and constant returns to scale (Hertel, 1997). To estimate the
impacts of changes in irrigation availability on agricultural
production and trade, we use a special version of this model
which takes into account irrigation water as an explicit input into
irrigated agriculture. This new model is dubbed GTAP-BIO-W and
is documented in Taheripour et al. (2013a, hereinafter THL). An
important improvement THL made to the GTAP model is to
distinguish irrigated and rainfed cropping such that water enters
irrigated production as a complementary input of land (Fig. A1).
Meanwhile, the land-water composite is substitutable for other
value-added inputs (labor, capital and energy), allowing for a
modest endogenous yield response to prices.