Soil-water budgetsSoil-water budgets

Considers all forms of soil moisture for a Considers all forms of soil moisture for a given regiongiven region

Indicates how much moisture is available Indicates how much moisture is available for plantsfor plants

Components of soil-water budgetComponents of soil-water budget

Precipitation input (PRECIP)Precipitation input (PRECIP) Actual evapotranspiration (ACTET)Actual evapotranspiration (ACTET) Potential evapotranspiration (POTET)Potential evapotranspiration (POTET) Deficit (DEFIC)Deficit (DEFIC) Surplus (SURPL)Surplus (SURPL) Soil-moisture storage (Soil-moisture storage (ΔΔSTRGE)STRGE)

EvapotranspirationEvapotranspiration

EvaporationEvaporation The change of liquid water into water vaporThe change of liquid water into water vapor

TranspirationTranspiration A cooling mechanism in plantsA cooling mechanism in plants

Evapotranspiration is therefore the release Evapotranspiration is therefore the release of water vapor from plants in order to cool of water vapor from plants in order to cool themthem

Evapotranspiration is highest on hot and Evapotranspiration is highest on hot and sunny dayssunny days

Potential EvapotranspirationPotential Evapotranspiration

The amount of water that would be The amount of water that would be evapotranspired under specific evapotranspired under specific temperature and moisture conditionstemperature and moisture conditions

This measurement ignores whether water This measurement ignores whether water is available for transpiration or notis available for transpiration or not

It is the DEMAND!It is the DEMAND!

INPUTS OUTPUTS

Deficit Deficit

Will occur if the requirements for Will occur if the requirements for potential evapotranspiration are not potential evapotranspiration are not metmet

SurplusSurplus

Will occur if the requirements for Will occur if the requirements for potential evapotranspiration are met potential evapotranspiration are met and there is extra moisture availableand there is extra moisture available

Soil moisture storageSoil moisture storage

Amount of moisture available to plantsAmount of moisture available to plants Change storage = amount of water taken Change storage = amount of water taken

from ST to help meet PE when P is lackingfrom ST to help meet PE when P is lacking

Water balance techniqueWater balance technique

Precipitation (P) vs potential Precipitation (P) vs potential evapotranspiration (PE)evapotranspiration (PE)

P = AE + S + STP = AE + S + ST PE = AE + DPE = AE + D AE = amount of water actually used by AE = amount of water actually used by

plants so if water is in good supply AE = plants so if water is in good supply AE = PE…. IF WATER IS LACKING THEN AE PE…. IF WATER IS LACKING THEN AE = P + ST= P + ST

POTET

Determining Determining water budgetswater budgets

For each month For each month the following can the following can be plottedbe plotted PRECIPPRECIP POTETPOTET ACTETACTET

Water BalanceWater Balance

Plants will not use more than PEPlants will not use more than PE

Once PE is used up plants will take it from Once PE is used up plants will take it from STST

1952 Mississippi

J F M A M J JL A S O N D

PE 1 1 1.2 2.3 4.6 7.1 7.3 6.2 4.3 1.5 1 0.5

P 3.5 3.1 5.5 2.3 3.2 0.3 2.1 2.7 1.2 0.3 2.7 4.6

P-PE 2.5 2.1 4.3 0 -1.4 -6.8 -5.2 -3.5 -3.1 -1.2 1.7 4.1

ST 6 6 6 6 4.6 0 0 0 0 0 1.7 5.8

∆ST 0 0 0 0 -1.4 -4.6 0 0 0 0 1.7 4.1

AE 1 1 1.2 2.3 4.6 4.9 2.1 2.7 1.2 0.3 1 0.5

D 0 0 0 0 0 2.2 5.2 3.5 3.1 1.2 0 0

S 2.5 2.1 4.3 0 0 0 0 0 0 0 0 0

1952 IS IT A WET OR A DRY YEAR?