Read the GLWD inland-water fraction on the 0.5-degree grid

Returns the Global Lakes and Wetlands Database surface-water fraction of each 0.5-degree cell. water_frac is a fraction of the whole cell, so the water area of a cell is water_frac * cell_area_ha.

This is the inland-water source for build_polycell_support(). It is preferred over ne_10m_lakes, which carries roughly half of global inland water and omits the Caspian Sea entirely.

The fraction is derived from the GLWD rasters inst/scripts/download/download_hydrology.R fetches from the published figshare DOI, through glwd_water_fraction() – the same derivation inst/scripts/prepare_spatialize_all.R uses to write LPJmL's own lakes_rivers input, so the two cannot drift.

Until WHEP settled on GLWD v2 this read LPJmL's glwd_lakes_and_rivers_30arcmin.clm and a companion grid.clm instead. That pair is derived from GLWD v1, no script in this repository produces it, and it gives 2.4759 Mkm2 of inland water over the 67,420-cell CRU land mask against v2's 3.2480 Mkm2. Any figure quoted against the old layer has to be re-measured rather than carried across.

Usage

read_glwd_water(dir = NULL)

Source

Lehner, B., Anand, M., Fluet-Chouinard, E. et al. (2025). Mapping the world's inland surface waters: an update to the Global Lakes and Wetlands Database (GLWD v2). Earth System Science Data 17, 2277-2329. doi:10.5194/essd-17-2277-2025

Arguments

dir

Directory holding GLWD/, as download_hydrology.R lays it out. Defaults to Sys.getenv("WHEP_LPJML_INPUT_DIR").

Value

A tibble with lon, lat and water_frac, one row per cell the rasters cover.

Examples

# Requires WHEP_LPJML_INPUT_DIR to be set; not run without it.
if (nzchar(Sys.getenv("WHEP_LPJML_INPUT_DIR"))) {
  read_glwd_water()
}