Impacts of California’s Ongoing Drought: Hydroelectricity Generation 2015 Update

Pacific Institute | February 1st, 2016

The Pacific Institute has released a comprehensive assessment of the costs to California of lost hydroelectricity during the four years of drought from October 2011 to th

The Pacific Institute has released a comprehensive assessment of the costs to California of lost hydroelectricity during the four years of drought from October 2011 to the end of September 2015 (the official California “water year” runs from October 1 to September 30). Under normal conditions, electricity for the state’s millions of users is produced from a blend of many sources, with natural gas and hydropower being the top two. Since the drought has reduced the state’s river flows that power hundreds of hydropower stations, natural gas has become a more prominent player in the mix. This is an expensive change. According to the Institute’s new report, the four years of drought led to an increase in electricity costs of more than $2.0 billion. The additional combustion of fossil fuels for electric generation also led to a 10 percent increase in the release of carbon dioxide from California power plants. “The impacts of the California drought – which is the driest and the hottest in 120 years of instrumental records and one of the worst in history – has had widespread  impacts on all water users, including farmers, industries, cities, and natural ecosystems,” said the report’s author, Pacific Institute President Peter Gleick. “And in fact, all California ratepayers are affected by the drought as they pay for electricity that is both dirtier and more expensive than in non-drought years.” In addition, the report notes that the ability to expand California’s hydroelectric capacity is limited, as there are few undammed rivers, little unallocated water, and growing environmental, economic, and political constraints to adding new hydropower capacity.

Impacts of the California Drought from 2007 to 2009: Surprising Outcomes for California’s Agriculture, Energy, and Environment

Pacific Institute | June 16th, 2011

California’s three-year drought, which ended with this season’s cool and wet weather, had complicated and serious impacts that have been poorly understood and reporte

California’s three-year drought, which ended with this season’s cool and wet weather, had complicated and serious impacts that have been poorly understood and reported. Some of the impacts were expected; others were surprising. The Pacific Institute has just completed a nine-month assessment of new data from California’s agricultural, energy, and environmental sectors to evaluate actual consequences of the drought for the state. Analysis of state and federal data released over the past year finds that contrary to much of the media reporting, California’s agricultural community proved flexible and resilient, generating agri­cultural revenues in 2007, 2008, and 2009 that were the highest on record. And agriculture-related occupations remained a stable portion of total jobs available in areas directly impacted by water supply restrictions. Less frequently reported were the substantial impacts on energy production and aquatic ecosystems during the drought, which were economically and environmentally significant. “More severe drought is inevitable, and the U.S. – and California in particular – has not reformed drought monitoring, evaluation, planning, and response strategies the way other countries and regions have,” said Juliet Christian-Smith, senior research associate at the Pacific Institute and lead author of the report. “To become more resilient to future droughts, it will be critical to shift from crisis-driven responses to long-term mitigation strategies.” The Pacific Institute analysis, Impacts of the California Drought from 2007-2009, focused on three drought-sensitive sectors: agricultural production, energy production, and ecosystem health.  

Improving the Federal Response to Western Drought: Five Areas for Reform

Public Policy Institute of California (PPIC) | January 26th, 2016

The federal government is deeply involved in western water. It is the largest landowner, major supplier of irrigation, principal supporter of the farm sector, primary sou

The federal government is deeply involved in western water. It is the largest landowner, major supplier of irrigation, principal supporter of the farm sector, primary source of water information, and chief environmental regulator. For more than a century, western states have relied on a complex partnership with numerous federal agencies to manage water. The latest widespread drought has revealed both strengths and weaknesses in the federal role. To weather a warmer and possibly drier future, and to prepare for and respond to drought more effectively , the states and the federal government must address these weaknesses and work together to strengthen their partnership. Timely solutions are critical, given the growing vulnerability of the region’s residents, businesses, and environment to drought . This report identifies a suite of federal actions that can help weste rn states better manage drought . These reforms are, by design, modest and pragmatic. They focus on enhancing existing federal capacities, rather than implementing sweeping initiatives that would require time-consuming new funding or legislation.

Increased drought and extreme events over continental United States under high emissions scenario

Nature Portfolio (Springer Nature) | December 6th, 2023

Increased future occurrences of the exceptional 2018–2019 Central European drought under global warming

Nature Portfolio (Springer Nature) | August 6th, 2020

Since the spring 2018, a large part of Europe has been in the midst of a record-setting drought. Using long-term observations, we demonstrate that the occurrence of the

Since the spring 2018, a large part of Europe has been in the midst of a record-setting drought. Using long-term observations, we demonstrate that the occurrence of the 2018–2019 (consecutive) summer drought is unprecedented in the last 250 years, and its combined impact on the growing season vegetation activities is stronger compared to the 2003 European drought. Using a suite of climate model simulation outputs, we underpin the role of anthropogenic warming on exacerbating the future risk of such a consecutive drought event. Under the highest Representative Concentration Pathway, (RCP 8.5), we notice a seven-fold increase in the occurrence of the consecutive droughts, with additional 40 ( ±5 ) million ha of cultivated areas being affected by such droughts, during the second half of the twenty-first century. The occurrence is significantly reduced under low and medium scenarios (RCP 2.6 and RCP 4.5), suggesting that an effective mitigation strategy could aid in reducing the risk of future consecutive droughts.

Increased Interannual Precipitation Extremes over California under Climate Change

American Meteorological Society (AMS) | August 10th, 2015

Changes to mean and extreme wet season precipitation over California on interannual time scales are analyzed using twenty-first-century precipitation data from 34

Changes to mean and extreme wet season precipitation over California on interannual time scales are analyzed using twenty-first-century precipitation data from 34 global climate models. Models disagree on the sign of projected changes in mean precipitation, although in most models the change is very small compared to historical and simulated levels of interannual variability. For the 2020/21–2059/60 period, there is no projected increase in the frequency of extremely dry wet seasons in the ensemble mean. Wet extremes are found to increase to around 2 times the historical frequency, which is statistically significant at the 95% level. Stronger signals emerge in the 2060/61–2099/2100 period. Across all models, extremely dry wet seasons are roughly 1.5 to 2 times more common, and wet extremes generally triple in their historical frequency (statistically significant). Large increases in precipitation variability in most models account for the modest increases to dry extremes. Increases in the frequency of wet extremes can be ascribed to equal contributions from increased variability and increases to the mean. These increases in the frequency of interannual precipitation extremes will create severe water management problems in a region where coping with large interannual variability in precipitation is already a challenge. Evidence from models and observations is examined to understand the causes of the low precipitation associated with the 2013/14 drought in California. These lines of evidence all strongly indicate that the low 2013/14 wet season precipitation total can be very likely attributed to natural variability, in spite of the projected future changes in extremes.

Increasing Hydroclimatic Whiplash Can Amplify Wildfire Risk in a Warming Climate

Global Change Biology (Wiley) | February 7th, 2025

The catastrophic January 2025 fires were propelled by an especially extreme combination of these two recognized risk factors: (1) downslope wind gusts over 80 mph (35 m/s

The catastrophic January 2025 fires were propelled by an especially extreme combination of these two recognized risk factors: (1) downslope wind gusts over 80 mph (35 m/s) and exceptionally dry vegetation following a historically dry start to the rainy season and unusually warm antecedent temperatures driving a prolonged episode of elevated atmospheric evaporative demand. But there was also a third contributor: two consecutive anomalously wet winters (in 2022–2023 and 2023–2024), which led to abundant growth of herbaceous vegetation across CSC. This remarkable wet-to-dry sequence, therefore, set the stage for the CSC wildfire disasters to unfold by first facilitating prodigious fuel accumulation during the previous growing seasons, then subsequently drying vegetation to produce exceptional flammability unusually far into winter (when Santa Ana winds are common). Globally, climate change has increased wildfire potential primarily through greater aridity (Jain et al. 2022). In CSC, hotter summer and autumn seasons drive this aridity by increasing evaporative demand (i.e., atmospheric “thirst”), subsequently drying out vegetation. This, in conjunction with an increasingly delayed onset of the rainy season (Goss et al. 2020), may also be increasing temporal overlap between critically dry vegetation and Santa Ana winds (Swain 2021). As the events of January 2025 vividly illustrate, however, transitions from anomalously wet to anomalously dry conditions may further amplify these risks by exacerbating fuel accumulation and desiccation cycles. Indeed, in fire regimes (including CSC) where fire occurrence varies strongly with inter-annual variations in biomass (Swetnam et al. 2016), increased hydroclimate volatility is causally linked to increased wildfire activity.

Increasing importance of 2021 temperature as a driver of streamflow drought spatial extent

Environmental Research Letters (IOP) | February 9th, 2021

Widespread streamflow droughts can pose substantially greater societal challenges than spatially less extensive events because of the complex realities of trans-regional

Widespread streamflow droughts can pose substantially greater societal challenges than spatially less extensive events because of the complex realities of trans-regional water management. In a warming climate, drought spatial extent may change along with changes in underlying hydro-meteorological contributors. Here, we assess changes in streamflow drought spatial extent over the period 1981–2018 across the conterminous United States, and how the importance of potential hydro-meteorological contributors has changed over time. We first derive a monthly time series of drought spatial extent and look at trends in streamflow drought spatial extent. We then determine the spatial percentage 'overlap' of precipitation droughts, temperature anomalies, snow-water-equivalent deficits, and soil moisture deficits with the area under streamflow drought to look at the changing influence of these contributors on spatial extent. Our results show that (1) the spatial extent of droughts has increased, mainly because of increases in the extent of small droughts; (2) streamflow drought extents overall substantially overlap with soil moisture deficits and the relationship of drought to precipitation and temperature anomalies varies seasonally; and (3) the importance of temperature as a contributor to drought extent has increased over time. We therefore conclude that continued global warming may further increase drought extents, requiring adaptation of regional drought management strategies.

Increasing precipitation volatility in twenty-first-century California

Nature Portfolio (Springer Nature) | April 23rd, 2018

Mediterranean climate regimes are particularly susceptible to rapid shifts between drought and flood—of which, California’s rapid transition from record multi-yea

Mediterranean climate regimes are particularly susceptible to rapid shifts between drought and flood—of which, California’s rapid transition from record multi-year dryness between 2012 and 2016 to extreme wetness during the 2016–2017 winter provides a dramatic example. Projected future changes in such dry-to-wet events, however, remain inadequately quantified, which we investigate here using the Community Earth System Model Large Ensemble of climate model simulations. Anthropogenic forcing is found to yield large twenty-first-century increases in the frequency of wet extremes, including a more than threefold increase in sub-seasonal events comparable to California’s ‘Great Flood of 1862’. Smaller but statistically robust increases in dry extremes are also apparent. As a consequence, a 25% to 100% increase in extreme dry-to-wet precipitation events is projected, despite only modest changes in mean precipitation. Such hydrological cycle intensification would seriously challenge California’s existing water storage, conveyance and flood control infrastructure.

Increasing water cycle extremes in California and in relation to ENSO cycle under global warming

Nature Portfolio (Springer Nature) | October 21st, 2015

Since the winter of 2013–2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and

Since the winter of 2013–2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and an extraordinary increase in wildfires. Identifying the effects of global warming on regional water cycle extremes, such as the ongoing drought in California, remains a challenge. Here we analyse large-ensemble and multi-model simulations that project the future of water cycle extremes in California as well as to understand those associations that pertain to changing climate oscillations under global warming. Both intense drought and excessive flooding are projected to increase by at least 50% towards the end of the twenty-first century; this projected increase in water cycle extremes is associated with a strengthened relation to El Niño and the Southern Oscillation (ENSO)—in particular, extreme El Niño and La Niña events that modulate California’s climate not only through its warm and cold phases but also its precursor patterns.