South Lahontan

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.

Snow-eater heat waves of the western United States

American Association for the Advancement of Science (AAAS) | August 5th, 2026

Abrupt snowmelt, triggered by rain-on-snow events or “snow-eater heat waves,” can cause flooding, initiate or accelerate snow drought, and affect water availability.

Abrupt snowmelt, triggered by rain-on-snow events or “snow-eater heat waves,” can cause flooding, initiate or accelerate snow drought, and affect water availability. However, the characteristics (e.g., area, duration, and frequency), impacts, and trends of snow-eater heat waves have received little attention. To address this gap, we developed a method to identify snow-eater heat waves and estimate their melt potential using 20th Century Reanalysis version 3 air temperature data, the TempestExtremes algorithm, and an operational snowmelt model (SNOW-17) across 1850–2015. Melt season snow-eater heat waves typically last 3 to 5 days, with three to five events, doubling snowmelt rates. Seven of 11 spring superfloods are shown to coincide with snow-eater heat waves. Since the 1850s, snow-eater heat waves have increased in area and frequency, decreased in duration, and shifted earlier in the melt season. Incorporating snow-eater heat-wave impacts into SNOW-17 enhances extreme melt estimates, improving water management support tools.

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.

Spring 2017 Groundwater Level Data Summary

California Department of Water Resources (DWR) | October 3rd, 2022

This document presents a summary of fall 2017 groundwater level data available in the DWR groundwater level database as of February 21, 2018 and includes a discussion of

This document presents a summary of fall 2017 groundwater level data available in the DWR groundwater level database as of February 21, 2018 and includes a discussion of fall 2017, data coverage and groundwater level trends. Statewide precipitation data come from the U.S. Climate Divisional Database, which has data from January 1895 to the present.

Stacked Incentives: Co-Funding Water Customer Incentive Programs

Pacific Institute | June 1st, 2021

Water utilities throughout the United States offer customer incentives to motivate action and foster engagement. Incentive programs can take many forms, such as rebate

Water utilities throughout the United States offer customer incentives to motivate action and foster engagement. Incentive programs can take many forms, such as rebates for high-efficiency fixtures and appliances, technical assistance for installing cisterns and rain gardens, and educational programs about water reuse. In addition to providing water-related benefits, many of these programs generate additional co-benefits, including reductions in energy use for heating or treating water and wastewater, increased carbon sequestration in landscapes, enhancements to local biodiversity, and more. These co-benefits present water utilities with an opportunity to build collaborative partnerships and co-funding for customer incentive programs through “stacked incentives.”

Standardized Regulatory Impact Assessment of Proposed Making Conservation a California Way of Life Regulation

California State Water Resources Control Board (SWRCB) | June 21st, 2024

Water conservation in California overall, due to the proposed regulation and other conservation efforts by water suppliers and Californians generally, plus passive conser

Water conservation in California overall, due to the proposed regulation and other conservation efforts by water suppliers and Californians generally, plus passive conservation from prior conservation efforts, is estimated to save levels of water consistent with the goal mentioned in the Water Supply Strategy of the reduction of the water demand of towns and cities by half a million acre-feet per year. The proposed regulation serves as a backstop that is expected to cause new savings and “lock in” these other savings. As shown in the graph below, staff estimated that the proposed regulation would save approximately 30,000 acre-feet of water in 2027 (compared to the assumed 2027 baseline water use) and increased amounts in subsequent years, reaching almost 235,000 acre-feet of water in 2050 (compared to the assumed 2050 baseline water use). The total cumulative amount of water savings in the 2025-2050 period would be approximately 3.9 million acre-feet. More than half of the estimated water savings (approximately 52 percent) would come from the assumed residential water conservation measures, and the remainder (approximately 48 percent) from CII (Commercial, Industrial, and Institutional) performance measures.

State of California Department of Natural Resources Fortieth Biennial Report of the Division of Fish and Game for the Years 1946-1948

State of California | July 1st, 1948

State of California Emergency Flood Fighting Methods

California Department of Water Resources (DWR) | August 1st, 2018

The ‘Flood Fighting Methods’ outlined in this booklet have proven effective during many years of use by DWR, United States Army Corps of Engineers, and local agencies

The ‘Flood Fighting Methods’ outlined in this booklet have proven effective during many years of use by DWR, United States Army Corps of Engineers, and local agencies on flood-related emergencies. This handbook is published by the DWR Flood Operations Branch and is designed to be used with the Flood Fighting Methods class.