The Physical Environment
                                          Contents | Glossary | Atlas |  Index | TPE Today | Google Earth | Search

The Hydrosphere

Soil Moisture Utilization

Table 10.5 Soil Moisture Utilization - Rockford, IL
Field Capacity = 90 mm

J

F

M

A

M

J

J

A

S

O

N

D

Year

P

50

49

66

78

100

106

88

84

86

73

56

45

881

PE

0

0

5

40

84

123

145

126

85

44

8

0

531

P-PE

50

49

61

38

16

-17

-57

-42

1

29

48

45

 

ΔST

0

0

0

0

0

-17

-57

-16

1

29

48

12

ST

90

90

90

90

90

73

16

0

1

30

78

90

AE

0

0

5

40

84

123

145

100

85

44

8

0

634

D

0

0

0

0

0

0

0

26

0

0

0

0

26

S

50

49

61

38

16

0

0

0

0

0

0

33

258

By the time June rolls around, temperatures have increased to the point where evaporation is proceeding quite rapidly and plants are requiring more water to keep them healthy. As potential evapotranspiration is approaching its maximum value during these warmer months, precipitation is falling off. During June P-PE is -17 mm. What this means is precipitation no longer is able to meet the demands of potential evapotranspiration. In order to meet their needs, plants must extract water that is stored in the soil from the previous months. This is shown in the table by a value of 17 in the cell for ΔST (change in soil storage).  Once the 17 m is taken out of storage (ST) it reduces its value to 73.

The month of June is considered a dry month (P<PE) so AE is equal to precipitation plus the absolute value of ΔST (P + |ΔST|). When we complete this calculation (106 mm + 17 mm = 123 mm) we see that AE is equal to PE. What this means is precipitation and what was extracted from storage was able to meet the needs demanded by potential evapotranspiration. Note that there is no surplus in June as the soil moisture storage has dropped below its field capacity. There is still no deficit as water remains in storage. The calculations for July is similar to June, just different values. Note that by the time July ends, water held in storage is down to a mere 16 mm.

Previous | Continue    


 

Contents |Glossary | Atlas Index  |  Blog | Podcast | Google Earth | Search Updates | Top of page

About TPE | Who's Used TPE |  Earth Online Media

Please contact the author for inquiries, permissions, corrections or other feedback.

For Citation: Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
Date visited.  https://www.earthonlinemedia.com/ebooks/tpe_3e/title_page.html

©2003 - 2016 Michael Ritter (tpeauthor@mac.com)
Last revised 6/5/12