59 research outputs found
Space-time Trends in U.S. Meteorological Droughts
Understanding droughts in a climate context remains a major challenge. Over
the United States, different choices of observations and metrics have often
produced diametrically opposite insights. This paper focuses on understanding
and characterizing meteorological droughts from station measurements of
precipitation. The Standardized Precipitation Index is computed and analyzed to
obtain drought severity, duration and frequency. Average drought severity
trends are found to be uncertain and data-dependent. Furthermore, the mean and
spatial variance do not show any discernible non-stationary behavior. However,
the spatial coverage of extreme meteorological droughts in the United States
exhibits an increasing trend over nearly all of the last century. Furthermore,
the coverage over the last half decade exceeds that of the dust bowl era.
Previous literature suggests that climate extremes do not necessarily follow
the trends or uncertainties exhibited by the averages. While this possibility
has been suggested for droughts, this paper for the first time clearly
delineates and differentiates the trends in the mean, variability and extremes
of meteorological droughts in the United States, and uncovers the trends in the
spatial coverage of extremes. Multiple data sets, as well as years exhibiting
large, and possibly anomalous, droughts are carefully examined to characterize
trends and uncertainties. Nonlinear dependence among meteorological drought
attributes necessitates the use of copula-based tools from probability theory.
Severity-duration-frequency curves are generated to demonstrate how these
insights may be translated to design and policy
Network science based quantification of resilience demonstrated on the Indian Railways Network
The structure, interdependence, and fragility of systems ranging from power
grids and transportation to ecology, climate, biology and even human
communities and the Internet, have been examined through network science. While
the response to perturbations has been quantified, recovery strategies for
perturbed networks have usually been either discussed conceptually or through
anecdotal case studies. Here we develop a network science-based quantitative
methods framework for measuring, comparing and interpreting hazard responses
and as well as recovery strategies. The framework, motivated by the recently
proposed temporal resilience paradigm, is demonstrated with the Indian Railways
Network. The methods are demonstrated through the resilience of the network to
natural or human-induced hazards and electric grid failure. Simulations
inspired by the 2004 Indian Ocean Tsunami and the 2012 North Indian blackout as
well as a cyber-physical attack scenario. Multiple metrics are used to generate
various recovery strategies, which are simply sequences in which system
components should be recovered after a disruption. Quantitative evaluation of
recovery strategies suggests that faster and more resource-effective recovery
is possible through network centrality measures. Case studies based on two
historical events, specifically the 2004 Indian Ocean tsunami and the 2012
North Indian blackout, and a simulated cyber-physical attack scenario, provides
means for interpreting the relative performance of various recovery strategies.
Quantitative evaluation of recovery strategies suggests that faster and more
resource-effective restoration is possible through network centrality measures,
even though the specific strategy may be different for sub-networks or for the
partial recovery
Explainable deep learning for insights in El Ni\~no and river flows
The El Ni\~no Southern Oscillation (ENSO) is a semi-periodic fluctuation in
sea surface temperature (SST) over the tropical central and eastern Pacific
Ocean that influences interannual variability in regional hydrology across the
world through long-range dependence or teleconnections. Recent research has
demonstrated the value of Deep Learning (DL) methods for improving ENSO
prediction as well as Complex Networks (CN) for understanding teleconnections.
However, gaps in predictive understanding of ENSO-driven river flows include
the black box nature of DL, the use of simple ENSO indices to describe a
complex phenomenon and translating DL-based ENSO predictions to river flow
predictions. Here we show that eXplainable DL (XDL) methods, based on saliency
maps, can extract interpretable predictive information contained in global SST
and discover SST information regions and dependence structures relevant for
river flows which, in tandem with climate network constructions, enable
improved predictive understanding. Our results reveal additional information
content in global SST beyond ENSO indices, develop understanding of how SSTs
influence river flows, and generate improved river flow prediction, including
uncertainty estimation. Observations, reanalysis data, and earth system model
simulations are used to demonstrate the value of the XDL-CN based methods for
future interannual and decadal scale climate projections
‘Bayesian source detection and parameter estimation of a plume model based on sensor network measurements’ by C. Huang et al .: Rejoinder
No AbstractPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78083/1/858_ftp.pd
- …