Correlation Between Flood Damage, Mitigation Spending Keeps Dropping

8/11/25 – The correlation between flood damage and flood-mitigation spending by Harris County Flood Control District (HCFCD) keeps dropping, indicating an increasing influence of other factors, such as race, on spending.

At the end of 2021, the coefficient of correlation between flood-mitigation spending and flood damage was .84. Statisticians consider that a strong correlation.
By the end of Q1 2024, it had dropped to .67, a positive but moderate correlation.
By the end of Q2 2025, it had dropped further to .64.

What is Coefficient of Correlation?

Coefficient of correlation measures the strength of association between two variables, for instance hours spent studying and exam scores.

Statisticians consider a correlation of 1.0 extremely strong. It is the highest possible and means that for every unit of change in one variable, there is a corresponding unit of change in another. As the coefficient decreases, the strength of the relationship also decreases.

Values close to +1 or -1 (e.g., 0.7 to 0.9 or -0.7 to -0.9) indicate a strong relationship.
Values between 0.3 and 0.7 (or -0.3 and -0.7) suggest a moderate relationship.
Values below 0.3 (or -0.3) indicate a weak relationship.

Less than Half of HCFCD Spending Today Explained by Flood Damage

Squaring the coefficient of correlation yields the coefficient of determination. That tells you the proportion of the variance in the dependent variable that’s explained by the independent variable.

Squaring .64 yields 41%. So, flood damage today accounts for less than half of Harris County’s flood-mitigation spending.

Harris County Commissioner Rodney Ellis’ has relentlessly pushed various prioritization formulas that rely increasingly on race while de-emphasizing damage and flood risk. In fact, his formula now totally ignores flood risk.

The major changes in his formula coincide with the drop in the correlation between flood damage and flood-mitigation spending. The 2022 Prioritization Framework marked the beginning of the huge drop in the correlation.

But in fairness, also understand that special circumstances may apply to investments, such as HCFCD’s Frontier Program. It buys land in developing watersheds for huge, regional detention basins, then sells capacity back to developers. Still…

Notice how the lines in the graph below diverge for some watersheds. Some have proportionally more dollars than damage and vice versa for others. Clearly, politics have skewed spending.

*A higher correlation would show the two lines more closely matching each other.* *Also note that the damage figures include five major floods since 2001. They are extracted from HCFCD Federal Reports.*

The watersheds where the two variables most greatly diverge reduce the coefficient of correlation.

Where does your watershed stand in the dollar derby? Do you think you’re getting your fair share?

Here are the actual dollars and damaged structures in a table format. The last column shows the dollars per damaged structure.

*Coefficient based on Spending and Damage Columns.*

Posted by Bob Rehak on 8/11/2025

2904 Days since Hurricane Harvey