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Global change in the Mediterranean basin

January 9th, 2019 Leave a comment Go to comments

The paleartic region with mediterranean climate (southern Europe and northern Africa; the Mediterranean Basin; Fig. 1) is a hotspot of biodiversity, a hotspot of climate change (warming of the region is above global average), and a hotspot of human population (a highly populated area and a top tourist and retirement destination). In addition, the Mediterranean Sea is the world’s largest inland sea, and climatic disruptions in the region have consequences in the large catchment area that includes central-eastern Europe (Fig. 1). That is, environmental changes and disruptions of the water cycling in the Mediterranean region have consequences affecting a large human population [1].

Fig. 1. Area with mediterranean climate (green) and limits of the Mediterranean catchment (red).  The European catchment limit based on Cortambert (1870). From [1].

The region, as all the planet, is subject to global warming. In addition there are three main local processes (not directly related to global warming) that are very important in understanding dynamic changes in the region [1]:

a) Rural abandonment in an environment depauperate of native herbivores; this increases wildlands (greening) but also the abundance and continuity of fuels that feed wildfires [2]

b) Increasing the wildland-urban interface; this increases biodiversity degradation (e.g., alien species), fire ignitions, and the vulnerability of the society to fires

c) Coastal degradation enhances drought (browning) through negative feedback processes; that is, the desiccation of coastal marshes, the deforestation for agriculture, and more recently, the explosive coastal urbanization, have drastically reduced the original ecosystems and thus the water available for the sea breeze that was once feeding the rain in the upper part of the mountains [1].

All these mechanisms act in different directions (greening, browning), and the current balance is still towards greening, as land abandonment is buffering the browning drivers; however, it is likely to switch with global warming. The challenge is to mitigate the browning processes. The good news is that the importance of small-scale drivers suggests that local policies and actions can make a difference in reducing overall impact on the landscape and society.

Mechanisms acting at a fine scale, together with global drivers (CO2 enrichment and climatic warming) interact and drive current vegetation changes in Mediterranean landscapes. Any model aiming to predict the future of our vegetation and climate must consider these local mechanisms; and failing to consider them at an appropriate scale is likely to produce inconclusive predictions.

Fig. 2. The disruption of the natural fire and drought regimes in Mediterranean landscapes is driven by global and local drivers. Increased fire activity is a response to the fuel amount and landscape homogeneity generated by rural abandonment (fire hazard) in an environment depauperated of herbivores and with increasing human ignitions (fire risk) and droughts (fire weather). The increased dry conditions are the consequence of global warming, but also of storm losses caused by the disruption of the water cycle generated by the coastal degradation. WUI: wildland-urban interface. From [1].

References

[1] Pausas J.G. & Millán M.M. 2019. Greening and browning in a climate change hotspot: the Mediterranean Basin. BioScience 69: 143-151 [doi | OUP | pdf]  

[2] Pausas J.G. & Fernández-Muñoz S. 2012. Fire regime changes in the Western Mediterranean Basin: from fuel-limited to drought-driven fire regime. Climatic Change 110: 215-226. [doi | springer | pdf]  

 

 

  1. January 13th, 2019 at 10:11 | #1

    You raised interesting points in your last post. I still struggle to understand how costal marshlands and vegetation act as a magnet to attract more rainfall. I’ll have a look at the paper where you explain this in more detail.

    Has a link been found between the amount of rainfall and the land cover?

  2. Juli G. Pausas
    January 15th, 2019 at 13:11 | #2

    Hola!
    The evapotranspiration of the coastal marshes and coastal vegetation provide the water vapour that goes up to the mountains. It accumulates there where it can generate storms (the water cycle). Salut

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