Drought and Groundwater Sustainability in California’s Farming Regions

Public Policy Institute of California (PPIC) | June 25th, 2024

Drought and ozone air quality in California: Identifying susceptible regions in the preparedness of future drought

Environmental Research (Elsevier) | October 19th, 2022

California experienced extreme and prolonged drought conditions during the early 2010s. To date, little is known regarding the influence of drought on air quality. Our st

California experienced extreme and prolonged drought conditions during the early 2010s. To date, little is known regarding the influence of drought on air quality. Our study quantified site-specific associations between drought (defined by the Standardized Precipitation-Evapotranspiration Index; SPEI) and daily maximum 8-h ozone (O3) concentrations for California, USA, and then pooled these associations for the years 2009–2015. Overall, ambient O3 concentration was higher during droughts by 1.18 ppb (95% confidence interval (CI) = 1.00–1.36). The sensitivity of O3 to drought was greater during the warm season than during the cool season (1.73 ppb versus 0.79 ppb higher O3 during droughts) with substantial regional variation. In a pooled analysis with meteorological parameters as potential effect modifiers, the spatial heterogeneity of drought-O3 associations was explained strongly by average relative humidity for each season (71.9% (warm season) and 73.4% (cool season) of the drought-O3 associations explained), followed by the drought-related changes in relative humidity (47.6% (warm season)) and temperature (53.6% (cool season)). The pooled regression further identified regions susceptible for drought-related O3 increases as those with relatively low average relative humidity (10–25th percentiles or 44.3–47.3%) and larger drought-related decrease in relative humidity and increase in temperature. As the drought events are projected to occur with increased frequency and intensity in the era of climate change, the excess health burdens from O3 exposures attributed to the projected drought events need to be taken into account when allocating air quality and health resources. The impacts of O3 on health during droughts would confound the health burdens from the drought itself.

Drought and the California Delta—A Matter of Extremes

University of California, Davis (UC Davis) | July 14th, 2014

California is in an extreme drought as a result of low precipitation in water year 2012, record low precipitation in 2013, and the remarkably dry first few months of 2014

California is in an extreme drought as a result of low precipitation in water year 2012, record low precipitation in 2013, and the remarkably dry first few months of 2014. We typically receive our largest precipitation totals in Decembers and Januaries (which provide about 36% of the precipitation in the Delta’s catchment), and when those months are as dry as they were this year, subsequent months have to be unseasonably wet to avoid drought. Most of the current winter, especially December 2013–January 2014, was dry because a persistent ridge of high (atmospheric) pressures set up offshore, diverting storms away from California and into Alaska. That same diversion gave the Delta’s catchment its warmest winter in 120 years, as well as bringing all that cold weather to the eastern US. While the February 2014 storms provided minor relief and momentarily slowed the spiral into deeper drought, the drought continues apace. Nonetheless, as harsh as it is, the current drought is not unprecedented in the Delta’s history, and even less so in its prehistory. In this essay, we consider the ways that droughts in California arise from a few missing storms and from long-term variations and changes in climate, in order to identify drought-science needs for Delta management. 

Drought and Water Year 2016: Hot and Dry Conditions Continue

California Department of Water Resources (DWR) | September 15th, 2016

Drought is a recurring feature of California’s climate. Paleoclimate information, such as streamflow or precipitation reconstructions developed from tree-ring d

Drought is a recurring feature of California’s climate. Paleoclimate information, such as streamflow or precipitation reconstructions developed from tree-ring data, can provide a perspective on long-term climate variability. Reconstructed hydrologic records show that California has experienced droughts of much longer duration than those in our century- plus recorded historical period. There is, however, one drought within the historical period on a par with driest events in the paleo record, if the comparison is made using driest 10-year streamflow periods. The prolonged off-and-on dry conditions of the 1920s-30s were severe in terms of their hydrology, but they occurred at a time when the state’s population was in the ballpark of 6 million and irrigated acreage was less than half of present levels.

Drought Attribution Studies and Water Resources Management

American Meteorological Society (AMS) | February 16th, 2023

Drought Contingency Planning (DCP) Negotiation #142, Attachment 1

California Department of Water Resources (DWR) | April 30th, 2020

This white paper describes current understanding of how the Department of Water Resources (DWR) would account for and administer the Delta Conveyance Facility (DCF) Bene

This white paper describes current understanding of how the Department of Water Resources (DWR) would account for and administer the Delta Conveyance Facility (DCF) Benefits. DWR will include information regarding the accounting and administration of water attributable to DCF in relevant Notice(s) to State Water Project Contractors consistent with prior practice. No legally binding obligations are created by this white paper. This white paper may be updated from time to time by DWR, in consultation with the Public Water Agencies (PWAs), in response to factors including, but not limited to, changes in laws, regulations or permits applicable to DWR and/or the State Water Project (SWP). Capitalized terms not defined herein shall have the meanings ascribed to them in the DCF Agreement in Principle (AIP).

Drought less predictable under declining future snowpack

Nature Portfolio (Springer Nature) | April 20th, 2020

Mountain snowpack serves as an immense natural water reservoir, and knowledge of snow conditions helps predict seasonal water availability and offers critical ear

Mountain snowpack serves as an immense natural water reservoir, and knowledge of snow conditions helps predict seasonal water availability and offers critical early warning of hydrologic drought. This paradigm faces an impending challenge given consensus that a smaller fraction of future precipitation will fall as snow. Here, we apply downscaled hydrologic simulations from 28 climate model projections to show that by mid-century (2036–2065), 69% of historically snowmelt-dominated areas of the western United States see a decline in the ability of snow to predict seasonal drought, increasing to 83% by late century (2070–2099). Reduced predictability arises when peak snowpack approaches zero or because of decreased warm-season runoff efficiency. Changes in drought prediction skill show significant (P < 0.01) elevation dependence, with lower-elevation coastal areas most impacted by warming. Ancillary predictive information can only partially mitigate snow-based predictability losses to 65% of areas, underscoring the importance of declining future snowpack.

Drought Management and Climate Adaptation among Small, Self-Sufficient Water Systems in California

California Natural Resources Agency (CNRA) | August 27th, 2018

 Examining human impacts, responses, and challenges to extreme climatic events can give insight into needed directions for climate adaptation to reduce future risks. Thi

 Examining human impacts, responses, and challenges to extreme climatic events can give insight into needed directions for climate adaptation to reduce future risks. This study focuses on the 2012-2016 Drought in California, documenting how small self-sufficient drinking water systems were affected and challenged by, and responded to the extreme event. The majority of small, self-sufficient water systems in the state serve rural, low income communities, and many have low technical, managerial, and financial capacity compared to larger systems. This increases the risk that these drinking water systems will be disproportionately impacted by droughts or other disruptions. To assess the impact of drought on small water systems, we employed an iterative approach to gathering perspectives and experiences from drinking water system managers across the state. The goal of employing these iterative methods is to better understand the breadth and scope of impacts, responses, and barriers to dealing with the 2012- 2016 Drought. The first stage of the data collection involved interviewing managers of drinking water systems, which were transcribed and analyzed using semi-grounded theory methods. To cross-check and advance findings from interviews in additional locations, we conducted three small regional workshops and then a larger policy forum. Multiple data collection methods allowed us to gather insights about experiences from nearly 200 water managers. This project uses local knowledge to document the social dimensions within drinking water systems during the 2012-2016 Drought and expresses the value of local knowledge in reflecting on future drinking water system needs in response to extreme events.  We found that drinking water systems, despite size or government project water reliance, experienced a similar set of drought impact, response, and barrier categories (e.g., water quantity and water quality). However, within these categories, the types of impacts, responses, and barriers differed based on both system size and water source portfolio. Common disadvantages that hinder drought resilience, and thus climate adaptation, of small self-sufficient drinking water systems include: staff capacity; financial burden of revenue loss during drought compounded with increased need for staff time for additional reporting; customer awareness and outreach challenges; and consolidation. We found that consolidation is valuable but in many case needs more state support to implement and incentivize. From a long term perspective, the absence of expressed duty and lack of concern for risks of climate change among water managers indicates a major dearth in adaptation planning among these drinking water systems. Documentation of experiences from the 2012-2016 Drought can be used to inform future planning for droughts and more broadly climate change. 

Drought Management and Climate Adaptation of Small, Self-Sufficient Drinking Water Systems in California

California Energy Commission (CEC) | August 15th, 2018

Examining human impacts, responses, and challenges to extreme climatic events can give insight into needed directions for climate adaptation to reduce future risks. This

Examining human impacts, responses, and challenges to extreme climatic events can give insight into needed directions for climate adaptation to reduce future risks. This study focuses on the 2012-2016 Drought in California, documenting how small self-sufficient drinking water systems were affected and challenged by, and responded to the extreme event.

Drought water right curtailment analysis for California’s Eel river

American Society of Civil Engineers (ASCE) | February 1st, 2018

Water users in California’s hybrid water rights system have different legal priorities to available surface water in times of water scarcity. A set of two linear progra

Water users in California’s hybrid water rights system have different legal priorities to available surface water in times of water scarcity. A set of two linear programming models was developed to determine curtailments of water use under drought conditions according to riparian and appropriative water right doctrines with spatially varying water availability and water rights within a basin. The models were implemented in spreadsheets and extended to estimate water right reliability and factors of safety in water rights administration. Alternate methods for calculating water use curtailments are discussed. Curtailments from the models are compared with actual water shortage notices issued by the state for the Eel River, California for June 30, 2014. Analyzing water use curtailments with an algorithm in spreadsheet software offers a mechanistic, transparent, accessible, and precise approach derived from legal doctrines to support water rights administration during drought.