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Towards a rapid assessment capability for dry and oppressive excessive heat events over the United States

We propose to disentangle the influences between a changing climate and the natural climate variability on the probability of occurrence of excessive heat events (EHEs) and in parallel, quantify uncertainties in the computation of the fraction of attributable ris (FAR). Our approach exploits Granger causality to investigate the magnitude with which specific physical processes influence the intensity and duration of EHEs. This process study will serve as a bridge between natural modes of variability and climate trends, and the evolution of EHEs, and will facilitate an almost real-time attribution capacity. Our research uses direct observations, reanalyses, and CMIP6 model experiments. 

The quantification of EHEs is related to the impacts of heat on human health and uses the Excessive Heat Factor (EHF). Methodologies are general enough to be easily applicable to other sectors, e.g., agriculture and energy. To accomplish our scope, we divide our wor plan into four objectives.Objective 1defines the optimal lin age between environmental conditions to casualties from heat stress as cataloged in NOAA’s Billion-Dollar Disaster database. Objective 2 investigates the processes that control the amplitude and longevity of EHEs. The focus will be on (1) summertime atmospheric bloc ing, especially on factors that control the probability of occurrence of quasi-stationary wavenumber 5–8 Rossby waves, (2) the importance of soil moisture and heat content conditions prior to and during an EHE, (3) the coupling between the troposphere and the land-surface through the planetary boundary layer during EHEs, and (4) the origin and trajectories of air masses affecting the region of excessive heat. Objective 3 explores how natural modes of variability (ENSO and its flavors, and the Atlantic/Pacific multi-decadal/decadal oscillation), and climate trends modulate the evolution of EHEs by influencing the causal factors established by objective 2. For example, natural modes of variability and climate change may affect precipitation patterns during winter and spring, thus affecting soil-moisture conditions prior to an EHE. Finally, Objective 4 applies the methodology to EHEs that occurred over the U.S. during the very active summers of 2018 and 2019, then to EHEs that will occur during the course of the proposal, i.e., the summers of 2020–2023. 

The proposed research leverages findings from the European project Eucleia by rigorously defining EHEs (Objective 1). The proposal fills the gap of process-oriented studies of extremes and the quantification of uncertainties as articulated by the National Climate Assessment (Objective 2). It responds to the current Type 1 MAPP call by building a bridge between extreme heat and large-scale variability through process understanding (Objective 3). Finally, this wor will provide a pilot attribution methodology and computations of uncertainty by studying EHEs in the summers of 2018–2023, which will support the Type 2 project in the development of a rapid assessment capability (Objective 4). The project leverages NOAA’s Billion-Dollars Disaster database and supports NOAA’s target to build resilience against weather and climate extremes. 

Climate Risk Area: Extreme Heat, Water Resources

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