In a recent study, a group of Australian scientists wished to dertermine the impact of global climate change on the local climate. The scientists were particularly concerned about flooding and drought. These natural occurances can have a major impact on human activities, perhaps even more so than rising sea levels or temperature increases. In agriculture for example, increasing the relative frequency of drought means running a higher risk of losing production due to lack of soil moisture. In addition, heavy rains that also cause flooding could damage crops during development, or prevent timely planting and/or harvesting as well. Many civil projects are undretaken with the intention of controlling water flow and designing their capactiy to fit the need. Increased floods mean higher costs of Civil projects such as drainage ditches, bridges, dams, and similar projects. The alternatuve to increasing the costs of these projects is not disirable either. Flooding disrupts lives due to minor inconviences such as bridge closings, detstroying homes and roads, and sometimes even results in drownings.

The Australian scientists chose a GCM called CSIRO0 for their research on flooding. They chose that particular GCM based primarily on its accuracy for predictiong the seasonal monsoons in that hemisphere. They compared relative results to other GCMs where comparison was valid. Specific results can't be compared due to the difference in the modeling within the GCMs. The Australian scientists found that the GCMs weren't particularly useful in predicting drought with current conditions. In order to compensate for this they added an off-line system which takes into account soil hydrology.

GCMs predict increased rainfall for the global climate as a whole. When analyzed further, the results were particularly interesting. The total amount of rain recieved for convective rainfall did indeed increase (approx. 10%), however non-convective rainfall fell slightly. Convective rainfall is rainfall that is due to the cyclying of layers in the atmosphere; ultimately what this implies is rainfall that is induced by evaporation of water over an ocean. While the amount of rainfall increased, the number of rain-days decreased. The results were graphed for present day climate and the 2x CO₂ climate. The results were put on a time scale of events ranging from 6 months to 100 years. This means a flood was a measure of two things, the intensity of it, and its frequency. The time scale was not at all linear but rather logarithmic in origin suggesting that for a given amount of increase in rainfall the frequency was amplified based on a logarithmic function. For annual events teh frequency doubled, however for 10 year events the frequecy was more than tripled.

In order that they may study drought, the scientists found it necessary to include an off-line system that takes into account soil hydrology. Without getting into details, the reason for doing so was seasonal variability in rainfall and evaporation potentials. When too much rain falls on soil, it is not stored until needed as assumed by the GCMs, but rather it runs off. In addition, GCMs fail to account for soil moisture content variability based on soil moisture potential and local vegetation. Once the off-line system was added, the scientists took another look at the drought potential. In particular, they found an increased tendency for drought in southern Australia during the winter. It might be noted that this part of Australia has a 'Mediterranean' Climate, similar to the costal areas of Spain, Italy, Greece, and California. The results for drought were also put on a frequency time scale with similar results as the flooding graph.

In summary, we should study more of flooding and drought conditions that are induced by any climate change, so that we may be better prepared to deal with new problems as they arise. In addition, studies like this gives policy makes foresite into what civil projects need to be able to withstand in terms of risks and benefits. It might be noted taht El Nino has a moderate effect on Australian climate. El Nino is not considered as part of the GCM model. This would skew the results slighly, and may serve to dampen or amplify the results on the study.

Resource

P.H. Whetton, A.M. Fowler, M.R. Haylock, A.D. Pittok, 1993. Implications of climate change due to enhanced greenhouse effect on flood and droughts in Australia. Cimatic Change, Dec 93, 289-317.