the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Mar 2026
Increase of water vapour above the Swiss Plateau from 1995 to 2025 observed by ground-based microwave radiometry
Abstract. For climate change research, it is important to have multiple independent measurement techniques. The ground-based microwave radiometer at Bern has been operated since 1994 and allows the independent derivation of the linear trend of the integrated water vapour column or integrated water vapour (IWV). According to the Clausius-Clapeyron equation, the water vapour saturation increases with increase of temperature. There is also a water vapour feedback since water vapour is a natural greenhouse gas and amplifies man-made global warming. In Switzerland, climate change is stronger than at many other places in the world. We analyse observations of the tropospheric water radiometer (TROWARA) which monitored IWV above Bern from 1995 to 2025. The relative IWV increase is 5.1 %/decade. Evaluation of coincident IWV data from ERA5 (reanalysis of European Centre for Medium-Range Weather Forecasts) gives a trend of 3.7 %/decade. The ERA5 surface air temperature in Bern increased by 0.47K/decade from 1995 to 2025. Thus, we get 10.9 % more IWV for a 1 K increase in case of TROWARA and 7.8 % more IWV for a 1K increase in case of ERA5. Though the IWV trends of TROWARA and ERA5 slightly differ, both datasets agree in the fact that water vapour above the Swiss Plateau significantly increased by 11 % or 16 % from 1995 to 2025. This strong increase of water vapour certainly has an impact on weather, climate, and hydrology.
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Status: open (until 06 May 2026)
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RC1: 'Review of "Increase of water vapour above the Swiss Plateau from 1995 to 2025 observed by ground-based microwave radiometry" by Hocke et al. ', Anonymous Referee #1, 31 Mar 2026
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AC2: 'Reply on RC1', Klemens Hocke, 06 Apr 2026
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Dear Reviewer 1,
Thank you for your careful review! We corrected the manuscript according to your 39 points. The manuscript is now much better.
Please find attached our point-to-point response to your review.
Best regards, Klemens Hocke
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AC2: 'Reply on RC1', Klemens Hocke, 06 Apr 2026
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AC1: 'Comment on egusphere-2026-989', Klemens Hocke, 06 Apr 2026
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Dear Reviewer 1,
Thank you for your careful review! We corrected all of the 39 points which you found and the manuscript is now much better.
Please find attached the pdf file with our point-to-point response to your review.
Best regards, Klemens Hocke
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AC4: 'Reply on AC1', Klemens Hocke, 16 Apr 2026
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Please ignore this comment. I wrongly posted the RC1 reply as a comment.
Best regards, Klemens Hocke
Citation: https://doi.org/10.5194/egusphere-2026-989-AC4
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AC4: 'Reply on AC1', Klemens Hocke, 16 Apr 2026
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RC2: 'Comment on egusphere-2026-989', Anonymous Referee #2, 14 Apr 2026
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-989/egusphere-2026-989-RC2-supplement.pdf
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AC3: 'Reply on RC2', Klemens Hocke, 16 Apr 2026
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Dear Reviewer 2,
Thank you for your careful review and the many comments and corrections which helped us to improve the article.
Please find our point-to-point response to your review in the attached pdf file.
Best regards,
Klemens Hocke
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AC3: 'Reply on RC2', Klemens Hocke, 16 Apr 2026
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- 1
A unique long record of atmospheric moisture is exploited as a ground truth measurement which is of importance in evaluating climate models and datasets, in particular in verifying the underlying phsyics of water vapour-climate amplifying feedback processes as well as determining the source of precipitation including extremes. The analysis is rigorous and of wider significance to the climate science community and my assessment is that the work merits publication subject to addressing some minor comments listed below.
1) Abstract - some of the introductory material could be removed to focus on the importance, key results and wider implications e.g. the importance of water vapour for climate, why independent measurements are important, the originality of this record, key results and wider implications. Improving the abstract could enhance the impact of this work.
2) L5 - suggest "man-made" --> "human-caused" (though I recognise that men are probably more guilty!). "many places around the world" is a bit vague so could state that "Surface air temperature in Switzerland has increased at about twice the global average rate since 1995."
3) L12 - suggest removing "certainly" since this is not directly demonstrated (e.g. "has implications for")
4) L15 - "nearly twice" would be more precise
5) L17 - a more up to date IPCC report could be cited. In fact the IPCC assesses multiple lines of evidence, not just climate models, to show that human caused emissions have driven warming of climate.
6) L17-20 - the 7%/K rate is applicable for temperatures at low altitudes away from, the poles since the Clausius Clapeyron rate depands upon the absolute temperature such that the rate is larger for cooler temepratures (e.g. Allan 2012 Surv. Geophys. 10.1007/s10712-011-9157-8). An altitude difference between the observing site and the ERA5 grid point could also cause a discrepancy in mean temperature and water vapour though I presume this is quite small (I see this correction is made on L123).
7) Fig.1 - the first and second box on the left are showing the same thing and the feedback does not look correct as the warming is feedbing back to greenhouse gas increases. I suggest: Emissions lead to increased CO2/CH4 --> warming of climate ---> increased water vapour ---> feedback to warmimg of climate
8) L24 - the feedback loop is fully realised once the Earth's radiative balance is attained which will also involve and equilibrium between evaporation and precipitation
9) L29 - Suggest new sentence at "For example"
10) L31 - Multiple aspects of the changing observing system could affect ERA5 including new and changing satellite instruments and their artificial drifts, changes from manual to automated ground-based humidity sensors, etc. There is evidence of an artificial drying over the global land in ERA5, particularly in the early 2000s. Although this is more pronounced in tropical regions, this effect could contribute to the smaller increases in water vapour compared to the measurements in Europe (Wang et al. 2026 Sci. Bull. https://doi.org/10.1016/j.scib.2026.01.045). In any case, changes in the observing system could indeed lead to spurious water vapour changes in ERA5.
11) L36 - See also surface water vapour changes in Switzerland from Philipona et al. (2007) GRL doi: 10.1029/2008GL036350 of around 3%/decade 1981-2005, which leads to a large increase in downward longwave radiation.
12) L42 - see also Wan et al. (2023) HESS doi:10.5194/hess-28-2123-2024
13) L46 - the larger increases in the northern hemisphere seems somewhat consistent with Allan et al. 2022 Fig.2. (changes in the Arctic are largest)
14) L65 - presumably there are other original aspects of the analysis that are introduced? Otherwise this can appear rather incremental.
15) L75 - a line intrododucing how the work aims to advance the knowledge already discussed may improve the flow and the impact.
16) L89 - if only non-rain conditions are observed, will this bias the actual water vapour content, which will tend to be higher in rainfall events? Changes in rainfall frequency, as well as natural shifts in the larger-scacle circulation, can also affect the record, in addition to the overall greenhouse gas induced warming
17) L98/L188 - "an indoor"
18) L102 - what is "on it's random"?
19) L123 - quote magnitude (e.g. 0.05 mm and also in %)
20) L141 - around 5-10%?
21) L147 - the value as a percentage could also be useful
22) L153 - please quantify
23) L155 - can the radiosonde or other independent data offer a clue?
24) L158 - mostly correct is vague
25) L159 - January looked consistent in Fig. 2?
26) Fig.6 - the trends look consistent to within uncertainty
27) L171 - the difference to Bernet et al. 2020 is negligible considering interannual variability
28) L174 - the latest IPCC report suggests an increase in contrasts between wet and dry events in a warming world (Douville et al. 2021 IPCC Chapter 8) which is consistent, though the record is short.
29) L179 - and presumably also surface station humidity which also displays a change from manual to automated sensors
30) L182 - quantify?
31) L184 - I do not understand the link to the radiosode from the microwave radiometer here? Is it meant that the radiosonde's affect ERA5?
32) L188 - could the drop in TROWARA IWV in 2002 that is larger in magnitude than ERA5 relate to the instrument site change?
33) L194 - what is wet random?
34) L196 - the increase in IWV in both makes the result more robust but does not on its own signify that it is caused by temperature changes. Saying both values are "reasonable" is vague.
35) L207 - better to quote as a % per decade as done later so this could be removed
36) L210 - the Clausius Clapeyron equation provides the physical basis for expecting increases but does not show the cause without other lines of evidence
37) L212 - trend studies over Europe?
38) L220 - are there independent coincident measurements of surface specific humidity that could compliment the IWV record?
39) Discussion/Conclusions - decreases in aerosol in the 1990s may also have impacted Europe's climate, directly through their diminishing effect on reflecting sunlight by the atmosphere and cloud (e.g. Schwarz et al. 2020 Nature Geosci. doi: 10.1038/s41561-019-0528-y) but also through altering wind patterns (e.g. Dong et al. 2023 Clim. Dyn. https://doi.org/10.1007/s00382-022-06438-3). To what extend can some of the changes relate to changes in atmospheric circulation that are related to or unrelated to greenhouse gas foreced climate change?