Precipitation and evapotranspiration rates
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1. The hydrological cycle diagram shows the annual water balance for an area, with 800 mm of precipitation, 350 mm of evapotranspiration, 425 mm of surface runoff, and 475 mm of groundwater recharge. 2. Effective precipitation is defined as the volume of precipitation available for groundwater recharge, and is calculated as total precipitation minus actual evapotranspiration, which depends on crop type. 3. Extreme precipitation events like the 1998 "Westlandbui" storm that dropped 100 mm of rain in 24 hours can cause hundreds of millions of euros in flood damage.
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Precipitation and evapotranspiration rates
- 2. Example Hydrological cycle evapotranspiration Transpiration 275 mm Evaporation 75 mm 350 mm Atmosphere Precipitation 800 mm Ground level Surface runoff 25 mm 250 mm 425 mm Sea 700 mm 275 mm Open surface water system Soil Moisture or Unsaturated zone crops Capillary rise 50 mm Absorption by roots Water table or Groundwater level Percolation or recharge 475 mm 1
- 3. Distribution Precipitation 1961 - 1990 mm per year 1
- 4. Shortage precipitation in summer -Average numbers - Depends on use of land 1
- 5. 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) 1
- 6. EP grassland and agriculture EP grassland EP agriculture 1
- 7. Extreme Precipitation (neerslag) 1998: The “Westlandbui” (100 mm in 24 hour) caused 0,5 billion euro damage. 2
- 8. 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 1/100 2
- 9. 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 2
- 10. Rainfall (mm), the storms year hours days 2
- 11. 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 3
- 13. Evapotranspiration • PE potential evapotranspiration: Crops have optimal supply of water. Evaporation and transpiration Depends on type of crops • AE Actual evapotranspiration; Is always less than the PE. In reality crops sometimes a shortage of water. • mm/day 4
- 14. Example Hydrological cycle evapotranspiration Transpiration 275 mm Evaporation 75 mm 350 mm Atmosphere Precipitation 800 mm Ground level Surface runoff 25 mm 250 mm 425 mm Sea 700 mm 275 mm Open surface water system Soil Moisture or Unsaturated zone crops Capillary rise 50 mm Absorption by roots Water table or Groundwater level Percolation or recharge 475 mm 4
- 15. PE potential evapotranspiration Netherlands: Makkink-reference Evapotranspiration (Em) (mm/day) Potential Evapotranspiration of grass International: Penman, is based on evaporation of surface water (Eo MOW) (mm/day) E MOW = 1,25 x E4
- 16. Crops factors (gewasfactoren) crops Uncovered soil Grass Grain Maize / corn Lily Narcissus Tulip Bulbous plant Leek Celeriac Chicory Sowing Onion Onion plants Legume Sugar Beets Potato's Large Fruit Tree cultivation Nature plants Poor grassland Heather Moorland