Estimated mean annual contribution to water supply from units of... Forest System (NFS) of the U.S. Forest Service
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18 September 2009 Water supply from the national forests 1 Estimated mean annual contribution to water supply from units of the National Forest System (NFS) of the U.S. Forest Service Thomas C. Brown and Pamela Froemke Rocky Mountain Research Station Fort Collins, Colorado In the two tables below we provide estimates of annual contribution to water supply from units of the NFS in the 48 contiguous states. These estimates were computed by overlaying ALP (Automated Lands Project) boundaries for the NFS units obtained in July 2009 1 onto the spatially distributed estimates of water supply that were produced for a 2008 publication by Brown et al. about the source of the U.S. water supply. 2 The total contribution from the NFS administrative units (based on the proclamation boundaries) reported here (329,525 million cubic meters per year) differs from that reported in Brown et al. (325,691 Mm3/yr) because of recent changes (both additions and corrections) to the ALP NFS boundary layer. 3 Brown et al. (2008) provided estimates of the contribution to water supply for states and major river basins. Estimates for smaller geographical units such as national forests were not released by Brown et al. because of concerns about the accuracy of the model at smaller spatial scales, especially in portions of the western U.S. These concerns arose because of two types of data limitations, as described below. Although the concerns remain, we nevertheless are providing the estimates because they may be the best that are currently available and may be useful for large-scale planning purposes. Table 1 provides estimates of mean annual contribution to water supply and surface area for 116 NFS units in the coterminous U.S. Table 2 summarizes the estimates for the eight NFS regions to which the units belong. In both tables, estimates are provided for administrative (proclamation) boundaries and for NFS ownership boundaries. In all but four cases the administrative area is larger than the ownership area, which is expected because the administrative area includes non-NFS private in-holdings. The four exceptions occur because the administrative boundaries for those units have not yet been fully updated in the ALP database to reflect recent changes. 1 The ALP is an ongoing project of the Forest Service to, among other things, update GIS coverages of land boundaries. 2 Brown, Thomas C., Michael T. Hobbins, and Jorge A. Ramirez. 2008. Spatial distribution of water supply in the coterminous United States. Journal of the American Water Resources Association 44(6):1474-1487, available at: www.fs.fed.us/rm/value/research_cpl.html. 3 For the analysis we converted both the ALP polygons and the 5 km water supply grid to congruent 250 m grids. 18 September 2009 Water supply from the national forests 2 A full explanation of the methodology used to estimate mean annual water supply is included in Brown et al. (2008). Here we briefly summarize some of the key points and qualifications: · · · · · · These estimates of mean annual contribution to water supply are based on data for 1953-94, which may not represent current or future hydrologic conditions. There is considerable year-to-year variation about the means reported here, variation that is not at all evident in the means. “Water supply” as used here was computed as precipitation minus natural evapotranspiration. (Evaporation occurs as water evaporates from soil and vegetation surfaces. Transpiration occurs as vegetation gives up water vapor to the atmosphere through small openings called stomata, principally in the process of photosynthesis.) Estimating water supply in this way makes the assumption that water entering the soil that is not evaporated or transpired eventually becomes available for use either by naturally returning to the surface at some point downstream or by being pumped to the surface. Evapotranspiration was estimated using computer models that rely on data from weather stations (for variables such as solar radiation, wind speed, and humidity). Values of weather variables for areas between stations were estimated by spatial interpolation. In addition, precipitation for areas between weather stations was estimated. Weather stations are particularly sparse in mountainous areas of the West. This estimation between stations introduces errors in the estimates of water supply. Such errors are more likely when applying the model to small areas, which may contain few or no weather stations within the boundary. In selected watersheds—relatively pristine watersheds that have stream gages at the outlet—the models were tested for accuracy and were further refined by comparing predicted water supply to measured streamflow. Natural discharge data were lacking for some areas of the U.S., especially in drier portions of the West, which hampered testing and refinement. The estimates of water supply for NFS units could not be tested for accuracy because of the lack of strategically located stream gages. Because of these limitations, the estimates of water supply originating in NFS units are indeed “estimates”, most appropriately used for large scale planning. To provide some perspective for these estimates of water volume, please consult the tables in the Appendix of the Brown et al. (2008) publication (see footnote 2), where it is seen, for example, that the NFS units in Montana and Colorado are estimated to provide 61% and 68%, respectively, of the water supply originating in those states in an average year. Across the 11 contiguous western states the NFS provides 51% of the water supply, with other federal lands yielding another 15%. 18 September 2009 3 Water supply from the national forests Table 1. Mean annual contributions to water supply from units of the NFS, arranged by region NFS unit Beaverhead-Deerlodge NF Bitterroot NF Clearwater NF Custer NF Dakota Prairie Grasslands Flathead NF Gallatin NF Helena NF Idaho Panhandle NF Kootenai NF Lewis and Clark NF Lolo NF Nez Perce NF Arapaho-Roosevelt NF Bighorn NF Black Hills NF Cimmaron NG Comanche NG Grand Mesa-Uncompahgre-Gunnison NF Medicine Bow-Routt NF Nebraska NF Pawnee NG Pike-San Isabel NF Rio Grande NF San Juan NF Shoshone NF Thunder Basin NG White River NF Apache-Sitgreaves NF Carson NF Cibola NF Coconino NF Coronado NF Gila NF Kaibab NF Lincoln NF Prescott NF Santa Fe NF Tonto NF Ashley NF Boise NF Bridger-Teton NF Caribou-Targhee NF NFS unit code State 102 103 105 108 118 110 111 112 104 114 115 116 117 208 202 203 218 219 201 206 207 222 212 209 213 214 224 215 301 302 303 304 305 306 307 308 309 310 312 401 402 403 415 MT MT ID MT ND/SD MT MT MT ID MT MT MT ID CO WY SD KS KS CO WY/CO NE CO CO CO CO WY WY CO AZ NM NM AZ AZ NM AZ NM AZ NM AZ UT ID WY ID Water volume 3 (Mm /yr) Admin Own bdy bdy 3165 3008 2650 2611 7330 7028 1006 980 100 45 7358 6998 3078 2652 1000 879 8025 7043 4952 4547 2804 2706 5000 4364 5305 5259 1276 1474 1244 1237 150 123 0 0 21 5 2954 3454 2701 2389 65 45 55 12 1600 1493 2021 2043 2372 1565 2920 2901 13 7 3070 2267 693 672 736 712 119 102 465 440 469 445 486 475 263 253 276 237 182 146 923 877 464 452 1189 1185 4811 4412 5460 5413 4442 4287 Area (1000 acres) Admin bdy 3567 1664 1951 1281 2747 2631 2157 1163 2895 2566 2001 2622 2252 1717 1112 1536 342 1117 3154 2697 2062 768 2505 1946 2094 2469 1820 2482 2110 1588 3215 2011 1776 3387 1601 1262 1411 1807 2968 1401 2599 3467 3071 Own bdy 3338 1595 1827 1188 1257 2348 1812 975 2445 2200 1864 2111 2224 1728 1105 1243 108 444 3526 2104 1052 192 2224 1708 1553 2438 551 1812 2016 1487 1841 1824 1663 3269 1549 1095 985 1643 2867 1378 2262 3420 2900 18 September 2009 NFS unit Dixie NF Fishlake NF Humboldt-Toiyabe NF Manti-La Sal NF Payette NF Salmon-Challis NF Sawtooth NF Uinta NF Wasatch-Cache NF Angeles NF Cleveland NF Eldorado NF Inyo NF Klamath NF Lake Tahoe Basin Mgt Unit Lassen NF Los Padres NF Mendocino NF Modoc NF Plumas NF San Bernardino NF Sequoia NF Shasta-Trinity NF Sierra NF Six Rivers NF Stanislaus NF Tahoe NF Columbia River Gorge NSA Colville NF Deschutes NF Fremont-Winema NFs Gifford Pinchot NF Malheur NF Mt Baker-Snoqualmie NF Mt Hood NF Ochoco NF Okanogan-Wenatchee NF Olympic NF Rogue River-Siskiyou NF Siuslaw NF Umatilla NF Umpqua NF Wallowa-Whitman NF Willamette NF Chattahoochee-Oconee NF 4 Water supply from the national forests NFS unit code State 407 408 417 410 412 413 414 418 419 501 502 503 504 505 519 506 507 508 509 511 512 513 514 515 510 516 517 622 621 601 602 603 604 605 606 607 617 609 610 612 614 615 616 618 803 UT UT NV UT ID ID ID UT UT CA CA CA CA CA CA/NV CA CA CA CA CA CA CA CA CA CA CA CA OR/WA WA OR OR WA OR WA OR OR WA WA OR OR OR OR OR OR GA Water volume 3 (Mm /yr) Admin Own bdy bdy 563 539 754 707 3092 2875 840 794 5140 4967 4401 4373 2582 2534 772 718 2759 1819 99 94 0 0 1806 1416 671 660 5184 4991 304 272 1880 1507 274 255 2477 2117 68 64 2525 2033 268 221 2290 2180 7640 5843 3517 3274 6102 5614 3867 3114 3169 2209 101 109 1844 1459 2286 2186 972 874 10261 9364 753 712 16310 14596 6610 6405 183 180 11230 10747 7306 6779 10617 10053 4593 3454 2255 2143 3418 3297 2395 2329 9778 9170 5225 2830 Area (1000 acres) Admin bdy 1965 1533 6791 1414 2433 4332 2190 984 1908 701 561 793 2041 1887 197 1487 1908 1073 2022 1430 808 1162 2707 1415 1082 1090 1179 24 1316 1869 2810 1506 1544 1958 1104 1155 4192 691 1837 699 1511 1030 2382 1794 1734 Own bdy 1886 1453 6256 1340 2343 4288 2110 890 1247 662 423 604 1984 1691 176 1151 1731 915 1679 1202 671 1114 2132 1320 974 898 825 27 1064 1609 2255 1374 1468 1729 1062 967 3940 630 1716 523 1406 986 2253 1683 866 18 September 2009 NFS unit Cherokee NF Daniel Boone NF Francis Marion-Sumter NF George Washington-Jefferson NF Kisatchie NF Land Between the Lakes NRA NFs in Alabama NFs In Florida NFs In Mississippi NFs In North Carolina NFs In Texas Ouachita NF Ozark-St Francis NF Allegheny NF Chequamegon-Nicolet NF Chippewa NF Green Mountain-Finger Lakes NF Hiawatha NF Hoosier NF Huron-Manistee NF Mark Twain NF Midewin National Tallgrass Prairie Monongahela NF Ottawa NF Shawnee NF Superior NF Wayne NF White Mountain NF NFS unit code State 804 802 812 808 806 860 801 805 807 811 813 809 810 919 913 903 920 910 912 904 905 915 921 907 908 909 914 922 TN KY SC VA LA KY/TN AL FL MS NC TX AR AR PA WI MN VT MI IN MI MO IL WV MI IL MN OH NH Total Water volume 3 (Mm /yr) Admin Own bdy bdy 2956 1644 4196 1447 2053 979 5835 2989 1915 1135 314 322 2882 1504 2208 1986 5303 2711 8850 4026 2594 891 4433 3354 2547 1928 1842 1275 2194 1681 805 344 2475 1219 1633 1158 1031 314 2709 1267 3630 1748 30 20 4642 2583 2234 1370 1231 474 2173 1366 1432 397 2986 2644 Area (1000 acres) Admin bdy 1222 2043 1377 3459 1029 167 1289 1328 2343 2978 1923 2382 1522 741 2001 1598 836 1263 646 1989 3087 27 1659 1514 740 3181 852 922 Own bdy 643 710 630 1781 608 171 670 1186 1193 1244 677 1783 1156 513 1520 673 400 868 201 964 1514 18 906 956 285 2072 235 800 329525 211357 169074 Table 2. Mean annual contributions to water supply by NFS region NFS Region 1 2 3 4 5 6 8 9 Total 5 Water supply from the national forests 3 Water volume (Mm /yr) Admin bdy Own bdy 51,772 48,119 20,460 19,015 5,077 4,810 36,804 34,622 42,142 35,863 90,912 83,855 51,311 27,747 31,048 17,862 329,525 271,892 Area (1000 acres) Admin bdy Own bdy 29,497 25,183 27,821 21,788 23,136 20,239 34,087 31,773 23,542 20,152 27,422 24,693 24,796 13,320 21,056 11,925 211,357 169,074 271892
