Uncertainties in Future Projections of Summer Droughts and Heat Waves over the Contiguous United States

Abstract

24 25Droughts and heat waves have important impacts on multiple sectors including water 26 resources, agriculture, electricity generation, and public health, so it is important to 27 understand how they will be affected by climate change. However, there is large 28 uncertainty in the projected changes of these extreme events from climate models. We 29 compare historical biases in models against their future projections to understand and 30 attempt to constrain these uncertainties. Historical biases in precipitation, near-surface air 31 temperature, evapotranspiration, and a land-atmospheric coupling metric are calculated 32 Similarly, it is challenging to predict greenhouse gas emissions because they depend on 85 human development and mitigation efforts. Uncertainty from climate models occurs 86 because they include different sets of physical processes, use different parameterizations, 87 or have different spatial and vertical resolutions, even though they share significant 88 components and seek to solve the same general physical equations (Knutti et al. 2013). 89 90The work presented here focuses on the uncertainty in future projections of droughts and 91 heat waves derived from the diversity of climate models in CMIP5, and seeks to 92 5 constrain it by using information on the models' historical biases. These biases are 93 calculated using observationally constrained model output for key variables of the land 94 surface, near-surface atmosphere, and their interactions, which are important in 95 representing and controlling the occurrence of droughts, heat waves, and their feedbacks. 96Land-atmospheric (L-A) coupling is one of the main physical processes examined. This 97 represents how much influence the land surface has on the lower part of the atmosphere 98 and vice versa. The type of coupling determines whether a region is water-limited 99

Model consensus projections of US regional hydroclimates under greenhouse warming

“…In addition, land-atmosphere feedbacks may amplify continental aridification (Berg et al 2016). The greenhouse-induced increases in dryness index DI are also consistent with other CMIP5 studies climate (Dai 2013, Seager et al 2013, Cook et al 2014Lin et al 2015;Scheff and Frierson 2015;Huang et al 2016;Bonfils et al 2017;Herrera-Estrada and Sheffield 2017), which use a variety of dryness measures to identify an increasing propensity for continental aridity in projections of greenhouse-warmed 21st century.…”

Response of electricity sector air pollution emissions to drought conditions in the western United States

“…Climate change could alter the pattern of drought frequency and severity in future decades, particularly during the spring and summer due to reduced snowpack (Seager et al 2007, Sheffield and Wood 2008, Rauscher et al 2008, Diffenbaugh and Ashfaq 2010, Seager and Vecchi 2010, 2015, Maloney et al 2014, Wuebbles et al 2014, Cook et al 2014, 2015, Herrera-Estrada and Sheffield 2017, Mankin et al 2017, Ting et al 2018. Even if aggressive global mitigation efforts consistent with the U.N. Paris Agreement (UNFCCC 2015) are achieved, regional drought-induced emissions are likely to continue at their historical levels (absent other interventions such as investments in renewable technology and thermoelectric power plants with more efficient cooling systems and emissions controls).…”

“…Fourth, sub-regional data on electricity generation (EIA 2017) and pollutant emissions (EPA 2017) are available. And fifth, several important droughts have affected the western US in recent years, and it is expected that the region will experience increasing likelihood of droughts due to climate change, in part due to reduced water availability during the spring and summer associated with decreased snowpack (Seager et al 2007, Sheffield and Wood 2008, Rauscher et al 2008, Diffenbaugh and Ashfaq 2010, Seager and Vecchi 2010, 2015, Maloney et al 2014, Wuebbles et al 2014, Cook et al 2014, 2015, Herrera-Estrada and Sheffield 2017, Mankin et al 2017, Ting et al 2018. This regional drought prevalence provides multiple events through which to measure the response of the electricity sector.…”

Climate Change Projected to Exacerbate Impacts of Coastal Eutrophication in the Northern Gulf of Mexico

“…Physical forcing promotes enhanced stratification amplifying the effect of climate change on eutrophication-induced oxygen loss and acidification. The wind distribution may vary with climate change (e.g., Bakun et al, 2010Bakun et al, , 2015, but there is high uncertainty (Herrera-Estrada & Sheffield, 2017;Wuebbles et al, 2014) and no clear picture for the northern Gulf as of yet (Kulkarni & Huang, 2014;Lehrter et al, 2017). Mixing events may also vary, with fewer but stronger hurricanes projected for the Gulf of Mexico (Bruyè re et al, 2017).…”