Diurnal and seasonal changes in near‐surface humidity in a complex orography

Abstract

Changes in near‐surface humidity are evaluated in relation to changes in other meteorological variables such as air temperature, precipitation, and sunshine duration for a 31 year period (1981–2011) using hourly time series recorded in Switzerland. Trends in meteorological variables are analyzed at the seasonal and subdaily scale, and changes in water vapor are tested for Clausius‐Clapeyron scaling. Results show a marked seasonality of climatic changes with a trend toward warmer, clearer, and drier near‐surface atmosphere strengthening from January to June. During this period considerable negative trends in relative humidity are detected. An abrupt shift in climatic trends occurs during the month of July, after which warming trends are considerably smaller and relative humidity remains constant or increases. An evaluation of reanalysis products demonstrates strong consistency with station observations and when combined with teleconnection indices supports the hypothesis that shifts in the general circulation patterns rather than local feedbacks are the principal drivers of observed seasonality of climate change. However, local feedbacks can play a role in enhancing summer humidity and convective activity (lightning and evening precipitation). Subdaily changes are significant with more pronounced daytime trends of temperature and humidity during spring and the opposite during summer. The strong seasonality and diurnal variability of changes in near‐surface meteorology over the last three decades in Switzerland warns against climate change impact assessments at local scale that consider uniform changes in air temperature and assume Clausius‐Clapeyron scaling for near‐surface humidity.

Long-term effects of drought on tree-ring growth and carbon isotope variability in Scots pine in a dry environment

“…Studies explicitly using VPD are still rare (Eamus et al 2013). Reliable local RH data may further be needed rather than large-scale extrapolated data due to the high spatial variability of this variable (Fatichi et al 2015). Our results indicate that the recent increase in VPD for trees growing under chronically low water supply may be detrimental for the most weakened individuals.…”

“…We used homogenized data, where artifacts in the series were removed, meaning that the historical measured values were adapted to current measuring conditions and non-climatic influences were excluded (Begert et al 2005). Reliable relative humidity (RH) data are often difficult to obtain due to measurement uncertainties and small-scale heterogeneity (Fatichi et al 2015), and, hence, such measurements were available for Sion for the 1960-2014 period only. Therefore, also VPD data were calculated for this period only (1960-2014) using temperature and the reliable RH data.…”

A review of studies on observed precipitation trends in Italy

“…This is related to the high noise to signal ratio of precipitation time series. However, trends which are not statistically significant at α = 0.05 can still be very important for the system experiencing the ongoing trend, with potentially important implications for water resources management and ecosystems (Fatichi et al ., 2015a).…”

Climate change and uncertainty in high-resolution rainfall extremes

“…These data have been used for investigations of multiscaling properties (Molnar and Burlando, 2008), analysis of storm convectivness (Gaal et al, 2014), and precipitation intensity-air temperature relations (Molnar et al, 2015). In terms of precipitation change in Switzerland there is some evidence of increases in daily maxima (Frei and Schaer, 2001), but hourly precipitation changes show a more complex and inconclusive pattern, with the exception of increases in late afternoon rainfall in summer (Fatichi et al, 2015).…”