the soil heat flux density (MJ m

^{−2}day

^{−1}) that can be ignored for daily calculations, T is the air temperature at 2 m height (°C), ${u}_{2}$ is the average wind speed at 2 m height (m s

^{−1}), ${e}_{s}$ is the vapor pressure of the air (kPa), ${e}_{a}$ is the actual vapor pressure (kPa), $\u2206$ is the slope of the vapor pressure curve (kPa °C

^{−1}), and $\gamma $ is the psychrometric constant (kPa °C

^{−1}). Allen et al. [32] suggested a comprehensive set of equations for computing all the parameters of Equation (1) in accordance with the available meteorological data and a time-step computation. In this study, we ignored G for estimating the daily PET. The sine method, which assumes that latent flux follows a sine curve throughout a day, was used to estimate the hourly PET from the daily values [33].

#### 2.3.3. Catchment Characteristic Variables

#### 2.4. Performance Evaluation

## 3. Results and Discussion

#### 3.1. Prediction of Flood Peaks in Ungauged Areas

#### 3.2. Predictive Performance Changes with Data Accumulation

#### 3.3. Minimum Number of Flood Events in Data Collection

## 4. Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**In this study, 40 small forested catchments were used, where water level gauge dams were installed.

**Figure 2.**Input and output data for developing flood peak predictive model. Six static variables for catchment characteristics and three dynamic variables for meteorological features were used to train the RF models. The warning lead times were 1 h and 6 h, based on the extremely short-term rainfall prediction system of the KMA.

**Figure 3.**Relationship between the observed and modeled flood peaks. Random forest predictive models were developed with two different warning lead times at (

**a**) 1 h and (

**b**) 6 h.

**Figure 4.**Flowchart of model building and performance evaluation processes for analyzing the minimum number of flood events required in data collection.

**Figure 5.**(

**a**) Relationship between the number of flood events used for training dataset (N1; defined in Figure 4) and the predictive performances; (

**b**) 0, 100, 250, 500, 1000, 1500, and 2167 flood events were selected, and the flood data of catchment C3, hypothesized as the ungauged catchment, were added repeatedly to the previous dataset to analyze the predictive accuracy.

**Figure 6.**Relationship between the number of flood events of 39 catchments and the performance increment ($\u2206NS)$. In this instance, data for 205 flood events were confirmed as the required number of flood events for effective flood peak prediction in an ungauged area when an $\u2206NS$ value of 0.1 was selected as a criterion.

**Figure 7.**Distribution of the minimum number of flood events in the collected data to develop an effective predictive model from a total of 7000 iterations. Dark gray indicates a probability of 95% and light gray indicates a probability of 90%.

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**MDPI and ACS Style**

Yang, H.; Lim, H.; Moon, H.; Li, Q.; Nam, S.; Choi, B.; Choi, H.T.
Identifying the Minimum Number of Flood Events for Reasonable Flood Peak Prediction of Ungauged Forested Catchments in South Korea. *Forests* **2023**, *14*, 1131.
https://doi.org/10.3390/f14061131

**AMA Style**

Yang H, Lim H, Moon H, Li Q, Nam S, Choi B, Choi HT.
Identifying the Minimum Number of Flood Events for Reasonable Flood Peak Prediction of Ungauged Forested Catchments in South Korea. *Forests*. 2023; 14(6):1131.
https://doi.org/10.3390/f14061131

**Chicago/Turabian Style**

Yang, Hyunje, Honggeun Lim, Haewon Moon, Qiwen Li, Sooyoun Nam, Byoungki Choi, and Hyung Tae Choi.
2023. "Identifying the Minimum Number of Flood Events for Reasonable Flood Peak Prediction of Ungauged Forested Catchments in South Korea" *Forests* 14, no. 6: 1131.
https://doi.org/10.3390/f14061131