File:fcetms6 nov13-03
Effect of land use change on estimates of evapotranspiration for Fall Creek NY
and southern NY based on difference between precipitation and stream discharge,
1926-1993.
D. R. Bouldin, S. D. Klausner, and Mark Cutts, SCAS,CALS, Cornell University,
Ithaca, NY
Abstract
Over the last 70 years, land use has changed dramatically in central NY. Land in
farms has gone from about 75% to about 35% of the land area in the period 1925
through 1992. The objective of this ms is to investigate how this change in land
use has impacted annual water yield/ evapotranspiration (ET). ET was estimated
as the difference between precipitation and stream discharge on a n annual basis
for 5 watersheds in central NY. One watershed, Fall Creek, was studied for the
period 1926 through 1992. Four other watersheds were studied for the period
1935 through 1957, during which time three were partially reforested by planting
evergreen seedlings and one was kept as a control. For Fall Creek the regression
of ET on time was not statistically significant at the 5% probability level. With the
other 3 watersheds, only the regression for the control watershed (not reforested)
was significant at the 5% probability level. Probably the ET on forested land
would need to exceed that on hay/ pasture/ tilled land by about 10% to have
significant effects on ET. Averages for the 5 watersheds were: precipitation =40
inches, steam flow=23 inches, ET=17.
For the most part the reforestation and abandoned agricultural land has
occurred on soils which are shallow to bedrock or have root restricting horizons
within the order of 25 to 50 cm; this means that grass, trees and other vegetation
have about the same rooting depth. During the summer months of June, July and
August, potential ET exceeds precipitation inputs by about 2.75 inches (70 mm)
on average. Probably the ET for all vegetation is not very different most years
because they all have about the same amount of water at their disposal and ET
exceeds seasonal precipitation. Hence differences in leaf area, reflection
coefficients, roughness etc. have little impact on ET under these conditions in
southern NY
Introduction
During the last 70 years, land use in the central NY region has changed
drastically (Stanton and Bills,1996). Tompkins County is typical of this region
and the following describes some changes which have occurred. In 1925 on the
order of 75% of the land was in farms and about 40% of the farm land was
cropland (hay and other crops) and about 60 % was pasture and woodland.
Currently about 30% of the land is in farms with most of the rest classed as
wooded or as abandoned farmland .
A subject of interest is how the changes in vegetation have influenced the
annual discharge (“water yield’) of the watershed. In NY about 50% of the
precipitation leaves as stream flow and the remainder is evaporated either from
the soil or plant leaves (collectively referred to as evapotranspiration or ET). Thus
the simplest annual water balance sheet contains 4 components: precipitation
2
inputs, annual discharge, evapotranspiration and any differences in soil water
storage at the beginning and end of the water year. The expectation is that changes
in annual discharge as a consequence of changes in vegetation should be primarily
the result of changes in ET. Substantial attention has been given to the effect of
reforestation and deforestation on water yield and other changes in vegetation
cover (Hewlett, 1967 and Bruijnzeel, 1996 are two summaries). Where water is
not limiting ET, reductions of as much as 400 mm per year in ET have been
observed when forests are clear cut and/ or replaced by grass and annual crops, but
when water is limiting the reductions have been much less (Bruijnzeel, 1996,
Shachori et al, 1967, Pereira, H.C. 1967a, Douglass, J. E. 1967, Hibbert, A. R.
1967, Pereira, A. C. 1967b).
Fall Creek, 1926-93
During the period 1926 through 1993, daily discharge records for Fall
Creek are available. This creek and its watershed are typical of the central NY
region. Precipitation data (PPT) is available for several locations in the watershed
or adjacent to the watershed. Thus yearly evapotranspiration (ET) can be
estimated as annual precipitation minus annual discharge for the Fall Creek
watershed. The temporal changes in ET can be used to examine the effects of land
use change on ET.
The objective of this discussion is a)to document precipitation, discharge
and ET as the difference between precipitation and discharge, b) to document
land use changes and c) to discuss the effects of land use changes on ET for the
period 1926-1993 for the Fall Creek NY watershed d)discuss these results in
relation to other data in central NY.
The Fall Creek watershed lies in the cool-temperate zone of the US with a
humid, continental climate. Elevations range from about 600 m in the northern
and eastern parts to 380 m at the gauging station near Forest Home. At the higher
elevations the soils are derived from acid or low lime glacial till while at the lower
elevations and along streams the soils are derived from a spatially complex
mixture of glacial outwash and lacustrine and alluvial deposits. The
unconsolidated mantle is underlain at variable depths by gently dipping siltstones
and shales. The area of the watershed is 337 km2 (126 mile2). Its location in NY is
illustrated in Figure 1.
Daily discharges for Fall Creek from 1926 to the present are tabulated in
the various USGS publications dealing with stream discharge records. At the
Forest Home gauging station, the stream flows through a small gorge cut in the
shale bedrock. The control section is a notched concrete dam. The water from the
control section flows through about 40 meters of the gorge before a drop of 3 to 5
meters to the slack pool of a small lake. USGS classifies the discharge records as
good.The major inaccuracy is likely to result from ice jams that occur in some
years during thaws. This is usually a short-term effect (less than 1 day) because of
the relatively short distance from the control section to the drop in elevation to the
slack pool; counteracting this is the fact that usually the gage height is high,
estimated flow is high and yet actual flow through the ice jam may be low. The
nature of the geology and configuration of the drainage basin indicate that
3
Figure 1. Outline map of Fall Creek watershed and location
of town boundaries.
avg_p_d
In c h e s p e r m o n t h
5
4
Ppt
3
Flow
2
PET
1
0
Jan
Mar May Jul
Month
S ept Nov
Figure 2. Precipitation, flow, estimated potential ET
For the period 1970-94 for Fall Creek.
File:D:\fcet\cum.w b2:tab1
Table 1.
Yearly precipitation (PPT), stream flow and estimates of ET as difference
and 5 year moving averages, inches.
4
-------------yearly-------------------Five year moving average---Stream
ET
stream
ET
Year
PPT
flow
ppt-flow
PPT
flow
ppt-flow
1926-27
38.0
24.7
13.3
NA
NA
NA
1927-28
40.1
25.3
14.8
NA
NA
NA
1928-29
34.4
18.3
16.0
NA
NA
NA
1929-30
43.1
25.5
17.6
NA
NA
NA
1930-31
30.3
13.3
17.0
37.2
21.4
15.8
1931-32
35.7
18.1
17.7
36.7
20.1
16.6
1932-33
31.6
16.8
14.8
35.0
18.4
16.6
1933-34
33.5
15.7
17.7
34.8
17.9
17.0
1934-35
32.4
17.5
15.0
32.7
16.3
16.4
1935-36
48.1
28.8
19.4
36.3
19.4
16.9
1936-37
32.7
16.9
15.8
35.7
19.1
16.5
1937-38
39.7
25.5
14.2
37.3
20.9
16.4
1938-39
36.7
20.4
16.2
37.9
21.8
16.1
1939-40
29.7
9.9
19.7
37.4
20.3
17.1
1940-41
35.8
22.1
13.7
34.9
19.0
15.9
1941-42
35.3
17.6
17.8
35.4
19.1
16.3
1942-43
42.2
22.9
19.3
35.9
18.6
17.3
1943-44
39.4
21.9
17.5
36.5
18.9
17.6
1944-45
38.5
21.3
17.2
38.2
21.1
17.1
1945-46
47.5
26.8
20.7
40.6
22.1
18.5
1946-47
40.6
18.0
22.5
41.6
22.2
19.5
1947-48
42.8
25.0
17.8
41.7
22.6
19.2
1949-49
39.4
19.1
20.3
41.7
22.0
19.7
1949-50
38.5
16.0
22.5
41.7
21.0
20.7
1950-51
40.2
28.2
12.0
40.3
21.3
19.0
1951-52
33.4
17.1
16.3
38.8
21.1
17.7
1952-53
37.4
18.0
19.4
37.7
19.7
18.1
1953-54
30.7
12.1
18.5
36.0
18.3
17.7
1954-55
40.1
22.8
17.3
36.3
19.7
16.7
1955-56
39.2
18.7
20.5
36.1
17.7
18.4
1956-57
34.0
21.8
12.2
36.2
18.7
17.6
1957-58
39.3
15.9
23.4
36.6
18.3
18.4
1958-59
42.0
28.0
14.0
38.9
21.4
17.5
1959-60
40.9
21.9
19.1
39.1
21.3
17.8
1960-61
34.3
18.0
16.3
38.1
21.1
17.0
1961-62
40.6
22.1
18.5
39.4
21.2
18.2
1962-63
33.6
15.5
18.1
38.3
21.1
17.2
1963-64
34.2
17.6
16.6
36.7
19.0
17.7
1964-65
27.7
10.5
17.3
34.1
16.7
17.3
1968-66
28.4
13.5
14.9
32.9
15.8
17.1
1966-67
33.6
15.1
18.5
31.5
14.4
17.1
1967-68
38.1
19.4
18.7
32.4
15.2
17.2
1968-69
39.1
19.4
19.7
33.4
15.6
17.8
1969-70
37.9
17.3
20.6
35.4
16.9
18.5
1970-71
44.9
25.7
19.2
38.7
19.4
19.3
1971-72
36.4
19.6
16.8
39.3
20.3
19.0
1972-73
47.5
31.6
15.9
41.2
22.7
18.4
1973-74
38.1
21.2
16.9
41.0
23.1
17.9
1974-75
38.2
20.9
17.4
41.0
23.8
17.2
1975-76
43.3
24.4
18.8
40.7
23.5
17.1
1976-77
42.0
26.9
15.1
41.8
25.0
16.8
1977-78
51.4
34.5
16.9
42.6
25.6
17.0
1978-79
33.2
17.7
15.5
41.6
24.9
16.7
1979-80
33.5
16.1
17.4
40.7
23.9
16.7
1980-81
31.5
15.6
15.9
38.3
22.2
16.2
1981-82
43.7
27.1
16.7
38.7
22.2
16.5
1982-83
29.2
14.2
15.0
34.2
18.1
16.1
1983-84
41.6
24.7
16.9
35.9
19.5
16.4
1984-85
38.1
22.4
15.7
36.8
20.8
16.0
1985-86
34.2
15.4
18.8
37.4
20.8
16.6
1986-87
37.0
18.2
18.9
36.0
19.0
17.0
1987-88
36.0
15.5
20.5
37.4
19.2
18.2
1988-89
34.3
13.2
21.1
35.9
16.9
19.0
1989-90
38.8
21.1
17.7
36.1
16.7
19.4
1990-91
44.1
26.3
17.9
38.1
18.8
19.2
1991-92
33.2
13.5
19.7
37.3
17.9
19.4
1992-93
49.6
33.4
16.1
40.0
21.5
18.5
Average
37.8
20.3
17.5
5
Table 2. Statisticall characteristics of yearly precipitation (ppt)
flow and evapotranspiration (ET). All in inches
ppt
flow
ET
Mean
37.76
20.29
17.47
Standard Error
0.63
0.65
0.29
Median
38.06
19.40
17.37
Standard Deviation
5.16
5.34
2.35
Minimum
27.72
9.94
11.96
Maximum
51.40
34.47
23.38
Confidence
intervall(0.95)
1.23
1.28
0.56
File:archive\fcet\tab3.doc
Table 3. Regressions of ET on time (years since 1926)
and time and precipitation.
ET on time and ppt
Regression Output:
Constant
14.7
Std Err of Y Est
2.3
R Squared
0.038
No. of Observations
67
Degrees of Freedom
64
Time
ppt
X Coefficient(s)
0.016
0.061
Std Err of Coef.
0.015
0.056
ET on time
Regression Output:
Constant
Std Err of Y Est
R Squared
No. of Observations
Degrees of Freedom
X Coefficient(s)
Std Err of Coef.
16.9
2.3
0.020
67
65
0.017
0.015
5 year moving average
45
40
35
in c h e s
ET
30
PPT
25
20
flow
15
10
0
10
20 30 40 50
Years since 1926
60
70
Figure 3. Five year moving average of precipitation,
flow and ET plotted against time since 1926.
6
P e rc e n t o f l a n d
100
Woodland
80
60
40
20
Corn + small grain
+hay +pasture
0
1920
Corn + sm all grain
1940
1960
Years
1980
2000
Figure 4. aggregated land use in Fall Creek extrapolated
from Tompkins County data.
“leakage” around the gauging station is likely to be very small on a percentage
basis and in any event will not change with time.
The precipitation was estimated by the Thiessen method (Linsley et al. ,
1975, p82). During the period several different stations were used because of
incomplete records. During the period 1926 through 1939, the 3 stations were
Ithaca, Cortland and Auburn. Since then these plus others were used for various
periods depending upon availability of records.
Shown in Figure 2 is the average monthly precipitation, flow and
estimated potential evapotranspiration (PET). PET is estimated as 0.8 of pan
evaporation at Ithaca. During the summer months, stream flow is much less than
precipitation because of ET. Note that PET exceeds PPT by a substantial amount
during the summer. The total PET in excess of PPT amounts to about 2.8 inches
summed over June, July and August; during this interval the vegetation must
utilize stored soil water in addition to current precipitation and hence the rooting
depth and soil water storage capacity in the rooting depth becomes critical. In the
period October through February, the stream flow is still less than precipitation
because the depleted soil water is being recharged and some is stored as ice and
snow during December, January and February. During March and April, flow
exceeds precipitation because of melting snow and ice.
Thus the soil and aquifer storage is replenished each year. The ending
period of each water year was selected at some time during late March or early
April (when daily ET is usually small) based on the following criteria: 3 or more
days since last precipitation event and cumulative discharge since last
precipitation event approximately equal to last precipitation input. Usually the
discharge during the last day of the water year was 3 mm or less when distributed
over the whole watershed area. Thus the expectation is that the amount of stored
water is the same at the end of each water year and hence the difference between
annual precipitation and annual discharge is an estimate of ET.
Table 1 lists the precipitation, discharge and ET for the period 1926
through 1993. A statistical characterization of these data are listed in Table 2. A
7
20 year moving average is shown in Figure 3. Finally the regression on years since
1926 are shown in Table 3. Inclusion of precipitation in the regression of ET on
time did not improve the amount of variation explained by regression.
The data in Figure 3 and Table 3 indicate there are no large temporal
changes in any of the 3 variables over the 67 years of record. The more
interesting observation is that the differences in land use described above seem
not to have influenced ET. However, as illustrated by the data in Table 2, there
are large differences among years which may obscure temporal changes. To
investigate the data further, the statistical characteristics of the first and last 20
years are presented in Table 4. Based on this data, the precipitation, flow and ET
are not different based on the 95% confidence intervals of the means. The 95%
confidence interval for the means is about 5% of the mean ET. Thus it appears
that any temporal changes are less than 5%.
Documentation of the vegetation cover for the Fall Creek watershed
during the period is uncertain. First, Agricultural Statistics includes only land in
farms and thus the fraction of the area documented has changed from about 75%
to 30% over the period of interest. Second, the watershed is part of 3 counties and
7 towns, as illustrated in Figure 1. Unfortunately no consistent set of data for any
of the above is available for the whole period and hence some approximations
were made.Three sources of data were used: a) data on the watershed b)data on
Tompkins County with the expectation that it was representative of the watershed
and c) data on averages for the towns of Dryden and Groton in Tompkins County
and Summerhill in Cayuga Counties which constitute a large part of the
watershed and the watershed is a substantial part of each. Based on a summary of
soil characteristics in 1935, the soils, farmland and land use in the towns of
Dryden, Virgil and Summerhill are similar and about equal to those of Tompkins
County as a whole. In the town of Groton, 90 % of the area was in the better land
classes compared to 65% of the whole county. Thus the soils in the Fall Creek
watershed are, on the average, better than the county as a whole.
Figure 4 is a graphical presentation of the results of several
approximations. The aggregation of vegetation cover/ land use for Figure 4 was as
follows. For purposes of effects on ET we have chosen a) “Corn + small grain”
which includes most of the land under active annual cultivation b) “corn + small
grain + hay + pasture” which includes most land in active agriculture (note that
the Agricultural Statistics includes hay but not pasture in their description of crop
land and c) “woodland” (farm and non-farm). The data for woodland in 1930 is
based on a detailed survey summarized by Lewis (1933). The data for woodland
in 1958 is based on Stout (1958) and for 1992 a linear extrapolation of the above
two points. The difference between the sum of the latter two ((b) + (c)) and total
area is mostly inactive/ abandoned agricultural land.
Other watersheds in central NY
A study was carried out in the central NY area on the effects of
reforestation on stream discharge (Schneider and Ayer, 1961). This data is from
the same region as Fall Creek and the climates are similar. Most of the area had
been cleared before 1900 but by 1933 substantial parts were abandoned farmland.
8
Briefly, in the period 1934 through 1941, gauging stations and precipitation
monitors were established in 4 watersheds. In three of the watersheds, from 35 to
58% of the watersheds were reforested by planting mostly with pine and spruce
while a 4th watershed was not reforested and served as a control. Monitoring of
stream flow and precipitation continued through 1957. In the meantime the trees
were allowed to grow and by 1957 the reforested areas had developed into
coniferous woodlands. Their location is shown in Figure 5. A brief description of
the watersheds follows.
The Sage Brook watershed is located near South New Berlin in Chenango
County , east of Norwich and near the border of Otsego County. The area is 1.80
km2 ( =0.7 mile2 ). Elevation ranges from 590 to 436 m. The trees were planted
in 1932 and stream gauging and precipitation measurements were begun in 1933.
The Cold Spring Brook watershed is located near China in Delaware
County near the Chenango-Broome County lines. The area is 3.89 km2 (=1.51
mile2 ). Elevation ranges from 665 to 452 m. Most of the trees were planted in
1934 and some additional trees were planted in 1940. Precipitation and stream
monitoring was begun in 1935
The Shackham Brook watershed in located near Truxton in southern
Onondaga County NY. The area is 8.04 km2 ( =3.12 mile2 ). Elevation ranges
from 610 to 393 m. Trees were planted in 1931 and 1932 with replanting in 1934
and 1939. Precipitation and stream gauging was begun in 1933.
The Albright Creek watershed is located near East Homer in Cortland
County north of Cortland. The area is 18.3 km2 ( =7.08 mile2 ). Elevation ranges
from 616 to 352 m. This watershed was not planted and the vegetation cover-land
use remained constant doing the period 1948-58. (See table 1602-1).
The data for Fall Creek from 1934 through 1957 was included for
reference. In the following tables and figures, these areas are referred to as
“Cold”, “Sage”, “Shack”, “Albright” and “Fall”, respectively.
Listed in Table 5 are statistical characteristics of the data. Because of the
differences in lengths of record, the data for all 5 watersheds for the period 194158 common to all were subjected to an analysis of variance (two way table
without replication) These analyses are presented in Tables 6. Finally regressions
of ET on time and precipitation are shown in Table 7. The types of cover in the
watersheds in shown in Table 8.
First, the statistical characteristics of the 5 location was similar with
respect to means and errors. Second, the analysis of variance shows the ET to be
not different among the watersheds at the 10% level although precipitation and
flow were different among the locations at the 5% level or higher (Table 6).
Finally, the regressions of ET on time were not significant at the 5% level except
for the Albright Creek area which was designated as a control (table 7). ET
increased in it but not in the ones which had been reforested.
9
Figure 5. Location of USGS watersheds.
File:c:\archive\fcet\tab5.doc
Table 5. Descriptive statistics for the 5 watersheds. Std Err = standard error of the
mean, Min=minimum, max= amximium, C.I.(0.95)= 95% confidence interval of
mean.
Descriptive statistics, Precipitation
Fall
Albright
Shack
Sage
Cold
Mean
960
1067
1030
978
1030
Std Err
24
27
26
26
30
Min
753
848
752
816
765
Max
1222
1246
1244
1255
1387
C.I. (0.95)
48
53
51
51
58
Descriptive statistics, Flow
Fall
Albright
Shack
Sage
Cold
Mean
512
602
628
535
616
Std Err
24
26
25
24
27
Min
252
415
418
328
353
Max
730
769
839
856
875
C.I. (0.95)
48
51
49
48
52
Descriptive statistics, ET
Fall
Albright
Shack
Sage
Cold
Mean
448
465
403
444
415
Std Err
15
20
17
14
22
Min
304
335
273
352
197
Max
572
652
619
549
599
C.I. (0.95)
29
40
33
27
43
10
File:D:\fcet\allforet:aov_eng
c:\archive\fcet\tab6ms.doc
Table 6a. Analysis of variance for all locations for 1941-57
Analysis of Variance, Precipitation, 1941-1957
Source of Variation
df
MS
F
P-value
Years
16
63.79
5.18 9.5E-07
Locations
4
39.16
3.18
0.0191
Error
64
12.32
Total
84
Analysis of Variance, Flow, 1941-1957
Source of Variation
df
MS
F
Years
16
65.07
8.87
Location
4
60.59
8.26
Error
64
7.33
Total
84
P-value
7.1E-11
1.9E-05
Analysis of Variance, ET, 1941-1957
Source of Variation
df
MS
F
P-value
Years
16
25.29
3.33 3.10E-04
Locations
4
12.51
1.65 1.73E-01
Error
64
7.59
Total
84
F@5%
1.80
2.52
F@5%
1.80
2.52
F@5%
1.80
2.52
Table 7. Regressions of ET on time and precipitation.
Y= a + b*years + c*precipitation where a, b and c
are regression coefficients. Ns= coefficients
significant at 5% level, *, ** coefficients significant
at 5 and 1% level respectively.
Location
Fall
Albright
Sage
Shack
Cold
a
b
10.31 0.036, ns
4.39
0.32*
8.61 0.081,ns
2.99 0.141,ns
0.96
0.02,ns
c
0.182,ns
0.261,ns
0.204,ns
0.273*
0.384**
d.f.
21
15
20
21
18
R^2
0.099
0.42**
0.20*
0.25*
0.37**
Discussion
The substance of the analyses of the Fall Creek data and the 4 watersheds
in the reforestation study is that changes in land use/ reforestation have not much
impact on ET as calculated by precipitation minus discharge. This calculated ET
is subject to many uncertainties: those associated with errors in measurement of
precipitation and discharge as well as substantial variation as a consequence of
year to year variation in weather. The statistical characteristics of the data shows
that the 95% confidence of the mean is about 5% of the mean. Thus if 50% of the
land is changed from agriculture/ abandoned agriculture to forest, ET of the
forested land would need to be increased about 10% so that the resulting
differences for the whole watershed would be about 5%.
The soils in the non-Fall Creek watersheds have similar characteristics: all
are underlain with sandstone or shale, the soil is developed in glacial till of
11
variable depth, substantial parts of the watersheds are shallow to bedrock, the
surface horizon is friable silt loam underlain by a relatively dense layer (referred
to as a “fragipan” in soil taxonomy) which impedes drainage and root penetration.
The Volusia-Mardin-Lordstown soil association is the predominant
association in the Albright Creek watershed and Shackham Brook watershed (Soil
Survey Report for Cortland county). The description of this association is a s
follows: “ Consists of gently sloping to sloping somewhat poorly drained Volusia
soils, moderately well-drained Mardin soils and shallow or moderately deep, welldrained Lordstown soils. The soils are strongly acid and low in fertility. The
Volusia and Mardin soils have a fragipan beginning at depths ranging from 15 to
17 inches. Depth to bedrock in the Lordstown series ranges from 10 to 40 inches,
with most in the range of 30 to 36 inches”.
A fragipan is a compact horizon,, rich in silt, sand or both, and generally
low in clay. The fragipan commonly interferes with root penetration. When dry
the compact material appears to be indurate but the apparent in duration
disappears when the soil is moistened.
The Mardin soils have a firm, dense fragipan that impedes drainage and
restricts rooting at a depth of 15 to 24 inches. The Volusia soils are similar except
the fragipan is at a depth of 10 to 16 inches. A seasonal high water table is
perched on this pan at a depth of 6 to 12 inches. The net effect is that these soils
are too wet in the spring for timely cultural operations and too dry in the summer
because of restricted rooting depth.
In a general discussion of yearly ET on a watershed basis, Linsley et al
emphasize a) solar radiation is the source of the approximately 600 cal of energy
required to evaporate 1 g of water and b)that the primary factors influencing
differences in ET are amount and nature of plant cover and the amount of
available water in the root zone.
Considering the nature of the plant cover in relation to ET, woodland and
non-woodland vegetative cover combined with the restricted rooting depth
referred to above will insure that ET will be restricted in most years to
precipitation during the summer months plus the same amount of stored water.
The result is that ET is not very different among the different vegetative covers.
Note that the results illustrate that in most years, deficits of available water will
limit ET to less than potential. Statistically, the variation in ET among years was
large enough to obscure any temporal effects. If we accept the statistical analysis
associated with the analysis of variance, ET differences of more than 5% would
have been statistically significant. If the ET for woodland is on the order of 10%
higher than for hay or pasture then converting 50% of the area of a watershed
from pasture/hay to woodland would change overall ET by 10%.
In the Fall Creek watershed in 1930, substantial areas of soils similar to
those in the watersheds studied by Schneider and Ayer were in farms and planted
to pasture and hay crops. Currently most of these soils are no longer farmed
because of low inherent productivity. The current farmland in the Fall Creek
watershed is on the more productive soils and land use on these soils is probably
not very different from 1930 to the present (e.g. corn, small grains, alfalfa). Thus
12
the net effect is that vegetative cover has changed from pasture/ hay to abandoned
farm land on those soils with restricted rooting depth and hence limited ability to
supply water to vegetation during the drier summer months. The net effect is no
major change in ET with changing land use in the Fall Creek watershed.
References:
Lewis, A. B. 1933. An economic study of land utilization in Tompkins county,
NY. PhD Thesis, Cornell University Library. Ithaca NY. 14853.
Neely, J. A., E. D. Giddings and C. S. Pearson. 1965. Soil Survey of Tompkins
County, NY. United States Department of Agriculture, Soil Conservation
Service.
Howe, F. B., H.O. Buckman and H. G. Lewis. 1924. Soil Survey of Tompkins
county, NY. United States Department of Agriculture. Bureau of Soils.
Bonsteel, J. A. , E. O. Fippin and W. T. Carter. 1906. Soil Survey of Tompkins
County , NY. United States Department of Agriculture. Bureau of Soils.
Linsley, R. K. , M. A. Kohler and J.L.K. Pulhus. 1975. Hydrology for Engineers.
McGraw-Hill. NY.NY.
Schneider, W. J. and G. R. Ayer. 1961. Effect of reforestration on stream flow in
central New York. Geological Survey Water-Suppy Paper 1602. 61pp.
Stanton, B. F. and N. L. Bills. 1996. The return of agricultural lands to forests.
E.B.96-03. Department of Agricultural, Resource, and Managerial Economics,
College of Agriculture and Life Sciences. Cornell University. Ithaca NY 148537801.
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waste and the environment. Ann Arbor Science Publishers. Ann Arbor. MI.
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Shachori, a., D. Rosenzweig, and A. Poljakoff-Mayber. 1967.Effect of
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tropical watersheds. in W. E. Sopper and H. W. Hull eds. International
symposium on forest hydrology. Pergamon Press. NY. pp435-450.
13
Douglass, J. E. 1967. Effects of species and arrangement of forests on
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Pereira, A. C. 1967b. Summary of forests and runoff session. in W. E. Sopper and
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