MESH-CTEM – Development and Testing of an Integrated Biogeochemical and Watershed Hydrological Modelling System

Abstract

This study developed an integrated biogeochemical and hydrological modelling system by incorporating the latest versions of the nitrogen coupled Canadian Land Surface Scheme-Canadian Terrestrial Ecosystem Model (CLASS-CTEM) into the Modelisation Environmentale Communautaire (MEC) Surface and Hydrology system (MESH), hereafter referred to as MESH-CTEM. The newly developed MESH-CTEM modelling system allows simulations of energy, water, carbon and nitrogen fluxes and their feedbacks on vegetation growth and exploration of impacts of future climatic changes on catchment-scale processes. Performance of the MESH-CTEM system was tested at the Big Creek watershed within Norfolk county, Ontario, Canada, which is a 573 km2 crop-dominated catchment with areas of broadleaf and needleleaf forests, using observed eddy covariance flux, meteorological and hydrological datasets from October 2004 to December 2017 at a grid resolution of 0.02o latitude × 0.02o longitude. MESH-CTEM showed a significant increase in the simulated streamflow as compared to MESH running with only CLASS, excluding dynamic vegetation growth and carbon fluxes, resulting in an overall increase in the accuracy of streamflow with Nash-Sutcliffe Efficiency (NSE) indices of 0.38 and 0.12 respectively. Significant improvements were also seen for each Plant Functional Type (PFT) within the catchment with respect to energy fluxes, evaporation and soil water regimes. Many of these improvements in simulated fluxes were due in part by changes in the canopy conductance formulation, more realistic soil heat and water processes due to the introduction of fine soil layers, inter-grid transfers of water and other spatial components and vegetation cover feedbacks on energy, water and carbon exchanges by using dynamic vegetation growth processes. Simulated averaged gross ecosystem productivity, ecosystem respiration, latent heat flux and sensible heat flux for the entire catchment were respectively 660 g C m−2 yr−1, 640 g C m−2 yr−1, 32.5 W m-2 and 27.1 W m-2. Application and use of MESH-CTEM will help to study the impact of climate change and extreme events on energy, water and carbon fluxes and associated feedbacks at the catchment scale. Additionally, this will help bridge a major gap in hydrologic modelling studies through integration of biogeochemical processes.