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Relationship between Climate Change and Gully Erosion

Author:
[ Majid Soufi ] -

Abstract:

Understanding processes of gully initiation and channel erosion in important in theoretical and practical viewpoint. One of the proposed causes of gully initiation is climate change, which has motivated a lot of controversy among geomorphologists. At the beginning, geomorphologists believed that guilty erosion was introduced dominantly by human impact in ecosystem, but lack of this phenomenon in other similar watersheds particularly in Holocene period resulted the hypothesis of climate change. It is defined as increasing rainfall and alternative arid and wet period. Lack of clear and strong evidence about the history of human interference in the ecosystem, especially climatic data such as daily rainfall, and the data of gully initiation and its extent in the past research, has produced unreasonable answer. This research has been done in a Eucalyptus forest in southeast Australia to answer some questions. One of the questions was determination of rainfall threshold in gully initiation in a cleares cut Eucalyptus forest. It is also intended to determine the behavior of degraded forest to climate components after clear cutting. In this research, chronology of gully initiation, forest clear cutting, and occurrence of daily rainfall has been constructed for pine plantations in Bomvala in southeast New South Wales, Australia. Results show that daily rainfall between 80 to 100 mm with a return period between 1.4 to 2 years caused gully initiation in a cleared cut Eucalyptus forest. Available evidence also proves that in the native Eucalyptus forest, caily rainfall equal to 400mm could not initiate gully erosion. Comparison of pine plantations with different chronology proved that degraded Eucalyptus forest is sensitive to the occurrence of rainfall in the first year of clear cutting and the probability of gully formation will be increased. Lack of or negligible gully erosion in 2 or 3 year plantations indicate that degraded Eucalyptus forest needs at least one year to recover and getting enough surface resistance against erosive factors. It means if daily rainfall around lOOmm occurs in the second year of plantation, its impact would be less than the first year.

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