Spatial realization uncertainty; Land-use reallocation; Urban simulation; Transport emissions; Scenario ensemble; Built-out district

We examine whether the magnitude and direction of these effects depend on which parcels are converted under the same area targets for each land-use class. In Futian District, Shenzhen, we compare tailpipe CO₂ from interzonal car travel under baseline, service-oriented, and residential-oriented scenarios.

Per scenario-year, repeated stochastic allocation generates 100 parcel maps (spatial realizations) meeting the same targets under a fixed land total. To assess spatial-realization and parameter uncertainty, each realization was evaluated through the same travel-demand and emission chain with the same 500 downstream parameter draws. The findings reveal that (1) with downstream parameters held fixed, service-oriented reallocation lowers mean emissions by 0.33% in 2025 and 1.21% in 2030 and emits less than the baseline in 84% and 93% of realizations, whereas residential-oriented reallocation shows no stable increase; (2) reduced trip generation contributes to lower emissions in every realization, and a smaller share of trips leaving their zone does so in most, while distance and car-share contributions vary in sign; and (3) among the represented uncertainty sources, spatial realization accounts for over nine-tenths of the variation in scenario differences.