Refining elevation data into soil moisture index

Digital elevation model (DEM) produced by the National Land Survey of Finland (NLS) provides the base for calculation of interesting derivatives of elevation data. For example, the investigation of water flow and its influence on soil moisture is possible after some DEM pre-processing and flow direction analysis. The oGIIR project enabled using the data and computing resources to calculate Topographic Wetness Index (TWI) over whole Finland in which basin boundaries (SYKE), elevation (NLS) and roads and streams from topographic database (NLS) were utilized.

TWI is a good baseline indicator describing the areas proneness to higher soil moisture and closeness to water elements. Indeed, the dataset seems to be useful, as in 2018 it was the most downloaded dataset produced by individual researcher in Paituli spatial data service. Due to the inherent nature of this index, the resolution was deliberately chosen to be coarser than the available 2m/10m DEM and 16m resolution was chosen since it matches the multi-source national forest inventory data and this is close to the reported optimal scale for this index. However, to provide more accurate information of soil moisture and allow consideration of dynamical aspect, Depth-To-Water (DTW) index maps are now being calculated in 2m resolution for the whole Finland and these will be made publicly available by the end of 2019.

Aura Salmivaara, Natural Resources Institute Finland

Figure 1 Topographic Wetness Index map for Finland in 16 m resolution. Available at