How to use Demeter outputs with Tethys

Demeter is a land-use and land-cover disaggregation and change detection model. Demeter results are irrigated cropland areas for each type of crops (12 crops , no biomass) in the fraction of a 0.5 degree grid cell by different years.

In Tethys, the data of irrigated cropland areas is originally from GMIA (2005) or HYDE (1900-2000) in harmonized_inputs according to the simulation years of GCAM. The GMIA or HYDE data does not separate the irrigated area of each grid cell by crop types. Thus, Tethys downscales the water demand of irrigation according to irrigated area of all crops.

By utilizing the outputs from Demeter, Tethys is able to downscale the water demand of irrigation by different crop types. To perform this function in Tethys, two steps required:

1. Prepare the folder contains Demeter outputs:

• A single csv file for each year whose filename is ended with "_[yearnumber].csv", e.g. "demeter_ssp1-rcp6p0_0p5deg_2010.csv"
• Each csv contains 67420 rows and several data columns, the following 12 headers representing 12 data columns are required for each file:
  • corn_irr
  • fibercrop_irr
  • foddergrass_irr
  • fodderherb_irr
  • misccrop_irr
  • oilcrop_irr
  • othergrain_irr
  • palmfruit_irr
  • rice_irr
  • root_tuber_irr
  • sugarcrop_irr
  • wheat_irr

2. Add two settings in [Project] section in the configuration file e.g. config.ini

• UseDemeter = 1 # Default is 0, if use data of irrigated area for each type of crop from Demeter, = 1

• DemeterOutputFolder = ./Demeter_Tethys/test_run_ssp1-rcp6p0 # Folder contains Demeter outputs in the fraction of a 0.5 degree grid cell

• 13 additional output files will be created for spatially downscaled irrigation water withdrawls by crop types.

  Tethys will automatically process the data files, the range of years with available Demeter outputs will be compared with the simulation years of GCAM and only the years with available Demeter outputs are downscaled by crop types. For example the available years for Demeter outputs are 2010-2100 by every 5 years. The GCAM years defined in configuration file (e.g. config.ini) is: GCAM_Years = 2005,2010,2015,2020 Tethys will start from 2010 that with available Demeter data rather than 2005. It is suggested to use the start year of Demeter outputs as the start year of GCAM_Years.

3. Temporal downscaling using Demeter outputs

• Temporal downscaling will be performed after spatial downscaling to irrigation water withdrawals. The spatially downscaled results will be downscaled into monthly values and then divided according to annually fraction of each crop type at each cell.
• 13 additional output files will be created for temporally downscaled irrigation water withdrawls by crop types.
• Temporal downscaling is performed according to the monthly profiles from other models (Please refer to Huang et al., 2017). The current available profile data sets is 1971-2010. For future years beyond 2010, the following criteria are used for different sections:
  • Irrigation: 40 years averaged monthly profile
  • Domestic and Electricity: monthly profile of year 2010
  • Other sections: uniformly distributed monthly profile