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The chapter discusses the bioclimatic regimes that are generally determined by temporal and spatial averaging of weather patterns. Local weather variations result from these broad geographic-scale phenomena, and local weather variables drive processes such as primary and nutrient cycling. These variables include seasonality of rainfall with respect to seasonal temperatures, frequency of precipitation events, frequency–event size relationships, return times of particular rain events, wind-season intensity, daily patterns of microclimates, and rainfall-potential evapotranspiration relationships. All of the major biotic regions (biomes) and their ecotones appear to be controlled by major climate patterns. Most of the desert areas of the world are characterized by a wet season. The primary factor affecting storm depth, intensity, and local climate is topography. Rare high-intensity long-duration events may change geomorphology, which may change the functional relationships and linkages among the ecosystems of a landscape. The high temperatures that characterize summers in deserts exacerbate the general dryness of the atmosphere over a desert. The decrease in temperature with increasing height above the soil surface occurs rapidly because air mixing breaks the boundary layer at the soil surface.