The region with the globally highest increase in air temperatures is the Arctic, which leads to subsequent warming of permafrost, thickening of the seasonally thawed active layer, and changes in the amount and distribution of snow and rain. All these changes influence the thermal and hydrological state of the soil, influencing soil stability, thermal and hydraulic conductivity of the soil, and eventually the movement of water and solutes across the landscape.

Water flow in the active layer typically only occurs under thawed soil conditions during the summer, while water movement is caused by precipitation and hydraulic gradients across the landscape. It is further limited by the transmissivity, which is a function of the thickness of the saturated layer, depending on the relative position of the water table to the frost table, and the permeability of the soil at which water flow occurs.

When the active layer is thickening (either due to increasing surface temperatures, or by surface alterations) decreasing the distance between soil surface and top of the permafrost, the water- and frost table are reacting to the thickening, and deeper soil layers with different permeabilities may become hydrologically active. Further complicating this, is that the thawing of the active layer does not occur uniformly across the landscape but is influenced by heterogeneities at the surface and in the soil, such as plant cover, micro-topography, or varying water/ice contents in the soil. Individually these processes are well described, yet the interplay between them remains poorly understood, and as a result water balance calculations of arctic slopes are often plagued by uncertainties.

This thesis aims to quantify changes in drainage patterns in response to temperature changes. In order to do so, two field experiments were performed and subsequently built into field informed physical models. This allows us to observe and subsequently simulate the individual parts of the water balance in detail. This approach is done in two steps with increasing complexity, moving from a simple one-dimensional model that explores the relationship between the water and frost table in response to surface alterations, to a more complex two dimensional model of an arctic slope, which includes the heterogeneous thawing of the active layer and the movement of solutes.

In the first experiment at Qaanaaq (North Greenland), we found that the frost table is more sensitive to local changes than the water table, which remains more stable despite surface changes. Lowering the surface of the landscape led to a deeper thawing of the active layer and a thicker saturation layer, leading to 119% faster thawing rates and an increase in potential drainage by 154%. On the contrary raising the surface thinned the saturated layer, slowing down permafrost aggregation and reducing the potential drainage to 72% compared to ambient conditions.

To understand how different thawing rates and transmissivity shape the drainage across the landscape, a secondary experiment was conducted, where the water table, frost table and solute movement was simulated with a validated model, covering a 147 m stretch of an arctic slope on Disko Island (West Greenland). We found that the dominant effect of warmer summers on the land is increased evapotranspiration, reducing the water available for discharge, and increasing the active layer thickness, lowering subsurface transport velocities. The movement of solutes is dominated by snowmelt and large precipitation events that move solutes rapidly in both peat and mineral layers.

Our results demonstrate that rising temperatures in the Arctic do not only degrade permafrost, but can also alter the total discharge from a slope, reduce travel velocities at individual layers and can thus have a large influence on the landscape connectivity, creating feedback loops of differing extents to permafrost degradation, ecosystem responses and eventually the carbon budget.

We expect that by quantifying those effects, future calculations of water movement in arctic landscapes can be handled more accurately, and that studies that discuss landscape transition can have a clearer understanding on how different parts of the landscape are interconnected. This interconnectivity is crucial when observing, understanding, and predicting the complex systems which Earth is, and enables us to better predict global climate developments.