Abstract. Runoff-based indicators of terrestrial water availability are appropriate for humid regions, but have tended to limit our basic hydrologic understanding of drylands – the dry-subhumid, semiarid, and arid regions which presently cover nearly half of the global land surface. In response, we introduce an indicator framework that gives equal weight to humid and dryland regions, accounting fully for both vertical (precipitation + evapotranspiration) and horizontal (groundwater + surface-water) components of the hydrologic cycle in any given location – as well as fluxes into and out of landscape storage. We apply the framework to a diverse hydroclimatic region (the conterminous USA) using a distributed water-balance model consisting of 53 400 networked landscape hydrologic units. Our model simulations indicate that about 21% of the conterminous USA either generated no runoff or consumed runoff from upgradient sources on a mean-annual basis during the 20th century. Vertical fluxes exceeded horizontal fluxes across 76% of the conterminous area. Long-term-average total water availability (TWA) during the 20th century, defined here as the total influx to a landscape hydrologic unit from precipitation, groundwater, and surface water, varied spatially by about 400 000-fold, a range of variation ~100 times larger than that for mean-annual runoff across the same area. The framework includes but is not limited to classical, runoff-based approaches to water-resource assessment. It also incorporates and reinterprets the green- and blue-water perspective now gaining international acceptance. Implications of the new framework for several areas of contemporary hydrology are explored, and the data requirements of the approach are discussed in relation to the increasing availability of gridded global climate, land-surface, and hydrologic data sets.

Flow-duration curves of simulated A, daily mean discharge; and B, minimum daily discharge at streamflow-gaging stations-Queen River at Exeter (QRPB), Queen River at Liberty (QRLY), and Usquepaug River near Usquepaug (USQU)made with the Hydrologic Simulation Program-FORTRAN

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Elevation, as used in this report, refers to distance above the vertical datum.

Accurate accounting of irrigation water use is an important part of the U.S. Geological Survey National Water-Use Information Program and the WaterSMART initiative to help maintain sustainable water resources in the Nation. Irrigation water use in the humid eastern United States is not well characterized because of inadequate reporting and wide variability associated with climate, soils, crops, and farming practices. To better understand irrigation water use in the eastern United States, two types of predictive models were developed and compared by using metered irrigation water-use data for corn, cotton, peanut, and soybean crops in Georgia and turf farms in

Cranberry Pond and Woods Lake are small, acidic headwater lakes in the west-central Adirondack region of New York State. The lakes differ in size and depth but have similar watershed characteristics. Both watersheds contain thin eolian and sandy till deposits overlying granitic gneiss and have limited capacity to store and transmit groundwater. Total lake inflow was calculated as a residual of a monthly hydrologic balance based on measured precipitation, lake outflow, change in lake storage, and estimated evaporation; surface-water and groundwater inflow to each lake also were estimated. Results indicate that the lakes are hydrologically similar and are dominated by surface-water systems with highly variable runoff that responds rapidly to precipitation. Groundwater, which constituted about 16% of the total inflow to Cranberry Pond and from 31 to 38% of the total inflow to Woods Lake in 1984–86, moves through a shallow flow system that provides little stabilizing influence on the hydrology or water chemistry of the lakes. Error analysis of the hydrologic balance indicated that total annual inflow, calculated as a residual of the hydrologic balance, is accurate to within 12%. Calculated monthly inflow values are subject to greater potential error that ranges up to 46%.