Flood Finder Chad 2017

Transcription

1 Flood Finder Chad 2017 Bulletin N 8 20 September This bulletin provides static maps showing the variation of accumulated rainfall and anomaly during the period 13 to 19 September and forecast rainfall and anomaly during 20 to 26 September in Chari and Logone river basin. Flood alert system within Flood Finder is operational (partially), based on the observed water level data. Hydrological forecasting is calibrated and operational at Bongor and Lai, other locations i.e. N DJamena, Moundou and Sarh are still in calibration. As observed from the forecasted water levels, Flood Alert at Bongor and Lai is Flood Warning We are closely monitoring the situation especially at Lai and Bongor as more rainfall is forecasted in the upper catchment area. A satellite image has been programmed for the Laï region. It will be acquired on Monday 2 September. Potential flooded areas will be presented in the next bulletin. 20 to 26 Sep, 2017: Flood alert system is operational (partial) 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 (13 to 19 September, 2017) The maps below shows 1) the spatial distribution of the accumulated rainfall between 13 to 19 September 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 more than 200 mm has occurred near Am Timan village, which is more than 20 mm/day above normal rainfall. Rainfall of 100 to 200 mm has occurred in Eastern (near Am Timan and Goz Beida) and Western (near Moundou) parts of the basin, which is more than 20 mm/day above normal rainfall. Remaining parts of the entire basin upstream of N DJamena has received rainfall between 20 to 100 mm, which is upto 10 mm/day above normal rainfall. 2

3 Forecast Rainfall Analysis (20 to 26 September, 2017) The maps below shows 1) the spatial distribution of the forecast rainfall between 20 to 26 September 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 10mm. During the next 7 days, predominantly 0 to 100 mm rainfall is expected to occur in most parts of the basin, which is an anomaly of to 10 mm/day of normal rainfall. However, about 100 to 200 mm rainfall is also expected to occur in some places in East, West and Central parts of the basin, which is an anomaly of more than 10 mm/day of normal rainfall. Some areas are expected to receive rainfall upto 0 mm, which is an anomaly of upto mm/day. 3

4 Flood Alert on Logone Bongor: Flood Warning Based on the hydrological forecast on 20 Sep., estimated average discharge during 13 to 19 Sep. is 1401 m 3 /s, when compared with the observed average discharge of 1832 m 3 /s. Average forecast discharge during 20 to 26 Sep. is 11 m 3 /s, which is about 1% less than the observed discharge during previous week. Forecast discharge is expected to increase upto 1610 m 3 /s till 21 Sep. and then decrease upto 101 m 3 /s by 26 Sep., which is less than alert level discharge of 130 m 3 /s (at water level of 400 cm). However, the observed discharge from 9 to 18 Sep. is above the alert level discharge of 132 m 3 /s. In view of this, in the coming week, the Flood alert for Bongor is Flood Warning. Flood Inundation expected to decrease Date of Forecast Estimated Average past 7 days Alert level Forecast Average for next 7 Days Discharge Trend 20/09/ Flood Warning 11 Overall increase in flow by 11 % 4000 Observed Bongor station in 2012 and 2017, Estimated and Forecast (2017) Logone River Return Period (Years) Sep 8-Sep 1-Sep 22-Sep 29-Sep 6-Oct 13-Oct 20-Oct Date Observed (1 18 Sep, 2017) Estimated (13 Sep 19 Sep, 2017) Forecast (20 26 Sep, 2017) 2012 Return Period 2. Year Return Period Year Alert_Level_Discharge 27-Oct 3-Nov 10-Nov 17-Nov 24-Nov 4

5 Flood Alert on Logone Lai: Flood Warning Based on the hydrological forecast on 20 Sep., estimated average discharge during 13 to 19 Sep. is 183 m 3 /s, when compared with the observed discharge of 1631 m 3 /s on 16 September. Average forecast discharge during 20 to 26 Sep. is 133 m 3 /s, which is about 6% less than the observed discharge of 1631 m 3 /s on 16 September. Forecast discharge is expected to decrease upto 1446 m 3 /s till 21 Sep. and then increase upto 1676 m 3 /s on 26 Sep. beyond the alert level discharge of 173 m 3 /s (at water level of 494 cm). However, the observed discharge on 16 Sep. is above the alert level discharge of 173 m 3 /s. In view of this, in the coming week, the Flood alert for Bongor is Flood Warning. Flood Inundation expected to decrease Date of Forecast Estimated Average past 7 days Alert level Forecast Average for next 7 Days Discharge Trend 20/09/ Flood Warning 133 Overall decrease in flow by 3 % 200 Observed Lai station in 2012 and 2017, Estimated and Forecast (2017) Logone River Return Period (Years) 0 1-Sep 8-Sep 1-Sep 22-Sep 29-Sep 6-Oct 13-Oct 20-Oct Date Observed (1 16 Sep, 2017) Estimated (13 Sep 19 Sep, 2017) Forecast (20 26 Sep, 2017) 2012 Return Period 2. Year Return Period Year Alert_Level_Discharge 27-Oct 3-Nov 10-Nov 17-Nov 24-Nov

6 Flood Alert on Chari N Djamena: No Warning Based on the observed data, average discharge during 13 to 18 Sep. is 1730 m 3 /s. The alert level discharge is about 343 m3/s. The current discharge is about 0% lower than the alert level discharge, so no danger of floods in N Djamena. Calibration and validation of the hydrological forecast model is still in progress. Hydrograph indicating the observed discharge data in 2012 (most recent past flood) and 2017 is shown in the figure below. In view of this, No flood inundation expected over N Djamena 000 Observed N'Djamena station in 2012 and 2017 Chari River Return Period (Years) 0 1-Sep 24-Nov 17-Nov 10-Nov 3-Nov 27-Oct 20-Oct 13-Oct 6-Oct 29-Sep 22-Sep 1-Sep 8-Sep Date Observed Return Period 2. Year Return Period Year Return Period 10 Year 6

7 Flood Alert on Chari Sarh: No Warning Based on the observed data, average discharge during 13 to 18 Sep. is 604 m 3 /s. Calibration and validation of the hydrological forecast model is still in progress. Hydrograph indicating the observed discharge data in 2012 (most recent past flood) and 2017 is shown in the figure below. In view of this, No flood inundation expected over Sahr Observed Sarh station in 2012 and 2017 Chari River Return Period (Years) Sep 8-Sep 24-Nov 17-Nov 10-Nov 3-Nov 27-Oct 20-Oct 13-Oct 6-Oct 29-Sep 22-Sep 1-Sep Date Observed Return Period 2. Year Return Period Year 7

8 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: