A good flood risk analysis combines geophysical and statistical data. It can and in good countries is reasonable accurate for individual lots. The first part requires a detailed model of the landscape, i.e. elevation relative to the water sources in the area, ground water level, ground water flow, sediment layering, soil water capacity etc. That's all data can be survived to any desirable resolution and approximated further as needed. The flood risk analysis now puts an environmental simulation on top. That requires estimating event probabilities and for extreme weather events, is the part that is most likely going wrong. You have for example an events like "5 weeks of continuous heavy rain". It's estimate to happen one a year and the simulation shows which part of the simulation area are flooded. Those get their flood risk updated by 5%.