Land use_change - PIK-LPJmL/LPJmL GitHub Wiki

Land-use change

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Description

With the implementation of agricultural modules in LPJ to create LPJmL, a routine was needed that helped to convert natural land to agricultural land and back. General assumptions are that total agricultural land (all crops, all managed grassland ) is cleared (liberated) at the beginning of each year as prescribed by the land-use input data. Uncultivated cropland (i.e. outside the cropping period) is merged in setaside stands, separated in irrigated and rainfed to prevent that irrigation water from irrigated stands is transferred to rainfed stands in off-seasons.

Details

Spatial units in LPJmL are grid-cells (dependent on spatial resolution of inputs, which can be separated into stands with specific land use (crops, managed grassland, natural, bioenergy) and irrigation (yes/no). The core of the land-use change routine is at landusechange.c adding up all the crop- and irrigation specific land use fractions to total cropland and total grassland. Total agricultural land cannot exceed 100% of the land, sequential cropping systems are covered by multiple cropping systems. Natural land fraction is increased/decreased accordingly. Land use data is read with landuse.c

To make room for agricultural land, natural-vegetation land is liberated via reclaim_land.
All liberated cropland is assigned to irrigation-specific setaside stands which can grow intercrops if specified. At the crop-specific sowing dates, the corresponding fraction is extracted from the setaside (copying all stand-specifics) after harvest, the crop-specific stands are returned to the corresponding setaside (irrigated/non-irrigated) stand and soil pools are mixed: setaside.c

Sowing dates are determined by as described in Waha et al. and if sowing dates are reached in the daily loop in
iterateyear.c
iterateyear_river.c
land is cultivated and sown.c
sowing.c
cultivate.c

Technical Note

Land-use settings can be any of the following: off (simulation with natural vegetation only), annually prescribed (default), constant, or allcrops (forcing all crops and all irrigation schemes everywhere). This is specified in
lpjml.conf
with the pre-compiler flag
#define WITH_LANDUSE
with the arguments

  • 1 (default, annually prescribed data from input file)
  • CONST_LANDUSE (or 3, constant land-use pattern in time, year for land-use pattern fixation is hard-coded in iterate.c to the year 2000, but ideally this could be specified in param.par, see #764)
  • ALL_CROPS (or 4, forces all crops/management types everywhere, standard application for generating data for the project:magpie model)

If simulations for natural vegetation only are wanted, the pre-compiler flag #define WITH_LANDUSE has to be removed (defining as 0 does not work to my knowledge)…

Standard land-use data set is based on MIRCA2000[2] as modified by Fader et al. 2010[3], most up-to-date (even though it’s not) description of the mechanisms in Bondeau et al[4]

A new land-use data set (2015) accounts for updated irrigated areas as in irrigation including irrigation areas from Siebert et al., 2015[5] and as used in Jägermeyr et al.,2015[6]

Developer(s)

S. Schaphoff, S. Zaehle, T. Beringer, S. Jachner, A. Bondeau, C. Müller

See Also

Sowing dates, Wiki, Crop functional types, stand, managed grassland, setaside

References

  1. Waha K, van Bussel L G J, Müller C and Bondeau A 2012 Climate-driven simulation of global crop sowing dates Global Ecology and Biogeography 21 247-59 http://dx.doi.org/10.1111/j.1466-8238.2011.00678.x

  2. Portmann F T, Siebert S and Döll P 2010 MIRCA2000-Global monthly irrigated and rainfed crop areas around the year 2000: A new high-resolution data set for agricultural and hydrological modeling Global Biogeochemical Cycles 24 Gb1011 http://dx.doi.org/10.1029/2008gb003435

  3. Fader M, Rost S, Müller C, Bondeau A and Gerten D 2010 Virtual water content of temperate cereals and maize: Present and potential future patterns Journal of Hydrology 384 218-31 http://dx.doi.org/10.1016/j.jhydrol.2009.12.011

  4. Bondeau A, Smith P C, Zaehle S, Schaphoff S, Lucht W, Cramer W, Gerten D, Lotze-Campen H, Müller C, Reichstein M and Smith B 2007 Modelling the role of agriculture for the 20th century global terrestrial carbon balance Global Change Biology 13 679-706 http://dx.doi.org/10.1111/j.1365-2486.2006.01305.x

  5. Siebert, S., Kummu, M., Porkka, M., Döll, P., Ramankutty, N., and Scanlon, B. R.: A global data set of the extent of irrigated land from 1900 to 2005, Hydrol. Earth Syst. Sci., 19, 1521–1545, doi: 10.5194/hess-19-1521-2015, 2015. 3, 14, 43

  6. Jägermeyr, J., et al. “Water savings potentials of irrigation systems: dynamic global simulation.” Hydrology and Earth System Sciences Discussions 12.4 (2015): 3593-3644.