Contribution of land-atmosphere processes to recent European summer heat – A New Paper

There is a new paper on the European heat wave of 2003 and of other years (thanks to Charles Muller for alerting me to this new contribution!). The paper is

Fischer E. M., S. I. Seneviratne, D. Lüthi, C. Schär (2007), Contribution of land-atmosphere coupling to recent European summer heat waves, Geophys. Res. Lett., 34, L06707, doi:10.1029/2006GL029068.

The abstract reads,

“Most of the recent European summer heat waves have been preceded by a pronounced spring precipitation deficit. The lack of precipitation and the associated depletion of soil moisture result in reduced latent cooling and thereby amplify the summer temperature extremes. In order to quantify the contribution of land-atmosphere interactions, we conduct regional climate simulations with and without land-atmosphere coupling for four selected major summer heat waves in 1976, 1994, 2003, and 2005. The coupled simulation uses a fully coupled land-surface model, while in the uncoupled simulation the mean seasonal cycle of soil moisture is prescribed. The experiments reveal that land-atmosphere coupling plays an important role for the evolution of the investigated heat waves both through local and remote effects. During all simulated events soil moisture-temperature interactions increase the heat wave duration and account for typically 50–80% of the number of hot summer days. The largest impact is found for daily maximum temperatures during heat wave episodes.”

Excerpts from the paper are

“As regards climate change, model simulations indicate that extraordinary hot summers over Europe and other mid-latitudinal regions will become more frequent, more intense and longer lasting in the future [e.g., Meehl and Tebaldi, 2004; Giorgi et al., 2004], partly associated with an increase in interannual temperature variability [e.g., Schär et al., 2004; Vidale et al., 2007]. Seneviratne et al. [2006] found that the latter variability increase is strongly related to land-atmosphere coupling.”

and

” The regional climate model experiments reveal a major contribution of land-atmosphere interactions to the spatial and temporal extent of all four heat waves. In all the cases considered, the difference between coupled and uncoupled simulations is considerably larger than the model biases. Land-atmosphere interactions over the drought regions account for typically 50–80% of the NHD. This is mainly due to local effects through the limitation of evaporation (and compensation by sensible heat flux) due to drought conditions. Additionally drought conditions may have remote effects on areas around or outside the actual drought region, through changes in atmospheric circulation and advection of air masses. These mechanisms enhance the anticyclonic circulation over or slightly downstream of a drought anomaly. However, a larger computational domain or global simulations would be needed to further explore this effect.”

This paper adds to the information on the reasons for these heat waves and how anomalous they are as discussed in

Chase, T.N., K. Wolter, R.A. Pielke Sr., and Ichtiaque Rasool, 2006: Was the 2003 European summer heat wave unusual in a global context? Geophys. Res. Lett., 33, L23709, doi:10.1029/2006GL027470.

The Fischer et al paper emphasizes a point that is made frequently on Climate Science that we need a regional focus on the role of human- and natural causes of climate variability and change. The use of the global average temperature completely misses these regional issues.

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