NRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle11NRES 201The Hydrologic Cycle2Today’s lecture topics- The global hydrologic cycle- Fate of precipitation and irrigation water- The soil-plant-atmosphere continuumThe Hydrologic CycleNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle23The global hydrologic cycleFundamental realities- The world’s water resourcesare not evenly distributed- Annual precipitation varies:• From ½ in. for theAtacama Desert in Chile• To > 460 in. for a rainforest region ofnortheastern India- Seasonal variation can alsobe extensive• When flooding is followedby droughtSource: http://news.softpedia.comMawsynram, IndiaSource: http://theatlantic.comAtacama Desert4- Water management haschanged- From the old way: adaptculture to environment• Settle near water• Harvest the rain• Live as nomads- To the new way: adaptenvironment to culture• Irrigate arid lands tomake them productive• Build cities in thedesert• Deplete the aquifersSource: http://eye4ethnic.blogspot.comSource: http://wellwornroad.comPalm Springs, CaliforniaNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle35Global stocks of water- 1400 million km3of water on Earth- Most of this water is in the oceans and does notcycle- Active cycling involves < 0.05% of the Earth’s water in:- The atmosphere- The surface layerof oceans- Shallow ground-water- Lakes and rivers- SoilsSource: Brady and Weil (2008)6Global water use- Dominated by irrigatedagriculture- Increases by 10% perdecade- Highest per capitaconsumption in the USASource: http://www.nap.eduSource: http://www.wrsc.orgSource: http://advisoranalyst.comPer capita water consumptionNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle47How water cycles- Solar energy drives evaporation- Water vapor forms clouds- The clouds move and form precipitation- Rain and snowfall return water to land and seas- And lead to runoff and percolation that resupplystreams, rivers, and the oceansSource: Brady and Weil (2008)(86%)(78%)8Water balance- The usual focus is a watershed- Land area drained by a single system of streams - Precipitation falling on a watershed can be:- Stored in the soil- Returned to the atmosphere by evaporation ortranspiration (evapotranspiration)- Discharged by surface or subsurface flow- Represented as:P = SS + ET + D, whereP = precipitation (+ irrigation)SS = soil storageET = evapotranspirationD = dischargeNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle59- Impacted by management- Irrigation increases the input of water• And calls for strategies to maximize soilstorage (SS) by minimizing discharge (D)- Clear-cutting trees in a forest will shift the output of water:• From evapo-transpiration (ET)• To discharge (D)Source: Brady and Weil (2008)10Interception, discharge, or soil storage- Precipitation intercepted directly by plant foliagemay not reach the soil- Up to 50% in forests- Increased by sublimation of snow collected on conifer branchesFate of precipitation and irrigation waterSource: Brady and Weil (2008)NRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle611- Water that reaches the ground may:- Enter the soil by infiltration• More likely with good soil structure- Or remain on the surface if rainfall (or snowmelt) exceeds infiltration• The result is ponding or runoffSource: http://ecointheknow.comPrairie potholes (South Dakota)12- Water that enters the soil willleave by:- Evaporation from the soilsurface- Plant uptake/transpiration- Subsurface drainage• Can account for up to 50%of water input• Some availability throughcapillary rise during dryperiodsSource: http://web2.geo.msu.eduNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle713Factors affecting infiltration- Type of vegetation- Runoff can be seriousfrom cultivated fields under row crops• Especially early inthe growing season- Very little runoff fromland under:• Undisturbed forests• TurfgrassSource: http://en.wikipedia.orgSource: http://josephforestenterprises.com14- Stem flow- Many plant canopies directrainfall toward the stem• Which increases waterinputs to the surroundingsoil• While decreasing themelsewhere - Corn canopies act likefunnels to redirect rainfallinto the crop row- Enhances saturated soilflowSource: Brady and Weil (2008)Contours indicate water potential in kPaNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle815- Snowfall- Can promote infiltration if it occurs beforefreezing weather• Acts as insulationto keep the soilunfrozen- Has the oppositeeffect if heavysnowfall occursafter freezing• Because theinsulating effectkeeps the soil frozenSource: Brady and Weil (2008)16- Soil management- Strategies to maximize infiltration while minimizing runoff:• Cover cropping Maintain dense vegetative cover between primary crops to: Open root channels Promote earthwormactivity Protect surface soilstructure Timely killing of thecover crop importantto control soil dryingSource: http://limecreekwatershed.wordpress.comNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle917• Furrow diking Tillage system thatcreates ridge-like barriers alongsiderow crops The ridges holdirrigation and rainwater to allow moretime for infiltrationSource: http://www.ars.usda.gov18• Minimizing compaction From heavy farm or forestry equipment Minimize wheel traffic Stay off wet soils Use wide tires From recreationalpressure Restrict foottraffic toexisting trails From cattle onrangeland Limit grazingdensitySource: Brady and Weil (2008)But not here Cattle were here...Note the pondingNRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle1019- Urban watersheds- Infiltration reduced by:• Soil compaction by heavyconstruction equipment• Land coverage byimpermeable pavementor buildings- The increased surface runoff:• Overwhelms stream flow• Causes flooding- Available options:• Permeable pavement• Rain gardensSource: http://wps.prenhall.comSource: http://www.wolfpaving.com20- Soil properties- Greater infiltrationfor:• Sands• Well-granulatedsoils- Greater runoff for:• Clays• Fragipan soilsSource: Brady and Weil (2008)Precipitation was the same for both watersheds.NRES 201 Lectures 18-19 (Fall 2014): The Hydrologic Cycle1121- Water flows:- From the soil tothe plant- From the plant tothe atmosphere- From higher tolower potential- Two critical factors:- Rate of watersupply to roots- Rate of water lossfrom