Plot showing the latitudinal dependence of Clausius-Clapeyron scaling.
Latitudinal dependence of Clausius-Clapeyron scaling. The dashed horizontal blue line represents the scaling that is directly derived from the Clausius-Clapeyron relation, equal to ~6-7 % more precipitation per degree of warming. The red bars represent the aggregate value of the scaling derived from observations, binned by latitude. By and large, for broad latitudinal belts where there is sufficient hourly and daily precipitation data, the estimate is consistent with theoretical scaling. Credit: Ali et al. [2021], Figure 3b
Source: Geophysical Research Letters

We all know that temperatures rise with the concentration of greenhouse gases in the atmosphere. How precipitation will change with warming is a trickier question. One way to form an expectation of precipitation change is to tie it to the temperature increase by way of the Clausius-Clapeyron (CC) relation: as the atmosphere warms, it holds more moisture. All else being equal, the increase in atmospheric humidity translates into increased potential for heavier precipitation. But how much heavier?

Ali et al. [2021] bring clarity on the subject in two ways. First, they show that dew point temperature, which despite the name is a measure of the humidity in the air, is more closely related to precipitation than temperature. (Dew point temperature is the temperature at which the air would saturate, triggering the condensation that produces dew. The larger its difference from actual temperature, the drier the air). Second, they show that in most places where we have adequate records of hourly and daily precipitation, variations in precipitation are much more spatially coherent and consistent with CC scaling, which predicts a change of ~6-7% in precipitation per degree of warming, than previously thought.

Citation: Ali, H., Fowler, H. J., Lenderink, G., Lewis, E., & Pritchard, D. [2021]. Consistent large‐scale response of hourly extreme precipitation to temperature variation over land. Geophysical Research Letters, 48, e2020GL090317.

―Alessandra Giannini, Editor, Geophysical Research Letters

Text © 2021. The authors. CC BY-NC-ND 3.0
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