[dropcap]C[/dropcap]limate change as one popular issues in last decades, it’s affect global average surface temperature and increased over 20th century by about 0.60 C. Forest are likely to experience dramatic changes as a consequence of increment rainfall by climate change. Forest directly affect climate change at the global scale by altering earth’s albedo, hydrological, regimes and atmospheric CO2 .Forest also affect climate at a local scale by altering temperature, humidity and solar radiation (Graham, 1990).
Another serious effect of climate change, related to forest stability is it increased total rain and rain intensity. According to report by Climate Change 2011: The Scientific Basis, Tropical land-surface precipitation measurements indicate that precipitation likely has increased by about 0.2 to 0.3%/ decade over the 20th century. Direct measurements of precipitation and model re analyses of inferred precipitation indicate that rainfall has also increased over large parts of the tropical ocean.
Rainfall correlation with forest
Increasing number of total rain and rain intensity affect the land stability, especially in forest with vary geomorphology (relief, drainage and slope gradient).
Effect of increasing total rain and rain intensity such as:
- Increase amount of water in catchment area
- Increase water table, affected by large amount of water seep into the ground
- Decrease of land stability
- Trigger landslide, erosion and hazard
- Biological aspect
- Change in plant species
In order to study about process of the influence rainfall increment induced by climate change to forest, in this exercise took numerical approach. Numerical approach was used to predict landslide triggered by rainfall induced. Rainfall induced also related to forest and this model also consider vegetation and amount water
One of numerical approach which can be used to study about process rainfall and it’s relation with land stability, especially landslide. SLIDE model has been used by Fredlund et al. (1996) and Montrasio and Valentino (2008). They present a mathematical model that translated the physical phenomenon of rainfall triggering processes. This model highlights the destabilizing forces by the water down-ﬂow and the contribution of partial saturation to the shear strength of the soil. Research by Liao et.al.(2010) give us explanation about prototyping early warning system for landslide using rainfall-induced parameter. Schematic SLIDE Model shows in figure below:
with this model, actually we want to know the relation between rainfall and land stability. Dealing with case studies which using this model, we can calculate FS ( factor of safety) in slope ( using numerical approach to predict FS number in specific place). This is the formulation of FS:
This is how to calculate each part in formula above:
Total Cohesion expressed as:
Information about symbol and values for calculation
Result of calculation is FS (Factor of Safety) can be used as parameter stability in Early Warning system design. The FS is defined as the ratio of resisting forces over destabilizing forces on a soil slope. FS=1 suggests that the slope is slipped, and the smaller the value the less stable the slope is.
More information about model, please refer link below.
Fredlund DG, Rahardjo H (1991) Calculation procedures for slope stability analyses involving negative pore-water pressures. Proc. Int. Conf. on Slope Stability Engineering, Development Applications, Isle of Wight, pp 43–50
Graham, Robin Lambert, et.al., How Increasing CO2 and Climate Change Affect Forests. American Institute of Biological Sciences.Vol. 40, No. 8 (Sep., 1990), pp. 575-587
Houghton , J.T.et.al. Climate Change 2001: The Scientific Basis. Intergovernmental Panel on Climate Change. Published by the Press Syndicate of the University of Cambridge.
Liao, Zonghu. et.al. 2010.Prototyping an experimental early warning system for rainfall-induced landslides in Indonesia using satellite remote sensing and geospatial datasets.Landslides (2010) 7:317–324 DOI 10.1007/s10346-010-0219-7 Received: 8 December 2009.
Montrasio L, Valentino R (2008) A model for triggering mechanisms of shallow landslides. Nat Hazards Earth Syst Sci 8:1149–1159