Terrestrial Flood Risk and Climate Change in the Yallahs River, Jamaica. An assessment of future flood risk. projections of future climate

Transcription

1 Terrestrial Flood Risk and Climate Change in the Yallahs River, Jamaica An assessment of future flood risk using hydrodynamic models driven by projections of future climate Matthew Wilson1, Arpita Mandal2, Michael Taylor3, Christopher Burgess3, Jayaka Campbell3 and Tannecia Stepphenson3 1. Department of Geography, University of the West Indies, St. Augustine, Trinidad & Tobago 2. Department of Geography and Geology, University of the West Indies, Mona, Jamaica 3. Climate Studies Group, Department of Physics, University of the West Indies, Mona, Jamaica

2 1. PAST FLOOD EVENT INTRODUCTION 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS Introduction Flooding is one of the major natural hazards affecting Jamaica. Has been negatively affected by severe weather events Repeated flooding (2004, 2007, 2008, 2010) has been very costly both in terms of lives and livelihoods. Analysis of the number of hurricanes/ tropical storms affecting Jamaica and the variability of the rainfall pattern has shown changes in trends in the years Shifts in traditional peak rainfall months of May and September- October has shifted to June and November in some years. Shorter duration high intensity rainfall associated with stationery fronts and troughs IPCC outlook shows an increasing likelihood of more intense hurricanes, which would result in increased frequency of flooding due intensive rainfall. 2

3 INTRODUCTION Types of flooding in Jamaica 1. PAST FLOOD EVENT Groundwater induced Depression Riverine 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS Storm Surge Urban Runoff GRAPHIC ID 1 3

4 INTRODUCTION Reported flood events 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT Data from Mona GeoinformatixInstitute, CEAC Solutions Ltd, ODPEM and Water Resources Authority of Jamaica GRAPHIC ID 2 4

5 INTRODUCTION Study site: Yallahs River 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT GRAPHIC ID 3 Title of Graphic : Upland catchment in south-east Jamaica, draining the Blue Mountains. Major riverineflooding associated with Hurricane Gustav (28 August 2008). 5

6 INTRODUCTION Title Flood analysis method summary 1. Past flood analysis 2. Current flood risk 3. Future flood risk Historical rainfall data (24 hr, , Mavis Bank gauge) Extract annual 24 hr maximum Baseline climate model: PRECIS Future climate model: ECHAM 1. PAST FLOOD EVENT GRAPHI C ID 4 24 hr rainfall for Tropical Storm Gustav (28 August 2008) Fit Gumbel distribution IDF Curves: present IDF Curves: future IDF Curve difference 2. RETURN PER RIOD ANALYSIS Temporal downscaling (NRCS Type II/ III distribution) 24 hr rainfall for 25, 50, 100 yr return periods Temporal downscaling (NRCS Type II/ III distribution) Scaling of current return periods Temporal downscaling (NRCS Type II/ III distribution) 3. FUTURE CLIMATE ANALYSIS Topography River network Land use/ cover Water balance Floodplain topography Channel geometry 15 min. rainfall Gustav catchment model Gustav hydraulic model 15 min. rainfall Current return periods catchment model Current return periods hydraulic model Inundation extents, depths and flood wave timings 15 min. rainfall Future return periods catchment model Channel inflow Channel inflow Channel inflow Future return periods hydraulic model HEC-HMS LISFLOOD-FP 6

7 1. PAST FLOOD EVENT INTRODUCTION 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS Fraction of 24-hr rainfall Rainfall (mm) NRCS 24-hour Rainfall Distributions Type 1 Type 1a Type 2 Type Hour Mavis Bank, Jamaica, 28 Aug 2008 Tropical Storm Gustav (419 mm 24-hour rainfall) Hour 7

8 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT 3. FUTURE CLIMATE ANALYSIS INTRODUCTION HEC-HMS model structure, Yallahs River 8

9 RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION 2. RETURN PER 1. Past flood analysis: Tropical Storm Gustav Landfall in Jamaica 28 August 2008 Major impact (US $210 M), including flooding in Yallahs 24-hr data for Mavis Bank and Ramble gauges NRCS Type II method used to generate 15-minute rainfall Flows generated from rainfall using HEC-HMS Rainfall (mm) Rainfall (mm) Mavis Bank (419 mm 24-hour rainfall) Ramble (298.4 mm 24-hour rainfall) Hour 3. FUTURE CLIMATE ANALYSIS Jamaica Jamaica 9

10 RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION 2. RETURN PER 15-minute rainfall HEC-HMS LISFLOOD-FP 1. Tropical Storm Gustav: Results Generation of flow data for upstream input and subcatchment inflows Routing of flood wave along main channel and across floodplain Maximum flood depth 3. FUTURE CLIMATE ANALYSIS (m) 10

11 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 11

12 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 12

13 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 13

14 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 14

15 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 15

16 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 16

17 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 17

18 Tropical Storm Gustav: Prediction of flood extent and depth over time (m) 18

19 RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION Early flooding in narrow section of valley (before flood peak) 1. Tropical Storm Gustav: Results Time of initial inundation Time of maximum inundation Flood peak upstream occurred ~1 hour it reached downstream 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER Hours (from start) Hours (from start) 19

20 1. PAST FLOOD EVENT INTRODUCTION RIOD ANALYSIS 2. RETURN PER 2. Estimation of current flood risk Daily data (24-hour) obtained for from Jamaica Met Service for Mavis Bank and Ramble Data prior to 1992 unavailable due to loss of records in fire Some historical data ( ) obtained from Jamaica Weather Reports from NOAA central library ( Annual maximum extracted: MAVIS BANK RAMBLE Hurricane Ivan Tropical Storm Gustav 3. FUTURE CLIMATE ANALYSIS RAINFALL (MM) Tropical Storm Nicole Annual maximum 24-hour rainfall 20

21 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION 24-hour Rainfall (mm) 2. Estimation of current flood risk Return periods calculated for 24-hour rainfall 24-hour maximum temporally downscaled using NRCS Type-II rainfall IDF curves generated for return period calculations Return period, Mavis Bank 24 hr rainfall estimated from hr rainfall period Return period (years) Rainfall Intensity (mm/hr) IDF Curve, Mavis Bank, data set from Duration (minutes) 5-Predicted 10-Predicted 25-Predicted 50-Predicted 100-Predicted 21

22 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION 2. Estimation of current flood risk: results HEC-HMS run for 25, 50 and 100 year rainfall events Flows from HEC-HMS routed through the LISFLOOD-FP model to predict inundation extents and depths Topographically constrained flooding 3. FUTURE CLIMATE ANALYSIS Right: Map of exceedance probability: Green: 4% (25 year return period) Blue: 2% (50 year return period) Red: 1% (100 year return period) Main difference between flood areas 22

23 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION 2. Estimation of current flood risk: results Depth difference: 100-year event maximum depth minus 25-year event maximum depth. Although the flood extents are similar, water depths are up to 2 m higher on the floodplain during a 100-year event 23

24 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION Intensity (mm/hr) Baseline (PRECIS) Duration (days) Percentage difference between baseline climate (PRECIS) and future climates (ECHAM) calculated for rainfall events down to 24-hour 3. Estimation of future flood risk Intensity (mm/hr) ECHAM , B Percentage change 20% 0% -20% -40% -60% -80% -100% Duration (days) Intensity (mm/hr) ECHAM , B Duration (days) Change factors for medium (2040 to 2070) and long term (2071 to 2099) Duration (days) 5 yr RP 10 yr RP 25 yr RP 50 yr RP 5 RP -mt 100 yr RP 10 RP -mt 25 RP -mt 50 RP -mt 100 RP -mt 5 RP -lt 10 RP -lt 25 RP -lt 50 RP -lt 100 RP -lt 24

25 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION 3. Estimation of future flood risk: results 25, 50 and 100 year rainfall scaled by change factor from ECHAM and temporally downscaled using NRCS Present return periods (analysis of gauge data) Future return periods (ECHAM, , B2) HEC-HMS run for futurereturn periods and flows routed through the LISFLOOD- FP model to predict inundation extents and depths 25

26 3. FUTURE CLIMATE ANALYSIS 2. RETURN PER RIOD ANALYSIS 1. PAST FLOOD EVENT INTRODUCTION 3. Estimation of future flood risk: results Maps of exceedanceprobability: Green: 4% (25 year return period) Blue: 2% (50 year return period) Red: 1% (100 year return period) Present annual exceedance probability annual exceedanceprobability (ECHAM, B1) No reduction in inundation risk in valley Lower risk downstream 26