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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