Answer to Question 1
Answer: potential evapotranspiration
Answer to Question 2
Answer: Koeppen looked at the world distribution of natural vegetation types, located the boundaries that separated them, and determined what combinations of monthly mean temperature and precipitation were associated with those boundaries. Thus, although its climatic types are determined by temperature and precipitation, Koeppen's system is inherently tied to natural vegetation.
A Tropical. Climates in which the average temperature for all months is greater than 18C (64F). Almost entirely confined to the region between the equator and the tropics of Cancer and Capricorn.
B Dry. Potential evaporation exceeds precipitation.
C Mild Midlatitude. The coldest month of the year has an average temperature higher than -3C (27F) but below 18C (64F). Summers can be hot.
D Severe Midlatitude. Winters have at least occasional snow cover, with the coldest month having a mean temperature below -3C (27F). Summers are typically mild.
E Polar. All months have mean temperatures below 10C (50F).
H Mountain environments
Organisms can be classified according to their source of energy
Distribution and Forms of Precipitation: Snow
Natural Causes of Climate Change
How Aerosols Influence Climate
Europe’s Climate
The impact of climate change is greater in some areas than in others