This looks like an island that's at most like a hundred thousand years old that has either low precipitation, or a high evaporation rate. ("Eventually" meaning potentially hundreds of millions of years depending on how high the ground started, and how hard the rock is.) If it doesn't evaporate as fast as it's flowing in, then the water level rises.įurthermore, flowing water erodes everything, so a river will eventually carve a channel down to sealevel. Water flows down to the lowest point, but then it has to evaporate. Anywhere that enough water collects up while flowing will become a river.īut then you need to add time to the mix. Any rainfall on your island will flow downhill and collect at the lowest points. Then sort the cell to start from the highest and repeat the depression fill cycle until all depressions are resolved.įor (var i = 0 i < land.The big question is how old is the island. The idea is to loop through the cells, detect depressed ones and add a bit of height to them. There are a lot of filling algorithms, including ones used by professional hydrologists, but, as usual, I am going to use the easiest one I can imagine. We cannot just ignore this problem and definitely need to solve it, i.e. There is a problem with the cells that are lower than all of its neighbors. This will allow us to trace the flux routes over the map and drain all precipitation into an ocean or lakes. For each cell we need to define a lowest neighboring cell. The next step is river paths calculation. The resultant precipitation map is rough, but it points on both humid and arid zones and ready to be used for further calculations. We can smooth it by taking the cell’s precipitation as the average of the values of its neighbors. Precipitation map with west prevailing winds. In the case there are two or more prevailing winds, just divide the initial precipitation by the prevailing winds count and repeat the logic for each particular wind. Move each ‘cloud’ while precipitation is more than zero or opposite border is not reached. Facing with mountains, ‘clouds’ disappear giving away all moisture to the land. Passing over the land ‘clouds’ precipitates out losing some of their initial precipitation. Then I move the ‘ clouds’ one by one towards the opposite border with a random side walk. Selected border depends on prevailing winds, so for westerlies I will select the left side. I select the narrow line of sites along the map border to represent a rain clouds. The code I use is pretty straightforward. This is especially important given the fact we are going to set a prevailing winds and not allow wind to significantly change its direction during precipitation modelling. Leeward side on the side usually remain dry and form a rain shadow. gif (it’s so cool that I had to copy it from Commons). As a result of orographic lift vapor cannot pass uplifted areas, so the greatest precipitation falls on the windward slopes of the hills as shown on the. Driven by winds water vapor precipitates out on saturation. Let’s keep it simple. Sun evaporates water from ocean into atmosphere. Despite this model is cool, it’s a bit over-complicated for a landscapes created via blobs approach and requires more detailed map. Here he shows how it can be easily used for biomes definition and here disclose a few info regarding rivers. The most interesting precipitation model I know is the Wind model presented by Scott Turner. It will be enough to create plausible rivers, but having a precipitation model is useful not only for rivers calculation, but also for biomes and erosion modeling. Frankly speaking, we can omit this step and consider that each cell has the same precipitation. The first step is to build a precipitation model. As we already have a heightmap we do not need to fabricate rivers out of nothing and will calculate river systems based on precipitation drainage. Now it’s a good time to draw some rivers.
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