Bridging Scales in Engineering and Natural Sciences

 

From Small to Large Scale Aeolian Processes: Combination of Numerical Modelling and Remote Sensing Techniques

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As part of the Exploratory Research Space (ERS) at RWTH Aachen University, an interdisciplinary project has been initiated that builds bridges between geography and engineering. The chosen thematic focus, aeolian transport processes, represents a thematic overlap between the participating disciplines. The aim of the project is a proof-of-concept study which investigates how aeolian transport processes can be recorded and processed at different scales using different methods. The micro scale is covered by numerical models from water management, while remote sensing methods are used for the meso and macro scale.

 

Thematic introduction

Aeolian forms at different spatial and temporal scales Copyright: © IWW / PGG Spatial and temporal scales of aeolian processes: conceptualised (top left), photographic (A: ripples, micro scale) and cartographic (B and C: barchans and dune field of Bor Khyar Els in western Mongolia, meso and macro scale).

More than 35 % of the world's population lives in the world's arid regions. Aeolian transport processes favor dune movements and thus threaten economic and residential areas, water resources, agriculture as well as infrastructure. Based on current projections of climate change, population increase, and land use change, this threat is expected to increase dramatically in the coming years.
Although there is already extensive research activity in the field of aeolian transport processes, mesoscale and macroscale processes still present us with significant challenges. While eolian or fluvial processes on the microscale leading to dune formation as well as dune migration are already based on a fundamental understanding of processes, the meso- and macroscale processes can only be described inadequately. The formation as well as dynamics of these still require further intensive research efforts.
A promising approach to bridge these space-time scales lies in the combination of small-scale numerical modeling techniques with mesoscale remote sensing methods. Freely available global remote sensing datasets achieve return rates of a few days and spatial resolutions of up to 5 meters. Numerical modeling methods usually operate on a spatial scale of a few centimeters to meters and on a time scale of seconds or more. A challenge is to apply these microscale numerical approaches to the mesoscale or macroscale. This is where the present proposal comes in and intends to provide a numerical description of remotely sensed dune shapes. If meso- and macroscale dune forms can be described and processed using numerical modeling techniques, then the future development of dunes and entire sand fields as a result of climate change and land use changes could also be better predicted.

 

Research hypothesis

By using numerical methods from water management to model the movement of small-scale dunes due to hydraulic processes, the movements of large-scale dunes due to aeolian transport can be described. The hypothesis gives rise to the following core research questions, among others, which need to be answered:

  • Is it possible to use numerical modelling methods to describe the transport processes of large-scale shifting sand dunes?
  • What are the requirements for remote sensing data – in particular, regarding their temporal and spatial resolution – in order to link them with numerical methods?
  • What adaptations are required in the area of numerical models?
  • Will it be possible in the long term to model anthropogenic effects at the meso level using numerical methods?

The interdisciplinary project goal can only be achieved through cooperation and complementary expertise from the fields of water management, sediment transport, morphodynamics, numerics and remote sensing. To this end, the partners are contributing their respective expertise to the planned ERS project:

  • Microscale observation of fluvial dunes on the river bed as well as aeolian dunes in the coastal area (IWW).
  • Numerical description of dune development (erosion) using various numerical modelling methods, e.g. XBeach (IWW)
  • In-situ investigations of dune development in coastal areas (IWW)
  • Experimental wind tunnel studies on aeolian sediment transport (IWW)
  • Use and processing of high-resolution satellite data (PGG)
  • In-situ experience on aeolian transport and sediments (PGG)
  • Spatial intersection of remote sensing and in-situ data using GIS (PGG)
  • Spatial intersection of climate data and remote sensing data in arid regions (PGG)

For the planned ERS project, the area of Western Mongolia was selected for the following reasons: (1) own on-site knowledge, (2) low anthropogenic influence and thus a natural system, (3) preliminary work on the meso- and macro-level by means of evaluation of topographic data and remote sensing data available. Building on the results of the proof-of-concept study, the model is to be adapted to other regions of the earth (e.g. sub-Saharan Africa, arid diagonal of South America), the model is to be extended to include the influence of anthropogenic interventions, and further research proposals (DFG, BMBF Sub-Sahara-Africa-Calls) are to be written.

 
Duration 08/2021 - 07/2022
Funding ERS OPSF612
Project partners Dr. Catrina Brüll – Institute of Hydraulic Engineering
and Water Resources Management, RWTH Aachen University