Réf. Lenderink & van Meijgaard 2010 - A

Référence bibliographique complète

LENDERINK, G., VAN MEIJGAARD, E. 2010. Linking increases in hourly precipitation extremes to atmospheric temperature and moisture changes. Environmental Research Letters, Vol. 5, doi :10.1088/1748-9326/5/2/025208. [Etude en ligne]

Abstract: Relations between hourly precipitation extremes and atmospheric temperature and moisture derived for the present-day climate are studied with the aim of understanding the behavior (and the uncertainty in predictions) of hourly precipitation extremes in a changing climate. A dependency of hourly precipitation extremes on the daily mean 2 m temperature of approximately two times the ClausiusClapeyron (CC) relation is found for temperatures above 10°C. This is a robust relation obtained in four observational records across western Europe. A dependency following the CC relation can be explained by the observed increase in atmospheric (absolute) humidity with temperature, whereas the enhanced dependency (compared to the CC relation) appears to be caused by dynamical feedbacks owing to excess latent heat release in extreme showers. Integrations with the KNMI regional climate model RACMO2 at 25 km grid spacing show that changes in hourly precipitation extremes may indeed considerably exceed the prediction from the CC relation. The results suggests that increases of + 70% or even more are possible by the end of this century. However, a different regional model (CLM operated at ETHZ) predicts much smaller increases; this is probably caused by a too strong sensitivity of this model to a decrease in relative humidity.

Mots-clés

Extreme precipitation - Climate change - Water vapour - ClausiusClapeyron relation

 

Organismes / Contact

• Royal Netherlands Meteorological Institute, PO Box 201, 3730 AE De Bilt, The Netherlands (lenderin@knmi.nl)

 

(1) - Paramètre(s) atmosphérique(s) modifié(s)

(2) - Elément(s) du milieu impacté(s)

(3) - Type(s) d'aléa impacté(s)

(3) - Sous-type(s) d'aléa

 Temperature, Precipitation, Moisture

 

 

 

 

Pays / Zone

Massif / Secteur

Site(s) d'étude

Exposition

Altitude

Période(s) d'observation

 Europe

 

 

 

 

 

 

(1) - Modifications des paramètres atmosphériques

Reconstitutions

 

Observations

 

Modélisations

The authors investigated the relations between hourly precipitation extremes, temperature and moisture in observations and regional climate model results, thus extending on the work by Lenderink and van Meijgaard (2008). They found that for the observations:

(i) The temperature dependency of hourly precipitation extremes of approximately two times the CC relation appears robust. It is found in four independent data sources in western Europe.

(ii) This scaling appears to be primarily linked to the increase in atmospheric moisture (or equivalently, the dew point temperature) with temperature. Two findings support this. First, the dependency of the hourly precipitation extremes on the dew point temperature reveals a more robust scaling behavior for the different percentiles and, second, this dependency is (slightly) stronger (compared to the temperature dependency) in all data sets.

(iii) The statistical influence on the scaling of frequency changes of different precipitation types with temperature is likely small. The primary reason for the super CC scaling appears to relate to the physics of the convective events themselves.

Two climate scenario integrations with the regional model RACMO2 show an increase of hourly precipitation extremes that considerably exceeds the prediction from the CC relation. Results from a different regional model, CLM, show a much lower response, which appears to be caused by the strong sensitivity of this model to a reduction in relative humidity. It is interesting that the version of CLM discussed here employs a closure of the convection scheme based on moisture convergence. Hohenegger et al (2009) showed that this closure led to a strong positive feedback with soil drying leading to a reduction in precipitation, opposing the results of a non-hydrostatic version of the model that gave rise to a negative soil moisture feedback.

From the results of the two regional climate models the following conceptual picture emerges. Two main factors play an important role in determining changes of hourly precipitation extremes in the climate scenario integrations: first, the response of the model to absolute humidity (dew point temperature), and second the response to relative humidity (dew point depression). Scaling relations derived from simulations of the present-day climate show that the two models considered here capture the response to absolute humidity reasonably well, although they tend to underestimate the dependency for the lower percentiles and in the high (dew point) temperature range. The response to relative humidity is not so well represented, in particular in CLM.

The characteristics of the two models considered here do not necessarily apply in general. However, the authors think that by employing the conceptual framework and the scaling relations presented in this paper a considerable part of the uncertainty in predictions of future (hourly) precipitation extremes can be understood.

Hypothèses

The primary reason why precipitation extremes are expected to increase follows from the fact that a warmer atmosphere can ‘hold’ more moisture. The increase in the moisture-holding capacity of the atmosphere with temperature occurs at a rate given by the ClausiusClapeyron relation: approximately 7% per degree temperature rise. If the relative humidity in the future climate remains approximately the same as in the present-day climate—which is generally expected based on model results and physical arguments (Held and Soden 2006)—the amount of water vapor in the atmosphere will increase at the same rate. Now, the commonly used argument is that in extreme precipitation events all water vapour in the air (or a constant fraction thereof) is converted to rain. Hence, extreme precipitation will scale with the ClausiusClapeyron relation.

 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

This study focus on western Europe, defined as the land area north of the Alps (>47◦N), south of Norway (<60◦N) and west of western Poland (<20◦E). This area is characterized by moderately high temperatures in summer (as opposed to the lower temperatures in northern Europe) and is not strongly affected by widespread shortage of soil water in summer (as opposed to the dry conditions in southern Europe and the Mediterranean).

Observations: The authors repeated the analysis in Lenderink and van Meijgaard (2008) using, besides the data of De Bilt, three other data sources: (i) data from 1950 to 2005 measured at Ukkel (Belgium), (ii) data from 1981 to 2008 measured at Bern, Basel and Zurich (Switzerland), and (iii) data from 27 stations within The Netherlands from 1995 to August 2009. Dependency on temperature: First, the hourly precipitation data was divided into bins of 2°C width based on the daily mean temperature. From the binned data the 90th, 99th and 99.9th percentiles of the distribution of wet events were computed. In addition to the percentiles computed from the raw data, the 99th and 99.9th percentile were also computed from a generalized Pareto distribution fitted to the upper 4% of the data. Uncertainty bands were computed using the bootstrap. Dependency on moisture: As a measure of atmospheric moisture we use the 2 m dew point temperature Td, which is defined as the temperature to which an air parcel must be cooled (at constant pressure) to reach saturation. A 1◦ increase in dew point temperature is equivalent to an increase of ∼7% in moisture content. A constant relative humidity is approximately equivalent to a constant dew point depression, which is defined by T − Td.

Models: The authors used results of two regional models, RACMO2 run at KNMI and a version of CLM run at ETHZ from the EU funded project ENSEMBLES (Hewitt and Griggs 2004), in which a large number of regional climate simulations for the present day and future climate have been performed at 25 km grid spacing.. These models were chosen because they are representative of the upper and lower bounds in the change of precipitation extremes (hourly as well as daily) within the model ensemble. The change in the 99.9th percentile of maximum hourly precipitation in summer between 2071–2100 and 1971–2000 were studied.

 

(2) - Effets du changement climatique sur le milieu naturel

Reconstitutions

 

Observations

 

Modélisations

 

Hypothèses

 

 

Sensibilité du milieu à des paramètres climatiques

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 

 

 

(3) - Effets du changement climatique sur l'aléa

Reconstitutions

 

Observations

 

Modélisations

 

Hypothèses

 

 

Paramètre de l'aléa

Sensibilité des paramètres de l'aléa à des paramètres climatiques

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

 

 

 

 

(4) - Remarques générales

 

 

(5) - Syntèses et préconisations

 

Références citées :

Held I M and Soden B J 2006 Robust responses of the hydrological cycle to global warming J. Clim. 19 5686–99.

Lenderink G and van Meijgaard E 2008 Increase in hourly precipitation extremes beyond expectations from temperature changes Nat. Geosci. 1 511–4.