Precipitation and evapotranspiration

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Example Hydrological cycleevapotranspiration

Transpiration275 mm

Evaporation75 mm

350 mm

Atmosphere

Precipitation800 mm

Ground level

Surfacerunoff25 mm 250 mm

425 mm

Sea

700 mm

275 mm

Open surface water system

Soil Moisture orUnsaturated zone

crops

Capillary rise50 mm

Absorption by roots

Water table orGroundwater level

Percolation orrecharge475 mm

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Distribution Precipitation1961 - 1990

mm per year

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Shortage precipitation in summer

-Average numbers

- Depends on use of land

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Effective precipitation (EP)(effectieve neerslag)

Volume of water available for recharge of groundwater.

Effective P = Precipitation - Evapotranspiration EP = P - EA (mm)

EA = Actual Evapotranspiration (depends on crops)

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EP grassland and agriculture

EP grassland(mm per year)

EP agriculture(mm per year)1

Extreme Precipitation (neerslag)

1998: The “Westlandbui” (100 mm in 24 hour) caused 0,5 billion euro damage.

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Policy on preventing flooding

• Nationaal Bestuursakkoord Water (2003)

Use of land Flooding Rainfall[1/year]

Grass 5 percent 1/10

Agriculture 1 percent 1/25

Horticulture 1 percent 1/50

Cultivation under glass 1 percent 1/50

Urban Area 0 percent 1/1002

STOWA rapport

• Conversion form standards (for example 1/10) to data for calculation / modelling

• Based on rainfall in the period 1906-2003 De Bilt.

• Use of statistics calculations

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Rainfall (mm), the stormsyear

hours days

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Rainfall distribution scheme

• Distribution scheme during rainfall• Standard schemes independent of rain

volume• There are 7 schemes which have the

same change • See excel-file

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Climate scenario’s

http://www.climatescenarios.nl/scenarios_summary/index.html

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Evapotranspiration

• PE potential evapotranspiration: Crops have optimal supply of water. Evaporation and transpirationDepends on type of crops

• AE Actual evapotranspiration; Is always less than the PE. In reality crops sometimes a shortage of water.

• mm/day

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Example Hydrological cycleevapotranspiration

Transpiration275 mm

Evaporation75 mm

350 mm

Atmosphere

Precipitation800 mm

Ground level

Surfacerunoff25 mm 250 mm

425 mm

Sea

700 mm

275 mm

Open surface water system

Soil Moisture orUnsaturated zone

crops

Capillary rise50 mm

Absorption by roots

Water table orGroundwater level

Percolation orrecharge475 mm

4

PE potential evapotranspirationNetherlands:Makkink-reference Evapotranspiration (Em)(mm/day)Potential Evapotranspiration of grass

International:Penman, is based on evaporation of surface water (Eo

MOW) (mm/day)

EoMOW = 1,25 x Em

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Crops factors (gewasfactoren)

cropsUncovered soilGrass

GrainMaize / corn

LilyNarcissusTulipBulbous plantLeekCeleriacChicorySowing OnionOnion plantsLegumeSugar BeetsPotato's

Large Fruit

Tree cultivation

Nature plantsPoor grasslandHeather

Moorland