If you want to create a calculated field that produces the percentage of the total land flooded during an event, we need to use a data source that has this information in it. Most stories need more than one data source. When you are adding in secondary data sources, it's important to know what the level of aggregation is if you have joined data sources with different levels of aggregation and have not accounted for that when blending them because if you fail to do so, you might get the wrong results in your calculated fields.

The flood data is aggregated at the event level. This means that for every major flood, we have summarized data—the start date, end date, location, total land area affected, and so on. This is moderately granular data. If it were even more summarized, it might be summed up as floods per year per country.

We want to know the total percent of land flooded each year, and for this, we will assume that the area of each country is static throughout time...