trends in precipitation and stream discharge over the past century for the continental united states...
TRANSCRIPT
Trends in Precipitation and Stream Discharge over the Past Century for the
Continental United States
Andrew Simon1 and Lauren Klimetz1,2
1USDA-ARS National Sedimentation Laboratory, Oxford, MS2Dept. Of Civil and Environmental Engineering, U. of Tennessee, Knoxville, TN
National Sedimentation Laboratory
Background and ContextThe National Sedimentation Laboratory has been conducting research
in support of U.S. EPA to determine “background” or “reference” rates of suspended-sediment transport in the continental United
States.• “Reference” defined as a “stable” (not static) channel where sediment
delivered from upstream can be transported through the reach without the channel aggrading, degrading widening or
narrowing over a period of years;
• Because of differences across the country in climate, topography, geology and land use, a regional approach was required;
• Level III Ecoregions were used.
Level III Ecoregions and Available Data
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Example: EPA Region 8
Example “Reference” Yield
MIDDLE ROCKIES ECOREGION 17
ME
AN
AN
NU
AL
SU
SP
EN
DE
DS
ED
IME
NT
YIE
LD
, IN
T/y
/km
2
1
10
100
UnstableStable
Median annualsediment yieldof stable sites
is 5.07 T/y/km2
10th
Percentile25th
Percentile50th
Percentile75th
Percentile90th
Percentile
However…• Questions raised about how current flow and transport
conditions may be different from historical, sampling periods;
• In Oklahoma, a mean-annual precipitation difference between wet and dry periods of 33% led to a 100% difference in runoff, which in turn led to a 183% difference in sediment yield. (Garbrecht, 2008);
• Results not surprising as more sediment moves at higher discharges;
• The question becomes do wet periods cause transport ratings to shift ?... AND/OR
• Do they de-stabilize channel systems?
Transport Ratings
06452000WHITE RIVER NEAR OACOMA,SD
1970s
L = 232 Q 1.59
r2 = 0.72
1980s
L = 52.5 Q 1.74
r2 = 0.76
2000s
L = 21.6 Q 1.88
r2 = 0.84
1990s
L = 49.45 Q 1.62
r2 = 0.82
0.1
1
10
100
1000
10000
100000
1000000
10000000
0.1 1 10 100 1000 10000
DISCHARGE, IN CUBIC METERS PER SECOND
LO
AD
, IN
TO
NN
ES
PE
R D
AY
06426500 BELLE FOURCHE RIVERBELOW MOORCROFT, WY
1976-1979
L = 37.4 Q 1.38
r2 = 0.90
1980-1982
L = 26.8 Q 1.23
r2 = 0.83
1990-1993
L = 30.92 Q 1.40
r2 = 0.89
1986-1987
L = 32.2 Q 1.44
r2 = 0.87
0.001
0.01
0.1
1
10
100
1000
10000
100000
0.0001 0.001 0.01 0.1 1 10 100
DISCHARGE, IN CUBIC METERS PER SECOND
LO
AD
, IN
TO
NN
ES
PE
R D
AY
Stable Ratings
Unstable Ratings
Precipitation Data
U.S. Historical Climatology Network (USHCN) operated by the National Climatic Data Center (NCDC) of NOAA;
http://www.ncdc.noaa.gov/oa/climate/research/ushcn/ushcn.html
Source:
Details:
• More than 1,000 station nationwide
• Monthly data to nearest 0.01”
• Does not differentiate between rainfall and snowfall
Discharge Data
U.S. Geological Survey gauging station records
http://nwis.waterdata.usgs.gov/nwis/dv
Source:
Details:
• More than 6,000 stations nationwide
• Used more than 2,900 (with minimum 30 suspended-sediment samples and associated instantaneous discharge)
• Mean-daily data to three significant figures
Summary of Data
Level III Ecoregion
Period of average annual
water yield
Maximum number of
water yield sites
Average annual water
yield in m3/s/km2
15 Northern Rockies 1929 -2006 15 0.01589 17 Middle Rockies 1924 - 2006 42 0.00995 42 Northwestern Glaciated Plains 1935 - 2007 31 0.002 43 Northwestern Great Plains 1911 - 2007 126 0.0001 46 Northern Glaciated Plains 1929 - 2006 27 0.00034
48 Lake Agassiz Plain 1932 - 2005 14 0.00169
Level III Ecoregion
Period of average annual
precipitation record
Maximum number of
precipitation sites
Average annual
precipitation in mm/y
15 Northern Rockies 1899 - 2006 12 590 17 Middle Rockies 1888 - 2006 22 384 42 Northwestern Glaciated Plains 1891 - 2006 19 379 43 Northwestern Great Plains 1889 - 2006 33 389 46 Northern Glaciated Plains 1888 - 2006 23 530 48 Lake Agassiz Plain 1891 - 2006 8 509
Precipitation(mm)
• All but ER 42 increasing
• Dust Bowl Era
• Wet period in 1990’s
Water Yield(m3/s/km2)
Shows combined effects of changes in
precipitation and anthropogenic influences
• All Ecoregions except ER 46* and ER 48 show less discharge per unit area
• Indication of significant human impacts
Annual Departure from Long-Term Mean Water Yield
(%)• Trends for all Ecoregions show decrease, except ER 46* and 48
• Most secondary peaks around 1970
• Less discharge per unit area
Water Retention: Dam
Construction Summary
DECADE
CU
MU
LA
TIV
E N
UM
BE
R
OF
DA
MS
PE
R S
QU
AR
E K
IL
OM
ET
ER
0.00001
0.0001
0.001
0.01
Ecoregion 15Ecoregion 17Ecoregion 42Ecoregion 43Ecoregion 46Ecoregion 48
NU
MB
ER
OF
DA
MS
CO
NS
TR
UC
TE
D
0
500
1000
1500
2000Ecoregion 15Ecoregion 17Ecoregion 42Ecoregion 43Ecoregion 46Ecoregion 48
DECADE
1
10
100
1000
Figure 9 Decadal trends in the number of dams constructed in each of the Mountain and Plains
Ecoregions (left) and the cumulative number of dams per unit drainage area (right).
DECADE
CU
MU
LA
TIV
E N
UM
BE
R
OF
DA
MS
PE
R S
QU
AR
E K
IL
OM
ET
ER
0.00001
0.0001
0.001
0.01
Ecoregion 15Ecoregion 17Ecoregion 42Ecoregion 43Ecoregion 46Ecoregion 48
NU
MB
ER
OF
DA
MS
CO
NS
TR
UC
TE
D
0
500
1000
1500
2000Ecoregion 15Ecoregion 17Ecoregion 42Ecoregion 43Ecoregion 46Ecoregion 48
DECADE
1
10
100
1000
Figure 9 Decadal trends in the number of dams constructed in each of the Mountain and Plains
Ecoregions (left) and the cumulative number of dams per unit drainage area (right).
•Reached peak retention per unit area
• Farm Bill led to significant upstream retention
1970-1980
Potential Human Impacts
• construction of thousands of dams
• agriculture
• logging
• surface mining
• coal-bed methane production
• channelization
• irrigation, tile drainage
Decadal Trends (Wet/Dry Periods)
Ecoregion 1900-1910
1911-1920
1921-1930
1931-1940
1941-1950
1951-1960
1961-1970
1971-1980
1981-1990
1991-2000
2001-2007
15 - - - - + + = = + + = 17 = + = - = - + = = + - 42 + = = - = - - = = + + 43 = + = - + - + + = + - 46 + = - - + - = = = + = 48 + = - - + = = - = + =
Ecoregion 1900-1910
1911-1920
1921-1930
1931-1940
1941-1950
1951-1960
1961-1970
1971-1980
1981-1990
1991-2000
2001-2007
15 n/a = + - = + = - - + - 17 n/a + + = + + + + - - - 42 n/a - - = + + + + - - - 43 n/a + + - = - - - - - - 46 n/a n/a n/a - - - = = - + + 48 n/a = - - - - = = - + +
Precipitation
Water Yield (m3/s/km2)
By 1970-1980, Ecoregions 17, 42 and 43 have the most dams
Water Yield Per Unit of Precipitation
Summary of Changes Over Past 100 Years
Note: * denotes that data period started during the 1920’s or 1930’s (Dust Bowl Era), resulting in higher than expected increases.
*
(in mm) (in percent) (m3/s/km2) (in percent)
15 Northern Rockies 85.9 15.7 -0.00026 -1.63 -26.4
17 Middle Rockies 4.01 1.04 -0.01066 -68.9 -81.8
42 Northwestern Glaciated Plains -7.74 -2.04 -0.00045 -20.6 -84.9
43 Northwestern Great Plains 24.7 6.35 -0.00131 -79.1 -74.4
46 Northern Glaciated Plains 11.1 2.09 0.00082 3043* 1070*
48 Lake Agassiz Plain 45.5 8.94 0.00261 353 0
Change in precipitation over 100 year period
Change in water yield over 100 year period
Level III Ecoregion
Change in water yield per unit
precipitation (in percent)
National Context
Winter: December – February
Spring: March – May
Summer: June – August
Autumn: September - November
Seasonal Breakdowns:
Seasonal Changes in Precipitation: 100 Years
Spring Summer
Autumn Winter
Change in Precipitation (Percent)
Change in Precipitation (mm)
Seasonal Changes in Water Yield: 100 Years
Spring Summer
Autumn Winter
Change in Water Yield (Percent)
Change in Water Yield Per Unit Precipitation
Indicative of Human Impacts
Median Suspended-Sediment Concentrations
42
63
6469
68
23
16
84
10
23
58
4
84
23
1
23
17
51
62
58
17
32
84
57
23
17
57
63
38
41
62
76
2
49
58
36
37
28
77
50
3
53
61
64
6059
8
66
48
32
79
6
33
82
19
74
52
7812
31
40
44
30
40
69
16
34
11
56
1015
51
23
55 70
83
4
58
7
72
54
29
1
39
25
5
9
81
67
18
20
71
73
14
75
21
17
46
80
50
35
6
26
45
24
42
25
22
47
27
13
65
43
14
74
43
65
13
27
47
22
25
42
24
45
26
6
35
50
80
46
17
21
75
14
73
71
20
18
67
81
9
5
25
39
1
29
54
72
7
58
4
83
7055
23
51
1510
56
11
34
16
69
40
30
44
40
31
1278
52
19
82
33
6
79
32
48
66
8
5960
64
61
53
3
50
77
28
37
36
58
49
2
76
62
41
38
63
57
17
23
57
84
32
17
58
62
51
17
23
1
23
84
4
58
23
23
44
10
84
16
23
68
69 64
63
42
Median Suspended-Sediment Yields
Summary and Conclusions• EPA 8: Although increased precipitation, significant reductions in water yield in the four western
ecoregions due to human impacts; well below average since the 1970s-80s when most dam construction in the region was completed.
• EPA 8: Changes in precipitation combined with human-induced changes have caused dramatic shifts in discharge rates such that historically diverse ecoregions now provide similar amounts of water (per unit drainage area) to streams (ie. Middle Rockies similar to the Northwestern Great Plains).
National Context• Most of the U.S. experiencing more precipitation than 100 years ago.• Dramatic shifts in timing: More in autumn, much less in winter nationwide.• Although numerous regions are experiencing significantly more precipitation, discharge per unit area has
been drastically reduced in many areas, particularly west of the Mississippi River.• The drastic reductions in water yield can be largely attributed to human impacts given the general increase
in precipitation in these regions. This probably has significant effects on geomorphic and ecological processes, and habitat.