Hearts of Iron IV - 28th Development Diary - Weather & Terrain

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Hello, and welcome to the 28th development-diary for Hearts of Iron IV. This time we talk about the things that you have the absolutely least control over in the game, and in real life. ie, Weather and Terrain.

We were not happy with the weather-system in HoI3. It was a complex simulation that tried to work as close to reality as possible. It was basically impossible to tweak to the situations we wanted (like very hot desert areas or cold winter in Russia in ’41), and players disliked it. It was a small performance hog and last but not least - all that effort was tucked away in a mapmode you had to keep checking (so most people did not). So for this iteration of the series, we decided to take an entirely different approach.

QOAY5j6.jpg


Full scripting control
Probability for each type of weather can now be scripted for each strategic region for each month, or a definable period. So for example we can get that hardcore, dirty, Russian mud everyone is craving for the months and locations where it makes sense. For modders out there we made a really nifty tool for setting up these values so its easy to tweak and work with (so when you guys make the Cats of the 4th Reich total conversion I’v been waiting for it will be easy). This means that since we can set everything ourselves we have full control over the gameplay effects we want rather than relying on a complex simulation to get it right.

There are 6 types of basic weather in the game. These directly affect air and navies and land units indirectly (we get to that)

Clear skies
Baseline weather with no modifiers. Just enjoy the sun bro :)

Light Rain
Harder to detect enemy air and navies.
Airplane attacks against ships less effective as well as ship-to-ship accuracy.
Higher risk of airplane accidents.​

Storm
A much stronger version of Light Rain.
Carrier planes won't be able to take off.
Bombers will have a hard time hitting targets.​

Snow
Harder to detect enemy air and navies.
Airplane attacks against ships less effective as well as ship-to-ship accuracy.
Higher risk of airplane accidents.​

Blizzard
A much stronger version of Snow.
Carrier planes won't be able to take off.
Bombers will have a hard time hitting targets.​

Sandstorm
Almost impossible to detect other aircraft.
Extremely high chance of airplane accidents.
Bombers won’t be able to hit targets on ground.​

Temperature
Temperature is tracked on province level and mainly affects attrition levels. If its very cold or very warm things will tend to break down a lot more often. You’ll want leaders with the Winter Specialist trait to maximize your efficiency in cold weather.

Mud and Snow (so, ok, there is a bit of simulation)
When it rains or snows we keep track of that (so we can show it on the map) but also to keep track of if it has gotten to extreme levels. Very high snow will affect unit movement speed, but Mud is going to increase attrition levels a lot as well as slow you down to a crawl. A smart player will try not to attack (as a wild example) The Soviet Union just as mud season begins or they might find a lot of their panzer divisions bogged down.
Ji9pVdX.jpg



Shown on map
Since weather has such a large impact we wanted to make sure it was always visible to the player. Snow/mud and such is shown directly on the map while storm clouds and rain is in a layer above which we fade away the closer you get so as not to obscure unit movements.

p112LQh.jpg

Big thunder storm over Russia (sorry I did not have the reflexes to be able to catch the lightning :()

Terrain
While we do quite a lot of things at the state-level, we still have terrain defined per actual province. The terrain-system is completely scriptable as in all Clausewitz games, but the terrains in Hearts of Iron IV is as follows.

Plains
Baseline terrain, so no modifiers, as everything is relative to this.​

Forest
50% added to time to move through.
20% penalty to attack.
20% smaller combat width.
10% better protection against enemy air superiority.​

Hills
50% added to time to move through.
20% penalty to attack.
33% smaller combat width
5% better protection against enemy air superiority.​

Mountains
100% added to time to move through.
40% extra attrition
66% smaller combat with
40% penalty to attack
10% better protection against enemy air superiority.​

Urban
20% added to time to move through.
30% penalty to attack​

Jungle
50% added to time to move through.
50% extra attrition
25% smaller combat with
30% penalty to attack
25% better protection against enemy air superiority.​

Marsh
100% added to time to move through.
80% extra attrition
25% smaller combat with
40% penalty to attack​

Desert
5% added to time to move through.
30% extra attrition​

Different types of battalions have either penalties or bonuses in terrain to attack, defence or movement, compared to a generic Infantry. A few examples. Cavalry has a minor -5% attack penalty in most rough terrain, while Mountaineers gets a movement bonus in hills & mountains, as well as attack and defence bonuses.

Unit-specific penalties that combine negatively with terrain penalties, creates some pretty bad situations. ie, attacking a mountain with heavy armor is NOT a good idea.

Next week, we’ll look at factions, and wargoals!
 
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LostinSpice

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Excellent DD! How can you help protect your soldiers from the cold for example? Is there a tech to research? Also in the snow/ desert would your troops switch to the appropriate uniforms?
 
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Rooz

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How long does the mud season last? Can we expect it to last a couple of months per year in some regions (like Soviet Union)?
 
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Denkt

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Can the battle planer ai calculate the correct spots for divisions such as sending mountaineers to mountains?

Temperature
Temperature is tracked on province level and mainly affects attrition levels. If its very cold or very warm things will tend to break down a lot more often. You’ll want leaders with the Winter Specialist trait to maximize your efficiency in cold weather.

Why not also have a tropical or desert specialist for hot weather?

I guess you could toogle if you wan't your aircrafts and ships to avoid bad weather or not.
 
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joe9594

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Nice DD. Quick question a state with less than a million people has 6 building slots (and possibly more with extra infra)?
That seems like quite a few. I previously assumed the number you would have was linear with population is this not the case?
Because if it isn't linear (or just barely takes any pop per building) it doesn't really make sense and would massively punish densely populated countries where industry is actually more efficient.
Not much point having 10 million people in NY when 3 mil would allow you to get 20 buildings.
 
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D3m0

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No info on how weather and terrain interacts with the supply system?

Really like that last screenshot, seems like the AI is capable of keeping reserves in the rear?
 
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No idea

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Hello Podcat, several things:

1. Why go from Light Rain to Storm? Where is "middle"/"normal" Rain?
2. How is mud "generated"? After it snows a lot and suddendly temperatures get higher? After it rains a lot? After it rains a bit but hundreds of panzers come through the same sand track?
3. Mountains units in mountain: I take that the movement speed bonus (or the attack bonus) is AFTER taking into account the normal penalty for moving through mountains?. Otherwise mountain units would move faster through mountains than through plains.

PS. Oh, supply and weather links would be welcomed. After all muddy roads should be a nightmare not just for your panzers, but for your supply trucks and horses.
 
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Denkt

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Because if it isn't linear it doesn't really make sense and would massively punish densely populated countries where industry is actually more efficient.

At some point it probably becomes less efficient to stack more and more industry in one area because of logistical and resource bottlenecks so paradox choice is not incorrect, also it is good for gameplay given some countries such as sweden was rather productive but did not have large population.
 

mursolini

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Will province/state infrastructure be taken into account in penalties? The #1 reason for Russian "mud" was the (lack of) quality of their mostly dirt roads. Highways and other well-planned roads should have proper drainage and thus be immune to mud. Easy example, Russian trains don`t suffer one bit from mud, as rails are actually built on proper foundation, unlike roads.
 
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Enigma1

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An important thing for me is weather forecasting, If I look out of the window and see it is raining then I don't take off in my Spitfire.
I would however rely on forecasting to tell me when weather was coming, and how long it would last, and what is coming next.

Obviously in the real world, then forecasting was a bit iffy at times.

So, does the game have 'forecasting' elements to the weather, or is there a compelling reason why we would not need it in game?
 
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LostinSpice

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Really great graphics! Clearly I haven't played HOI4 yet but how does naval and air missions interact with the weather? For example, if you're sending up your fighters and bombers and a storm comes along to batter them is there a toggle to ground them (a bit like damage to fleets) if you prefer or is this something you'll have to constantly watch?
 

Big Nev

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Does the AI understand about terrain?

Yes, it's dumb to attack in to moutains (or any other type of difficult terrain)) with any kind of armour*, the heavier the armour, the worse it gets.

But please tell us that the AI "knows" this?





Edit: * Unless you're the IJA of course :eek:
 
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wingo

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Nice, but I'm not sure about attrition - for example 100% extra attrition for serious mud/snow, that is probably from base attrition. So if base is for example 5% for a reliable tank, that would mean 10% in terrain that is extremely unfavourable - I'm not sure that is much deterrent from continuing the offensive regardless of the weather. But for an unreliable tank with 25% base attrition, that would mean 50% losses just by moving, which would simulate nicely Germans only doing serious offensives in Russia during summer in nice weather.
 
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