Upper Rio Grande Basin water-resource status and trends: Focus area study review and synthesis

Authors: Mankin, Kyle; RUMSEY, CHRISTINE - Us Geological Survey (USGS); SEXSTONE, GRAHAM - Us Geological Survey (USGS); IVAHNENKO, TAMARA - Us Geological Survey (USGS); HOUSTON, NATALIE - Us Geological Survey (USGS); CHAVARRIA, SHALEENE - Us Geological Survey (USGS); SENAY, GABRIEL - Us Geological Survey (USGS); FOSTER, LINZY - Us Geological Survey (USGS); THOMAS, JONATHAN - Us Geological Survey (USGS); FLICKINGER, ALLISON - Us Geological Survey (USGS); GALANTER, AMY - Us Geological Survey (USGS); MOESER, C - Us Geological Survey (USGS); WELBORN, TOBY - Us Geological Survey (USGS); PEDRAZA, DIANA - Us Geological Survey (USGS); LAMBER, PATRICK - Us Geological Survey (USGS)

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2022
Publication Date: 8/1/2022
Citation: Mankin, K.R., Rumsey, C.A., Sexstone, G.A., Ivahnenko, T.I., Houston, N.A., Chavarria, S.B., Senay, G.B., Foster, L., Thomas, J.V., Flickinger, A.K., Galanter, A.E., Moeser, C.D., Welborn, T., Pedraza, D.E., Lamber, P.M. 2022. Upper Rio Grande Basin water-resource status and trends: Focus area study review and synthesis. Journal of the ASABE. 65(4):881-901. https://doi.org/10.13031/ja.14964.
DOI: https://doi.org/10.13031/ja.14964

Interpretive Summary: The Upper Rio Grande Basin (URGB) is a critical international water resource under pressure from a myriad of climatic, ecological, infrastructural, water-use, and legal constraints. This study summarizes how water resources (snow, evapotranspiration, streamflow, and groundwater) have varied across the Basin over the past three decades. A snow model used to simulate snowpack in the northern, high-elevation regions of the Basin found snowpack has declined from -35 to -75 mm (as liquid water) per decade with widespread variability across elevations and land-cover types. Over the same three-decade period, model results showed that evaporation from all land-cover types has declined from -14 to -80 mm per decade. A technique to use water chemistry to separate streamflow into surface (runoff) and subsurface (baseflow) contributions found baseflow ranging from 29 to 69% (49% average) of total streamflow at 17 sites upstream of Albuquerque, NM. Groundwater-flow models showed a decline in storage for much of the Basin. Observed Rio Grande streamgage flows were found to have declined 40% or more compared to simulated near-native flows (with minimal influence of reservoirs or diversions). Overall, significant 30-year declines in precipitation, snowmelt rate, streamflow, and baseflow at many streamgages throughout the basins suggests declining water availability and that help explain declines in crop and plant water use in the basin, with negative implications for both agricultural production and groundwater availability. Together, these trends indicate a higher fraction of precipitation as rain (rather than snow), slower snowmelt rates leading to decreasing streamflow production, and an increasing fraction of baseflow, all of which will affect the timing and magnitude of water available for human needs in the basin.

Technical Abstract: The Upper Rio Grande Basin (URGB) is a critical international water resource under pressure from a myriad of climatic, ecological, infrastructural, water-use, and legal constraints. The objective of this study is to provide a comprehensive assessment, as well as integrated analyses, of the spatial distribution and temporal trends of selected water-budget components (snow hydrology, evapotranspiration, streamflow processes, and groundwater storage) and integrated products (watershed modeling, and water availability and use) in the URGB. A spatially distributed snow evolution modeling system was used to simulate snowpack processes over a 34-year period (1984–2017) and highlighted snow water equivalent declines from -35 to -77 mm/decade with widespread variability across elevation zones and land cover types. Gridded actual ET data from the SSEBop model were developed and tested for the URGB, and demonstrated all land-cover types had significant decreasing trends (1986-2015) ranging from -14 to -80 mm/decade. Conductivity-mass-balance (CMB) hydrograph separation results found baseflow ranging from 29 to 69% (49% average) of total streamflow at 17 URGB sites upstream of Albuquerque, NM. Three of 4 graphical hydrograph separation methods in the USGS Groundwater Toolbox were found to be inappropriate for estimating baseflow in the URGB; the most promising method, BFI Standard, was optimized using CMB data and tested at three URGB sites, with resulting overestimation of 0 to 47%. Historical and recent groundwater-flow models show a decline in storage for many of the alluvial basins from about 1960 through the period of record for that basin. The PRMS model was successfully calibrated for 9 near-native subbasins (Nash-Sutcliffe efficiency 0.47 to 0.85) and parameters translated to the remaining subbasins; compared to simulated near-native flows (with minimal influence of reservoirs or diversions), observed Rio Grande streamgage flows demonstrated reductions of 40% or more for New Mexico and Texas areas of the basin. Significant decreasing trends (1980-2015) in precipitation, snowmelt rate, streamflow, and baseflow were observed at many of the 12 streamgage basins studied, which suggests that the decreasing trends for actual ET may be related to overall decreasing water availability in the basin, with negative implications for agricultural production and groundwater abstraction. Water security implications of these trends include a higher fraction of precipitation as rain, slower snowmelt rates leading to decreasing streamflow production, and an increasing fraction of baseflow, all of which will affect the timing and magnitude of water available for human needs in the basin.