Spatial-temporal Bayesian hierarchical model for summer monsoon
precipitation extremes over India
Abstract
India receives more than 80% of annual rainfall during the summer
monsoon season of June – September. Extreme rainfall during summer
monsoon season causes severe floods in many parts of India, annually.
The floods in Kerala in 2019; Chennai during 2015 and Uttarakhand in
2013 are some of the major floods in recent years. With high population
density and weaker infrastructure, even moderate precipitation extremes
result in substantial loss to life and property. Thus, understanding and
modeling the return levels of extreme precipitation in space and time is
crucial for disaster mitigation efforts. To this end, we develop a
Bayesian hierarchical model to capture the space-time variability of
–summer season 3-day maximum precipitation over India. In this
framework, the data layer, the precipitation extreme – i.e., seasonal
maximum precipitation, at each station in each year is modeled using a
generalized extreme value (GEV) distribution with temporally varying
parameters, which are decomposed as linear functions of covariates. The
coefficients of the covariates, in the process layer, are spatially
modeled with a Gaussian multivariate process which enables capturing the
spatial structure of the rainfall extremes and covariates. Suitable
priors are used for the spatial model hyperparameters to complete the
Bayesian formulation. With the posterior distribution of spatial fields
of the GEV parameters for each year, posterior distribution of the
nonstationary space–time return levels of the precipitation extremes
are obtained. Climate diagnostics will be performed on the 3-day maximum
precipitation field to obtain robust covariates. The model is
demonstrated by application to extreme summer precipitation at 357
stations from this region. Preliminary model validation indicates that
our model captures historical variability at the stations very well.
Maps of return levels provide spatial and temporal variability of the
risk of extreme precipitation over India that will be of great help in
management and mitigation of hazards on natural resources and
infrastructure.