Name:________________________________________________ Section:________________

Part 1: Soil Moisture Budget Tables and Graphs

1. Complete the water budget below for Stevens Point, Wisconsin (Table 9.4), a location with a rather different climate than Vancouver. Start calculations in the month following the black background and bold white ST value. Refer back to the sections above explaining the calculations for the Vancouver example whenever necessary. Remember to include the signs in the P-PE and DST blanks!

TABLE 9.4 Soil Moisture Budget for Stevens Point, Wisconsin

	Stevens Point, Wisconsin					45°N/90°W		Elev. 329 m				Fine sand			Field capacity = 102 mm
		JAN	FEB	MAR	APR		MAY		JUN	JUL	AUG		SEP	OCT		NOV	DEC	YR
P		28	27	47	70		99		99	90	100		102	60		57	34	812
PE		0	0	0	31		65		91	106	98		72	41		5	0	509
P-PE		+28	+27	+47	+39		+34		+8	-15	+2		+29	+18		+52	+34
DST		0	0	0	0		0		0	-15	+2		+13	0		0	0
ST		102	102	102	102		102		102	87	89		102	102		102	102
AE		0	0	0	31		65		91	105	98		72	41		5	0	509
D		0	0	0	0		0		0	0	0		0	0		0	0	0
S		28	27	47	39		34		8	0	0		16	18		52	34	303

2. Does Stevens Point have a wet or dry climate? How did you know?

Wet. Annual P > annual PE

3. September's P-PE is +30, but only 13 of this returns to the soil as DST.

a. How much of the 30 mm do we still need to account for? 16 mm

b. Where does this excess moisture go in September? To Surplus (runoff into streams)

4. a. What soil moisture season occurs for three quarters of the year in Stevens Point?

Surplus

b. What soil moisture season occurs in July at Stevens Point?

Utilization

5. In Figure 9.2, which site has the shortest duration (horizontal extent of shading) of runoff during surplus? Boulder (only 1.5 months)

6. In Figure 9.2, which site has the highest intensity (vertical extent of shading) of runoff during surplus? Vancouver (in December)

7. Seemingly at odds with what its graph indicates, there is a creek running through Boulder that has flooded several times in the months of July and August. How can this possibly occur, since Boulder receives insufficient precipitation in July and August to have runoff? Where could the floodwater come from? [Hint: consult a map of Colorado topography]

Boulder Creek is what we call an “exotic stream”. The water comes from elsewhere, not from local precipitation; in this case, from the high Rocky Mountains just west of Boulder.

8. Suppose Stevens Point experienced an unusual drought that started in July and lasted through the following February, and that during this time, Stevens Point received no precipitation whatsoever. If normal precipitation resumed in March, why would a drought not necessarily occur the following summer? The total precipitation for March through June is 315 mm, while the total PE for the same period is only 187 mm. The extra 128 mm of moisture, which normally would leave the site as runoff, instead would entirely replenish the soil to its 102 mm field capacity. While a drought would not occur, stream levels would be much lower because they would receive no moisture until June.

9. a. Viewing the maps in Figure 9.3, what states or provinces have the largest differences between annual PE and annual AE? California, Arizona, Sonora

b. What do the Annual P and Annual D maps in Figure 9.3 indicate as occurring in these areas? low precipitation and large deficit; this is a desert

c. Which of the five cities shown in Figure 9.3 has the largest difference between annual PE and AE? Refer to their tables (Tables 9.3, 9.4, 9.5a, 9.6, 9.7).

Boulder

d. Using the graphs in Figure 9.2, does the city you listed as an answer to part (c) also have the precipitation and deficit conditions that best match your answer to part (b)? yes

Figure 9.2 Soil Moisture Budget Graphs (Fine Sand for All Sites)

Figure 9.3 Annual Soil Moisture Budget Variables Maps for North America (in mm/yr)

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part 2: Comparative Field Capacities

1. Complete the first water budget below for Houston, Texas (Table 9.5a). Notice differences occur by changing the soil texture. The first ledger is for fine sand, and the second is for silty loam. Start your calculations in the month following the black background and bold white ST.

TABLE 9.5 Two Soil Moisture Budgets for Houston, Texas

30°N/095°W

Elevation 19 m

Fine sand

Field capacity = 102 mm

JAN

FEB

MAR

APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

YR