Pulses of evapotranspiration (ET) after extreme events

ET is a critical land surface flux affecting crop yields, drought status and flood risk. Recent measurements show that ET occurs mostly in short episodic pulses. This project will enhance our understanding of fine-resolution ET pulses and their relation to extreme events by applying multivariate tools to analyse newly available large datasets able to delineate these pulses more precisely (e.g. UKCEH’s COSMOS/UKSCAPE sites, Germany’s TERENO network). The world-class characterisation of landscape-variation in ET produced will support climate-smart, precision agriculture and validation of the Land Surface Model JULES.
Funding: Global Challenges Research Fund

More information:

• The Penman-Monteith method for calculating evapotranspiration misses several crucial terms, notably (i) evaporation from inundated water and (ii) hillslope processes (Cuxart et al. 2019). Why is this a problem? In areas of the world covered for example by oil palm grown on slopes, or crops grown under inundated conditions such as rice, this means that Penman-Monteith cannot be used without modification to calculate ET. However, land surface models such as JULES do not modify P-M, therefore their estimates of ET from rice and oil palm plantations must have high uncertainty.
• Following this logic, there is an unrecognised problem here for land surface modellers: of the 1560 million ha total cropland in the world, 162 million ha are rice paddies (2019) and 20 million ha are oil palm plantations (2018). It seems that we cannot trust ET estimates from 12% of global croplands because we know there are missing fluxes there.
• First steps: talk to Hollie and maybe do a review paper.
• For ET flux from inundated water, see my email to ER Feb 2019 pasted into my ppt from the GEWEX workshop Feb 2021.

In October 2019 we organised a GHP cross-cutting workshop Determining Evaporation led by Prof. Joan Cuxart in Sydney, Australia. See here. I presented a talk Evapotranspiration in the JULES land surface model.

The 2nd GEWEX Evapotranspiration workshop was hosted by Univ. Wageningen online in February 2021.

Prof. Henk de Bruin visited CEH Wallingford on 8th March 2019 and gave a wide-ranging talk entitled Evapo(transpi)ration: How to model it? How to measure it? A critical review of the state of the art and a call for novel research. The seminar attracted several senior hydrologists and micro-meteorologists from pre-CEH days. CEH article in The Grapevine is here and the slides and audio are here (including the energy balance closure blues!).

Photo: L-R: Chris Taylor, John Gash, Colin Lloyd, Jim Shuttleworth, Eleanor Blyth, Henk de Bruin, Richard Harding, Anne Verhoef , Jim Wallace, Jonathan Evans.