Post on 23-May-2018
Introduction to Hydrological Modelling
Key Issues & Implication of Climate Change on Hydrological Modeling and Policy
George J. Nasr,
ESCWA Consultant
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How does it all fit in?Policy Makers
Managers Hydrologists Issues
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Outline1. Hydrologic Cycle and Watersheds2. Weather and the Hydrologic Cycle3. Hydrologic Modeling4. The Modeling Process
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Hydrologists
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Stages of the Hydrologic Cycle• Elements of a
Hydrological Model:
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Source: http://www.dcr.virginia.gov/stormwater_management/documents/Chapter_4.pdf
– Precipitation– Infiltration– Interception– Storage
– Run-off– Evaporation– Transpiration– Groundwater
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Key Unit: Watershed
Source: http://www.ourwatershed.ca/swp/watersheds.php
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Concepts: Watershed Divide
Source: http://echo2.epfl.ch/VICAIRE/mod_1`a/chapt_2/text.htm
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Concept: Karst Formations
Source: http://www.nzap.ca/graphics/karst_cave.jpg
1• Flow path routes:
– Converging conduits,– Unrelated to
topography
• Flow velocities: – Comparatively Fast
• Macropores/swallow holes;– Recharge bypasses the
filtering capability of soil
– Little/No filtration
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Characteristics of watershed• Size: Rainfall received, retained, amount of runoff ...• Shape: Morphological parameters (geological structure),• Slope: Rainfall distribution and movement,• Drainage: Flow characteristics, erosion,• Soil: Infiltration rates,• Land use, land cover: Overland flow of the rainwater,• Main channel and tributaries: Stream flow,
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Characteristics of watershed• Size: Rainfall received, retained, amount of runoff ...• Shape: Morphological parameters (geological structure),• Slope: Rainfall distribution and movement,• Drainage: Flow characteristics, erosion,• Soil: Infiltration rates,• Land use, land cover: Overland flow of the rainwater,• Main channel and tributaries: Stream flow,
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Outline1. Hydrologic Cycle and Watersheds2. Weather and the Hydrologic Cycle3. Hydrologic Modeling4. The Modeling Process
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Issues
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Weather and the Hydrologic Cycle• Weather: day-to-day temperature and precipitation activity, • Climate: average atmospheric conditions over 30-yr periods
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Source: Gleckler, P. J.; Taylor, K. E.; Doutriaux, C.; 2008: Performance Metrics for Climate Models, Journal of Geophysical Research, Vol. 113.
While the weather of a given day cannot be predicted in the far future, the change in prevailing future climate trends can be forecasted with relative accuracy
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Climate Change and the Hydrologic Cycle2
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Outline1. Hydrologic Cycle and Watersheds2. Weather and the Hydrologic Cycle3. Hydrologic Modeling
• Problem Structure• Model Types
4. The Modeling Process
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Hydrologists
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Model: Problem Structure3
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Models: Spatial Scale3
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Models: Time Scale
Diminished Surface Flow
DepletedGroundwater
Time span
Scale
Small Turbulent Eddies
Thunderstorms
2000 km
Seconds Minutes Hours
mic
rosc
ale
mes
osca
leSy
nopt
icG
loba
l
200 km
20 km
2 m
Days Weeks
Winds:Land/SeaMountain/Valley
HurricanesTropical Storms
Weather Fronts
Months Years
Droughts
Floods
Seawater Intrusion
Sea Level Rise
Weather Phenomena Climate ImpactsLegend:
Hydrological Impact
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Outline1. Hydrologic Cycle and Watersheds2. Weather and the Hydrologic Cycle
3. Hydrologic Modeling• Problem Structure• Model Types:
• Conceptual • Mathematical: Forecasting / Simulation
4. The Modeling Process
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Hydrologists
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Models • Conceptual
– Qualitative, usually based on graphs– Represent important system: components, processes,
linkages, Interactions– used as:
• Initial step;– Hypothesis testing– Mathematical model development
• Framework– Future monitoring , research, management actions.
• Mathematical– Representation of real world structure, phenomena,– Addresses wide range of conditions,– Forecasting impacts of changing climatic conditions
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Conceptual Model: Example3
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Mathematical Model: Basic Structure
Source: http://www.nptel.iitm.ac.in/courses/105101002/1
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Mathematical Models: Discretization3
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Conceptual Model: Discretization Steps3
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Types of Mathematical Models1. Hydrological simulation model:
– Synthesizing a (continuous) record of some hydrological variable
– for a period of time– from available concurrent records of other variables
2. Hydrological forecasting model– Synthesizing a record of some hydrological variable– or Estimating some of its states – in an interval of time– from available records of:
• The same variable • Other variables• Obtained in a an immediately preceding time period
Hydrological simulation can operate in a "forecasting mode" if estimates of the predictors for the forecast time interval are available through an independent forecast.
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Hydrologic Simulation ModelModel Selection: study objectives, watershed
characteristics, data availability, project budget .
1. Equations:• Governing hydrologic processes,
2. Maps:• Delimit/Define the study area
3. Database: • Model parameters• Data on study area• Climatic Variables
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Hydrologic Simulation Model
Equations Maps Database
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Input: (2) Map Data
Source:http://www.isiimm.agropolis.org/OSIRIS/satellite_image/lbLit_FAOProject_5VillagesOfCnal900.jpghttp://daac.ornl.gov/LBA/guides/CD06_Landuse_Landcover_Map.png
Litani – sub-watershed
Parana
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Input: (3) Database• Soil:
– type , texture , and structure– condition ,– Grain-size distribution,– porosity, – moisture content, capillary pressure,– Steady-state infiltration,– Saturated hydraulic conductivity,
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Input: (3) Database• Soil:
– type , texture , and structure– condition ,– Grain-size distribution,– porosity, – moisture content, capillary pressure,– Steady-state infiltration,– Saturated hydraulic conductivity,
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Input: (3) Climactic Variables• Rainfall,• Snowfall,• Radiation,
• Humidity,• Vapour pressure,• Temperature,
3 • Sunshine hours,• Wind velocity • ...
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Outline1. Hydrologic Cycle and Watersheds2. Weather and the Hydrologic Cycle3. Hydrologic Modeling4. Conclusion: The Modeling Process
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Policy MakersManagers
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Modeling ProcessConceptual Model
Mathematical Model
Computational Model
CalibrationVerification
DataModel Modification
Results
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Model Development & Policy
Thank you
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