The desert research institute (DRI) prepared this work as part of the klamath river revised natural flow study (krrnfs)

The Desert Research Institute (DRI), operating under the Nevada System of Higher Education, received a $488,329 Cooperative Agreement from the Bureau of Reclamation under the SECURE Water Act – Research Agreements program (CFDA 15.560) awarded September 15, 2025, with a completion date of September 30, 2028. DRI is delivering evapotranspiration (ET) analysis and geospatial datasets to support the Klamath River Revised Natural Flow Study (KRRNFS), a comprehensive natural streamflow assessment commissioned by the Department of the Interior in 2020. The work specifically produces annual estimates of actual ET, effective precipitation, and net ET for croplands and wetlands; groundwater ET from phreatophyte shrubland vegetation; and supporting geospatial datasets characterizing irrigated areas, irrigation system types, and cropland field boundaries throughout the Klamath River Basin.

These products are designed to quantify the hydrologic budget and consumptive water use necessary for hydrologic modeling activities conducted by the Bureau of Reclamation's Technical Service Center. The resulting natural streamflow estimates and underlying datasets are intended to support downstream applications in habitat studies, drought planning, and water supply allocation decision-making throughout the Klamath River Basin, advancing scientific understanding of basin hydrology by improving upon previous natural flow estimates and incorporating recommendations from the National Research Council.

In 2020 as part of the klamath basin science initiative, the united states (U.S.) department of the interior (DOI) tasked reclamation with estimating refined natural streamflow estimates throughout the klamath river basin in a comprehensive natural flow study (NFS). For the NFS, we define natural streamflow as the streamflow that would have occurred in the absence of land use changes (agriculture, forestry, etc.), major development (roads, railroads, municipalities, etc.), and water management (dams, hydroelectric plants, etc.). This study aims to advance science in the klamath river basin, and thereby support future analyses and studies throughout the basin. Primarily, the krrnfs leverages current science, data, methods, and tools to develop revised natural streamflow estimates for the klamath river basin, while improving upon limitations of previous estimates (reclamation, 2005 hardy addley, 2006) and incorporating comments provided by the national research council (NRC) (2008). The resulting natural streamflow estimates may be of use in habitat studies, drought planning, and water supply allocation decision making. This report describes the evapotranspiration task to support the krrnfs with the development of annual estimates of 1) actual ET (ETA), effective precipitation, and net evapotranspiration (ET) for croplands, 2) ETA and net ET for wetlands, 3) groundwater ET (ETG) from phreatophyte shrubland vegetation. This work included the development of numerous supporting and derived geospatial datasets describing irrigated area, irrigation system type, and cropland field boundary extents. These datasets are fundamental for quantifying the hydrologic budget, consumptive water use, and model boundary conditions that will support conceptual and numerical modeling activities being conducted by the bureau of reclamations technical service center (TSC) and the USGS to arrive at daily naturalized streamflow estimates in the klamath river basin over water years 19812020.this work improves on previous analyses which relied on assumed or static rates of ET and effective precipitation, through the application of the best available science which combines cutting-edge cloud-computing, manually-edited agricultural field boundaries depicting the maximum irrigated extent, long-term remote sensing data provided by landsat (19852020), and daily calculations of meteorological conditions produced by gridmet (19792020). The produced data were dynamic over the period of study and represent real, on-the-ground conditions of the study area. The primary results from this effort are compiled into a series of field specific .CSV files which are formatted for use in modeling and analysis using computer scripting languages. The data produced by the ET task may be aggregated to irrigation districts or to hydrologic units as suitable for analysis and implementation into the krrnfs. The crop ET and effective precipitation estimates were provided for the purpose of estimating surface water irrigation deliveries. Irrigation delivery and wetland ET estimates are primary inputs in the development of natural streamflow estimates for the klamath river basin.