Integrating models, paleoclimate, and recent observations to develop process-level understanding of projected changes in US drought

Problem Introduction: Droughts rank among the most disruptive and expensive extreme climate
events in the United States, with significant impacts to ecosystems and agriculture. Climate change
is expected to increase the frequency and intensity of drought events for much of the United States
by the end of the 21st century. However, significant uncertainties remain regarding the importance
of various processes (e.g., precipitation, evapotranspiration), how climate change will affect
droughts across the hydrologic cycle (e.g., soil moisture versus runoff), and in our ability to detect
an anthropogenic influence on recent events. Unless resolved, these issues may limit the utility of,
and our confidence in, climate model-based drought projections, including those from models
participating in the forthcoming Phase 6 of the Coupled Model Intercomparison Project (CMIP6).
Rationale for Proposed Work: Improving confidence in climate model-based drought projections
requires (1) better estimates of natural drought variability, (2) an improved understanding of the
underlying processes most likely to influence drought risk in the future, and (3) a thorough
evaluation of how well the models simulate drought variability and trends over the United States.
To make these improvements, we need detailed analyses of drought variability in climate models,
including comparisons against drought variability in the historical and paleoclimate records.

Summary of Proposed Work: We will analyze drought (precipitation, soil moisture, runoff)
variability and trends in the CMIP6 models over the Contiguous United States (CONUS),
validating against observations and new and updated tree-ring based drought reconstructions of
the last millennium. We will use these models to estimate climate change contributions to recent
droughts, determine the expected time of emergence of climate change signals for different
drought types and characteristics in the coming decades, and identify the most important processes
affecting drought risk in the CMIP6 ensemble. The result will be an improved, process-level
understanding of how drought dynamics are represented in the CMIP6 projections and simulations,
informing our understanding of climate change and drought risk from now out to the end of the
21st century.

Competition Relevance: The proposed work explicitly “leverage[s] CMIP6 modeling
experiments” to consider the impacts of climate change on multiple categories and characteristics
of drought and the associated processes. This broad perspective goes “beyond assessing changes
in individual climatic quantities or phenomena and instead consider[s] the combined changes of
multiple major climate factors”. We will use the CMIP6 archive to investigate detection and
attribution of recent droughts and determine the time of emergence in the projections out to the
end of the 21st century, thus “consider[ing] changes over different future time horizons and
identify[ing] time horizons for changes beyond a given threshold of relevance to the targeted
application.” Our work therefore responds to Priority Area A in the solicitation, analyzing drought
in climate change projections in the CMIP6 database over CONUS to “[d]evelop integrated
predictions/projections of long-term climate changes affecting the U.S. within the global context
at national or large regional scale, and/or for specific applications.” The proposed work is aligned
with NOAA’s research strategy to address challenges in “(1) Weather and climate extremes” and
“(2) Climate impacts on water resources”, informing our understanding of drought and climate
change for the US from recent decades to the end of the 21st century.

Climate Risk Area: Water Resources