Abstract
The Mediterranean climate is principally characterized by warm, dry summers and cool, wet winters. However, there are large variations in precipitation dynamics in regions with this climate type. We examined the variability of precipitation within and among Mediterranean-climate areas, and classified the Mediterranean climate as wet, moderate, or dry based on annual precipitation; and strongly, moderately, or weakly seasonal based on percentage of precipitation during summer. Mediterranean biomes are mostly dry (<700 mm annually) but some areas are wet (>1300 mm annually); and many areas are weakly seasonal (>12% of annual precipitation during summer). We also used NOAA NCDC climate records to characterize interannual variability of annual and dry-season precipitation, as well as trends in annual, winter, and dry-season precipitation for 337 sites that met the data quality criteria from 1975 to 2015. Most significantly, sites in many Mediterranean-climate regions show downward trends in annual precipitation (southern California, Spain, Australia, Chile, and Northern Italy); and most of North America, the Mediterranean basin, and Chile showed downward trends in summer precipitation. Variations in annual and summer precipitation likely contribute to the high biodiversity and endemism characteristic of Mediterranean-climate biomes; the data indicate trends toward harsher conditions over the past 40 years.
Highlights
Climate is among the most fundamental features that define the human–natural system [1].Patterns of temperature and precipitation influence biotic community composition and structure [2,3,4,5], as well as the extent of feasible human development and the water resource development necessary to meet human needs [6,7,8]
The Mediterranean biome generally fits within the climate characteristics described above, though portions of each region do not fit these criteria (Figure 1)
Our results indicate that the climate of the Mediterranean biome can be any combination of our annual precipitation and seasonality categories, as well as two additional categories we did not initially classify: very dry conditions and non-seasonal
Summary
Climate is among the most fundamental features that define the human–natural system [1].Patterns of temperature and precipitation influence biotic community composition and structure [2,3,4,5], as well as the extent of feasible human development and the water resource development necessary to meet human needs [6,7,8]. Precipitation variability is important for defining human–natural systems: differences in annual precipitation and seasonal variability from one year to the characterize the capacity to sustain ecosystems and associated provisioning, regulating, and supporting services across the years and in the long term [6]. Changes in these patterns can cause fundamental shifts in the capacity for ecosystems to re-organize to preexisting steady states (resilience) [9], and can influence water resource planning for human development [10].
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