Fire Weather and Land Degradation

Abstract

Recent years have witnessed a global increase in more intense, widespread and frequent fires that threaten human security and ecosystems and contribute to green house gas emissions which result in climate change with feed-backs on both fire patterns and land degradation. The interplay between fire weather-risk and land degradation is complex and involves several non linear inter-actions that influence trends in both fire patterns and land degradation processes. Majority of fires are lit by humans but the influence of humans on fire patterns is closely related to fire weather. Weather conditions are the main factors of fire readiness in a given fire prone area. Frequent and more intense fires reduce bio-mass supported in an area, affecting the productive soil layer which leads to soil erosion, change in species composition and a general decline in biodiversity and hence land degradation. In this regard fire is an agent of land degradation which is defined here as a persistent reduction in the capacity of ecosystems to supply services. In arid to semi-arid and dry sub-humid areas, extensive burning may be followed by low rainfall periods thus exposing soil to erosion agents such as heat, and wind and subsequent encroachment of the area by fast growing weeds when normal rainfall return which increases fire risk in that area than before.

Of major concern is how climate change will influence the interaction between fire weather and land degradation. Observations in different regions already link more intense fires witnessed in the past decade to climate change generated hotter and drier summer weather, in addition to fire suppression practices. Prolonged drought under climate change is likely to intensify land degradation due to land use pressure setting conditions for the spread of more fast growing highly flammable weeds during the onset of rainfall. Current evidence suggests that in arid to semi-arid lands, invasive highly flammable herbaceous species associated with degraded lands may out-compete native vegetation during abnormally wet periods under climate change. And with increased fire weather-risk, these areas will undergo increased hot fires facilitated by accumulated dry highly flammable biomass of these invasive species and hence putting the landscape under a perpetual cycle of increased susceptibility to land degradation and fire. Future land degradation studies need to put greater emphasis on the role of fire weather for a better assessment of burning conditions and interaction with land degradation processes.