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HYDROLOGIC CYCLE & WATER BUDGETS

A. INTRODUCTION

• Already examined: 

  • evaporation

  • moisture transport

  • condensation & cloud formation

  • precipitation

• What happens to precipitation?

• Water budget: local scale examination of the gains, uses, and losses of water

 

B. WATER ON EARTH'S SURFACE

Arrival

• direct precipitation on surface (bare ground), in rivers, lakes, oceans, glaciers

• interception by plants

Fate

• evaporation, overland flow (surface runoff), infiltration
  

Soil Water

• infiltration & percolation

  • permeability

  • porosity

• zone of aeration

  • soil water storage

  • plant uptake & transpiration
    

  • evaporation

  • throughflow

• water table

• zone of saturation

  • groundwater flow

  • aquifer

Stream Flow

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C. WATER BALANCE

Gains: precipitation Soil moisture storage Losses: utilization and evapotranspiration actual evapotranspiration (AE) potential evapotranspiration (PE) Simple water balance     moisture abundant environments P > PE and therefore AE = PE moisture limited environments P < PE and therefore AE < PE seasonal moisture environments

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D. CALCULATING A MONTHLY WATER BUDGET

P:	precipitation	DST:	change in storage
PE:	potential evapotranspiration	AE:	actual evapotranspiration
P - PE:		D:	deficit PE - AE
ST:	soil moisture storage (field capacity)	S:	surplus (AE = PE, ST = field capacity, and   excess P is available)

 

Water Budget for Kingsport, Tennessee
	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
P	97	99	97	84	104	97	132	112	66	66	66	99	1119
PE	7	8	24	57	97	132	150	133	99	55	12	7	781
P-PE	90	91	73	27	7	-35	-18	-21	-33	11	54	92	XXX
DST	0	0	0	0	0	-35	-18	-21	-26	11	54	35	XXX
ST	100	100	100	100	100	65	47	26	0	11	65	100	XXX
AE	7	8	24	57	97	132	150	133	92	55	12	7	774
D	0	0	0	0	0	0	0	0	7	0	0	0	7
S	90	91	73	27	7	0	0	0	0	0	0	57	345

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E. SUMMARY

• Water on the earth's surface may:

  • evapotranspire (go to the atmosphere)

  • infiltrate the soil

  • be used by plants

  • become groundwater flow

  • become surface runoff

  • become stream flow

• Water balance - accounting of:

• how much water comes in (P)

• how much water the atmosphere can take away (PE), and

• how much water the atmosphere actually takes away (AE)

• Deficits: times of stress for plants and animals

• Surplus: times of potential flooding (and stress to humans)