airGR_GM: modified airGR package with glacier module

Summary

This package is a modification based on the airGR package version 1.7.6, developed to include glacier ablation in addition to the existing suite of conceptual rainfall-runoff models. The original airGR package, developed by INRAE-Antony (HYCAR Research Unit, France), includes models like GR4H, GR5H, GR4J, GR5J, GR6J, GR2M, GR1A, and the snow accumulation and melt model (CemaNeige).

This modification includes mainly two changes:

1. The introduction of aglacier module

2. The ability to adjust the temperature and precipitation lapse rates.

1. Glacier Module

This modification adds two main functions: RunModel_CemaNeigeGR4J_Glacier and RunModel_CemaNeigeGR6J_Glacier. They are built upon the functions RunModel_CemaNeigeGR4J and RunModel_CemaNeigeGR6J from the original airGR package. The package works in combination with the modified airGRdatassim package, which also allows these adjusted conceptual models to run with data assimilation. In this development, a glacier module is added to the RunModel_CemaNeigeGR4J and RunModel_CemaNeigeGR6J.

SWE is modeled within the CemaNeige compartment and provided as input to the glacier module. Ice melt occurs only when both temperature and SWE thresholds are exceeded, and is modeled using the equation below:

$$ M_i = \begin{cases} F_i \times (T - T_m) \times A_i & \text{if } SWE \geq SWE_{th} \text{ and } T \geq T_m \\ 0 & \text{if } SWE < SWE_{th} \text{ or } T < T_m \end{cases} $$

Where:

• $M_i$ is the daily ice melt from glaciers [mm/day].
• $F_i$ is the ice melting factor $[mm/°C/day]$.
• $T$ is the daily temperature $[°C]$.
• $T_m$ is the ice melting threshold temperature $[°C]$.
• $A_i$ is the area of the glacier ice that contributes to melting.
• $SWE$ is the Snow Water Equivalent [mm].
• $SWE_{th}$ is the threshold amount of SWE on the glacier before ice melt occurs $[mm]$.

$M_i$, $F_i$, and $SWE_{th}$ are three new calibration factors. Glacier melt in the elevation layers is given as liquid input into the GR4J model in the same way than in the CemaNeige layer with the snow melt.

The modification for the glacier module includes new functions and changes to existing functions, such as:

• RunModel_CemaNeigeGR4J_Glacier.R: New function that runs the CemaNeigeGR4J model with the glacier module.

• RunModel_CemaNeigeGR6J_Glacier.R: New function that runs the CemaNeigeGR6J model with the glacier module.

• TransfoParam_Glacier.R: New function that transforms the three additional glacier parameters for calibration.

• CreateRunOptions.R: Include the relative ice area in the run options. Add RunModel_CemaNeigeGR4J_Glacier, RunModel_CemaNeigeGR6J_Glacier

• CreateCalibOptions.R: Include default parameter distributions for the glacier module.

• Utils.R: Get the correct name also with the glacier module.

• UtilsCalibOptions.R: Include the glacier module for the calibration.

• UtilsRunModel.R: Get ice melt and SWE as output.

• RunModel.R: Minor changes regarding parameter.

2. Lapse rate for temperature and precipitation

The modification for the lapse rate for temperature and precipitation includes changes to existing functions, such as:

• DataAltiExtrapolation_Valery: Possibility to add custom daily temperature lapse rates and altitudinal correction factors for precipitation.

• CreateInputsModel: Possibility to add custom daily temperature lapse rates and altitudinal correction factors for precipitation which is used in DataAltiExtrapolation_Valery.

Installation

Prerequisites

Before installing airGR_GM, ensure you have the following prerequisites installed on your system:

• R: Version 4.1.1 or higher.

• RTools (Windows only): Required for building packages from source.

• Homebrew (macOS only): Required for managing installations like the Fortran compiler.

1. Install Homebrew (macOS only)

If you're on macOS, install Homebrew by running the following command in your terminal:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

2. Install the Fortran Compiler (gfortran)

macOS: Open your terminal and run the following commands:

2.1 Install gcc which includes gfortran using Homebrew:

brew install gcc

You can check the installation by running:

gfortran --version

and find the path where gfortran is installed by running:

2.2 Set up the Makevars file for R to find the C and Fortran libraries:

1. Find the Path for the Fortran Compiler (gfortran):

which gfortran

This should return something like:

/opt/homebrew/bin/gfortran

2. Find the Path for the Fortran Libraries:

Identify the specific version of GCC installed by running:

brew --prefix gcc

Then, use the following command to get the path to the Fortran libraries

echo $(brew --prefix gcc)/lib/gcc/$(gcc-14 -dumpversion)

This should return a path similar to:

/opt/homebrew/Cellar/gcc/14.1.0/lib/gcc/14/

3. Create a Makevars file in your R directory:

nano ~/.R/Makevars

Add the paths obtained from above to your Makevars file to ensure R finds the necessary compilers and libraries (The following are example paths)

FC = /opt/homebrew/Cellar/gcc/14.1.0/bin/gfortran
F77 = /opt/homebrew/Cellar/gcc/14.1.0/bin/gfortran
FLIBS = -L/opt/homebrew/Cellar/gcc/14.1.0/lib/gcc/14/ -lgfortran -lquadmath -lm

Save the file.

4. Install airGR_GM

With all dependencies installed, you can now install the airGR_GM package using the devtools package in R. First, ensure that devtools is installed:

# install.packages("devtools")
devtools::install_github("hydrosolutions/airGR_GM")

Load the library:

library(airGR)

Please pay attention: the library is called airGR and not airGR_GM.