Why is the atmosphere over land becoming drier? Exploring the roles of atmospheric and land-surface processes on relative humidity

Since leaving the Grantham Centre, Florentine Weber took up a fellowship at the European Centre for Medium-Range Weather Forecasts where she will work to improve high-resolution simulations of the water cycle. As a Grantham Scholar Florentine explored why the atmosphere is drying. 

Atmospheric drying and why it matters: Florentine Weber interview. For an easy to understand overview of Florentine’s research, read our interview with her. Or you can listen to a short ‘audiogram’ of the highlights from the interview.

The project

Climate change is a long-term shift in the properties of our atmosphere. One of these properties is relative humidity. Relative humidity describes the amount of water vapour in the air, relative to the temperature of the air. Dry air has a low relative humidity, while fog has a high relative humidity. Observation data shows that relative humidity is decreasing globally over land since the year 2000, especially in regions of mid-latitudes.

My project will be exploring 3 possible causes, or drivers, for declining near surface relative humidity over land:

♦ Dynamical drivers, so called modes of variability (e.g. wind and pressure pattern)

♦ Thermodynamical drivers (temperature and, consequently, greenhouse gases)

♦ Land-based drivers (transpiration of plants and large-scale land cover changes, such as deforestation)

I am working with global monitoring products and earth observation data for land use, evapotranspiration and soil moisture. I will also be using computer simulations based on this data, and ecosystem studies. I hope to find out more about water, the fundamental element for life, and the representation of atmosphere-land exchange processes in climate models that predict the future.

This interdisciplinary research is carried out in collaboration with the Climate Monitoring and Attribution Group of the Met Office.

Outreach and Engagement

Florentine Weber on Arran measuring relative humidity.
Florentine Weber on Arran measuring relative humidity.

Along with other Grantham Scholars, Florentine featured in a series of films made by Curious Earth on Instagram. The films showcased 20 female scientists and asked them, ‘what advice would you give your younger self?’.

Climate change expert, COP26 Universities Network. The COP26 Universities Network is a growing group of more than 40 UK-based universities working together to raise ambition for tangible outcomes from the UN COP26 Climate Change Conference.

Co-chair Environmental Sustainability Rotary Action Group (ESRAG) Great Britain & Ireland. ESRAG assists Rotary clubs, districts and multi-districts in planning, implementing and evaluating service projects, building awareness, and inspiring action.

In December 2019 Florentine gave a gave a 90 second speech on sustainability alongside globalism and growth to House of Lords. Find out more here.

Along with another Grantham Scholar Florentine wrote a blog about her experiences at COP24. Read: A day at COP: what’s it like to be at the biggest climate conference in the world?

In May 2018 Florentine and other Scholars hosted an event for Chevening Scholars. Chevening: supporting the development of the world’s future decision makers.

Florentine Weber’s publications

Weber, Kirsten Maria Florentine (2022) Why is the atmosphere over land becoming drier? Exploring the roles of atmospheric and land-surface processes on relative humidity. PhD thesis, University of Sheffield.

Simionesei et al., 2018 – Modeling Soil Water Dynamics and Pasture Growth in the Montado Ecosystem Using MOHID Land

Florentine gave a talk at the American Geophysical Union Fall Meeting 2019 in San Francisco – and also wrote a paper about her talk. 

Why is the atmosphere becoming drier? – An investigation of the role of dynamical drivers on recent trends in relative humidity

Social media

You can find Florentine on Twitter.

Florentine Weber



Dr Rob Ryant

Department of Geography

Dr Kate Willett

UK Met Office Hadley Centre