Adaptive water management solutions such as controlled drainage have raised interest in Nordic areas due to climate variability. It is not fully known how controlled drainage affects seasonal field water balance or can help in preventing water scarcity during dry growing seasons (GSs). The objective was to simulate the effects of controlled drainage on field hydrology using a well-tested, process-based hydrological model. The FLUSH model was calibrated and validated to an experimental field. The model performance with non-local input data was moderate but acceptable for running the controlled drainage scenarios to test the response of the water management method to meteorological forcing. Simulation results showed that controlled drainage reduced drain discharge while increasing surface layer runoff and shallow groundwater outflow. Groundwater depths from the scenario simulations demonstrated that controlled drainage could keep the depth closer to the soil surface, but the effect diminished during the dry conditions. Controlled drainage can be used to change the water flow pathways but has a secondary effect compared with the primary meteorological drivers. The field data set and FLUSH formed a novel computational platform to study the impacts of different water management options on the whole water balance and spatial variability of groundwater depths.

<p>Drained peatlands have peculiar hydrological properties and cause environmental concerns due to carbon dioxide emissions and nutrient fluxes resulting from decomposition of organic matter in peat. As peat degradation is strongly controlled by soil moisture conditions, it is assumed that flexible water management methods, such as controlled drainage, can be used to reduce the environmental impacts of drained peatlands in agriculture. While peat soils have been extensively researched, there is a need for increased understanding about the hydrological responses of peatlands to various water management schemes. Research is needed to quantify these responses, and a promising approach is to exploit simulation models for describing peatland hydrology at field scale. The goal was to calibrate and validate a hydrological model FLUSH to describe the hydrology of an agricultural field block having a shallow peat cover and managed with controlled drainage. FLUSH is a spatially distributed three-dimensional (3D) process model which simulates the hydrology of agricultural fields managed with controlled subsurface drains and open ditches. The soil description of FLUSH includes both soil matrix and macropores accounting preferential flow. Richards equation and Mualem-van Genuchten water retention model are applied for subsurface flow. The modeled field block is located in Ruukki, northwestern Finland, and the study period was from August 2018 to October 2021. Groundwater table depth and drain discharge observations were used for the calibration and validation. The Kling-Gupta efficiencies for the simulated groundwater table depths in soil matrix and macropore domains were 0.50 and 0.47, respectively, during the calibration period, and 0.23 and 0.33 during the validation period. The efficiency values for the simulated drain discharge during the calibration and validation periods were 0.18 and 0.19, respectively. Limiting the modeled area to the block lead to cumulative drain discharges clearly smaller than the observations. The underprediction was improved by extending the modeled area beyond the block, which suggested a presence of a hydrological connection in terms of groundwater flux originating from outside the block. Thus, the surrounding environment can play a role in the hydrology of peatland fields, and this should be considered in water management design. Despite the large difference between observed and simulated cumulative drain discharges, the main hydrological dynamics were captured, and the model formed a useful tool to simulate drainage scenarios in peatlands and to study the role of the surrounding areas on field hydrology.</p>

This simulation study focused on the hydrological effects of climate change and controlled drainage operated with subsurface drains and an open collector ditch in an agricultural field. The objective was to understand the potential of controlled drainage and open ditch schemes for managing groundwater levels and field water balance in climate conditions projected to take place in Finland during the 21st century with representative concentration pathways 8.5 and 2.6. A methodological aim was to find ways to condense hourly hydrological results to understand future changes in field hydrology. During the historical reference interval (1970–2005), controlled drainage caused 17–36 cm higher mean groundwater levels and decreased the mean annual drain discharge by 11–23% compared to conventional subsurface drainage. Controlled drainage was projected to increase groundwater levels by additional 1–4 cm in the future compared to its effect on drainage during the reference interval. The effect on annual drain discharge did not change significantly. The open collector ditch lowered groundwater tables and diminished the effect of controlled drainage on groundwater levels in the vicinity of the ditch. Controlled drainage was shown to remain an effective method for countering early summer drought and reducing drain discharge.

<p>Climate change is projected to result in higher temperatures, higher annual precipitation and more uneven distribution of precipitation in the northern regions. This requires adaptation in agriculture where both excessively wet and dry cycles pose challenges to cropping. Until now, water management in northern agricultural fields has been resting primarily on efficient drainage, but interest towards more flexible measures has increased.</p><p>This study focuses on the hydrological effects of climate change and controlled drainage operated with subsurface drains and an open collector ditch in an agricultural field. The objective was to computationally estimate how groundwater levels and water balance respond to controlled drainage and open ditch scenarios in climate conditions projected to take place in Finland during this century. A hydrological model FLUSH was used to simulate the hydrology of an experimental field in Sievi, Northern Ostrobothnia, Finland during years 1970–2100. Down-scaled climate projections from EURO-CORDEX (RCP 8.5 and RCP 2.6) were used as meteorological input. The temporal development of the field hydrology and the effects of controlled drainage were examined by dividing the time series into four subsequent time intervals (historical period and three future periods).</p><p>Two different control scenarios were studied. Drainage intensity was reduced during growing seasons in summers (Jun.–Aug.) and either in autumn (Oct.–Nov.) or from autumn to spring (Oct.–Mar.). During these periods, groundwater table was on average 17–29 cm, 28–30 cm and 36–40 cm higher, respectively, in the control scenarios when compared to conventional subsurface drainage in different study intervals and emission scenarios. The implementation of controlled drainage reduced annual drain discharge by 21–46 mm. The projected temporal evolution of the effects of controlled drainage on groundwater levels and annual drain discharges were not monotonous, but the projected effects were larger during the future periods when compared to the historical period. Controlled drainage effect on groundwater levels was seen during both dry and wet years. Controlled drainage was assessed to be an effective method to control field water processes currently and in the future decades. The open collector ditch lowered groundwater levels within a distance of 115 m from the ditch.</p>