Change: Rivers may start in desert when no rainforest exists #9635
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Motivation / Problem
Rivers cannot currently start in the desert. This is normally fine, but when the desert percentage is 100%, it is impossible for rivers to generate since the only non-desert surrounds ocean and isn't wide enough to fit the minimum length river starting at a higher elevation.
Description
When the desert percentage is 100, allow rivers to start in the desert. Lakes are also allowed to generate, as the game already generates inland sea as oases into which rivers can flow.
Not that OpenTTD always reflects reality, but the real-world precedent for rivers starting in the desert would be water emerging from an underground spring like those which feed qanats.
If a player wants a 100% desert map without rivers, they can set rivers to "none".
Limitations
Checklist for review
Some things are not automated, and forgotten often. This list is a reminder for the reviewers.