South Lahontan

Sierra Nevada Regional Report - California’s Fourth Climate Change Assessment

California Natural Resources Agency (CNRA) | August 16th, 2018

The Sierra Nevada region is critical to the environment and economy of California. Its places and peoples provide essential natural resources including fresh wate

The Sierra Nevada region is critical to the environment and economy of California. Its places and peoples provide essential natural resources including fresh water, clean power, working lands, and famous wilderness. The region encompasses tremendous geographical, climatological, and ecological diversity that spans majestic mountains to deep desert basins. The climate consists of cool, wet winters and warm, dry summers with large differences due to latitude (e.g., the southern Sierra is snowier than northern Sierra) and topography (e.g., the Westside is wetter than the Eastside). Variability is another notable feature of the climate with the region experiencing some of the largest year-to-year climatic fluctuations in the United States. Herein we summarize our assessment of climate-change vulnerabilities and adaptation actions in the region.

Simulating and Evaluating Atmospheric River-Induced Precipitation Extremes along the U.S. Pacific Coast: Case Studies from 1980-2017

American Geophysical Union (AGU) | January 29th, 2020

Atmospheric rivers (ARs) are responsible for a majority of extreme precipitation and flood events along the U.S. West Coast. To better understand the present‐day charac

Atmospheric rivers (ARs) are responsible for a majority of extreme precipitation and flood events along the U.S. West Coast. To better understand the present‐day characteristics of AR‐related precipitation extremes, a selection of nine most intense historical AR events during 1980–2017 is simulated using a dynamical downscaling modeling framework based on the Weather Research and Forecasting Model. We find that the chosen framework and Weather Research and Forecasting Model configuration reproduces both large‐scale atmospheric features—including parent synoptic‐scale cyclones—as well as the filamentary corridors of integrated vapor transport associated with the ARs themselves. The accuracy of simulated extreme precipitation maxima, relative to in situ and interpolated gridded observations, improves notably with increasing model resolution, with improvements as large as 40–60% for fine scale (3 km) relative to coarse‐scale (27 km) simulations. A separate set of simulations using smoothed topography suggests that much of these gains stem from the improved representation of complex terrain. Additionally, using the 12 December 1995 storm in Northern California as an example, we demonstrate that only the highest‐resolution simulations resolve important fine‐scale features—such as localized orographically forced vertical motion and powerful near hurricane‐force boundary layer winds. Given the demonstrated ability of a targeted dynamical downscaling framework to capture both local extreme precipitation and key fine‐scale characteristics of the most intense ARs in the historical record, we argue that such a configuration may be highly conducive to understanding AR‐related extremes and associated changes in a warming climate.

Simulation of Ground-Water Flow and Land Subsidence in the Antelope Valley Ground-Water Basin, California

U.S. Geological Survey (USGS) | June 30th, 2003

Antelope Valley, California, is a topographically closed basin in the western part of the Mojave Desert, about 50 miles northeast of Los Angeles. The Antelope Valley grou

Antelope Valley, California, is a topographically closed basin in the western part of the Mojave Desert, about 50 miles northeast of Los Angeles. The Antelope Valley ground-water basin is about 940 square miles and is separated from the northern part of Antelope Valley by faults and low-lying hills. Prior to 1972, ground water provided more than 90 percent of the total water supply in the valley; since 1972, it has provided between 50 and 90 percent. Most ground-water pumping in the valley occurs in the Antelope Valley ground-water basin, which includes the rapidly growing cities of Lancaster and Palmdale. Ground-water-level declines of more than 200 feet in some parts of the ground-water basin have resulted in an increase in pumping lifts, reduced well efficiency, and land subsidence of more than 6 feet in some areas. Future urban growth and limits on the supply of imported water may continue to increase reliance on ground water. To better understand the ground-water flow system and to develop a tool to aid in effectively managing the water resources, a numerical model of ground-water flow and land subsidence in the Antelope Valley ground-water basin was developed using old and new geohydrologic information.

Simulation of Ground-water Flow in the Mojave River Basin, California

U.S. Geological Survey (USGS) | July 1st, 2001

Simulation of Water-Management Alternatives in the Mojave River Ground-Water Basin, California

U.S. Geological Survey (USGS) | July 1st, 2002

Small Water Systems and Rural Communities Drought and Water Shortage Contingency Planning and Risk Assessment, Part 1

California Department of Water Resources (DWR) | March 25th, 2021

This report is submitted pursuant to California Water Code (CWC) Section 10609.42, which directs the California Department of Water Resources (DWR) to identify small wate

This report is submitted pursuant to California Water Code (CWC) Section 10609.42, which directs the California Department of Water Resources (DWR) to identify small water suppliers and rural communities that may be at risk of drought and water shortage vulnerability, and to propose recommendations and information in support of improving their drought preparedness. The report is published in two parts: Part 1 deals with drought and water shortage contingency planning recommendations, and Part 2 presents a methodology of drought and water shortage vulnerability assessment and risk scoring. Additionally, below are links for Part 1 appendices. Appendix 1: Literature Review Appendix 2: Proposed Water Shortage Contingency Plan Components for Small Water Systems Serving 1,000 to 2,999 Service Connections Appendix 3: Proposed Umbrella Water Shortage Contingency Plan Components Appendix 4: Indian Health Service Template for a Drought Contingency Plan for a Tribal Public Water System Appendix 5: County Drought Advisory Group General Funding and Financing Issues

Small Water Systems and Rural Communities Drought and Water Shortage Contingency Planning and Risk Assessment, Part 2

California Department of Water Resources (DWR) | March 25th, 2021

This report is submitted pursuant to California Water Code (CWC) Section 10609.42 which directs California Department of Water Resources (DWR) to identify small water sup

This report is submitted pursuant to California Water Code (CWC) Section 10609.42 which directs California Department of Water Resources (DWR) to identify small water suppliers and rural communities that may be at risk of drought and water shortage vulnerability and propose recommendations and information in support of improving the drought preparedness of small water suppliers and rural communities. The report is published in two parts: Part 1 dealing with drought and water shortage contingency planning recommendations, and Part 2 presenting a methodology and results of drought and water shortage vulnerability assessment and risk scoring. Additionally, below are links for Part 2 appendices. Appendix 1: Drought and Water Shortage Risk Scoring: California’s Small Water Supplier and Self-Supplied Communities Appendix 2: Drought and Water Shortage Risk Scoring: Risk Score Results of Small Water Suppliers Appendix 3: Drought and Water Shortage Risk Scoring: Risk Score Results of Self-Supplied Communities

Snow monitoring at strategic locations improves water supply forecasting more than basin-wide mapping

Nature Portfolio (Springer Nature) | August 15th, 2025

In the Western United States, water supply forecasting has traditionally relied on snow water equivalent measurements at ground-based stations due to their strong correla

In the Western United States, water supply forecasting has traditionally relied on snow water equivalent measurements at ground-based stations due to their strong correlations with streamflow volume during spring and summer. However, stations are sparse and sample a small area, prompting interest in spatially complete – but costly – basin-wide mapping from airborne surveys or future satellite missions. Here we show that adding strategic measurements at snow hotspots – localized areas with untapped information for predicting streamflow – consistently outperforms spatially complete surveys that provide basin-average snowpack, both in basins with and without existing stations. While both improve forecast skill, hotspot monitoring increases correlations with streamflow volume by 11-14% (median) across 390 basins, compared to 4% from basin-wide surveys. These findings hold across snowpack datasets, skill metrics, and statistical models. The greatest gains in water supply prediction come from leveraging existing stations and expanding snow measurements to the right places, rather than everywhere.

Snowmelt risk telecouplings for irrigated agriculture

Nature Portfolio (Springer Nature) | October 31st, 2022

Climate change is altering the timing and magnitude of snowmelt, which may either directly or indirectly via global trade affect agriculture and livelihoods dependent on

Climate change is altering the timing and magnitude of snowmelt, which may either directly or indirectly via global trade affect agriculture and livelihoods dependent on snowmelt. Here, we integrate subannual irrigation and snowmelt dynamics and a model of international trade to assess the global redistribution of snowmelt dependencies and risks under climate change. We estimate that 16% of snowmelt used for irrigation is for agricultural products traded globally, of which over 70% is from five countries. Globally, we observe a prodigious snowmelt dependence and risk diffusion, with particularly evident importing of products at risk in western Europe. In Germany and the UK, local fraction of surface-water-irrigated agriculture supply exposed to snowmelt risks could increase from negligible to 16% and 10%, respectively, under a 2 °C warming. Our results reveal the trade-exposure of agricultural supplies, highlighting regions and crops whose consumption may be vulnerable to changing snowmelt even if their domestic production is not.

Source, movement and age of groundwater in the upper part of the Mojave River Basin, California, USA

Proceedings of the 1994 International Symposium on Application of Tracers in Arid Zone Hydrology | August 22nd, 1996

Water samples from wells were collected and analysed for oxygen-18, deuterium, tritium, carbon-14, and carbon-13 to determine the source, movement and age of groundwate

Water samples from wells were collected and analysed for oxygen-18, deuterium, tritium, carbon-14, and carbon-13 to determine the source, movement and age of groundwater in the upper part of the Mojave River basin. Water in the alluvial aquifer has a median deuterium composition of — 66% and contains tritium, and was recently recharged by water from the Mojave River. Water in the regional aquifer near the Mojave River, near Summit Valley, and underlying several small washes has deuterium compositions heavier than — 60 %. Although some water in the regional aquifer near the Mojave River contains tritium, most of this water does not contain tritium. Carbon-14 data indicate that this water was recharged less than 2400 years ago. Water in the remainder of the regional aquifer has a median deuterium composition of — 84 %, which is as much as 20 % lighter than the volume-weighted deuterium composition of present-day precipitation. These data show that this water was recharged under climatic conditions different from average conditions today. Carbon-14 data indicate that some water in the regional aquifer was recharged more than 20,000 years ago.