Seasonal Weather

[ledpup]

Assuming northern hemisphere, temperature decreases as you go north. Temperature oscillates on a sine wave, from turn to turn, to simulate seasonal weather.

Temperatures decrease based on the distance from the coast.

A northern map:

Summer Autumn Winter Spring Fine Wet Cold Wet Fine Fine Wet Fine Dry Fine Fine Fine

A map further north:

Summer Autumn Winter Spring Fine Cold Cold Cold Fine Wet Cold Wet Fine Fine Wet Fine

This can be easily turned upside-down for southern hemisphere maps.

Effects on terrain: All tiles have a base type of terrain, assuming a spring/autumn temperature.

Dry

• Affects Lake, Wetland and Grassland hexes
• Lake -> Wetland, Wetland -> Grassland, Grassland -> Desert

Fine

• The default

Wet

• Affects Arid, Grassland, Wetland and Mountain hexes
• Desert -> Grassland, Grassland -> Wetland, Wetland -> Lake
• Negates the move bonus of roads

Cold

• Lakes freeze - units can now treat a frozen lake as land
• Rivers freeze - units can now cross rivers without a movement penalty
• Grassland, Hill, Forest, and Mountain become snow covered
• Unit morale drops from the cold if not in a structure or not on preferred terrain
• Some units aren't hindered by the cold (no morale loss)

Problems with this system:

• Units that were in a wetland might find themselves in a lake in the following turn

[ledpup]

Mountains -10 temp Hill -5 temp

[ledpup]

Consistency and Relationships between Temperature and Precipitation

Observed changes in regional temperature and precipitation can often be physically related to one another. This section assesses the consistencies of these relationships in the observed trends. Significant large-scale correlations between observed monthly mean temperature and precipitation (Madden and Williams, 1978) for North America and Europe have stood up to the test of time and been expanded globally (Trenberth and Shea, 2005). In the warm season over continents, higher temperatures accompany lower precipitation amounts and vice versa. Hence, over land, strong negative correlations dominate, as dry conditions favour more sunshine and less evaporative cooling, while wet summers are cool. However, at latitudes poleward of 40° in winter, positive correlations dominate as the water-holding capacity of the atmosphere limits precipitation amounts in cold conditions and warm air advection in cyclonic storms is accompanied by precipitation. Where ocean conditions drive the atmosphere, higher surface air temperatures are associated with precipitation, as during El Niño events. For South America, Rusticucci and Penalba (2000) showed that warm summers are associated with low precipitation, especially in northeast and central-western Argentina, southern Chile, and Paraguay. Cold season (JJA) correlations are weak but positive to the west of 65°W, as stratiform cloud cover produces a higher minimum temperature. For stations in coastal Chile, the correlation is always positive and significant, as it is adjacent to the ocean, especially in the months of rainfall (May to September), showing that high SSTs favour convection.

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch3s3-3-5.html

[ledpup]

To do:

• wet negates the move bonus of roads
• Lakes freeze - units can now treat a frozen lake as land
• Rivers freeze - units can now cross rivers without a movement penalty
• Some units aren't hindered by the cold (no morale loss)

[ledpup]

From Victory in Europe: