SME
Hydrology · Problem type
Monthly surplus and deficit
Use this for “A basin’s rain and potential ET are given for each month. When does the soil dry out, and by how much?”
Record and look
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
mm
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Precipitation
80
70
75
70
65
55
45
50
60
75
85
90
Potential ET
10
15
35
60
95
125
140
120
80
45
20
10
Precipitation
Potential ET
Where PET passes precipitation (May to Sep here), soil water runs down by 285 mm in all; where precipitation passes PET, 350 mm refills it or runs off.
Tap a bar at the height you want.
Assumptions
•
Potential ET (PET) is what plants and soil would give off if water never ran short.
•
Where PET passes precipitation, the shortfall comes out of soil water; where rain passes PET, the extra refills it or runs off.
•
A made-up mid-latitude basin, in mm of water each month.
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