North American droughts of the mid to late nineteenth century: a history, simulation and implication for Mediaeval drought

Holocene (Sage Journals) | February 1st, 2006

Unlike the major droughts of the twentieth century that are readily identified in the instrumental record, similar events in the nineteenth century have to be identified

Unlike the major droughts of the twentieth century that are readily identified in the instrumental record, similar events in the nineteenth century have to be identified using a combination of proxy data, historical accounts and a sparse collection of early instrumental records. In the USA, three distinct periods of widespread and persistent drought stand out in these records for the latter half of the nineteenth century: 1856-1865, 1870-1877 and 1890-1896. Each of these events is shown to coincide with the existence of an anomalously cool, La Nifia-like tropical Pacific. To examine the physical mechanisms behind these droughts two ensembles of simulations with an atmosphere general circulation model (AGCM) were generated: the first forces an AGCM with the observed history of Sea Surface Temperatures (SSTs) everywhere from 1856 to 2001 (the GOGA experiment), the second forces the AGCM only with tropical Pacific SSTs, being coupled to a two-layer entraining mixed layer (ML) ocean elsewhere (the POGA-ML experiment). Owing to a sparsity of instrumental precipitation data at this time, proxy evidence from tree rings is used as verification. A comparison of modelled soil moisture with tree-ring reconstructions of the Palmer Drought Severity Index (PDSI), a proxy for soil moisture, from the North American Drought Atlas is made. Both the POGA-ML and GOGA ensemble means capture the three multi-year droughts of the mid to late nineteenth century, indicating that the droughts were SST forced. The similarity of the POGA-ML and GOGA simulations implies that the component of each drought signal that is forced by the SST is driven ultimately by the La Nifia-like tropical Pacific. The global atmosphere-ocean context of each of the mid to late-nineteenth century droughts reveals a zonally and hemispherically symmetric pattern consistent with forcing from the tropics. In addition, Rossby wave propagation from the cooler equatorial Pacific amplifies dry conditions over the USA. Finally, using published coral data for the last millennium to reconstruct a NINO 3.4 history, the modern-day relationship between NINO 3.4 and North American drought is applied to recreate two of the severest Mediaeval ‘drought epochs’ in the western USA. The large-scale spatial similarity to the Drought Atlas data demonstrates the potential link between a colder eastern equatorial Pacific and the persistent North American droughts of the Mediaeval period.

Observations of the spawning ecology of the imperiled Clear Lake Hitch

California Department of Fish and Wildlife (CDFW) | October 13th, 2019

Observed and anticipated impacts of drought on forest insects and diseases in the United States

Forest Ecology and Management (Elsevier) | May 11th, 2016

Future anthropogenic-induced changes to the earth’s climate will likely include increases in temperature and changes in precipitation that will increase the fre

Future anthropogenic-induced changes to the earth’s climate will likely include increases in temperature and changes in precipitation that will increase the frequency and severity of droughts. Insects and fungal diseases are important disturbances in forests, yet understanding of the role of drought in outbreaks of these agents is limited. Current knowledge concerning the effects of drought on herbivorous insect and pathogen outbreaks in U.S. forests is reviewed, and compared between the relatively mesic and structurally diverse forests of the eastern U.S. and the more xeric forests of the western U.S. Theory and limited evidence suggests a non-linear relationship between drought intensity and outbreaks of aggressive bark beetle species (i.e., those capable of causing extensive levels of tree mortality), where moderate droughts reduce bark beetle population performance and subsequent tree mortality, whereas intense droughts, which frequently occur in the western U.S., increase bark beetle performance and tree mortality. There is little evidence for a role of drought in outbreaks of the southern pine beetle (Dendroctonus frontalis), the only bark beetle species that causes large amounts of tree mortality in the eastern U.S. Defoliators do not show consistent responses to drought. The response of sap-feeders to drought appears non-linear, with the greatest performance and impacts at intermediate drought intensity or when drought is alleviated by wetter periods. Interactions between tree pathogens and drought are poorly understood, but available evidence suggests reduced pathogen performance and host impacts in response to drought for primary pathogens and pathogens whose lifecycle depends directly on mois- ture (humidity). In these cases, rates of reproduction, spread, and infection tend to be greater when conditions are moist. In contrast, secondary fungal pathogens (i.e., those that depend on stressed hosts for colonization) are anticipated to respond to drought with greater performance and host impacts. In the western U.S., drought increases stress on trees severely infected by mistletoes thereby predisposing mistletoe-infected trees to attack by insects, particularly bark beetles and wood borers. Research needed to advance understanding of drought impacts on forest insects and diseases, and the role of forest man- agement in mitigation of infestations during drought are discussed.

Past and Projected Future Droughts in the Upper Colorado River Basin

American Geophysical Union (AGU) | February 29th, 2024

Past Groundwater Drought in the North American Cordillera

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

Piloting a Water Rights Information System for California

Center for Law, Energy, and the Environment (CLEE) | July 15th, 2021

California’s complex water management challenges are growing and intensifying. Systemic stressors like the more frequent and severe droughts and floods driven by climat

California’s complex water management challenges are growing and intensifying. Systemic stressors like the more frequent and severe droughts and floods driven by climate change are only making it harder to respond. Accordingly, California needs to dramatically improve the ability of local, regional, and State entities to make agile and effective water management decisions. We believe doing so will require enhanced understanding of our water resources and how they align with the needs of a range of agencies and stakeholders. Water rights data provide a crucial opportunity for advancing this understanding. We find that modernizing water rights data is feasible, affordable, and can increase transparency and clarity for better decision-making.

PPIC Statewide Survey: Californians and the Environment

Public Policy Institute of California (PPIC) | July 28th, 2022

With California facing a severe drought and wildfire season, public awareness has risen of the impact of climate change as well as state policies to reduce greenhouse gas

With California facing a severe drought and wildfire season, public awareness has risen of the impact of climate change as well as state policies to reduce greenhouse gas emissions. A sharp increase in petroleum prices has led to discussions about expanding oil production and renewable energy sources. These are among the key findings of a statewide survey on environmental issues conducted by the Public Policy Institute of California from July 8 to 15, 2022.

Precipitation in a warming world: Assessing projected hydro-climate changes in California and other Mediterranean climate regions

Nature Portfolio (Springer Nature) | September 7th, 2017

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. In California, however, proj

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. In California, however, projections of changes in annual precipitation are inconsistent. Analysis of daily precipitation in 30 GCMs reveals patterns in projected hydrometeorology over each of the five MedClm regions globally and helps disentangle their causes. MedClim regions, except California, are expected to dry via decreased frequency of winter precipitation. Frequencies of extreme precipitation, however, are projected to increase over the two MedClim regions of the Northern Hemisphere where projected warming is strongest. The increase in heavy and extreme precipitation is particularly robust over California, where it is only partially offset by projected decreases in low-medium intensity precipitation. Over the Mediterranean Basin, however, losses from decreasing frequency of low-medium-intensity precipitation are projected to dominate gains from intensifying projected extreme precipitation. MedClim regions are projected to become more sub-tropical, i.e. made dryer via pole-ward expanding subtropical subsidence. California’s more nuanced hydrological future reflects a precarious balance between the expanding subtropical high from the south and the south-eastward extending Aleutian low from the north-west. These dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events.

Precipitation variability increases in a warmer climate

Nature Portfolio (Springer Nature) | December 21st, 2017

Understanding changes in precipitation variability is essential for a complete explanation of the hydrologic cycle’s response to warming and its impacts. Whil

Understanding changes in precipitation variability is essential for a complete explanation of the hydrologic cycle’s response to warming and its impacts. While changes in mean and extreme precipitation have been studied intensively, precipitation variability has received less attention, despite its theoretical and practical importance. Here, we show that precipitation variability in most climatemodels increases over a majority of global land area in response to warming (66% of land has a robust increase in variability of seasonal-mean precipitation). Comparing recent decades to RCP8.5 projections for the end of the 21st century, we find that in the global, multi-model mean, precipitation variability increases 3–4% K−1 globally, 4–5% K−1 over land and 2–4% K−1 over ocean, and is remarkably robust on a range of timescales from daily to decadal. Precipitation variability increases by at least as much as mean precipitation and less than moisture and extreme precipitation for most models, regions, and timescales. We interpret this as being related to an increase in moisture which is partially mitigated by weakening circulation. We show that changes in observed daily variability in station data are consistent with increased variability.

Preparing for California’s Next Drought—Changes Since 1987-92

California Department of Water Resources (DWR) | July 19th, 2000

Preparation of this report was initiated in response to the unusually dry conditions experienced through January 2000. California was in the second year of a La Niña eve

Preparation of this report was initiated in response to the unusually dry conditions experienced through January 2000. California was in the second year of a La Niña event, typically characterized by dryer than normal conditions in the southern part of the State. December 1999 was one of the driest Decembers on record. Snowpack levels in early January in the northern Sierra, the source of much of California’s developed water supply, were only some 20 percent of seasonal average. Given that California had previously experienced a record five consecutive wet years, it seemed probable that 2000 would not be another wet year.  Subsequently, climatic conditions demonstrated the great variability typical of California. Substantial precipitation and snowpack accumulation brought Northern California to near average water conditions before the end of February. A dry 2000 would not have constituted a drought for most Californians, especially not with storage in the State’s major reservoirs at above average levels as a consequence of the past five wet years. It was recognized, however, that planning should begin for actions to be taken in the event that the following year was also dry. In response to the substantial public interest created by the dry weather conditions, the Department evaluated water supply conditions, changed circumstances since the last drought, and other factors that would affect drought readiness in 2001. The purpose of this report is to review items that the Department should consider in near-term drought planning, putting California’s conditions today into perspective with experiences gained in the 1987-92 drought. The report begins with an overview of California hydrology and water supply, then describes conditions encountered in the 1987-92 drought. Changed conditions since that drought are summarized, and their implications discussed. The report concludes with a list of actions that the Department could take to respond to future drought conditions. It is essential that California prepare for the return of very dry conditions. On June 9, 2000 Governor Davis and Interior Secretary Babbitt announced a “Framework for Action” as the completion of a five-year planning program to implement specific actions of the CALFED Bay-Delta Program. The Framework included a recommendation that Governor Davis appoint a panel to develop a Drought Contingency Plan by the end of 2000. This report will be used to brief the panel on drought actions considered to date, with the expectation that further and more focused actions/programs may be included in the Governor’s Drought Contingency Plan.