Mekong Bulletin Mekong River Commission Secretariat (MRCS)

Regional Flood and Drought Management Center (RFDMC) P.O. Box 623 #576, National Road #2, Chak Angre Krom, Meanchey, Phnom Penh, Cambodia

Tel: (855-23) 425353, Fax: (855-23) 425363, Email: floodforecast@mrcmekong.org

Products of the MRC Flash Flood Guidance System (MRCFFGS) On 20 August 2021 at 06:00 UTC (01:00 PM Local time)

Main conclusion and guidance for flash flood in the Lower Mekong Basin (LMB): (In critical weather conditions, the text below will be changed to red colour)

• In the next 1, 3 and 6 flash flood risk has been detected may occur at some areas in the LMB.

• Details on the location of the flash flood risk areas in the LMB are in the attached excel file and on the webpage: http://ffw.mrcmekong.org/ffg.php

• In the next 24- hour, flash flood risk has been detected may occur at some areas in northeast Cambodia (see Flash Flood Risk (FFR) map below).

• The updated flash flood information will be provided at 8:00 am on 21 August 2021; and available on the webpage.

Small rainfall occurred at some areas in the LMB in the last 01- and 24-hour. Soil moisture was normal status in some areas in the LMB in the last 06-hour.

Flash floods will possibly occur within the next 01-, 03-, and 06-hour in the LMB.

Figure 1: 01-hour Mean Areal Precipitation (1-hr MAP)

Figure 2: 24-hours Mean Areal Precipitation (24-hr MAP)

Figure 3: 06-hours Average Soil Moisture (6-hr ASM)

Figure 4: 01-hour Flash Flood Guidance (1-hr FFG)

Figure 5: 03-hour Flash Flood Guidance (3-hr FFG)

Figure 6: 06-hour Flash Flood Guidance (6-hr FFG)

Small rainfall is forecasted for the next 01-, 03-, and 06-hour in the LMB.

Small rainfall will likely occur in the LMB in the next 24-hour. Flash food risk for the next 24-hour has been detected that may occur at some areas in northeast Cambodia.

Forecaster

Nguyen Quoc Anh

Figure 7: 01-hour Forecast Mean Areal Precipitation (1-hr FMAP)

Figure 8: 03-hours Forecast Mean Areal Precipitation (3-hr FMAP)

Figure 9: 06-hour Forecast Mean Areal Precipitation (6-hr FMAP)

Figure 10: 24-hour Forecast Mean Areal Precipitation (24-hr FMAP)

Figure 11: 12-hour Flash Flood Risk (12-hr FFR)

Figure 12: 24-hour Flash Flood Risk (24-hr FFR)

Disclaimer and Remarks:

FFG - Flash Flood Guidance: The amount of rainfall over a given duration (1, 3, 6 hours) which is just enough to cause bank-full flow in the draining stream outlet.

MAP - Mean Areal Precipitation: Derived mean areal precipitation estimates from bias-adjusted Micro-Wave Global Hydro Estimator (MWGHE) and GHE.

ASM - Average Soil Moisture: Soil water saturation fraction (dimensionless ratio of contents over capacity) for the upper zone (approximately 20-30 cm depth).

FMAP - Forecast Mean Areal Precipitation: Accumulations of forecasted mean areal precipitation produced by numerical forecasts from the Weather Research

and Forecasting (WRF) model. Each data product reflects basin-average precipitation accumulations from the navigation hour over the corresponding interval.

FFR - Flash Flood Risk: Products for forecast periods of 12, 24 and 36 hours (forecast periods 12 and 24 hours are shown in this bulletin). These products are

computed every six hours and measure the occurrence of positive forecast flash flood threat (FMAP > FFG) over a given forecast period using forecast precipitation

to drive the Soil and FFG models.

For more clarification of the MRCFFGS products please go to the Sheet "Explanation" in the attached excel file.

Note: The presented maps show not only the LMB but also areas outside of the LMB. This setup is based on the system configuration defined by the provider.

However, in the attached excel file only FFG values are published from within the LMB. Please be aware of the different color bar codes of each product.

→ The present bulletin provides the results of the MRCFFGS to inform and guide. It is not a warning nor alert notification.

Head of RFDMC

(For critical weather condition)

Lam Hung Son