Trends in atmospheric patterns conducive to seasonal precipitation and temperature extremes in California seasonal precipitation and temperature extremes

American Association for the Advancement of Science (AAAS) | April 1st, 2016

Recent evidence suggests that changes in atmospheric circulation have altered the probability of extreme climate events in the Northern Hemisphere. We investigate northe

Recent evidence suggests that changes in atmospheric circulation have altered the probability of extreme climate events in the Northern Hemisphere. We investigate northeastern Pacific atmospheric circulation patterns that have historically (1949–2015) been associated with cool-season (October-May) precipitation and temperature extremes in California. We identify changes in occurrence of atmospheric circulation patterns by measuring the similarity of the cool-season atmospheric configuration that occurred in each year of the 1949–2015 period with the configuration that occurred during each of the five driest, wettest, warmest, and coolest years. Our analysis detects statistically significant changes in the occurrence of atmospheric patterns associated with seasonal precipitation and temperature extremes. We also find a robust increase in the magnitude and subseasonal persistence of the cool-season West Coast ridge, resulting in an amplification of the background state. Changes in both seasonal mean and extreme event configurations appear to be caused by a combination of spatially non-uniform thermal expansion of the atmosphere and reinforcing trends in the pattern of sea level pressure. In particular, both thermal expansion and sea level pressure trends contribute to a notable increase in anomalous northeastern Pacific ridging patterns similar to that observed during the 2012–2015 California drought. Collectively, our empirical findings suggest that the frequency of atmospheric conditions like those during California’s most severely dry and hot years has increased in recent decades, but not necessarily at the expense of patterns associated with extremely wet years.

Two-dimensional and three-dimensional digital flow models of the Salinas Valley ground-water basin, California

U.S. Geological Survey (USGS) | November 16th, 1978

The Salinas Valley is a topographic and ground-water basin in central coastal California. The ground-water basin extends from Monterey Bay south­eastward along the Salin

The Salinas Valley is a topographic and ground-water basin in central coastal California. The ground-water basin extends from Monterey Bay south­eastward along the Salinas River to San Arda, a distance of 70 miles, and has a maximum thickness of 2,000 feet. Annual recharge to the ground-water basin, which is derived mostly from the Salinas River, is about 290,000 acre­feet. Annual discharge, which is mostly from pumpage but also includes the consumptive use of ground water by riparian vegetation along the Salinas River, is about 507,000 acre-feet. About 45 percent of the pumpage, or 217,000 acre-feet of water annually, returns to the ground-water system. A group of interacting hydrologic models was developed for the Salinas Valley. These models include the small-stream model, river model, two­dimensional ground-water model, and three-dimensional ground-water model. The small-stream model simulates ground-water recharge from small streams that are tributary to the Salinas River. The river model simulates ground­water recharge from and surface-water discharge in the Salinas River. The two-dimensional and three-dimensional ground-water models simulate hydraulic head in the ground-water basin. The ground-water models were calibrated by comparing water level com­puted by the models to the corresponding measured water level for both steady-state and transient-state simulations. For the steady-state simulation, which was used to calibrate transmissivity for the two-dimensional model and hydraulic conductivity for the three-dimensional model, the median deviation of the model-generated water level from measured water level was 6 and 5 feet for the two-dimensional and three-dimensional models, respectively. For the transient-state simulation, which was used to calibrate storage coefficient for the two-dimensional model and specific storage for the three-dimensional model, the median deviation of the model-generated water level (at the end of a 3-year calibration period) from measured water level was 6 feet for both models.

Two-dimensional, steady-state model of ground-water flow, Nevada Test Site and vicinity, Nevada- California: U.S. Geological Survey Water-Resources Investigations Report 82-4085

U.S. Geological Survey (USGS) | July 1st, 1962

UC groundwater research: A survey

California Agriculture (UCANR) | March 13th, 2018

As California implements the Sustainable Groundwater Management Act (SGMA), UC research is building knowledge and supporting innovation in groundwater recharge, groundwat

As California implements the Sustainable Groundwater Management Act (SGMA), UC research is building knowledge and supporting innovation in groundwater recharge, groundwater accounting, groundwater quality, groundwater governance and more. Here's a sample of work from across the UC system: whole watershed accounting; water availability for recharge; precision data on snowmelt; spatial data on well vulnerability; large scale groundwater recharge and agricultural systems; groundwater-surface water interactions; groundwater quality and salinity; water supply, land use and rural communities; data on water use and water rights; managed aquifer recharge on farmland; soil suitability for recharge; distributed stormwater collection; net metering for groundwater; geophysical imaging; groundwater governance; lessons on groundwater permitting from around the West; supporting Groundwater Sustainability Plan development; the economics of sustainable groundwater management; and considerations for groundwater markets.

Uncertainty in El Niño-like warming and California precipitation changes linked by the Interdecadal Pacific Oscillation

Nature Portfolio (Springer Nature) | November 10th, 2021

Marked uncertainty in California (CA) precipitation projections challenges their use in adaptation planning in the region already experiencing severe water stress. Under

Marked uncertainty in California (CA) precipitation projections challenges their use in adaptation planning in the region already experiencing severe water stress. Under global warming, a westerly jet extension in the North Pacific analogous to the El Niño-like teleconnection has been suggested as a key mechanism for CA winter precipitation changes. However, this teleconnection has not been reconciled with the well-known El Niño-like warming response or the controversial role of internal variability in the precipitation uncertainty. Here we find that internal variability contributes > 70% and > 50% of uncertainty in the CA precipitation changes and the El Niño-like warming, respectively, based on analysis of 318 climate simulations from several multi-model and large ensembles. The Interdecadal Pacific Oscillation plays a key role in each contribution and in connecting the two via the westerly jet extension. This unifying understanding of the role of internal variability in CA precipitation provides critical guidance for reducing and communicating uncertainty to inform adaptation planning.

Understanding End-of-Century Snowpack Changes Over California’s Sierra Nevada

American Geophysical Union (AGU) | January 29th, 2019

Understanding the Contributions of Paleo-Informed Natural Variability and Climate Changes to Hydroclimate Extremes in the San Joaquin Valley of California

American Geophysical Union (AGU) | November 13th, 2023

Understanding the recent increase in multiyear La Niñas

Nature Portfolio (Springer Nature) | September 18th, 2023

Understanding Uncertainties in Future Colorado River Streamflow

American Meteorological Society (AMS) | January 1st, 2014

The Colorado River is the primary water source for more than 30 million people in the United States and Mexico. Recent studies that project streamf low changes in the Col

The Colorado River is the primary water source for more than 30 million people in the United States and Mexico. Recent studies that project streamf low changes in the Colorado River all project annual declines, but the magnitude of the projected decreases range from less than 10% to 45% by the mid-twenty-first century. To understand these differences, we address the questions the management community has raised: Why is there such a wide range of projections of impacts of future climate change on Colorado River streamflow, and how should this uncertainty be interpreted? We identify four major sources of disparities among studies that arise from both methodological and model differences. In order of importance, these are differences in 1) the global climate models (GCMs) and emission scenarios used; 2) the ability of land surface and atmospheric models to simulate properly the high-elevation runoff source areas; 3) the sensitivities of land surface hydrology models to precipitation and temperature changes; and 4) the methods used to statistically downscale GCM scenarios. In accounting for these differences, there is substantial evidence across studies that future Colorado River streamflow will be reduced under the current trajectories of anthropogenic greenhouse gas emissions because of a combination of strong temperature-induced runoff curtailment and reduced annual precipitation. Reconstructions of preinstrumental streamflows provide additional insights; the greatest risk to Colorado River streamf lows is a multidecadal drought, like that observed in paleoreconstructions, exacerbated by a steady reduction in flows due to climate change. This could result in decades of sustained streamflows much lower than have been observed in the ~100 years of instrumental record.

Unprecedented 21st century drought risk in the American Southwest and Central Plains

American Association for the Advancement of Science (AAAS) | February 12th, 2015

In the Southwest and Central Plains of Western North America, climate change is expected to increase drought severity in the coming decades. These regions never

In the Southwest and Central Plains of Western North America, climate change is expected to increase drought severity in the coming decades. These regions nevertheless experienced extended Medieval-era droughts that were more persistent than any historical event, providing crucial targets in the paleoclimate record for bench- marking the severity of future drought risks. We use an empirical drought reconstruction and three soil moisture metrics from 17 state-of-the-art general circulation models to show that these models project significantly drier conditions in the later half of the 21st century compared to the 20th century and earlier paleoclimatic intervals. This desiccation is consistent across most of the models and moisture balance variables, indicating a coherent and robust drying response to warming despite the diversity of models and metrics analyzed. Notably, future drought risk will likely exceed even the driest centuries of the Medieval Climate Anomaly (1100–1300 CE) in both moderate (RCP 4.5) and high (RCP 8.5) future emissions scenarios, leading to unprecedented drought conditions during the last millennium.