Streamflow contributions from tribal lands to major river basins of the United States

Abstract

While many studies on tribal water resources of individual tribal lands in the United States (US) have been conducted, the importance of tribal water resources at a national scale has largely gone unrecognized because their combined totals have not been quantified. Thus, we sought to provide a numerical estimate of major water budget components on tribal lands within the conterminous US and on USGS hydrologic unit codes (HUC2) regions. Using existing national-scale data and models, we estimated mean annual precipitation, evapotranspiration, excess precipitation, streamflow, and water use for the period 1971–2000. Tribal lands represent about 3.4 percent of the total land area of the conterminous US and on average account for 1.9 percent of precipitation, 2.4 percent of actual evapotranspiration, 0.95 percent of excess precipitation, 1.6 percent of water use, and 0.43 percent of streamflow origination. Additionally, approximately 9.5 and 11.3 percent of US streamflow flows through or adjacent as boundaries to tribal lands, respectively. Streamflow through or adjacent to tribal lands accounts for 42 and 48 percent of streamflow in the Missouri region, respectively; and for 86 and 88 percent in the Lower Colorado region, respectively. On average, 5,600 million cubic meters of streamflow per year was produced on tribal lands in the Pacific Northwest region, nearly five times greater than tribal lands in any other region. Tribal lands in the Great Lakes, Missouri, Arkansas-White-Red, and California regions all produced between 1,000 and 1,400 million cubic meters per year.

Projecting Surface Water Area Under Different Climate and Development Scenarios

“…The U.S. Geological Survey (USGS) uses a hierarchical system to delineate hydrologic units using hydrologic unit codes (HUCs) (Seaber et al., 1987). Water resource regions (HUC02s) are the first level in the hierarchy, and they are the drainage areas for major rivers or a series of rivers (Blasch et al., 2018; Seaber et al., 1987). Subregions (HUC04s) are the second level of classification and are nested within the water resource region.…”

Effects of Climate and Anthropogenic Drivers on Surface Water Area in the Southeastern United States

“…This study estimates percent surface water area at the resolution of the 310 eight‐digit hydrologic unit code watersheds (hereafter, “HUCs” or “watersheds”; right map, Figure 1; Duan et al., 2017) in the southeastern U.S. The watersheds can be aggregated into four water resource regions (two‐digit hydraulic unit codes; lower left map, Figure 1), which represent drainage areas of major rivers or a series of rivers (Blasch et al., 2018; Seaber et al., 1987). The water resource regions are the first of six levels of hydrologic units in the hydrologic unit system developed by the U.S. Geological Survey (USGS) and the watersheds are the fourth level in the hierarchical system (Seaber et al., 1987).…”