Short answers, pulled from the story.
The Köppen climate classification was created by Wladimir Köppen (1846-1940), a German-Russian climatologist and botanist, who first published the system in 1884. He made notable modifications in 1918 and 1936. Rudolf Geiger (1894-1981) later introduced additional changes in 1954 and 1961, giving rise to the alternate name Köppen-Geiger climate classification.
The five main groups are A (tropical), B (arid), C (temperate), D (continental), and E (polar). Each group is assigned a first letter, and most groups also receive a second letter indicating seasonal precipitation patterns and a third letter indicating temperature levels.
Af indicates a tropical rainforest climate. The A means the region has tropical conditions with every month averaging 18 degrees Celsius or higher, and the f means there is no dry season, with all 12 months receiving at least 60 mm of average precipitation. These climates usually occur within 10 degrees latitude of the equator.
Köppen designed the system from his background as a botanist, observing that vegetation boundaries closely tracked temperature and precipitation patterns. His main climate groups represent classifications by vegetation type, making the system useful for predicting the dominant plant life of a region and for analyzing how plant communities may change as climates shift.
A 2015 Nanjing University paper published in Scientific Reports found that between 1950 and 2010, approximately 5.7 percent of all land area worldwide shifted from wetter and colder Köppen classifications to drier and hotter ones. The authors concluded this change cannot be explained by natural variation and is driven by anthropogenic factors.
BWh designates a hot desert climate, found in low-latitude regions where the average annual temperature exceeds 18 degrees Celsius, typically between 20 and 33 degrees north and south latitude. BWk designates a cold desert climate, found in middle-latitude regions with an average annual temperature below 18 degrees Celsius; the Gobi Desert in northern China and Mongolia is a well-known example of BWk.