Characteristic Drought

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Characteristic drought time-scale determine different response of vegetation to drought across different regions and biomes. The future climate models reveal an increasing frequency of extreme climate episodes. Furthermore extreme climate episodes are expected to increase their frequency and intensity. Drought episodes appear as one of these climate episodes. Drought is a complex natural hazard characterized by climatological and hydrological parameters. Drought is considered when the supply of water is not enough to furnish the demand due to long periods without sufficient water availability. The main factor driving drought phenomena is precipitation, long periods with lack of precipitations can dramatically reduce the water availability…show more content…
Currently ecologists are intensely paying attention to the role that drought play in ecosystems. Events of tree mortality and die-off caused by drought have been reordered (Bershears et al)and are likely to increase (Adams et al.) and because of these kind of mortality events vegetation shifts are happening (Allen et al, Mueller et al). Contrarily of one can think not only arid systems are vulnerable to drought, so the 2005 drought in the Amazon rainforest caused a great impact on its carbon sink (Philips et al). Actually studies showed that there is a forest global vulnerability to drought (Choat et al). However, a general and global theory of how ecosystems respond to drought is yet not found. In this study the authors wanted to found a global pattern of the different biomes response to drought episodes. To address this question the authors analyzed the drought impacts in three vegetation parameters, all of them indicators of vegetation activity and growth: vegetation activity and greenness, tree radial growth and Aboveground Net Primary Productivity (ANPP). In order to evaluate this parameters they used three different datasets. Activity and greenness was recorded by satellite images using the…show more content…
Even if they found that vegetation activity generally respond to short drought time scale, some patterns were observed. Shorter time-scales response where found in semiarid and arid regions than in humid ones. Although when they analyzed separately the biomes with positive and negative water balance the most interesting results rise up. They results showed that in biomes with positive water balance time scale drought response tend to be shorter as the average water balance increase. In the other hand in areas with negative water balance the opposite pattern was found, where the increase of the average water balance was reflected with an increasing time-scale responses. Thus the study revealed that the arid and the humid biomes tend to respond in short time-scales to drought. Contrarily semiarid and subhumid systems have longer time scale response to drought. It must be said that these common short term response of arid and humid regions to drought, and long term responses of semiarid and subhimid regions, are not necessary linked with a common impact on the vegetation neither to the effects of drought on them. The study just reveals how different biomes respond in terms on time to the drought. So short time-scale means that with few months of drought the first consequences appear. Opposed long term response means that the first consequences on vegetation

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