A decrease in rockfall probability under climate change conditions in Germany
Abstract. The effect of climate change on rockfall in the German low mountain regions is investigated following two different approaches. The first approach uses a logistic regression model that describes the combined effect of precipitation, freeze-thaw cycles and fissure water on rockfall probability. The climate change signal for past decades is analysed by applying the model to meteorological observations. The possible effect of climate change until the end of the century is explored by applying the statistical model to the output of a multi-model ensemble of 23 regional climate scenario simulations. It is found that the number of days per year exhibiting an above-average probability for rockfall has been mostly decreasing during the last decades. Statistical significance is, however, present only at few sites. A robust and statistically significant decrease can be seen in the RCP8.5 climate scenario simulations for Germany and neighbouring regions, locally falling below -10 % when comparing the last 30 years of the 20th century to the last 30 years of the 21st century. The most important factor determining the projected decrease in rockfall probability is a reduction in the number of freeze-thaw cycles expected under future climate conditions.
For the second approach four large-scale meteorological patterns that are associated with enhanced rockfall probability are identified from reanalysis data. The frequency of all four patterns exhibits a seasonal cycle that maximizes in the cold half of the year (winter/spring). Trends in the number of days that can be assigned to these patterns are determined both in meteorological reanalysis data and in climate simulations. In the reanalysis no statistically significant trend is found. For the future scenario simulations all climate models show a statistically significant decrease in the number of rockfall promoting weather situations.
Katrin M. Nissen et al.
Status: open (until 21 Apr 2023)
- RC1: 'Comment on egusphere-2023-94', Anonymous Referee #1, 01 Mar 2023 reply
Katrin M. Nissen et al.
Katrin M. Nissen et al.
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I’ve read with interest this article. It presents an application of two different methods to evaluate the impact of climate change on rockfall probability in Germany. The article is clear, overall well-written, and well-structured, following the IMRAD structure. The literature review is appropriate. The figures are sufficiently good.
I think that the manuscript deserves publication in NHESS journal after minor revisions. I listed below some specific comments and some suggestions for technical corrections.
- Line 39. Some interesting references: https://doi.org/10.1007/s11069-017-3003-3 ; https://doi.org/10.5194/nhess-16-2085-2016 ; https://doi.org/10.1016/j.scitotenv.2014.02.102
- Line 60. Do you have any information on the accuracy with which the rockfalls were mapped or localized spatially?
- Line 74. Any consideration regarding the use of rainfall data with a daily temporal resolution for rockfalls?
- Line 76. Are the E-OBS and REGNIE spatial resolutions in accordance with the spatial resolution of the rockfall database? Or perhaps they are too coarse?
- Line 85. Why did you decide to use the 1971-2000 period and not the "common" 30-year period 1981-2010?
- Line 88. This is interesting about RCP8.5: https://www.nature.com/articles/d41586-020-00177-3. However, why have you not used also another RCP?
Two general comments:
- Have you checked the presence of change points and structural breaks rockfall time series (e.g. Pettitt test)?
- Have you checked if the series can be correlated (e.g. if a correlation coefficient can be calculated or if a Kendall test (correlation rank) can be applied)?
- Line 103. Why 9 days? Probably it was defined in Nissen et al 2022, however, I would suggest adding some details here.
- Line 111. The observational period is 1950-2020, while the period considered for the present-day greenhouse as forcing is 1971-2000. Some details should be added regarding this inhomogeneity.
- Lines 162-169. These sentences are not very clear.
- Line 179. “The trend is statistically significant only at few sites”. It seems they are very few. How many? What's the percentage with respect of the total?
I would suggest adding in the conclusions section more findings and the main novelty of the present work. Eventually also limitations (also considering my comments above) and future perspectives could be added.
- Use either “rockfalls” or “rock falls” to be consistent in the whole text.
- Line 1. change “rockfalls” or “rockfall probability”
- Line 116. perhaps “statistically significant”?
- Figures 1 and 2. I'd suggest adding in the caption the projection used.
- Figure 3. Check the abbreviations in the caption and in the figure legend.
- Figure 4. I would separate the two labels in each bar vertically, for better readability.
- Figure 5. I would reduce the font of the 1,2,3,6, labels. Perhaps the a), b), c), and d) labels should be added.
- Figure 6 I would add the abbreviations in the caption, e.g. (FTC, light blue) and (PRECIP, dark blue).