January 2022 – incamodels.org

Modelling DOC in the Canadian Sub-Arctic

Shanta Sharma recently defended her Masters thesis on modelling dissolved organic carbon (DOC) in the Canadian sub-Arctic. This was one of the most northerly applications of the INCA family of models and brought some unique challenges and insights.

The sub-Arctic in Canada and elsewhere is likely to experience hydroclimatic regime change associated with a rapidly changing climate. Simulations of landscape-scale carbon (C) budgets and pollutant transfer are needed by northern managers and stakeholders to understand and mitigate these possible impacts. The project simulated dissolved organic carbon (DOC) fluxes in a hydrologically complex watershed (Baker Creek) in the Northwest Territories. Discharge, DOC concentration, and DOC export were simulated PERSiST and INCA-C. The models were calibrated against available (2012-2016) discharge and DOC concentration data in sub-catchments of Baker Creek. The model successfully reproduced flow (R²: 0.87–0.94; NS: 0.82–0.91) and captured some aspects of DOC concentration dynamics (R²: 0.19–0.31).

Possible future conditions were simulated using two climate scenarios (elevated temperature (T), elevated temperature and precipitation (T+P)), and compared against a baseline scenario. Average discharge is projected to decrease under scenario T (22–27% of baseline) and increase (116–175% of baseline) under the T+P scenario. In this scenario, early winter increases in discharge suggest a change in hydroclimatic regime from nival to combined nival and pluvial. Future DOC fluxes are projected to decrease (24–27% of baseline) under scenario T and increase (64–81% of baseline) in the T+P scenario, with much of the increase in DOC export occurring during early winter. Any future increase in DOC export from Baker Creek may increase the mobility of previously deposited airborne metal contaminants, e.g., arsenic from Giant Mine.

Hydrological regime shifts in Central European forests?

Petr Kupec and colleagues have published a new paper about possible future hydrological regime shifts in Central European forests. They used long-term data, detailed field measurements from an experimental forest catchent and PERSiST modelling, we show that there is a prolonged and persistent decline in annual runoff:precipitation ratios. This decline is most likely linked to the longer growing seasons associated with global warming. They performed a long term (1950–2018) water balance simulation for a Czech upland forest headwater catchment calibrated against measured streamflow and transpiration from deciduous and coniferous stands. Their simulations were corroborated by long-term (1965–2018) borehole measurements and historical drought reports. A regime shift from positive to negative catchment water balances likely occurred in the early part of this century. Since 2007, annual runoff:precipitation ratios have been below the long-term average. Notably, annual average temperatures have increased, but there have been no notable long term trends in precipitation. Since 1980, there has been a pronounced April warming, likely leading to earlier leaf out and higher annual transpiration, making water unavailable for runoff generation and/or soil moisture recharge. Their results suggest a regime shift due to second order effects of climate change where increased transpiration associated with a longer growing season leads to a shift from light to water limitation in central European forests. If their finding can be generalized, it will require new approaches to managing forests where water limitation has previously not been a problem.