Flood Finder Chad 2017

Bulletin N°14 01 November 2017

Flood Finder alert system is operational using observed water level data. Based on hydrological forecast, flood alerts are issued at N’DJamena, ‘Bongor’, ‘Lai’, Moundou and Sarh stations one week before.

Flood Alerts during 01 to 07 November is ‘ No Warning’

At N’DJamena, Bongor, Lai, Moundou and Sarh

This bulletin provides static maps showing the variation of accumulated rainfall and anomaly during the period 25 to 31 October and forecast rainfall and anomaly during 01 to 07 November in Chari and Logone river basin. It contains also detailed information on the observed and forecasted water discharge levels for the locations of N’Djaména, Bongor, Lai, Moundou and Sahr.

Alert Level:

Severe Flood Warning: Expect serious flood and imminent danger to life and property.

Flood Warning: Expect flooding that will cause disruption.

Flood Watch: Possibility of some flooding.

No Warning: No flood warning is in force.

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

2

Accumulated Rainfall Analysis (25 to 31 October, 2017)

The maps below shows 1) the spatial distribution of the accumulated rainfall between 25 to 31 October over the Chari/Logone Basin, and 2) the spatial distribution of rainfall anomalies during the same period. The anomaly is shown in millimeters per day (mm/d). A value of 10 mm/d would indicate that the average daily rainfall in a given week has exceeded normal rainfall by 10mm.

Predominantly, rainfall between 10 to 50 mm has occurred in the South of Chad basin, especially in upstream catchment area of Sarh and Moundou gauging stations, which is an anomaly upto 5 mm/day

predominantly. Overall rainfall occurred during this week was less than the previous week and was less than the forecast rainfall during the previous week.

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

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Forecast Rainfall Analysis (01 to 07 November, 2017)

The maps below shows 1) the spatial distribution of the forecast rainfall between 01 to 07 November, 2017 over the Chari/Logone Basin, and 2) the spatial distribution of forecast rainfall anomalies during the same period. The anomaly is shown in millimeters per day (mm/d). A value of 10 mm/d would indicate that the average daily rainfall in a given week has exceeded normal rainfall by 10 mm.

During the next 7 days, about 20 to 100 mm rainfall is expected in the South of the basin, in the upper areas of Sarh and Moundou catchments, which is an anomaly of upto 10 mm/day. Remaining areas in the basin are expected not to receive any rainfall, which is below normal rainfall. Overall the rainfall forecasted during the next 7 days, is more than rainfall received during previous week.

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

4

0

500

1000

1500

2000

2500

3000

3500

4000

1-Sep

8-Sep

15-Sep

22-Sep

29-Sep

6-Oct

13-Oct

20-Oct

27-Oct

3-Nov

10-No

v

17-No

v

24-No

v

Dis

char

ge (m

3 /s)

Date

Observed Discharge @ Bongor station in 2012 and 2017, Estimated and Forecast (2017)

Observed (01 Sep - 31 Oct,2017) Estimated (25 - 31 Oct, 2017) Forecast (01 - 07 Nov, 2017) 2012

Return Period 2.5 Year Return Period 5 Year Alert_Level_Discharge

Retu

rn P

erio

d (Y

ears

)

2.5

5

1850

2100

Logone River

1530

Flood Alert on Logone river @ Bongor: No Warning

Based on observed water levels and trends provided by the Flood Finder model, the forecast flow

rate of the Logone is expected to decrease gradually until 07 November in Bongor. The Logone's water level should reach 260 cm, 140 cm below the warning level of 400 cm.

During the next 7 days, the Flood alert for Bongor is No Warning

Date of Forecast

Estimated Average Discharge (m3/s)

past 7 days

Flood Alert Forecast Average Discharge (m3/s) for

next 7 Days

Discharge Trend

01/11/2017 737 No

Warning 639

Overall decrease in

flow by 15 %

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

5

0

500

1000

1500

2000

2500

31-Jul

7-Aug

14-Aug

21-Aug

28-Aug

4-Sep

11-Sep

18-Sep

25-Sep

2-Oct

9-Oct

16-Oct

23-Oct

30-Oct

6-Nov

13-No

v

20-No

v

27-No

v

Dis

char

ge (m

3 /s)

Date

Observed Discharge @ Lai station in 2012 and 2017, Estimated and Forecast (2017)

Observed (01 Sep - 09 Oct,2017) Estimated (25 - 31 Oct, 2017) Forecast (01 - 07 Nov, 2017) 2012

Return Period 2.5 Year Return Period 5 Year Alert_Level_Discharge

Retu

rn P

erio

d (Y

ears

)

2.5

5

1700

2200

Logone River

1573

Flood Alert on Logone river @ Lai: No Warning

Based on observed water levels and trends provided by the Flood Finder model, the forecast flow rate of the Logone is expected to decrease gradually until 07 November Laï. The Logone's water level should reach 270 cm, 224 cm below the warning level of 494 cm.

During the next 7 days, the Flood alert for Lai is No Warning.

Date of Forecast

Estimated Average Discharge (m3/s)

past 7 days

Flood Alert Forecast Average Discharge (m3/s) for

next 7 Days

Discharge Trend

01/11/2017 615 No

Warning 432

Overall decrease in flow by 42 %

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

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0

200

400

600

800

1000

1200

1400

1-Sep

8-Sep

15-Sep

22-Sep

29-Sep

6-Oct

13-Oct

20-Oct

27-Oct

3-Nov

10-Nov

17-Nov

24-Nov

Dis

char

ge (m

3 /s)

Date

Observed Discharge @ Sarh station in 2012 and 2017

Observed (01 Sep - 31 Oct,2017) 2012 Return Period 2.5 Year Return Period 5 Year

Retu

rn P

erio

d (Y

ears

)

2.5

5

1050

Chari River

Flood Alert on Chari river @ Sarh: No Warning

On the basis of observed water levels at Sarh, the flow rate in Chari river is expected to decrease

gradually. The Chari's water level should reach 449 cm by 07 November.

During the next 7 days, the Flood alert for Sahr is No Warning

based on the observed water levels.

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

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0

1000

2000

3000

4000

5000

1-Sep

8-Sep

15-Sep

22-Sep

29-Sep

6-Oct

13-Oct

20-Oct

27-Oct

3-Nov

10-Nov

17-Nov

24-Nov

Dis

char

ge (m

3 /s)

Date

Observed Discharge @ N'Djamena station in 2012 and 2017

Observed (01 Sep - 31 Oct,2017) Estimated (25 - 31 Oct, 2017) Forecast (01 - 07 Nov, 2017)2012 Return Period 2.5 Year Return Period 5 YearReturn Period 10 Year Alert_Level_Discharge

Retu

rn P

erio

d (Y

ears

)

2.5

5

10

2300

2900

3550

Chari River

3453

Flood Alert on Chari river @ N’Djamena: No Warning

Based on observed water levels and trends provided by the Flood Finder model, the forecast flow rate of the Chari should continue to decrease gradually next week below the alert level. However observed water level on 31 October, 2017 was 651 cm, about 99 cm less than the warning level of 750 cm.

During the next 7 days, the Flood alert for N’Djamena is No Warning.

Date of Forecast

Estimated Average Discharge (m3/s)

past 7 days

Flood Alert Forecast Average Discharge (m3/s) for

next 7 Days

Discharge Trend

01/11/2017 3187 No Warning 3167 Overall decrease in

flow by 1 %

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

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0

500

1000

1500

2000

2500

31-Jul

7-Aug

14-Aug

21-Aug

28-Aug

4-Sep

11-Sep

18-Sep

25-Sep

2-Oct

9-Oct

16-Oct

23-Oct

30-Oct

6-Nov

13-Nov

20-Nov

27-Nov

Dis

char

ge (m

3 /s)

Date

Observed Discharge @ Moundou station in 2012 and 2017, Estimated and Forecast (2017)

Observed (01 Sep - 23 Oct,2017) Estimated (25 - 31 Oct, 2017) Forecast (01 - 07 Nov, 2017)

2012 Return Period 2.5 Year Return Period 5 Year

Retu

rn P

erio

d (Y

ears

)

2.5

5

1750

2100

Logone River

Flood Alert on Logone river @ Moundou: No Warning

On the basis of observed water levels and trends provided by the Flood Finder model, the forecast

flow rate of the Logone is expected to decrease rapidly until 07 November at Moundou. The Logone's water level should reach 195 cm.

During the next 7 days, the Flood alert for Moundou is No Warning.

Date of Forecast

Estimated Average Discharge (m3/s)

past 7 days

Flood Alert Forecast Average Discharge (m3/s) for

next 7 Days

Discharge Trend

01/11/2017 270 No Warning 146 Overall decrease in

flow by 85 %

Flood Finder Chad 2017 Bulletin N° 14 01 November 2017

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Data sources:

- Accumulated rainfall is from Global Satellite Mapping of Precipitation (GSMAP) of JAXA/EORC, Japan.

More details are available at http://sharaku.eorc.jaxa.jp/GSMaP_crest/ - Accumulated rainfall anomaly is calculated using the normal rainfall data of climate change

knowledge portal of World Bank. More details are available at http://sdwebx.worldbank.org/climateportal/index.cfm?page=country_historical_climate&ThisCCode=TCD

- Forecast Rainfall is from Global Forecasting System of NOAA, USA. More details are available at https://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-forcast-system-gfs

- Forecast Rainfall Anomaly is calculated using the normal rainfall data of climate change knowledge portal of World Bank. More details are available at http://sdwebx.worldbank.org/climateportal/index.cfm?page=country_historical_climate&ThisC

Code=TCD Disclaimer: This is a preliminary analysis based on forecasting models and satellite based observations and has not yet been validated in the field. It is important to note that there are limitations in these data sources, and flood warnings included in this report should be treated with caution. The depiction and use of boundaries, geographic names and related data shown here are not warranted to be error-free nor do they imply official endorsement or acceptance by the United Nations. Please send ground feedback to UNITAR – UNOSAT.

This flood bulletin has been produced by UNITAR-UNOSAT with the collaboration of:

Ministère de l’Eau et de l’Assainissement du Tchad (Field data)

CIMA Research Foundation (Hydrological forecast)

UNICEF with funding from:

European Civil Protection and Humanitarian Aid Operations (ECHO)

UNITAR / UNOSAT Contact: Email: unosat@unitar.org Ph : +41 22 767 4020 (UNOSAT Operations), 24/7 hotline: +41 75 411 4998

http://www.unitar.org/unosat