A population already has basic mortality rates built in, for each sex and age group. Aid packages change those basic rates. But at any point, the population as a whole has some per capita mortality rate. Call this the "base mortality rate".

Capacity Effects wants to apply more mortality as the population reaches carrying capacity (100% maximum). The idea here is that food is not produced perfectly or distributed evenly. The less advanced the society's infrastructure, the higher its base mortality rate, and the more devastating the effects of running low on ability to produce food. Note this isn't mortality past carrying capacity, but below it.

So, this Capacity Effect is defined as a multiplier on the base mortality rate. If that multiplier is 1.0, when this effect reaches its maximum, as many people die of this distribution effect as die of the base mortality rate. In other words, at 100% capacity, mortality is doubled if mortality multiplier = 1.0.

So what happens below 100% capacity? The extra mortality is found via the formula:

baseMort * mortMultiplier / (100.0 * (1.0 - capacity))

So for example if the base mortality rate is 10%, and capacity is 90%, the distribution effect applies extra mortality of (.10 * 1.0) / (100.0 * (1.0 - .9)) = .01, or 1%. Since the min extra mortality to apply = 0.005 (or half a percent), the population would get its extra 1% mortality from this Capacity Effect.

Note that Capacity Effects are weighted by the population's original mortality rates. I.e., if infant mortality is 3x that of teenage boys, it stays that way including all extra capacity effects.

• This effect can be turned off by setting mortality multiplier to 0.0.

Simple enough - if the population size is at 115% capacity, 15% die outright. This is in addition to those who die of distribution effects and the base mortality rates.

You rarely see on the display that a population exceeded 100% capacity and was pruned back. The display is updated after mortality is applied. Also, the distribution effect prevents it happening very often with the default parameter values.

• The only way to turn this off is to turn off all capacity effects.

If there's an unlimited supply of land available for agriculture, there's not much reason to overwork it. If the livestock have started eating holes in a slope, you move them. If the soil is getting a little salty from irrigation, you let it rest for rain to flush it out eventually, and plant elsewhere.

As capacity utilization gets higher, farmers rarely have this luxury. The livestock have nowhere else to go. The fishermen keep fishing though the stocks have declined. If the farmer doesn't water the land, his family doesn't eat. And the land and resources gradually dwindle.

This is vastly complex in the real world, and resources aren't "good" or "destroyed" but almost always somewhere in between. But for our purposes here, there's a threshold, capacity damage begins at. This says that below that level, the resources can more or less be renewed along the way. But above it, irreparable damage sets in.

Note that most damage isn't truly irreparable. But its timeframe or cost may make it irreparable in the span of a human generation. The simulator doesn't restore destroyed land.

So above this threshold, previously food-producing resources are rendered useless at a rate of capacity damage multiplier times percent over-utilization, per time step (5 years). The default capacity damage begins at = 0.9, so this effect kicks in above 90% capacity (before bonus mortality is applied, bringing it back down). The default capacity damage multiplier is .15. So if the population reaches 115% capacity (before getting pruned back), it is 25% above the threshold. Then (0.25) * (0.15) = .0375, or 4%, of the land is damaged beyond repair. It turns yellow for desert in the resource map display.

Play Suggestion: The parameter capacity damage multiplier is pretty sensitive. Try using the plain Wisteria Intro scenario (with or without any aid package) and set this parameter to 0.05, 0.15, 0.25, 0.35, and 0.5. You'll find the trajectory of the population (and the fate of the land) changes pretty dramatically.

Which value makes the most sense? It's very hard to say. If a country has great rainfall, essentially good soil, plenty of level land, maybe a lower value is best. If a country is drawing down aquifers for crop irrigation faster than rain can replenish them, a higher value is justified. But whether any particular country is best described as a .03 or .25, I don't know how one could say.

• To turn this off, set capacity damage begins at to 100.0.

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