Flood Finder Chad 2017

Transcription

1 Flood Finder Chad 2017 Bulletin N October 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 11 to 17 October is At Bongor, Flood Warning At Sarh Flood Watch At N DJamena, Lai and Moundou No Warning This bulletin provides static maps showing the variation of accumulated rainfall and anomaly during the period 04 to 10 October and forecast rainfall and anomaly during 11 to 17 October in Chari and Logone river basin. Analysis of RADARSAT-2 Satellite data acquired on October, 2017, indicate that localized standing flood water with very little impact on population and agriculture area was observed along Logone river between Lai and Bongor as shown in the map on page 9. 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.

2 Accumulated Rainfall Analysis (04-10 October, 2017) The maps below shows 1) the spatial distribution of the accumulated rainfall between 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. The accumulated rainfall of mm has occurred in the South of Chad basin, especially upstream of Sarh and Moundou gauging stations, which is an anomaly of to 20 mm/day. Rainfall of 20 mm also occurred in some Southern and Central parts, which is an anomaly of mm/day. Overall rainfall occurred during this week was much less than the previous week and was almost same as the forecast rainfall during the previous week. 2

3 Forecast Rainfall Analysis (11 to 17 October, 2017) The maps below shows 1) the spatial distribution of the forecast rainfall between 11 to 17 October, 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 0 to 100 mm rainfall is expected in the South of the basin, upstream of Béboro, which is an anomaly of to 10 mm/day. Remaining areas in South of the basin are expected to receive 10 to 0 mm rainfall, which is an anomaly upto mm/day in some areas. Overall the rainfall forecasted during the next 7 days, is much less than what is received during this week. 3

4 Flood Alert on Logone Bongor: Flood Warning Based on the hydrological forecast on 11 Oct., estimated average discharge during 04 to 10 October is 1733 m 3 /s, which is 20% less than the average observed discharge of 217 m 3 /s during 04 to 10 October. Average forecast discharge during 11 to 17 October is 129 m 3 /s, which is 38% less than the average observed discharge of 217 m 3 /s. Forecast discharge is expected to decrease upto 1112 m 3 /s (forecasted water level of 360 cm, which will be 40 cm below the alert level of 400 cm). Hydrograph indicating the observed discharge data in 2012 (most recent past flood), available observed, estimated and forecasted discharge data for 2017 is shown in the figure below. During the next 7 days, the Flood alert for Bongor is Flood Warning, based on observed water levels. Flood Inundation is expected Date of Forecast Estimated Average past 7 days Flood Alert Forecast Average for next 7 Days Discharge Trend 11/10/ Flood Warning 129 Overall decrease in flow by 38 % 4000 Observed Bongor station in 2012 and 2017, Estimated and Forecast (2017) Logone River Return Period (Years) Sep 6 Oct 29 Sep 22 Sep 1 Sep 8 Sep 13 Oct Date 3 Nov 27 Oct 20 Oct Observed (01 Sep 10 Oct,2017) Estimated (04 10 Oct, 2017) Forecast (11 17 Oct, 2017) Nov 17 Nov 24 Nov Return Period 2. Year Return Period Year Alert_Level_Discharge 4

5 Flood Alert on Logone Lai: No Warning Based on the hydrological forecast on 11 Oct., estimated average discharge during 04 to 10 October is 1273 m 3 /s, which is 18% less than the average observed discharge of 19 m 3 /s during 04 to 09 October. Average forecast discharge during 11 to 17 October is 982 m 3 /s, which is 9% less than the average observed discharge of 19 m 3 /s during October. Forecast discharge is expected to decrease upto 931 m 3 /s (forecasted water level of 390 cm) continuously till 17 October, which is 104 cm below the alert level of 494 cm. Hydrograph indicating the observed discharge data in 2012 (most recent past flood), available observed, estimated and forecasted discharge data for 2017 is shown in the figure below. During the next 7 days, the Flood alert for Lai is No Warning. No Flood Inundation expected Date of Forecast Estimated Average past 7 days Flood Alert Forecast Average for next 7 Days Discharge Trend 11/10/ No Warning 982 Overall decrease in flow by 30 % Observed Lai station in 2012 and 2017, Estimated and Forecast (2017) Logone River Return Period (Years) Jul 7 Aug 14 Aug 21 Aug 28 Aug 4 Sep 11 Sep 18 Sep 2 Sep Date 2 Oct 9 Oct 16 Oct 23 Oct 30 Oct 6 Nov 13 Nov 20 Nov 27 Nov Observed (01 Sep 09 Oct,2017) Estimated (04 10 Oct, 2017) Forecast (11 17 Oct, 2017) 2012 Return Period 2. Year Return Period Year Alert_Level_Discharge

6 Flood Alert on Chari Sarh: Flood Watch Based on the hydrological forecast on 11 Oct., estimated average discharge during 04 to 10 October is 1004 m 3 /s, which is 29 % more than the average observed discharge of 778 m 3 /s during 4 to 10 October, Average forecast discharge during 11 to 17 October is 1128 m 3 /s, which is about 31% more than the observed discharge of 778 m 3 /s during 4 to 10 October, Forecast discharge is expected to increase upto 1171 m 3 /s (forecasted water level of 680 cm) continuously till 17 October. Hydrograph indicating the observed discharge data in 2012 (most recent past flood), available observed, estimated and forecasted discharge data for 2017 is shown in the figure below. During the next 7 days, the Flood alert for Sahr is Flood Watch. No Flood Inundation expected Date of Forecast Estimated Average past 7 days Flood Alert Forecast Average for next 7 Days Discharge Trend 11/10/ Flood Watch 1128 Overall increase in flow by 11 % 1200 Observed Sarh station in 2012 and 2017 Chari River Return Period (Years) Nov 17 Nov 10 Nov 3 Nov 27 Oct 20 Oct 13 Oct 6 Oct 29 Sep 22 Sep 1 Sep 8 Sep 1 Sep Date Observed (01 Sep 10 Oct,2017) Estimated (04 10 Oct, 2017) 2012 Return Period 2. Year Return Period Year Forecast (11 17 Oct, 2017) 6

7 Flood Alert on Chari N Djamena: No Warning Based on the hydrological forecast on 11 Oct., estimated average discharge during 04 to 10 October is 2896 m 3 /s, which is 20 % more than the average observed discharge of 2421 m 3 /s during 4 to 11 October, Average forecast discharge during 11 to 17 October is 3301 m 3 /s, which is 36 % more than the observed discharge of 2421 m 3 /s observed during 4 to 11 October, Forecast discharge is expected to increase upto 3498 m 3 /s (forecasted water level of 70 cm) by 17 October, which is same as the alert level of 70 cm. Hydrograph indicating the observed discharge data in 2012 (most recent past flood), available observed, estimated and forecasted discharge data for 2017 is shown in the figure below. During the next 7 days, the Flood alert for N Djamena is No Warning, based on the observed water levels. Date of Forecast Estimated Average past 7 days Flood Alert Forecast Average for next 7 Days Discharge Trend 11/10/ No Warning 3301 Overall increase in flow by 12 % Observed N'Djamena station in 2012 and 2017 Chari River Return Period (Years) Nov 17 Nov 10 Nov 3 Nov 27 Oct 20 Oct 13 Oct 6 Oct 29 Sep 22 Sep 1 Sep 8 Sep 1 Sep Date Observed (01 Sep 11 Oct,2017) Estimated (04 10 Oct, 2017) Forecast (11 17 Oct, 2017) 2012 Return Period 2. Year Return Period Year Return Period 10 Year Alert_Level_Discharge 7

8 Flood Alert on Logone Moundou: No Warning Based on the hydrological forecast on 11 Oct., estimated average discharge during 04 to 10 October is 94 m 3 /s, which is 8% less than the average observed discharge of 64 m 3 /s during 4 to 10 October, Average forecast discharge during 11 to 17 October is 61 m 3 /s, which is 6 % more than the average observed discharge of 64 m 3 /s during 4 to 10 October, Forecast discharge is expected to decrease upto 41 m 3 /s (forecasted water level of 300 cm) by 17 October. Hydrograph indicating the observed discharge data in 2012 (most recent past flood), available observed, estimated and forecasted discharge data for 2017 is shown in the figure below. During the next 7 days, the Flood alert for Moundou is No Warning. Date of Forecast Estimated Average past 7 days Flood Alert Forecast Average for next 7 Days Discharge Trend 11/10/ No Warning 61 Overall decrease in flow by 6 % Observed Moundou station in 2012 and 2017, Estimated and Forecast (2017) Logone River Return Period (Years) Jul 7 Aug 14 Aug 21 Aug 28 Aug 4 Sep 11 Sep 18 Sep 2 Sep Date 2 Oct 9 Oct 16 Oct 23 Oct 30 Oct 6 Nov 13 Nov 20 Nov 27 Nov Observed (01 Sep 10 Oct,2017) Estimated (04 10 Oct, 2017) Forecast (11 17 Oct, 2017) 2012 Return Period 2. Year Return Period Year 8

9 Satellite Based Near Real-Time Flood Inundation Bongor Based on the flood warning of 4 October, rapid mapping UNOSAT has programmed and acquired RADARSAT-2 satellite SAR image on October and flood inundation occurred along the river Longone between Lai and Bongor was mapped and shown in figure below. As observed from the map, which indicates localized standing flood water along Logone river between Lai and Bongor with very little impact on population and agriculture area. Please download map from here: 9

10 Data sources: - Accumulated rainfall is from Global Satellite Mapping of Precipitation (GSMAP) of JAXA/EORC, Japan. More details are available at - Accumulated rainfall anomaly is calculated using the normal rainfall data of climate change knowledge portal of World Bank. More details are available at Code=TCD - Forecast Rainfall is from Global Forecasting System of NOAA, USA. More details are available at - Forecast Rainfall Anomaly is calculated using the normal rainfall data of climate change knowledge portal of World Bank. More details are available at 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 errorfree 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: unosat@unitar.org Ph : (UNOSAT Operations), 24/7 hotline: