Hydrologic Cycle & Global Water Balance

Hydrologic Cycle & Global Water Balance

• The water cycle comprises flows and stores of water
• Water moves between stores in the atmosphere, glaciers (two-thirds of fresh water); storage is temporary
• Precipitation includes liquid, solid, and vapor forms, falling on oceans, streams (streamflow), and land
• Water can be intercepted (through plants and trees), or run above non-permeable surfaces
• Percolation involves gravity pulling water through soil layers like topsoil, gravel, bedrock, fractures, and aquifers
• The deeper the flow, the slower it moves
• Evaporation, or water in gas form, arises from wet surfaces through reparation and transportation through plants
• Evapotranspiration occurs when evaporation goes through groundwater, up plants, and into the atmosphere
• Condensation makes clouds, which grow bigger, heavier and fall as precipitation

Water Balance

• Runoff (Q) can be calculated by Rainfall (P) minus Infiltration (F)
• This equates to flows plus changes in water storage areas in the form of groundwater or lakes
• These can be supplied through precipitation/river inflow, and removed via evaporation/river outflow
• Inflow equaling outflow represents balances
• More water inflow leads to flooding; more water outflow results in droughts
• Climate change is increasing evaporation, leading to more outflow and potentially drier conditions/water shortage

Fluxes and Reservoirs

• Matter and energy circulate within or between systems
• A revisor serves as a storage location for water resources
• Uptakes refer to the resource entering the reservoir
• Influx is the resource entering the system, while outflux is the earth system leaving, and drawdown denotes the resource leaving reservoir
• Residence time indicates how long water remains in the reservoir

Watersheds & Drainage Basins

• Watershed delineation utilizes topographic maps to identify key features
• Outlets describe areas where water flows out
• High points are the tallest elevations
• Valleys are spots where contour lines dip and rise and ridges represent the highest possible elevation
• The entire area is considered the watershed

Drainage Basin and Catchment Hydrology Flow Paths

• Water drains into rivers or reservoirs
• The water table exists between unsaturated and saturated zones
• Pore water pressure equals the air pressure of overlying air
• Precipitation exits as surface water flow
• Topographic boundaries usually define catchment boundaries
• Rain or flowing water from upslope can enter subsurface permeable layers and discharge in another catchment
• Water infiltrates into the subsurface (unsaturated) via infiltration
• Water passes through the soil matrix or bypass to contribute to the surface water, known as "soil water flux"
• Soil water can be stored to the point of groundwater storage through percolation
• Slow sustained water flow describes the groundwater flow, which becomes water storage
• Water flows through rivers and streams as discharge, and channel precipitation falls directly on the stream
• Leakage occurs when water leaves via parts other than the outlet, due to incomplete sealing

Precipitation Processes & Types

• Liquid rain, solid snow, and freezing rain represent kinds of precipitation
• Silt occurs when what a liquid falls as, freezes on the way to the ground
• Hail forms as hard balls of ice in updrafts of thunderstorms
• Water vapor condenses to form clouds
• If clouds freeze, they become ice/snow

Bergeron Process

• Takes place in high, cold clouds at mid-latitudes with water in all three phases
• Ice crystals grow faster than water droplets
• A net movement of water vapor transpires to ice crystals
• Air mass cooling reaches the saturation point of ice prior to water
• Particles shift from high to low concentration
• Ice crystals expand, reducing molecules of water
• A net movement of water molecules transpires out of the liquid through droplet evaporation, and deposition of ice crystals transfers new water
• Tall cumulonimbus clouds see uplift in the cloud to create ice, descending as rain

Collision Coalescence

• Involves liquid water in low clouds below freezing
• Droplets collide, and break apart if they reach the maximum size (5 mm)
• Electrostatic charges drive this process
• Sole condensation is insufficient; collision is required for droplet enlargement

Interception & Forest Hydrology

• Gross precipitation refers to the amount of rain falling on the canopy per unit of time
• Interception is all the water stored on a plant's surface (rain, snow, or ice)
• Interception evaporation transpires when intercepted water evaporates off plants
• Transpiration describes evaporation through stomata (small pores in plants)
• Throughfall includes precipitation falling through canopy spaces, such as dripping from branches
• Stem flow is water flowing down the tree stem, and can be a large quantity since it is commonly more than the canopy water
• Net precipitation is the quantity of precipitation hitting the soil surface, made up of throughfall and steam flow
• Water enters soil through infiltration and moves through the unsaturated zone with percolation

Physical and Chemical Properties of Water

• Water’s molecules are polar and have a tetrahedral shape
• Electromagnetic oxygen molecules hold electrons closer than hydrogen bonds, creating slight negative oxygen and positive hydrogen charges
• Water bonds easily
• Hydrogen bonds connect Hydrogen (+) to Oxygen (-)
• Water travels up xylem via adhesion and cohesion
• Cohesion creates surface tension, allowing bugs to walk on water
• Powerful solvents can dissolve other molecules, especially polar and ironic compounds
• Water serves a solvent in kidneys
• Water expands and becomes less dense as it freezes, so ice floats due to hydrogen bonds
• Freezing involves a hydrogen bond break
• A lattice of hydrogen-bonded molecules is set

Specific Heat

• When 1g changes by 1 degree, this indicates absorbed or lost specific heat
• Water remains cool on a hot day, absorbing more heat without reaching super high temperatures
• It releases heat when cooling in the winter

Surface Tension Capillarity

• Kinetic energy causes random liquid particle arrangement
• Intermolecular attraction affects the surface
• Molecules pull each other in different directions underneath
• Molecules pull down and to the side at the surface, creating negligible intermolecular attraction and causing net downwards force
• Surface particles pull down, offset by compression resistance of the liquid causing the surface to be tightly compact
• Water droplets exhibit tension pulling towards the center, shaping them spherically

Latent Heat-Specific Heat Water

• Bonds break, transferring energy to molecules and quickening movement
• Temperature is a measure of the movement of molecules in water
• Heat absorbed first goes to breaking bonds, so there is no temperature increase

Rainfall Data & IDF Analysis

• Depth intensity assesses the quantity of rainfall (mm or inches)
• Rainfall intensity/rate outlines the rainfall depth over a given period, like mm/hr
• Light intensity is identified as less than 0.1mm/hr
• Light intensity rainfall events are usually long or longer
• Moderate intensity has a measurement of 0.1 to 0.3 mm/hr, and heavy has greater than 0.3 mm/hr, but are usually short

IDF Graph/Analyzing Curves

• The IDF represents Intensity Duration Frequency
• The x-axis showcases duration, the y-axis represents intensity and the curves showcase return period or Annual exceedance of likely rainfall
• The Annual exceedance probability (P) is the probability of rainfall recurring
• Probability of 0.5%-50% chance of recurring in any given year
• Return period (T) is the inverse of how likely rainfall can occur
• The duration increase increases proportionally with intensity
• Increased return periods see increased duration and decreased intensity
• This illustrates long rainfall events are not very intense

Evaporation & Evapotranspiration

• Evapotranspiration Penman-Monteith estimates parameters and their effect on actual evaporation
• Meteorological stations measure wind direction/speed, solar radiation, temp, relative humidity and precipitation with a tipping bucket
• Vapor pressure is measured, depending on saturation percentage, and is a function of temperature, changing as it does

Humidity and Rate

• Humidity rises, as relative humidity (RH) shifts from high when cold in the morning, to low while warm at midday
• Evaporation rate is a measurement of the energy it take to defuse water vapor in the atmosphere
• Physics estimate actual evaporation using demands in the atmosphere, and energy balance/transfer is neglected
• Aerodynamic resistance (Ra) is found when water vapor finds resistance diffusing into vegetation
• Resistance grows while intercepting evaporation, while rough surfaces give more wind with turbulent mixing and less resistance to evaporation
• Surface resistance (Rs) is a physiological resistance from plant structures controlling water vapor transpiration

Albedo/Refection Coefficient

• This measures the fraction of incoming radiation that is reflected
• Parts are absorbed- shortwaves, because the sun is at a high temp
• Outgoing- the longwave, because the earth has low temp
• Radiation at the surface measures the difference incoming net radiation and net outgoing radiation
• Net radiation (Rn) is used to warm the soil below
• Transfer of latent heat is caused by evaporation from the surface- with a positive score when directing away from it
• Evaporation is determined as the difference between measured saturation and water deficit

ET vs PET

• PET represents the theoretical conditions that show what could evaporate at maximum
• Those conditions are determined by temp, humidity and windspeed
• AET showcases what is realistically shown through evaporation, through influences like accessibility of water/atmospheric conditons
• High AET levels represent crop and low means drought levels, with soil sensors monitoring it
• Crops need different levels of water, so young crops get proper distribution like those in arid regions
• Etc is a value showing how much water is needed for crop evaporation

Snowpack Formation and Melting

• Processes include solid precipitation
• Larger snowflakes closer at 0 degrees
• Tiny ice crystals stick together at this point
• A condensation nucleus forms a pattern over sand/dirt through aerosols
• Snow becomes powdery/doesn't stick if it falls from cold air
• Formation happens through: water vapor+ nucleus+ T