The xeric moisture regime (Gr. xeros, dry) is the typical moisture regime of Mediterranean climates, where winters are moist and cool and summers are warm and dry. The moisture, coming during the winter when potential evapotranspiration is at a minimum, is particularly effective for leaching. In a xeric moisture regime the soil moisture control section, in 6 or more out of 10 years, is dry in all parts for 45 or more consecutive days in the 4 months following the summer solstice, and moist in all parts for 45 or more consecutive days in the 4 months following the winter solstice. Also, in 6 or more out of 10 years, the moisture control section is moist in some part for more than half the cumulative days per year when the soil temperature at a depth of 50 cm from the soil surface is higher than 5°C, or for 90 or more consecutive days when the soil temperature at a depth of 50 cm is higher than 8°C. The mean annual soil temperature is lower than 22°C, and mean summer and mean winter soil temperatures differ by 5°C or more either at a depth of 50 cm from the soil surface, or at a densic, lithic, or paralithic contact if shallower.

7/15/98