Supplement to the 2007 Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead

U.S. Bureau of Reclamation (USBR) | May 6th, 2024

This ROD revises the 2007 Interim Guidelines for the near-term operation of Glen Canyon and Hoover Dams to address the potential for continued low-runoff conditions in th

This ROD revises the 2007 Interim Guidelines for the near-term operation of Glen Canyon and Hoover Dams to address the potential for continued low-runoff conditions in the Basin. Reclamation has concluded that the potential impacts of low-runoff conditions pose unacceptable risks to routine operations of Glen Canyon and Hoover Dams during the remainder of the interim period (through the end of the 2026 operating year) and that modified operating guidelines need to be expeditiously developed.

Sustainable Management of a Water Reservoir System Facing Climate Uncertainty

Social Science Research Network (SSRN) | November 27th, 2024

Water scarcity is a growing global issue. It affects even highly developed regions like California, the world's fifth largest economy, where years of severe droughts inte

Water scarcity is a growing global issue. It affects even highly developed regions like California, the world's fifth largest economy, where years of severe droughts interspersed with unusually wet seasons have caused societal debates over the management of the water resources stored in the state's extensive reservoir system. This paper presents a strategic optimization model for the long-term, sustainable management of such a system. Introducing a new modeling paradigm based on cycles of stochastic length, defined by the event when all reservoirs are simultaneously full, we avoid the limitations of traditional models and obtain sustainable management policies. To address the unpredictable effect of climate change on future water supply, we adopt a distributionally robust framework where nature chooses adverse inflow distributions. This leads to a stochastic shortest path problem under distributional ambiguity. Using tools from stochastic dynamic programming and aggregation methods, we obtain policy insights and overcome the curse of dimensionality typically associated with systems models. In a case study for California's Sacramento River Basin, we report suboptimality gaps between 3% and 15%, with our sustainable management policy reducing average cycle shortage costs by 40% compared to the current policy, demonstrating the significant cost saving potential.

Tahoe: State of the Lake Report 2025

University of California, Davis (UC Davis) | July 18th, 2025

UC Davis has conducted research at Lake Tahoe since 1950, and scientists from UC Davis Tahoe Environmental Research Center have been monitoring conditions at the lake con

UC Davis has conducted research at Lake Tahoe since 1950, and scientists from UC Davis Tahoe Environmental Research Center have been monitoring conditions at the lake continuously since 1968. This has created a unique document of change for one of the world’s most iconic and vulnerable lakes.

Taming wildfires in the context of climate change: The case of the United States

Organisation for Economic Co-operation and Development (OECD) | January 22nd, 2024

Shifts in climate cycles (e.g., Pacific Decadal Oscillation, El Niño-Southern Oscillation), combined with ongoing changes in drought, temperature and snowmelt, together,

Shifts in climate cycles (e.g., Pacific Decadal Oscillation, El Niño-Southern Oscillation), combined with ongoing changes in drought, temperature and snowmelt, together, have contributed to the overall warmer, drier conditions that fuel extreme wildfires (Environmental Protection Agency, 2022[4]; Kitzberger et al., 2007[10]; Westerling, 2016[11]). The period with the largest increase in area burned coincides with many of the warmest years on record nationwide (Environmental Protection Agency, 2022[4]). Such changes are especially visible in the western United States, where the peak extent of area burned now occurs about one month earlier than just two decades ago. Other factors including longer dry seasons and drier soils and vegetation are increasingly creating the conditions for catastrophic wildfires (Environmental Protection Agency, 2022[4]; US Global Change Research Program, 2018[9]). Wildfires are also further spreading into areas historically unaccustomed to fire, including high elevation areas in the west of the country (Figure 1.2) (OECD, 2023[2]; Alizadeh et al., 2021[12]), which may be less prepared for wildfires and potentially harmed by its impacts.

Temporal and Spatial Patterns of Groundwater Recharge Across a Small Watershed in the California Sierra Nevada Mountains

Frontiers in Water (Frontiers) | May 17th, 2022

Mountain-block groundwater recharge is a crucial freshwater source in arid to semiarid watersheds worldwide; yet its quantification is difficult due to (1) hydrogeologica

Mountain-block groundwater recharge is a crucial freshwater source in arid to semiarid watersheds worldwide; yet its quantification is difficult due to (1) hydrogeological heterogeneities especially in bedrock-dominated regimes, (2) drastic altitudinal ranges in climate, land use and land cover, and (3) mixing with deep groundwater derived from adjacent basins (i.e., interbasin groundwater flow). In this study, we test the utility of soil water-balance (SWB) modeling to quantify mountain-block groundwater recharge in the South Fork Tule River watershed in the California Sierra Nevada Mountains. This 1,018 km2 watershed is instrumented with 3 USGS stream gages that allow for the development of a refined recharge (i.e., baseflow) calibration dataset via multi-objective optimization-based hydrograph separation. The SWB model was used to compute groundwater recharge and other water balance components at a daily time step using a 30-m grid cell size for a 40-year (1980–2019) study period. Mean annual recharge and runoff were estimated at 3.7 in/yr (3.0 m3/s) and 1.4 in/yr (1.2 m3/s), respectively, with modified Nash Sutcliffe Efficiency indices of 0.61 between baseflow and SWB-derived recharge, and 0.90 between hydrograph separation- and SWB-derived runoff. There is a strong correlation between annual recharge and rainfall (Pearson R = 0.95, p < 0.001) which attests to short residence times in the unsaturated zone and the immediate impact of droughts in 1990, 1999, and 2013. However, results of a modified Mann-Kendall trend analysis indicate no directional trends in recharge or runoff throughout the study period. Parameter sensitivity analyses reveal a persistent overprediction of recharge over baseflow that is particularly pronounced in the upper reaches of the watershed. This is likely related to the SWB model only considering soil characteristics at the surface and not simulating the fate of potential recharge below the root zone where it may be impeded from reaching the aquifer by shallow, impermeable bedrock. This limitation should be considered carefully for future water supply projections in this and comparable bedrock-dominated settings.

The Benefits of Headwater Forest Management

Public Policy Institute of California (PPIC) | April 1st, 2020

Forests in California are increasingly vulnerable to major wildfires and droughts that threaten the benefits they provide. Improving the health of headwater forests in th

Forests in California are increasingly vulnerable to major wildfires and droughts that threaten the benefits they provide. Improving the health of headwater forests in the Sierra, in particular—where most of the state’s surface water supplies originate—will provide an array of social, economic, and environmental benefits across multiple sectors and geographies. Research by forest ecologists and wildfire behavior experts finds that the best way to realize these benefits is to reestablish and maintain lower densities of trees, which will help make these forests more resilient to fire, drought, and pests.  Healthier forests can support rural communities, reduce air quality impacts from wildfires, securely store carbon and reduce greenhouse gas emissions, protect water quality from post-fire erosion, and increase water supply. The broad base of beneficiaries of headwater forest management includes rural communities in the headwater region, regions that are vulnerable to smoke impacts from major wildfires, and major urban areas and agricultural regions that receive water and hydropower from headwater forests.  Improving forest health will require a substantial lift from an array of private and public entities—along with new policies and sources of funding to facilitate complex, collaborative management. Clarifying the benefits and beneficiaries of forest management is a critical step in motivating long-term stewardship, and will inform efforts to craft financial tools, policies, and other governance solutions needed to make this heavy lift. By assessing what is known about the benefits of forest management, this report provides crucial information for ongoing policy discussions on long-term stewardship of California’s headwater forests. 

The Disposition of Mining Debris in California

Scientific American | July 18th, 1891

Among the reports submitted to the last Congress was one from the Secretary of War on the treatment of mining debris in California. The report contained the conclusion

Among the reports submitted to the last Congress was one from the Secretary of War on the treatment of mining debris in California. The report contained the conclusions of the Board of Engineer officers which was prepared in compliance with an act of Congress, approved October 1st, 1888, which directed that three officers from the Engineer Corps of the United States army be constituted a commission for the purpose of making a thorough examination of the mining debris question in California, and determining whether some plan cannot be devised whereby the present conflict between the mining and farming sections may be adjusted, and the mining industry rehabilitated.

The Essential Role of Local Context in Shaping Risk and Risk Reduction Strategies for Snowmelt-Dependent Irrigated Agriculture

American Geophysical Union (AGU) | June 11th, 2024

The evolution of dam induced river fragmentation in the United States

Nature Portfolio (Springer Nature) | June 28th, 2023

The Importance of Interflow to Groundwater Recharge in a Snowmelt-Dominated Headwater Basin

American Geophysical Union (AGU) | May 23rd, 2019

Understanding the sensitivity of groundwater generation to climate in a mountain system is complicated by the tight coupling of snow dynamics to vegetation and topogr

Understanding the sensitivity of groundwater generation to climate in a mountain system is complicated by the tight coupling of snow dynamics to vegetation and topography. To address these feedbacks, we combine LiDAR-derived snow observations with an integrated hydrologic model to quantify spatially and temporally distributed water fluxes across varying climate conditions in a Colorado River headwater basin. Results indicate annual groundwater flow is an important and stable source of stream water. However, interflow decreases during drought as a function increased plant water use and the relative fraction of groundwater to streams increases. Seasonal snowmelt and vegetation water use regulate small recharge rates in the lower portions of the basin, but snowmelt transported via interflow from high mountain ridges toward convergent topographic zones define preferential recharge in the upper subalpine. Recharge in this zone appears decoupled from annual climate variability and resilient to drought.