Soil Moisture Regimes

aridic
arid; not moist for +90 consec. days
ustic
semi arid; dry <45 consec. days in summer
xeric
mediterranean; semi arid; dry >45 consec. days after summer solstice; moist >45 days after winter solstice
udic
humid; dry <90 days cum.

days and <45 days consec. in summer

perudic
ppt exceeds evapotrans. in all months but soil is not saturated for long periods
aquic
soil saturated long enough for anaerobic conditions; redox.