Adaptation of the Integrated Nitrogen Model for Catchments (INCA) to seasonally snow-covered catchments

Abstract

Testing of the Integrated Nitrogen model for Catchments (INCA) in a wide range of ecosystem types across Europe has shown that the model underestimates N transformation processes to a large extent in northern catchments of Finland and Norway in winter and spring. It is found, and generally assumed, that microbial activity in soils proceeds at low rates at northern latitudes during winter, even at sub-zero temperatures. The INCA model was modified to improve the simulation of N transformation rates in northern catchments, characterised by cold climates and extensive snow accumulation and insulation in winter, by introducing an empirical function to simulate soil temperatures below the seasonal snow pack, and a degree-day model to calculate the depth of the snow pack. The proposed snow-correction factor improved the simulation of soil temperatures at Finnish and Norwegian field sites in winter, although soil temperature was still underestimated during periods with a thin snow cover. Finally, a comparison between the modified INCA version (v.1.7) and the former version (v.1.6) was made at the Simojoki river basin in northern Finland and at Dalelva Brook in northern Norway. The new modules did not imply any significant changes in simulated NO 3 concentration levels in the streams but improved the timing of simulated higher concentrations. The inclusion of a modified temperature response function and an empirical snow-correction factor improved the flexibility and applicability of the model for climate effect studies.

Screening variability and change of soil moisture under wide-ranging climate conditions: Snow dynamics effects

“…1 and 2 because only the liquid water part of P , P water [LT −1 ], in addition to a snow-melt contribution, S M [LT −1 ], can effectively contribute to changes in water storage and in the depth of the groundwater table. The P eff value is then obtained from a simple snowpack model proposed by Rankinen et al ( 2004a ), based on a degree-day conceptualization. Such models have been developed (Vehviläinen 1992 ; Tobin et al 2013 ) and widely used for different regional conditions (Braithwaite and Zhang 2000 ; Tobin et al 2011 ), including for Scandinavia (Mörth et al 2007 ; Juston et al 2009 ).…”

“…The modeling approach of Rankinen et al ( 2004a ) was developed within the frame of the Integrated Nitrogen Model for Catchments (INCA) model and tested for conditions in Finland (Limbrick et al 2000 ; Granlund et al 2004 ; Rankinen et al 2004b ). Following this approach, the manifestation of measured precipitation P as snow ( P snow ) or liquid water rainfall ( P water = P − P snow ) is at any point in time first determined on the basis of mean air temperature T A [Θ] as with T U [Θ] and T L [Θ] being temperature thresholds, above and below which precipitation is considered to fall entirely as water (Eq.…”

“…The original model presented by Rankinen et al ( 2004a ) accounts also for evaporation from the snow. Here, however, the effects of basin-scale evapotranspiration, which includes evaporation in addition to transpiration, are explicitly accounted for in Eqs.…”

The INtegrated CAtchment model of phosphorus dynamics (INCA-P): Description and demonstration of new model structure and equations

“…For regions with significant winter snow accumulation, a snow module provides an estimate of snow depth, for use in soil temperature calculations, and of snow melt, which may be used when calculating infiltration rate (Equation A-10). Snow module equations are described more fully in Rankinen et al (2004b). Briefly, snow depth in water equivalents is calculated as a function of inputs minus outputs (Equation C-1) and then converted to actual snow depth (Equation C-2).…”

Applying profile- and catchment-based mathematical models for evaluating the run-off from a Nordic catchment

“…Calculation of river flow is based on mass balance of flow and on a multi-reach description of the river system (Whitehead et al, 1998). The model incorporates an empirical function for simulating soil temperature changes below the seasonal snow pack and a simple degree-day model to simulate the depth of the snow pack (Rankinen et al, 2004). The heat flux from the snow surface to the soil is calculated by the heat conduction equation.…”