Future extreme hourly wet bulb temperatures using downscaled climate model projections of temperature and relative humid
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ORIGINAL PAPER
Future extreme hourly wet bulb temperatures using downscaled climate model projections of temperature and relative humidity Marc J. Alessi 1 & Arthur T. DeGaetano 1 Received: 31 March 2020 / Accepted: 26 August 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Extreme wet bulb temperatures are important for a number of applications including the proper and efficient design of building cooling systems. Since wet bulb temperature is not directly available from climate model output and design specifications require information at hourly resolution, whereas twice-daily resolution is more typical of climate models, the ability of climate models to replicate the observed climatology is evaluated at a set of US stations. Observed wet bulb extremes can be replicated by applying a spline fit to the twice-daily humidity and temperature observations that simulate the data available from climate models and then minimizing the residual of the equation specifying the change in enthalpy of moist air. On average, these ersatz values are 1 °C colder than the observed values. Climate model simulations for the period 1950–2005 also generally agree with the ersatz observations. At most locations, the model bias is negative (model values colder than the simulated observations) and on average near 1 °C. The largest positive biases occur at the most arid stations and the largest negative biases are found at the coldest locations. Model projections for the mid-twenty-first century indicate that the most extreme wet bulb temperatures will increase by between 1 and 2.3 °C, with the largest increases at the most northern locations. Future warming and wetting appear to result in a translation of the entire wet bulb cumulative distribution function, leading to similar increases regardless of wet bulb temperature. The increase is fairly consistent among different climate models and at each station.
1 Introduction Wet bulb temperature (Twet) is an important consideration for the design of cooling systems (ASHRAE 2017). Traditionally coincident Twet and dry bulb (Tdry) data have been presented; however, the recent American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) Handbook includes annual extrema of Twet for return periods ranging from 5 to 50 years. Over the 5 years from 2013 to 2017, the 0.4% annual cooling wet bulb was found to increase by 0.01 °C. Albeit consistent with a warmer and wetter climate (Roth 2017), it is not possible to attribute this small change to broader climate change, especially given the short time interval used.
* Arthur T. DeGaetano [email protected] 1
Northeast Regional Climate Center, Department of Earth and Atmospheric Science, Cornell University, 1119 Bradfield Hall, Ithaca, NY 14853, USA
Since the dominant factor affecting cooling loads transitions from Tdry to Twet moving from colder to warmer climates in China (Li et al. 2018), it is argued that humidity should be considered to improve building energy efficiency, especially in commercial an
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