Prediction of daily rainfall state in a river basin using statistical downscaling from GCM output |
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Authors: | S Kannan Subimal Ghosh |
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Institution: | (1) Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400 076, India; |
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Abstract: | Conventional statistical downscaling techniques for prediction of multi-site rainfall in a river basin fail to capture the
correlation between multiple sites and thus are inadequate to model the variability of rainfall. The present study addresses
this problem through representation of the pattern of multi-site rainfall using rainfall state in a river basin. A model based
on K-means clustering technique coupled with a supervised data classification technique, namely Classification And Regression
Tree (CART), is used for generation of rainfall states from large-scale atmospheric variables in a river basin. The K-means clustering is used to derive the daily rainfall state from the historical daily multi-site rainfall data. The optimum
number of clusters in the observed rainfall data is obtained after application of various cluster validity measures to the
clustered data. The CART model is then trained to establish relationship between the daily rainfall state of the river basin
and the standardized, dimensionally-reduced National Centers for Environmental Prediction/National Center for Atmospheric
Research (NCEP/NCAR) reanalysis climatic data set. The relationship thus developed is applied to the General Circulation Model
(GCM)-simulated, standardized, bias free large-scale climate variables for prediction of rainfall states in future. Comparisons
of the number of days falling under different rainfall states for the observed period and the future give the change expected
in the river basin due to global warming. The methodology is tested for the Mahanadi river basin in India. |
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