Evaluation of Non-hydrostatic Simulations of Northeast Pacific Atmospheric Rivers and Comparison to In-situ Observations

American Meteorological Society (AMS) | August 31st, 2015

Atmospheric rivers are long, narrow bands of concentrated atmospheric water vapor transport that provide an important atmospheric linkage between the subtropics and the m

Atmospheric rivers are long, narrow bands of concentrated atmospheric water vapor transport that provide an important atmospheric linkage between the subtropics and the midlatitudes, facilitating over 90% of meridional water vapor flux and often resulting in extreme precipitation events in regions of enhanced coastal orography. In this investigation, the authors conduct continuous (3 month), large-domain (3600 km × 3200 km), high-resolution (4 km), nonhydrostatic simulations using the Weather Research and Forecasting (WRF) Model and compare the observations to previously reported dropsonde observations from the California Land-Falling Jets Experiment (CALJET) and the Pacific Land-Falling Jets Experiment (PACJET) in order to address an existing gap in knowledge regarding the ability of atmospheric models to simulate the finescale vertical and horizontal structure of atmospheric rivers. The WRF simulations reproduce key structural and thermodynamic characteristics of atmospheric rivers—including well-defined corridors of strong water vapor transport, moist-neutral stability in the lower troposphere, and strong low-level jet/water vapor transport maxima near ~1 km MSL. While WRF does generally capture the extreme values of instantaneous vertically integrated water transport—a defining feature of real-world atmospheric rivers—constituent variables exhibit biases relative to observations, including −11.2% for integrated vapor transport, +5.9% for integrated water vapor, and −17.7% for 1 km MSL wind speed. Findings suggest that high-resolution nonhydrostatic atmospheric simulations are an appropriate tool for investigating atmospheric rivers in contexts where finescale spatial structure and realistic water vapor transport maxima are important.

Evapotranspiration frequently increases during droughts

Nature Portfolio (Springer Nature) | October 27th, 2022

Changes in evapotranspiration (ET) affect water availability and ecosystem health. Higher evaporative demand during drought acts to increase ET, but droughts also reduce

Changes in evapotranspiration (ET) affect water availability and ecosystem health. Higher evaporative demand during drought acts to increase ET, but droughts also reduce the moisture supply necessary for ET, limiting predictions of even the sign of ET anomalies. Drought-driven increases in ET (ET+drought) are of particular concern because they quickly deplete water resources, causing flash droughts and acute stress on ecosystems. Here, using a water balance approach, we show that ET+drought is globally widespread, occurring in 44.4% of drought months. The sign of ET’s drought response depends most on the magnitude of precipitation and total water storage anomalies, rather than its location. The Coupled Model Intercomparison Project Phase 6 Earth system models underestimate the ET+drought probability by nearly one-half, and more so in drier regions, primarily due to missing representations of soil structure effects on soil evaporation, as well as incorrectly parameterized plant and soil traits. These processes should be prioritized to reduce model uncertainties in the water–energy–food nexus.

Evolution of global snow drought characteristics from 1850 to 2100

Environmental Research Letters (IOP) | June 6th, 2023

Examining the Contribution of the Observed Global Warming Trend to the California Droughts of 2012/13 and 2013/14

American Meteorological Society (AMS) | September 30th, 2014

In this study, we examine the November–February California droughts of 2012/13 and 2013/14. During 2013/14, California had its warmest and third driest rainy se

In this study, we examine the November–February California droughts of 2012/13 and 2013/14. During 2013/14, California had its warmest and third driest rainy season on record (1895–2014), while the 2012/13 season registered as the 45th warmest and 38th driest (Vose et al. 2014). The 2013 January–December calendar year was the driest on record (Water CA 2014). These consecutive below-normal seasons conspired with warm temperatures to reduce California’s snowpack to the second lowest level since 1960, when recording began, with snowpack at 24% of normal (Water CA 2014). Between January 2013 and January 2014, satellite observations documented dramatic snowpack-related land cover change (NASA Earth Observatory 2014): in 2014, the Cascade, Sierra Nevada, and Coastal ranges were almost completely devoid of snow. In February and March of 2014, air temperatures were extremely warm (NOAA NCDC 2014; HPRC 2014), and U.S. Geological Survey (USGS) observations indicated extreme or moderate hydrologic drought (USGS 2014) and high levels of vegetation stress (VegDRI 2014). The state declared a drought emergency (NIDIS 2014). While it is too soon to assess the full impact of the 2012/13 and 2013/14 California droughts, they seem likely to substantially impact the state’s ability to generate hydrologic power, support agriculture, reduce the risk of forest and bush fires, and protect fragile ecosystems (Huffington Post 2014). *Chapter 4, Explaining Extreme Events of 2013 from a Climate Perspective, Bull. Amer. Meteor. Soc., 95 (9)

Executive Order N-4-23

State of California | March 10th, 2023

Expansion and Intensification of the North American Monsoon During the Pliocene

American Geophysical Union (AGU) | November 10th, 2022

Exploring the Spatially Compounding Multi‐Sectoral Drought Vulnerabilities in Colorado's West Slope River Basins

American Geophysical Union (AGU) | November 9th, 2024

Exploring Water System Vulnerabilities in California's Central Valley Under the Late Renaissance Megadrought and Climate Change

American Geophysical Union (AGU) | April 24th, 2025

Exposure history determines pteropod vulnerability to ocean acidification along the US West Coast

Nature Portfolio (Springer Nature) | July 3rd, 2017

The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar  < 1) along the US West Coast and is recognized as

The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar  < 1) along the US West Coast and is recognized as one of the species most susceptible to ocean acidification (OA). Yet, little is known about their capacity to acclimatize to such conditions. We collected pteropods in the California Current Ecosystem (CCE) that differed in the severity of exposure to Ωar conditions in the natural environment. Combining field observations, high-CO2 perturbation experiment results, and retrospective ocean transport simulations, we investigated biological responses based on histories of magnitude and duration of exposure to Ωar < 1. Our results suggest that both exposure magnitude and duration affect pteropod responses in the natural environment. However, observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions. Pteropods from the coastal CCE appear to be at or near the limit of their physiological capacity, and consequently, are already at extinction risk under projected acceleration of OA over the next 30 years. Our results demonstrate that Ωar exposure history largely determines pteropod response to experimental conditions and is essential to the interpretation of biological observations and experimental results.

Extreme and compound events in lakes

Nature Portfolio (Springer Nature) | August 19th, 2025

Key points Lake heatwaves have increased in average intensity, average duration and total duration globally, at rates of 0.15 ± 0.3 °C per decade, 2.1 

Key points Lake heatwaves have increased in average intensity, average duration and total duration globally, at rates of 0.15 ± 0.3 °C per decade, 2.1 ± 3.1 days per decade and 8.8 ± 7.6 days per decade, respectively, since the 1980s. The probability of lake heatwave events is three times more likely in a 1.5 °C warming scenario and 25 times more likely in a 3.5 °C scenario compared with pre-industrial conditions. Half of the world’s largest lakes experienced declines in water storage between 1992 and 2020, accompanied by corresponding reductions in surface extent. Extreme events in lakes can cause considerable impacts, including the onset of hypoxia, harmful algal blooms, disruption of food webs and loss of ecosystem services. Basin-scale anthropogenic stressors, such as nutrient enrichment, land-use change and water withdrawal, interact with climate extremes to increase the frequency, intensity and ecological consequences of in-lake extremes.