The effect of rainfall event sequencing on erosion

Jantiene EM BaartmanAJAM Temme, A Veldkamp, VG Jetten, JM Schoorl

Introduction & Objective

Extreme rainfall events contribute disproportionally to total erosion The timing of these events seems to be of importance Climate change predictions (Mediterranean)

● Less total rainfall; but● More intense events

Evaluate the effect of rainfall sequencing on long-term (centennial) erosion

Methods

Methods: LAPSUS landscape evolution model

● Long-term redistribution of sediment

Study area: Prado, SE Spain• ~50 km2

• 435 – 1150 m.a.s.l.• Semi-arid: 250-530 mm/y• High inter-annual variation

Methods

Rainfall data: 1997 – 2006; 9-yr record Repeated 11x to get a 99-yr rainfall timeseries Vary the order of occurrence of rainfall:

• 1997-2006 record repeated 11x• Order of years changed randomly, keeping total rainfall and

frequency the same (50 simulations)• Minimum scenario: 11x lowest year; 11x one-but-lowest year; etc• Maximum scenario: 11x highest year; 11x one-but-highest year; etc

Note: total P is equal in all runs!

Results & Discussion

Results & Discussion

Event sequencing: no linear relation between (high or low) rainfall and (high or low) net erosion

Results & Discussion

Event sequencing: no linear relation between (high or low) rainfall and (high or low) net erosion

Conclusions & Outlook

Non-linear behaviour is evident: ● Non-varying, average annual rainfall as input results

in peaks in simulated net erosion ● Variability in rainfall as input does not necessarily lead

to a corresponding peak in simulated erosion and peaks occur at points in time when no rainfall peak occurs.

What is the cause of this non-linear behaviour?● Change in connectivity?● Next step: analyse the spatial dynamics

Thank you!

Based on:Baartman et al., 2013. Exploring the role of rainfall variability and extreme events in long-term landscape development. Catena 109: 25-38.

Input: effective rainfall

Peff = P that becomes overland flow Determined based on LISEM simulated hydrographs and

Q/P ratios

More extreme events

Inclusion of more extreme events• 10x erosivity of the most extreme event of the 1997-2006 record• Different frequencies of occurrence of such extreme event

Increased erosivity

Land use change scenario