Technical note: Precipitation-phase partitioning  at landscape scales to regional scales

Lynn, Elissa; Cuthbertson, Aaron; He, Minxue; Vasquez, Jordi P.; Anderson, Michael L.; Coombe, Peter; Abatzoglou, John T.; Hatchett, Benjamin J.

doi:10.5194/hess-24-5317-2020

Cited by 34 publications

(23 citation statements)

References 55 publications

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“…In comparison, for the San Joaquin River region, only one model ("complement") projects a significant negative trend under the lower emission scenario and three models (all but the "average" model) suggest a significant negative trend under the higher emissions scenario. This result suggests that the San Joaquin River region is less hydrologically sensitive in a warming climate as compared with the Sacramento River region, a finding that is replicated in previous studies [52,71,72].…”

Section: Attribution Of Potential Changessupporting

confidence: 79%

Projected Changes in Water Year Types and Hydrological Drought in California’s Central Valley in the 21st Century

He¹,

Anderson²,

Lynn³

et al. 2021

Climate

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The study explores the potential changes in water year types and hydrological droughts as well as runoff, based on which the former two metrics are calculated in the Central Valley of California, United States, in the 21st century. The latest operative projections from four representative climate models under two greenhouse-gas emission scenarios are employed for this purpose. The study shows that the temporal distribution of annual runoff is expected to change in terms of shifting more volume to the wet season (October–March) from the snowmelt season (April–July). Increases in wet season runoff volume are more noticeable under the higher (versus lower) emission scenario, while decreases in snowmelt season runoff are generally more significant under the lower (versus higher) emission scenario. In comparison, changes in the water year types are more influenced by climate models rather than emission scenarios. When comparing two regions in the Central Valley, the rain-dominated Sacramento River region is projected to experience more wet years and less critical years than the snow-dominated San Joaquin River region due to their hydroclimatic and geographic differences. Hydrological droughts in the snowmelt season and wet season mostly exhibit upward and downward trends, respectively. However, the uncertainty in the direction of the trend on annual and multi-year scales tends to be climate-model dependent. Overall, this study highlights non-stationarity and long-term uncertainty in these study metrics. They need to be considered when developing adaptive water resources management strategies, some of which are discussed in the study.

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Section: Attribution Of Potential Changessupporting

confidence: 79%

Projected Changes in Water Year Types and Hydrological Drought in California’s Central Valley in the 21st Century

He¹,

Anderson²,

Lynn³

et al. 2021

Climate

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“…This seasonality of western inland warming has been associated with declining snowpack and earlier snowmelt as part of spring’s progressively earlier start observed since the 1970’s (Cayan et al 2001 ). With continued warming observed across all months over the Southwestern US, snow accumulation has been decreasing as more of the precipitation falls as rain (Knowles et al 2006 ; Lynn et al 2020 ). The warming, accentuated in spring, is also causing a tendency for snow to melt earlier (Mote et al 2018 ).…”

Section: Resultsmentioning

confidence: 99%

Hot and cold flavors of southern California’s Santa Ana winds: their causes, trends, and links with wildfire

et al. 2021

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Santa Ana winds (SAWs) are associated with anomalous temperatures in coastal Southern California (SoCal). As dry air flows over SoCal’s coastal ranges on its way from the elevated Great Basin down to sea level, all SAWs warm adiabatically. Many but not all SAWs produce coastal heat events. The strongest regionally averaged SAWs tend to be cold. In fact, some of the hottest and coldest observed temperatures in coastal SoCal are linked to SAWs. We show that hot and cold SAWs are produced by distinct synoptic dynamics. High-amplitude anticyclonic flow around a blocking high pressure aloft anchored at the California coast produces hot SAWs. Cold SAWs result from anticyclonic Rossby wave breaking over the northwestern U.S. Hot SAWs are preceded by warming in the Great Basin and dry conditions across the Southwestern U.S. Precipitation over the Southwest, including SoCal, and snow accumulation in the Great Basin usually precede cold SAWs. Both SAW flavors, but especially the hot SAWs, yield low relative humidity at the coast. Although cold SAWs tend to be associated with the strongest winds, hot SAWs tend to last longer and preferentially favor wildfire growth. Historically, out of large (> 100 acres) SAW-spread wildfires, 90% were associated with hot SAWs, accounting for 95% of burned area. As health impacts of SAW-driven coastal fall, winter and spring heat waves and impacts of smoke from wildfires have been recently identified, our results have implications for designing early warning systems. The long-term warming trend in coastal temperatures associated with SAWs is focused on January–March, when hot and cold SAW frequency and temperature intensity have been increasing and decreasing, respectively, over our 71-year record.

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“…Moreover, studies have shown that for the S/P ratio, the trends are the most noticeable in spring 39 , at low to mid-elevations typically between 1500 and 2500 m near the climatological freezing level 32 , 37 , 39 , 40 . These elevations have been identified as the most vulnerable to warming 41 .…”

Section: Conclusion and Discussionmentioning

confidence: 99%

The latitudinal dependence in the trend of snow event to precipitation event ratio

Shi

Liu

2021

Sci Rep

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Precipitation phase is expected to shift from solid to liquid with temperature rising, which would in turn bring challenges to regional water resource management. Although in recent decades, consistent decreasing trends in the ratio of snowfall to precipitation rate in a warming climate have been found across multiple regions, a global view of the trends in the precipitation partitioning has not been established. In this study, we investigated the global trends of annual rain and snow frequency of occurrences and the ratio of number of snow events to number of precipitation events (SE/PE ratio) using land station and shipboard synoptic present weather reports from 1978 to 2019. Results show that when averaged over all qualified land stations and over the shipboard reports, both the annual rain frequency and snow frequency decrease over the 42 years. Over both land and ocean, the averaged SE/PE ratio has a significant decreasing trend. Moreover, the trend of SE/PE ratio shows a strong latitudinal dependence. At the mid- and low latitudes in the Northern Hemisphere, the SE/PE ratio has a decreasing trend. In contrast, at high latitudes, the SE/PE ratio has an increasing trend.

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Technical note: Precipitation-phase partitioning at landscape scales to regional scales

Cited by 34 publications

References 55 publications

Projected Changes in Water Year Types and Hydrological Drought in California’s Central Valley in the 21st Century

Projected Changes in Water Year Types and Hydrological Drought in California’s Central Valley in the 21st Century

Hot and cold flavors of southern California’s Santa Ana winds: their causes, trends, and links with wildfire

The latitudinal dependence in the trend of snow event to precipitation event ratio

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