Relating remotely sensed forest damage data to wind data: storms Lothar (1999) and Vivian (1990) in Switzerland

Abstract

This study compares the surface wind speed and forest damage data of two exceptionally severe winter storms, Vivian 1990 and Lothar 1999. The study area comprises the region that suffered damage in Switzerland. The wind speed data were derived from simulations of MeteoSwiss (Federal Office of Meteorology and Climatology), measurements during the storm periods and expert analyses of the data. The remotely sensed forest damage data were provided by the Federal Office for the Environment and the forest cover data by Swiss Federal Statistical Office. We compared data on the peak gust and maximum average wind speed, with data on the spatially related forest area and forest damage area, and found some clear differences in the correlations between the different wind data and forest damage. Our results point generally to the damage-causing role of near-surface gusts at maximum wind speeds during the storm. These tended to be spatially distributed on a fine scale. In only a few cases were the results statistically significant. However, these results could probably be improved with better wind data. For example, gust measurements spatially closer to forests or simulations of gusts at maximum wind speed could be produced with a spatially higher resolution.

Comparison and validation of three versions of a forest wind risk model

“…This reflects the extremely localised effects of variations in wind speed during a storm. Usbeck et al (2012) found that wind gust speed at the surface was the most important factor leading to damage and dominated all other factors, but found it very difficult to correlate wind speeds directly with damage to particular stands. Schütz et al (2006) and Albrecht et al (2012) also could not find a correlation between damage and measured wind speeds; this is probably a reflection of the spatial resolution of the measurements or model simulations used, and points to the extremely local variability in wind speeds during storms (Boose et al, 1994).…”

“…Until there are improvements in meso-scale airflow modelling (e.g. Lopes da Costa et al, 2006), accurate prediction of damage at a stand level in complex terrain remains extremely challenging (Usbeck et al, 2012). Another possible cause for the over-prediction of damage to older stands is the accuracy of available stand data for input to the models.…”

“…The comprehensive review in Usbeck et al (2012) of previous statistical modelling of the factors leading to wind damage in forests shows how difficult it is to ascribe particular stand, tree or meteorological factors to enhanced stand vulnerability. There can often be conflicting evidence for the importance of a particular factor, with the relative importance of tree characteristics often very dependent on the exact site conditions, e.g.…”

Projection of impacts of climate change on windthrows and evaluation of potential adaptation measures in forest management: A case study from empirical modelling of windthrows in Hokkaido, Japan, by Typhoon Songda (2004)

“…Usbeck et al, 2011 andKlaus et al, 2011). If topographic exposure is used, however, it is difficult to separate effects of hazards and exposure in climate-change impact assessments.…”

Is there added value of convection-permitting regional climate model simulations for storms over the German Bight and Northern Germany?

“…The high-resolution RCM run realistically reproduced observed storm features and the gusts along the cold front were often close to observations and exceeded hurricane strength. Other extratropical winter storms were investigated in RCM studies, such as Anatol (Nilsson et al 2007), Lothar and Vivian (Usbeck et al 2012), and Xynthia (Liberato et al 2013). These studies showed that an RCM with a high resolu-tion of 2 km produces a realistic wind field compared with observations.…”