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Rachel Clemesha

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Actionable Science to Understand the Effects of Recent Temperature Increases to Inform Natural Resources Management in the Southwestern United States
In recent decades, average temperatures across the U.S. Southwest have increased substantially and precipitation patterns have increased in variability. The warmer temperatures directly impact water availability within Southwest ecosystems, including earlier snowmelts; reduced snowpacks, soil moisture, and streamflow; and lower humidity. Collectively, this has led to an increase in aridity across this region. This in turn affects terrestrial and aquatic ecosystems, increases wildfire severity, and impacts human activities such as agriculture and municipal water use. These well-documented trends are at the forefront of the concerns of natural resource managers in the Southwest. This project aims to strengthen partnerships...
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How do Atmospheric Rivers and Downslope Winds Affect Wildfire Risk and Water Resources in the Arid Southwest?
The complex mountain and valley chains of the Southwest exert a strong influence on precipitation and wind patterns. Atmospheric rivers deliver some of the most extreme precipitation events to west-southwest-facing slopes of the mountains where strong gusty downslope winds can also spread wildfires. Climate change is making the southwest warmer and dryer resulting in more fire-prone vegetation and more frequent and extreme atmospheric rivers. Understanding this changing system is critical for managing water resources and wildfire in the region. This project will study how climate change is impacting precipitation and winds to create fire weather and drive fire spread on heavily vegetated slopes of coastal mountains....
Abstract Low-level stratiform clouds modulate California's coastal climate during the warm season. Previous work describing the seasonal and daily variability of coastal low cloudiness (CLC) suggests that in July, August, and September southern California's CLC is under the influence of an additional driver, which has less impact in northern California. In this work, we introduce the link in which free-tropospheric moisture dictated by North American Monsoon (NAM) processes can impact southern California CLC. We use in situ and remote sensing observations, as well as reanalysis and single column model simulations to identify and investigate this previously missing component. We find that monsoonal moisture advected...
Categories: Publication; Types: Citation
Atmospheric rivers (ARs) and Santa Ana winds (SAWs) are impactful weather events for California communities. Emergency planning efforts and resource management would benefit from extending lead times of skillful prediction for these and other types of extreme weather patterns. Here we describe a methodology for subseasonal prediction of impactful winter weather in California, including ARs, SAWs and heat extremes. The hybrid approach combines dynamical model and historical information to forecast probabilities of impactful weather outcomes at weeks 1–4 lead. This methodology uses dynamical model information considered most reliable, that is, planetary/synoptic-scale atmospheric circulation, filters for dynamical...
Categories: Publication; Types: Citation
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Understanding the Effects of Seasonal Precipitation Changes on Hydrology and Ecosystems in the Colorado River Basin
The Colorado River provides water to 40 million people in the southwestern United States. Consistent water level declines in Colorado River Basin reservoirs have focused research attention on the long-term changes in winter precipitation and the timing of snowmelt and runoff. Research on how warming temperatures affect winter precipitation and spring snowmelt is ongoing, however, less attention has been given to changes in spring and summer precipitation which also affects water supply, plant growth, and competition between native and non-native plants, and, in turn affects wildfire dynamics and wildlife habitat. The amount and timing of summer precipitation is largely influenced by variation in the North American...
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