The need for explicitly considering equity in adaptation planning is
increasingly being recognized. However, quantitative evaluations of
adaptation options often adopt an aggregated perspective, while
disaggregation of results is important to learn about who benefits when
and where. A typical example is adaptation of rice agriculture in the
Vietnam Mekong Delta. In the past two decades, efforts focused on flood
protection have mainly benefitted large-scale farmers while harming
small-scale farmers. To investigate the distributional consequences of
adaptation policies in the Vietnam Mekong Delta, we assess both
aggregate efficiency and equity indicators, as well as disaggregated
impacts in terms of district-level farmers profitability. Doing so
requires an adequate representation of the co-evolutionary dynamics
between the human and environmental systems which influence farmers
profitability. We develop a spatially-explicit integrated assessment
model that couples inundation and sedimentation dynamics, soil fertility
and nutrient dynamics, and behavioral land-use change and farmers
profitability calculation. We find that inter-district inequality
responds in a non-linear way to climatic and socio-economic changes and
choices of adaptation policies. Distinctive inequality patterns emerge
from even slightly different combinations of policies and realizations
of uncertain futures. We also find that there is no simple ranking of
alternative adaptation policies, so one should make trade-offs based on
the agreed preferences. Accounting for equity implies exploring the
distribution of outcomes over different actor groups over a range of
uncertain futures. Only by accounting for multisectoral dynamics can
planners anticipate the equity consequences of adaptation options and
prepare additional measures to aid the worse-off actors.