Storms and dryland vegetation patterns
How do hydrologic processes on storm timescales influence vegetation patterns on yearly - decadal timescales?
It is hypothesised that spatial patterns of dryland vegetation be used to predict catastrophic shifts, and a lot of research tackled this with simple mathematical models of spontaneous pattern formation and remote sensing morphometric analysis. Among simplifications in this type of work, hydrodynamics of overland flow are neglected. In particular, the redistribution of overland flow between bare soil and vegetated areas on storm timescales in not included.
This study asks about the relationship between the characteristics of individual storms and long term vegetation patterns. To do this, ML emulation of the Saint Venant Equations was used to add a realistic representation of overland flow to a pattern-forming model.
We then assessed how resolving overland flow on storm timescales changed predictions made by a simple pattern-forming model.
Read more: Crompton, O. V., & Thompson, S. E. (2021). Sensitivity of dryland vegetation patterns to storm characteristics. Ecohydrology, 14(2), e2269.
After Rietkerk et al., 2002, AmNat
It is hypothesised that vegetation patterns can provide early warning signs of catastrophic shifts, where irreversible transitions occur between alternate stable states. These catastrophic shifts have been studied using mathematical models of pattern formation, describing competitive and cooperative interactions between plants.
The resulting patterns reflect how much water enters the soil system, which depends both on the total annual rainfall – which is included in models – but also the intensity of individual storms, which is not.
To bridge the timescale separation between individual storms and longer-term vegetation growth and development, an overland flow model (the SVE model) was coupled to a dryland vegetation model (the Rietkerk/Guttal model).
This approach makes it possible to directly integrate predictions of overland flow and infiltration into a vegetation model.
Accounting for overland flow in the dryland vegetation model allows us to assess vegetation vulnerability to the characteristics of individual storms, in addition to total annual rainfall. The coupled model simulations show how predicted vegetation patterns are sensitive to storm intensity and duration. For example, the image on the left shows 16 patterns generated by the Rietkerk model using different storm climatologies, with annual rainfall inputs fixed at 365 mm.