Tag Archive for: Michael Bloom

Inherent Bias and Limitations of Flood-Mitigation Benefit Index

In the last few weeks, Michael Bloom, a fellow member of the Harris County Community Flood Resilience Task Force, and I have debated the inherent bias and limitations of a Flood-Mitigation Benefit Index (FMBI) proposed by a majority of the Task Force to Harris County Commissioners Court.

According to Mr. Bloom, the index will:

  • Reveal and document patterns of historical discrimination.
  • Help plan where additional flood-risk reduction investments should be made.

Population-Based, Not Damage-Based Mitigation

The formula is: 

Benefit = Total Cost/(Population X Risk)

…where:

  • Cost = total flood-mitigation construction spending (and only construction spending) that benefits a census tract.
  • Population = the number of people who live in census tracts.
  • Risk = the annual chance of flooding (applied to census tract(s)) expressed as a whole number. For instance, a 1% annual chance equals 1. And a 10% annual chance equals 10, etc.

The Task Force hopes to calculate and compare the results for each census tract in the county.

The formula measures the historical per capita flood-mitigation costs 
supposedly associated with the “current” level of risk in a census tract – NOT historical flood damage.

According to proponents, “a high benefit score means no more mitigation spending is needed. And a low score means more spending is needed.”

But consider these two examples: 

  1. 4,000 people live with a 1% annual chance of flooding and have received $200 in prior investment. Their FMBI would be 0.05. That’s extremely low. And scores that low indicate such areas need help “regardless of prior investment.”
  2. 8000 people live in the 10-year flood plain and have received $10 million in prior investment. Their FMBI equals 125. That’s 2,500 times higher. 

According to a spokesperson for the FMBI, “A high FMBI means we don’t need to make more investments in that location.” Yet twice as many people live with ten times the risk in the area with the higher index.

So, who deserves the most help? Residents with the lowest FMBI? The formula SAYS they need help the most. But they actually have the lowest risk.

The Value of Market Testing

None of the hypothetical examples used to “sell” the formula hint at the possibility of such an upside-down result. 

The example above proves several things: 

  • The formula can produce inconsistent and misleading results.
  • It doesn’t always measure what it purports to measure. It has validity problems, as previously discussed.
  • Adjusting for population doesn’t prove historical discrimination. The most densely populated area has 50,000 times more investment.

The formula needs rigorous testing and ground-truthing before going any further. This is a best practice for any new scientific formula – especially one intended to guide future investment. 

In addition to producing unintended results, the formula has several other problems that require discussion. 

No Right-Of-Way Acquisition Costs Included

The FMBI formula includes only construction costs. It excludes right-of-way acquisition costs by assuming that they are “uniform throughout the county.” Therefore, “…costs included or excluded will not adversely impact results.”

In fact, Right-of-Way (ROW) Acquisition costs are huge and NOT UNIFORM throughout the county. I have documented that ROW costs typically comprise the second most expensive part of flood-control projects.

All Flood Control and partner spending on all capital improvement projects from 1/1/2000 through the end of Q3 2021. Data obtained via FOIA Request from HCFCD.

A quick glance at the Appraisal District website will tell you that land costs vary widely throughout Harris County and change over time.

The cost of buying floodplain land or wetlands for preservation in rural parts of Harris County pales in comparison to land acquisition costs in densely populated parts of the county.

In fact, acquiring land in densely populated areas for flood mitigation often costs more than construction, according to several engineers I consulted.

Compounding Problems?

I worry that other methodological issues may compound each other, not cancel each other out.

Map of Census tracts in Harris County, Texas.

Consider that:

  • Census tract population typically varies by up to 4X (2,000 to 8,000), according to the Census Bureau. This will produce deceptive spatial comparisons.
  • Some Census tracts may comprise dozens of square miles while others comprise a few city blocks. Typically, flood mitigation projects are not considered at the Census-tract level. According to three engineers I consulted, that’s too small in most cases to be workable.
  • Larger Census tracts may contain multiple watersheds, each with independent levels of risk – or individual watersheds with varying levels of risk. In such cases, the formula would average risk. But averaging can mask a serious problem in one area with a non-problem in another. Thus, the formula has a bias in favor of spatially smaller Census tracts.
    Smaller tracts tend to be more uniform in risk, so problems will likely stand out rather than get lost in an average. But in larger watersheds, flood risk will feather out with increased elevation and distance from a river. That will make it extremely difficult to calculate the number of people exposed to varying degrees of risk.
    Averaging takes the simple way out. But averaging risk is like comparing saints and sinners, then declaring “No problem.”
  • The data collection effort for the index omits many sources of funding. So the formula will calculate investment dollars from some entities and areas, but not others. For instance, the formula will NOT measure drainage funding from Harris County Commissioner Precincts, dozens of cities, and 389 municipal utility districts in unincorporated areas. The difficulty of data collection in these areas will produce another spatial bias. Likewise, the FMBI formula will omit the considerable drainage-improvement contributions of reputable private developers. 

No one has tested how these inconsistencies will affect each other. But there’s an even bigger data integrity issue.

Partially Updated Data

HCFCD and its partners invested more than $1.5 billion in flood mitigation between Harvey and the end of 2021. Since 2000, they’ve invested more than $3.5 billion. But as of this writing, new MAAPnext flood maps only reflect the POST-mitigation risk associated with projects in FIVE bayous: Brays, Greens, White Oak, Sims, and Hunting. The Army Corps partnered with HCFCD in those.

Unfortunately, according to a knowledgeable source, HCFCD has not yet updated the risk maps for its own Capital Improvement Projects in other watersheds. So if you ran the allocation formula now, it would compare PRE-mitigation risk in 18 watersheds with POST-mitigation risk in 5. 

Mitigation in those five watersheds totals $439 million out of $1.5 billion since Harvey. So true, current risk is reflected in only 29% of spending since Harvey and 13% in this century. Those percentages will no doubt increase in the future. But if you ran the numbers today, you would compare numbers with PRE- and POST-mitigation risk.

And consider this. With HCFCD spending at the current rate of about $80 million per quarter, “current risk” is a constantly changing target. So we’ll never be able to compare apples to apples in all watersheds anytime soon.

And we want to use this formula to guide future mitigation spending? Using it could send more money back to fix areas we already fixed!

Difficulty of Assigning Investments to Census Tracts

Another challenge: How do you determine which census tract(s) to apportion project benefits among? Example: Addicks and Barker Reservoirs. The Army Corps developed those back in the 1930s to protect downtown Houston…15-20 miles away! 

Do you credit the investment to:

  • All of downtown?
  • People living inside the reservoirs (who have their own census tract)?
  • The current population of the entire Addicks and Barker Watersheds?
  • All census tracts along Buffalo Bayou and parts of White Oak Bayou, our second and third most populous watersheds?

The Corps certainly didn’t build the reservoirs to protect the people living inside them. That’s what all the lawsuits are about!

And virtually all residents of the Addicks and Barker watersheds live upstream from the Corps’ investment, so they will not benefit from the investment either.

Downtown has immense commercial and economic value but relatively few permanent residents. 

So, who gets the benefit? Again, lots of room for interpretation and misplaced assumptions here that numbers can easily mask! Now, multiply this problem times thousands of Census tracts.

Anti-Commercial Bias

The population-based FMBI has a built-in bias against commercial areas that have little to no residential population. For example, consider the cases of Downtown, the Texas Medical Center, and the Port of Houston. Such areas support employment throughout the region, but the formula discriminates against them by giving huge weight to population and omitting actual damage.

No Thresholds Defined

To my knowledge, the task force has never discussed threshhold “benefit” levels that correlate to “needs help” or “doesn’t need help.” The extremes may sometimes be easy to determine. But what about outcomes in the middle? 

Offsetting Variables

Variables in the formula can offset each other as we saw above. In tight races for funding, who gets the next flood-mitigation investment? The area with the lowest investment, highest risk, or largest population? Such quandaries have not yet been addressed. 

No Agreement on Weights of Other Factors

To help make future flood-mitigation decisions, proponents of the formula also suggest weighing (separately) other factors, such as the CDC’s Social Vulnerability Index. It includes the percentage of Low-to-Moderate residents in an area. However, no one has yet discussed the weight given the Benefit Index relative to other factors.

No Consideration of Actual Flood Damage

In deciding where to put flood mitigation projects, engineers traditionally look for damage clusters. It’s that simple. Dollars flow to damage.

Reducing flood damage is a tried and true, measurable way to evaluate projects. So why all the complexity? 

What’s The Point?

What is this formula trying to prove? Is it attempting to develop a new approach to mitigation funding that eliminates a perceived bias in Benefit/Cost Ratios? 

Commissioner Rodney Ellis often talks about how calculating the value of avoided damages in higher value homes disadvantages projects in poorer neighborhoods. That can be true in some instances. Expensive homes can ratchet up benefits (measured in dollars) faster than lower value homes can. And that can result in higher Benefit/Cost Ratios for projects in affluent neighborhoods – assuming density is held constant. But…

One high-value home on an acre would likely appraise less than an apartment building, also on an acre. In Kingwood, I compared the valuations of an expensive single-family home with a large apartment complex one block away. The appraised cost per acre (including structures) of the apartment complex is 4X higher.

Now consider that apartments accommodate almost half of Harris County’s population.

According to the latest census data, 54.9% of Harris County residents live in owner-occupied homes. The rest, 45.1 percent, live in apartments.

Most Americans aspire to and encourage home ownership, in part, because of the stability it fosters in communities. But this formula – because of its emphasis on population density – favors apartment areas over areas with owner-occupied homes. There’s nothing inherently wrong with that. You just need to understand what the formula does.

Difference Between Vertical and Horizontal Density

The Benefit Index favors all areas with dense population. Proponents argue that helping more people is better. I don’t argue with that. However, the generalization masks the financial pain inflicted by a flood on owners vs. renters, and on the people who live at ground level compared to those who live above it. 

Ground floor renters may lose contents in a flood, but they won’t be responsible for making structural repairs. The owner will. 

And many living above the ground floor may find themselves more inconvenienced by flooding than financially devastated. So, is it fair to count all people on all floors when determining who suffers the most pain? 

Five-story apartment buildings crowding Brays Bayou with ground-level parking underneath. HCFCD has no way of knowing how many people live in apartments like this, yet HCFCD will be responsible for compiling the data.

In the proposed formula, higher population will lower the benefit index, making it look as though all renters (almost half the county’s population) suffered more than owners of single-family homes. 

The premise underlying such “equity” arguments is that poor people can least afford floods. But most people in apartments like those shown above won’t make structural repairs as a homeowner would.

No Perfect Formula

No perfect formula exists that’s equally fair to all in all circumstances. That’s why FEMA, HUD and the Army Corps allow consideration of multiple factors when determining which projects to fund. 

The Flood Mitigation Benefit Index focuses totally on population, risk, and past investment. It ignores actual flood damage. 

If we use ANY formula to HELP allocate future flood-mitigation funds, we should all strive to:

  • Understand its built-in biases
  • Maintain high standards for data integrity.

If we want to test a hypothesis of historical discrimination in flood-mitigation funding, there’s a much simpler way. It’s called direct measurement. Simply locate damage centers from past storms and compare funding in the following decade designed to mitigate those areas.

For More Information

For more background on issues with the formula, see my earlier posts:

Or consult Mr. Bloom’s rebuttals.

Posted by Bob Rehak on 7/14/22

1780 Days since Hurricane Harvey

Response to Concerns About Flood Mitigation Benefits Index (Part II)

The letter below expresses disagreement with two recent ReduceFlooding.com posts about a proposed Flood Mitigation Benefits Index. It is from Michael Bloom, P.E. While I disagree with almost all of his claims, I am reprinting his letter verbatim because I encourage healthy debate. Compare the posts and draw your own conclusions. – Bob Rehak, Host, ReduceFlooding.com.

This is Part II of my two-part article providing responses to concerns raised by my colleague on the Community Flood Resilience Task Force (CFRTF), Mr. Bob Rehak about the FMBI. If you missed Part I, you can read it here.

Why are we Using the Index When it Produces Inconsistent Results that are Not Intuitive? Mr. Rehak provides an example that holds the current population and current risk the same, but changes the total prior investment amounts, as illustrated in the table below:

Prior
Investment
($)		Current
Population
(Number)		Current
Risk
(% Annual Chance)		FMBI
Area A100,0005,000102
Area B1,000,0005,0001020

Mr. Rehak looks at these results and writes: “So, spending more money to get the same results increases benefits? Shouldn’t it be the opposite? That’s both depressing and confusing. You spend 10X the money; flood risk remains the same; and the “benefit” increases!!!??? You would think spending less money to achieve identical results would be more beneficial. It certainly is for taxpayers.”

Everyone should be depressed and confused by this result if the FMBI was illustrating the results for the same location. Mr. Rehak appears to make that inference when he writes: “spending more money to get the same results increases benefits.”

But Area A and Area B are two different locations. The FMBI is just telling us what the current conditions are at two different locations in the county. One location had 10 times the prior investment than the other – but both locations still have the same current risk.

Worse, in this case, BOTH locations have risks that are ten times the current standard of care for new developments – which require structures to have less than a 1% annual chance of inundation. Clearly, both locations need more flood risk investment. The FMBIs of 2 and 20 both are extremely low, meaning they need help, regardless of the prior investments. A high FMBI indicates that no additional help is needed in that location. A low FMBI indicates that additional help is needed in that location.

The table included in the middle of my February 17, 2022, post entitled “How Should We Decide Where to Invest in Flood Risk Reduction?” presents additional examples showing how the FMBI changes from location to location with only one changed variable. It also provides narrative explanations of each sequence. Notice how the index values are greater than 3,000 (sometimes greater than 20,000 or 100,000) in locations where the current annual chance of inundation is less than 1%? Again, a high FMBI means we don’t need to make more investments in that location. A low FMBI means that location needs more help.

Isn’t the FMBI Trying to Prove Inequitable Investments in Flood Risk Reduction? To some extent, partially, yes, it is. This was always an important aspect of the FMBI, when it was originally proposed as the “Flood Benefits Index (FBI)” by Dr. Erthea Nance and Iris Gonzalez in May 2021. I have continued to advocate for its use as one of four input variables we should use to create our county-wide “heat map.” This is explained in more detail in my other article. Mr. Rehak is concerned about the taxpayer. I am also. I don’t think the taxpayers of Harris County should pay for flood risk reduction projects in areas that already have a high FMBI. Said another way, it is a waste of taxpayer money to invest in additional flood risk reduction projects in areas currently with less than a 1% annual chance of inundation.

Isn’t the FMBI Measuring per capita Investment Associated with a Certain Level of Flood Risk and Mistakenly Calling that a “Benefit?” Mr. Rehak writes: “The more people you help with any given sum, the more the benefit goes down. Voila! That makes it look as though the highly populated watersheds (that have received the overwhelming majority of prior investments) have received little benefit. And that may be the point of this formula. It will send even more money to those same areas.”

This interpretation again seems to stem, I think, from Mr. Rehak’s belief that the index will be used to compare the same location at different times – before and after various investments. This is not the proposed use of the index. The proposal is to use the index to describe the current conditions at all locations in the county at the same time.

I’m not sure I understand Mr. Rehak’s concern about the index being a per capita value. The more people in an area who benefit from prior investments the better. Wouldn’t we want to invest in areas that help the most people?

The blue-shaded area of the table in my earlier post illustrates how population differences between locations will change the index value among those locations. For convenience I’ve repeated the table below:

Hypothetical examples.

Mr. Rehak accurately notes that the index goes up in locations with fewer people and down in locations with more people; this will incentivize planners to direct future investments in those higher population areas. He writes: “The more people you help with any given sum, the more the benefit goes down.” This is true, but Mr. Rehak’s statement doesn’t connect it to the past and it omits how the index will be normalized by area size. Index values will be calculated for similarly sized areas. This will allow an apples-to-apples comparison of per capita investments. The index is intended to incentivize future investments in areas with more people in cases where risk and prior investments are equal because we want to help as many people as possible.

By Michael Bloom, P.E.

Posted by Bob Rehak on 7/10/2022

1776 Days since Hurricane Harvey

If you have views on this subject, please share them through the contact form on this website.

Response to Concerns About Flood Mitigation Benefits Index (Part I)

The letter below expresses disagreement with two recent ReduceFlooding.com posts about a proposed Flood Mitigation Benefits Index. It is from Michael Bloom, P.E. While I don’t agree with all of his claims, I am reprinting his letter verbatim because I encourage healthy debate. Compare the posts and draw your own conclusions. – Bob Rehak, Host, ReduceFlooding.com.

One of my colleagues on the Harris County Community Flood Resilience Task Force (CFRTF) – Mr. Bob Rehak, as well as Commissioner Tom Ramsey, P.E., and others have asked me about the proposed Flood Mitigation Benefits Index (FMBI). After hearing some of the questions, and reading two recent blog posts by Mr. Rehak at Reduce Flooding, one on July 2, 2022 – Questionable Validity of Flood-Mitigation Equity Formula and on July 6, 2022 – Formula for Allocating Future Flood-Mitigation Funding Deceives, I figured I should provide a more detailed explanation of the index and directly address some of Mr. Rehak’s concerns.

In addition to getting to know Mr. Rehak while attending CFRTF meetings, Mr. Rehak and I have sat down, in person, a few times since both being appointed to the Task Force in order to discuss difficult issues, in particular the FMBI. I appreciate his candor and our ability to respectfully debate things – one might say – politely argue. This post (and Part II) are extensions of those discussions so others can benefit from the exchange.

I first described the FMBI in an article I published on February 17, 2022, entitled “How Should We Decide Where to Invest in Flood Risk Reduction?” The FMBI is explained about halfway down the post. To recap, the index is equal to:

Variation on formula presented to Commissioners Court on 6/28/22. It omits the word “Density” after population. See discussion below.

The index is intended to be calculated for all locations in the county at one particular time to help define the baseline conditions. The index will be used to help plan where additional flood risk reduction investments should be made. An area with a high FMBI has already received higher per capita investments, has a low risk, and therefore doesn’t need additional help. An area with a low FMBI has received little per capita prior investments, has a high risk, and therefore does need additional help.

Responses to Specific Concerns

Which Type of Project Costs Are Included? Does including construction costs, but excluding design, right-of-way acquisition, and operational costs skew the data? Since this is an index that will be calculated for all areas of our county, costs included or excluded will not adversely impact the results.  Using the index to compare conditions in various areas within our 1,700 square mile county will still be valid if the index is calculated in all areas of the county the same way. This is an example of “normalizing” the data. It allows for an apples-to-apples comparison among and between locations. It will help us pick where to invest in the future. Since land acquisition, design, and other non-construction costs are often a similar percentage of the construction costs, their exclusion from all index calculations will keep things consistent and unskewed.

Which Agency Investments are Included? Will excluding investments from Harris County Commissioner Precincts, cities, municipal utility districts, and other entities skew the data. I actually agree with this, the investment dollars will be slightly low, but only by a little bit. I anticipate that the total amount of flood risk reduction investment dollars made by these entities will be very, very, very small compared to those made by the Harris County Flood Control District (HCFCD) and the Civil Works program of the U.S. Army Corps of Engineers (USACE). Because of this difference in the size of these investments, I anticipate that the impact on the index calculation will be negligible. HCFCD has agreed to provide their investments from 2000 to 2020. Dr. Denae King and I have submitted a Freedom of Information Act (FOIA) request to the U.S. Army Corps of Engineers, the Federal Emergency Management Agency (FEMA), and the Natural Resource Conservation Service (NRCS) to identify all flood risk reduction investments going back to 1937 – the year the HCFCD was created to serve as the “local partner” to help secure federal investments through the USACE. These requests exclude repair and recovery dollars since those expenditures don’t permanently reduce flood risks.

What Risk is Included in the Index? Does the risk used in the calculation reflect the risk before or after mitigation efforts? The risk value used is the current risk. It is the risk remaining after accounting for all risk reduction investments “counted” in the numerator. The index reflects one point in time and should be recalculated every five years or ten years, much like the Social Vulnerability Index published by the Centers for Disease Control. The population and risk values will be based on the same snapshot in time. The investment value will be based on the sum of all investments made prior to that moment in time (adjusted for inflation).

Why Include Investments Back to 1937? Why consider investments made in areas of the county that were undeveloped back then? Won’t this radically skew the comparisons? Including all investments back to 1937 is vitally important because the vast majority of the flood risk reduction investments made in the county were made by the federal government through the Civil Works program of the USACE. HCFCD was CREATED in 1937 to be the local sponsor for USACE projects. Addicks, Barker, Buffalo Bayou, Brays, White Oak, Sims, Clear Creek, and many other projects, many of them initiated prior to 2000, all significantly reduced flood risks for structures that exist today. Even if the project was initially constructed in an undeveloped area, it still benefits structures that were built later and that exist today. That’s why the investment amount is a cumulative value (inflation-adjusted) and the risk value is today’s value. This approach won’t radically skew comparisons because all three of the values will be determined for all parts of the county in the same way.

Why only Consider Mitigation Investments? Doesn’t flood risk depend on many factors – not just mitigation investments? Yes, current flood risk depends on many factors, including development rules, building codes, finished floor elevations, development locations, and improvements to our understanding of rainfall statistics. The risk value in the index is not intended to measure the risk reduction obtained from prior investments. The risk value in the index is intended to present the current risk. The current risk reflects all factors, including prior mitigation investments, development, rainfall, and everything else. The risk value is not a measure of the change in risk, it is a statement of the current risk, no matter the cause or the contributing factors.

Why Use US Census Tracts? Don’t they change over time? US Census Tracts do periodically change, however, that will not diminish the value of the index. US Census Tracts are areas that can more closely match the scale of typical flood risk reduction projects; watersheds are too large to be informative; and smaller areas would be too complex for our planning work.

Harris County outlined in red, census tracts in blue. Map supplied by Michael Bloom.

The originally proposed FMBI used the population density in the denominator. This, admittedly, would cause issues when comparing index values between large US Census Tracts and small US Census Tracts. To address this issue, the CFRTF and the Infrastructure Resilience Team (IRT) have agreed to proceed with the calculation using just population. This will make the index a per capita value. Prorating investment amounts and risk to each Census Tract can be reasonably accomplished using area ratios or other methods. This will be useful as the CFRTF and IRT work together to prepare the 2050 Flood Resilience Plan.

How Can We Use Information From 1937 When the County is So Different Now? How can this approach work without considering the construction of Lake Houston in 1954, the interstate system, Beltway 8, and the conversion of farmland and prairies into entire communities? The risk value captures all of this. The risk value used in the index reflects the current risk of any part of the county. It will be based on state-of-the-art modeling being conducted as part of the MAAPNext project. The current risk is the current risk, regardless of past changes in the watershed.

Why are we Using the FMBI Formula to Reduce Flood Damage when it Doesn’t Measure Flood Damage? The FMBI is not a tool to directly reduce flood damage and it’s not designed to measure flood damage. The FMBI is a tool to better understand past investment patterns and current risk. The FMBI is proposed to be one of four datasets used to create a baseline conditions heat map. The other three under consideration include current inundation risk, social vulnerability index, and community resources. The baseline conditions heat map will then be used to figure out WHERE flood risk reduction and flood damage reduction projects should be located. 

How Can the FMBI Compare Benefits  without Using Before and After Comparisons? The index is not intended to compare the flood mitigation benefits of the same location at different times. The index is intended to show how different locations across the county at the same time vary when compared to each other. This will help us identify WHERE we have neighborhoods that desperately need help and WHERE we have neighborhoods that don’t.

By Michael Bloom, P.E.

Posted by Bob Rehak on 7/9/22

1775 Days since Hurricane Harvey

Part II will be posted tomorrow. If you have thoughts you would like to share on this subject, please send them via the contact form on this website.