1. Soil-water budgets  Considers all forms of soil moisture for a given region  Indicates how much moisture is available for plants

2. Components of soil-water budget  Precipitation input (PRECIP)  Actual evapotranspiration (ACTET)  Potential evapotranspiration (POTET)  Deficit (DEFIC)  Surplus (SURPL)  Soil-moisture storage (ΔSTRGE)

3. Evapotranspiration  Evaporation The change of liquid water into water vapor The change of liquid water into water vapor  Transpiration A cooling mechanism in plants A cooling mechanism in plants  Evapotranspiration is therefore the release of water vapor from plants in order to cool them  Evapotranspiration is highest on hot and sunny days

4. Potential Evapotranspiration  The amount of water that would be evapotranspired under specific temperature and moisture conditions  This measurement ignores whether water is available for transpiration or not  It is the DEMAND!

5. INPUTS OUTPUTS

6. Deficit  Will occur if the requirements for potential evapotranspiration are not met Surplus  Will occur if the requirements for potential evapotranspiration are met and there is extra moisture available

7. Soil moisture storage  Amount of moisture available to plants Change storage = amount of water taken from ST to help meet PE when P is lacking Change storage = amount of water taken from ST to help meet PE when P is lacking

8. Water balance technique  Precipitation (P) vs potential evapotranspiration (PE)  P = AE + S + ST  PE = AE + D  AE = amount of water actually used by plants so if water is in good supply AE = PE…. IF WATER IS LACKING THEN AE = P + ST

10. POTET

11. Determining water budgets  For each month the following can be plotted PRECIP PRECIP POTET POTET ACTET ACTET

13. Water Balance  Plants will not use more than PE  Once PE is used up plants will take it from ST

14. 1952 Mississippi JFMAMJJLASOND PE111.22.34.67.17.36.24.31.510.5 P3.53.15.52.33.20.32.12.71.20.32.74.6 P-PE2.52.14.30-1.4-6.8-5.2-3.5-3.1-1.21.74.1 ST66664.6000001.75.8 ∆ST0000-1.4-4.600001.74.1 AE111.22.34.64.92.12.71.20.310.5 D000002.25.23.53.11.200 S2.52.14.3000000000 1952 IS IT A WET OR A DRY YEAR?