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9.2: Climate

  • Page ID
    14471
  • Climate as a soil-forming factor helps determine soil differences on a regional scale (e.g. arid desert vs. humid forest ecosystem) or on a local level (micro-climatic differences). The important components of climate influencing soil formation include precipitation and temperature. As precipitation increases from one locale to another, more water is available to move downward through the soil profile. As water percolates downward (called leaching), water-soluble soil constituents such as soluble salts (bicarbonates, chlorides, nitrates) are translocated from upper soil horizons and are moved deeper into the soil profile.

    Other materials including clay minerals do not dissolve in water, but the clay particles can be suspended in the soil solution and may leach into subsoil horizons. The greater the amount of precipitation, the deeper these dissolved and suspended materials are leached. The consequences of leaching include a lower pH (greater acidity), fewer basic cations (Ca2+, Mg2+, K+, Na+), and a lower nutrient content. As a result of variations in rainfall, little leaching occurs in desert soils while extensive leaching occurs in humid forest soils.

    Soil temperature regulates the amount of evapotranspiration. The higher the temperature, the greater the amount of evapotranspiration. In hot, dry regions, any precipitation (rainfall) added to the soil may quickly evaporate into the atmosphere. In cool, moist regions, precipitation accumulates in the soil and leaching results. If two regions have the same amount of precipitation, the region having the lower soil temperatures will have more "effective" precipitation and soils will be more highly leached in the cooler region. On a local scale in the Northern Hemisphere, this concept explains the differences between soils on north-facing slopes compared with those on south-facing slopes. The soils on the north-facing slopes receive less direct solar radiation (lower temperatures, less evaporation). These soils on north-facing slopes are more highly weathered, deeper, and subject to greater leaching than are the soils on the south-facing slopes where the microclimate is warmer and drier.

    Temperature regimes:

    Moisture regimes:

    Gelic: < 0 oC

    Aquic: (or Perudic): Saturated with water long enough to cause oxygen depletion

    Cryic: 0-8 oC (cold summers)

    Udic: Humid or subhumid climate

    Frigid: 0-8 oC (warm summers)

    Ustic: Semiarid climate

    Mesic: 8-15 oC

    Aridic (or Torric): Arid climate

    Thermic: 15-22 oC

    Xeric: Mediterranean climate (cool, moist winters and warm, dry summers)

    Hyperthermic: >22 oC

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