  Floods are highly uncertain events, occurring in different regions, with
varying prerequisites and intensities. A highly reliable flood disaster risk
map can help reduce the impact of floods for flood management, disaster
decreasing, and urbanization resilience. In flood risk estimation, the widely
used analytic hierarchy process (AHP) usually adopts pixel as a basic unit, it
cannot capture the similar threaten caused by neighborhood source flooding
cells at sub-watershed scale. Thus, an extended watershed-based zonal
statistical AHP model constraining runoff converging related indicators by
sub-watersheds (WZSAHP-Slope & Stream) is proposed to fill this gap. Taking the
Chaohu basin as test case, we validated the proposed method with a real-flood
area extracted in July 2020. The results indicate that the WZSAHP-Slope &
Stream model using multiple flow direction division watersheds to calculate
statistics of distance from stream and slope by maximum statistic method
outperformed other tested methods. Compering with pixel-based AHP method, the
proposed method can improve the correct ratio by 16% (from 67% to 83%) and fit
ratio by 1% (from 13% to 14%) as in validation 1, and improve the correct ratio
by 37% (from 23% to 60%) and fit ratio by 6% (from 12% to 18%) as in validation
2.
