Modelling and evaluation of land use changes through satellite images in a multifunctional catchment: social, economic and environmental implications

Abstract

Floods are recurrent phenomena with significant environmental and socio-economic impacts. The risk of flooding increases when land use changes. The objective of this research is to detect land cover changes via Sentinel-2 images in the Umia Basin (Galicia, NW Spain) in 2016–2021 and to analyse the associated flood risk. This study focuses on how forest use and nature-based solutions (NBS) can reduce the risk and hazard of flooding in cities and crops in the high-risk area. A flood simulation was performed with the land use obtained from Sentinel-2 (Observed) and three more simulations were performed changing the location of afforestation and NBS, i.e. “S-Upstream”, “S-Downstream” and “S-Total”. Finally, the environmental, economic and social impacts of the scenarios designed and estimated are analysed and discussed. Land cover change was successfully monitored with Sentinel-2 imagery. The catchment area showed noteworthy changes in land use, most notably for the category of trees, which covered 6700 ha in 2016 and 10,911 ha in 2021. However riparian vegetation decreased by almost 11%. For the flood hazard simulations, an average reduction in peak discharge was obtained for all three scenarios (9.3% for S-Up; 8.6% for S-Down and 13% for S-Total). From the economic perspective, all three scenarios show a positive net present value for the period studied. However, S-Down is the scenario with the lowest benefits (€15,476,487), while S-Up and S-Total show better values at €29,580,643 and €65,158,130 respectively. However, investment cost is much higher for the S-Total scenario, and upstream actions affect the whole catchment, so S-Up is the best decision. This study concludes that the information provided by satellites is a large-scale analysis tool for small heterogeneous plots that facilitates the comprehensive analysis of a territory. This information can be incorporated into flood analysis models, facilitating simulation through the use of NBS. It has been proven that the use of reforestation upstream only is almost as beneficial as reforestation in the entire catchment and is economically more viable. This confirms that the methodology used reduces flood hazard, despite the territorial complexity, facilitating decision making on the use of NBS.