Public defence, Water and Environmental Engineering, DI Aleksi Salla

Title of the thesis: Controlled drainage and climate change in Finnish agriculture

Thesis defender: Aleksi Salla
Opponent: Professor Arvydas Povilaitis, Vytautas Magnus University, Lithuania
Custos: Professor Harri Koivusalo, Aalto University School of Engineering, Department of Built Environment

Conventional drainage practices used in agricultural fields are not suited to responding to varying drainage needs. This hampers the efficiency and sustainability of high-latitude crop production and makes it more vulnerable to the impacts of climate change. Controlled drainage is a potential method for regulating the amount and timing of subsurface drainage and improving the flexibility of agricultural water management. However, understanding of how different types of fields respond to controlled drainage under various meteorological conditions is limited. This doctoral thesis aimed to computationally quantify the field-scale hydrological effects of controlled drainage in Finland and how these effects change under future climate scenarios.

Under the reference climate conditions, controlled drainage reduced average growing season groundwater table depths by 0.06–0.26 m and reduced average annual drain discharge by 7–23%, depending on the climate model and field type. Controlled drainage was also able to reduce the occurrence of deep groundwater table depths, although it was not sufficient to maintain desired groundwater levels during dry growing seasons. The climate change scenarios did not result in large changes in the average efficacy of controlled drainage in altering field hydrology. However, future increases in drain discharge could not be completely offset by controlled drainage. In peat subsidence simulations, controlled drainage reduced subsidence rates by 14–22%.

The results suggest that controlled drainage is a valid tool for improving sustainable crop production and adapting to climate change in Finland. However, proper management is needed to achieve the desired effects. The results also showed some limitations regarding the efficacy of controlled drainage, encouraging the exploration of subsurface irrigation, which can be implemented in controlled drainage systems.

Key words: controlled drainage, agricultural hydrology, climate change, hydrological modeling

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.