ANNUAL FLOOD REPORT 2016 FLOOD FORECASTING & WARNING CENTER PROCESSING & FLOOD FORECASTING CIRCLE BANGLADESH WATER DEVELOPMENT BOARD TABLE OF CONTENTS TABLE OF CONTENTS ................................................................................................................. I LIST OF TABLES .......................................................................................................................... II LIST OF FIGURE ......................................................................................................................... III PREFACE ........................................................................................................................................ V EXECUTIVE SUMMARY ........................................................................................................... VII LIST OF ABBREVIATIONS .................................................................................................... VIII CHAPTER 1: INTRODUCTION ............................................................................................... 10 1.1. THE PHYSICAL SETTING ............................................................................................................... 10 1.2. THE RIVER SYSTEM ..................................................................................................................... 10 1.3. ACTIVITIES OF FFWC ................................................................................................................... 12 1.4. OPERATIONAL STAGES BEFORE FORECAST MODEL RUN ............................................................. 13 1.5. NATURE AND CAUSES OF FLOODING .......................................................................................... 14 1.5.1. Causative Factors ............................................................................................................................. 14 1.5.2. Statistics of Flooding ........................................................................................................................ 15 CHAPTER 2 : RAINFALL SITUATION................................................................................... 17 2.1 MAY ............................................................................................................................................ 17 2.2 JUNE ........................................................................................................................................... 19 2.3 JULY ............................................................................................................................................ 20 2.4 AUGUST ...................................................................................................................................... 21 2.5 SEPTEMBER ................................................................................................................................ 22 2.6 OCTOBER .................................................................................................................................... 23 CHAPTER 3: RIVER SITUATION ..................................................................................... 30 3.1 THE BRAHMAPUTRA BASIN ................................................................................................................ 30 3.2 THE GANGES BASIN ........................................................................................................................... 33 3.3 THE MEGHNA BASIN ......................................................................................................................... 36 3.4 THE SOUTH EASTERN HILL BASIN ...................................................................................................... 39 3.5 RECORDED HIGHEST WATER LEVEL ................................................................................................... 41 CHAPTER 4: FORECAST EVALUATION- 2016 ................................................................. 60 4.1 GENERAL ........................................................................................................................................... 60 4.2 EVALUATION CRITERIA OF FORECAST PERFORMANCE ...................................................................... 61 4.2.1. Mean Absolute Error (MAE) ........................................................................................................... 61 4.2.2. Co-efficient of Determination, r2 .................................................................................................... 61 4.3 PRE-DEFINED SCALES TO EVALUATE FORECAST PERFORMANCE ....................................................... 62 4.4 FORECAST STATISTICS AND MODEL PERFORMANCE, 2016 ................................................................ 62 4.4.1. Deterministic forecast performance ................................................................................................ 62 4.4.2 Medium Range (upto 10-days) Probabilistic Forecast Performance................................................. 72 CHAPTER 5 : INUNDATION STATUS ................................................................................... 79 CHAPTER 6: CONCLUSIONS ................................................................................................. 85 ANNEX-1 ...................................................................................................................................... 86 ANNEX-2 ...................................................................................................................................... 87 ANNEX-3 ...................................................................................................................................... 88 Annual Flood Report 2016, FFWC, BWDB i LIST OF TABLES TABLE 1. 1 :YEAR-WISE FLOOD AFFECTED AREA IN BANGLADESH ................ 16 TABLE 2.1: RAINFALL STATISTICS FOR THE MONSOON 2016 OVER THE FOUR BASINS ...................................................................................................................... 17 TABLE 2. 2 : SUMMARY OF THE RAINFALL SITUATION DURING THE MONTH OF MAY 2016 ............................................................................................................ 18 TABLE 2. 3: SUMMARY OF THE RAINFALL SITUATION DURING THE MONTH OF JUNE 2016 ............................................................................................................ 19 TABLE 2.4: SUMMARY OF THE RAINFALL SITUATION DURING THE MONTH OF JULY 2016 ............................................................................................................ 20 TABLE 2.5: SUMMARY OF THE RAINFALL SITUATION DURING THE MONTH OF AUGUST 2016 ..................................................................................................... 21 TABLE 2.6: SUMMARY OF THE RAINFALL SITUATION DURING THE MONTH OF SEPTEMBER 2016 .............................................................................................. 22 TABLE 2.7: SUMMARY OF RAINFALL FOR THE MONTH OF OCTOBER-2016 .... 23 TABLE 3. 1 : COMPARISON OF WATER LEVEL OF 2016 AND HISTORICAL EVENTS OF 1988 & 1998 OF SOME IMPORTANT STATIONS IN THE BRAHMAPUTRA BASIN. ........................................................................................ 33 TABLE 3.2 : COMPARISON OF WATER LEVEL OF 2016 AND HISTORICAL EVENTS OF 1988 & 1998 OF SOME IMPORTANT STATIONS IN GANGES BASIN ......................................................................................................................... 36 TABLE 3.3: COMPARISON OF WATER LEVEL OF 2016 AND HISTORICAL EVENTS OF 1988 & 1998 OF SOME IMPORTANT STATIONS IN MEGHNA BASIN. ........................................................................................................................ 39 TABLE 3.4 : COMPARISON OF WATER LEVEL OF 2016 AND HISTORICAL EVENTS OF 1988 AND 1998 OF SOME IMPORTANT STATION IN SOUTH EASTERN HILL BASIN. ........................................................................................... 40 TABLE 3.5: RECORDED PEAK WATER LEVEL WITH DATE DURING THE MONSOON 2016 ....................................................................................................... 41 TABLE 3.6: RECORDED HISTORICAL HIGHEST WATER LEVEL WITH DATE ... 42 TABLE 4.1: SCALES USED FOR PERFORMANCE EVALUATION ........................... 62 TABLE 4.2: STATISTICS FOR 24- HOUR FORECAST PERFORMANCE .................. 63 TABLE 4.3: STATISTICS FOR 48- HOUR FORECAST PERFORMANCE .................. 64 TABLE 4.4: STATISTICS FOR 72- HOUR FORECAST PERFORMANCE .................. 65 TABLE 4.5: STATISTICS FOR 96- HOUR FORECAST PERFORMANCE .................. 66 TABLE 4.6: STATISTICS FOR 120- HOUR FORECAST PERFORMANCE ................ 67 TABLE 4.7 : PERFORMANCE OF 3-DAY PROBABILISTIC FORECAST .................. 73 TABLE 4.8: PERFORMANCE OF 5-DAY PROBABILISTIC FORECAST ................... 74 TABLE 4.9: PERFORMANCE OF 7-DAY PROBABILISTIC FORECAST ................... 75 TABLE 4.10: PERFORMANCE OF 10-DAY PROBABILISTIC FORECAST ............... 76 Annual Flood Report 2016, FFWC, BWDB ii LIST OF FIGURE FIGURE 1 : BASIN MAP OF BANGLADESH WITH WATER LEVEL GAUGE STATIONS ................................................................................................................. IX FIGURE 2.1 : ISOHYETS OF ACTUAL RAINFALL (MAY 2016) ................................ 24 FIGURE 2.2 : ISOHYETS OF ACTUAL RAINFALL (JUNE 2016) ............................... 25 FIGURE 2.5 : ISOHYETS OF ACTUAL RAINFALL (SEPTEMBER 2016) .................. 28 FIGURE 2.6 : ISOHYETS OF ACTUAL