The NOAA CPO Modeling, Analysis, Prediction, and Projections (MAPP) program hosted a webinar on the topic of Drought Understanding, Monitoring, and Prediction on Tuesday, June 9, 2015. The announcement is provided below; you are invited to remotely join the session.
Marty Hoerling - Major boreal spring rainy seasons across the globe have failed in the recent decade.
Droughts have increased over the Greater Horn of Africa, Southwest Asia, Southeast China, the Murray Darling Basin, the US Great Plains and the American Southwest.
This study seeks to understand this global pattern of observed trends in March-May precipitation. Using a hierarchy of model simulations, both with historical forcings of the atmosphere since 1979 and idealizations of recent ocean conditions, it probes the factors responsible for the observed drying trends. We wish to learn whether the various drought trends are correlated with each other, and if so, to understand the physical factors operating. Has the global pattern of drying unfolded because there exist common sensitivities of each region’s rainfall to a forcing? If some forcing has been responsible for the springtime drought trends across numerous continents, what are its origins? Better understanding this emergent situation is central to an improved awareness of whether and when these drought trends are likely to either accelerate or to reverse.
Tom Delworth - Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus – a decadal period with little increase in global mean surface temperature. We use climate models and observational analyses to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought. When we insert observed tropical Pacific wind stress anomalies into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In our simulations the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes. This suggests that anthropogenic radiative forcing is not the dominant driver of the current drought, unless the wind changes themselves are driven by anthropogenic radiative forcing. The anomalous tropical winds could also originate from coupled interactions in the tropical Pacific or from forcing outside the tropical Pacific. The model experiments suggest that if the tropical winds were to return to climatological conditions, then the recent tendency toward North American drought would diminish. Alternatively, if the tropical winds were to persist, then the impact on North American drought would continue; however, the impact of the enhanced Pacific easterlies on global temperature diminishes after a decade or two due to a surface reemergence of warmer water that was initially subducted into the ocean interior.
John Nielsen-Gammon - This talk will present an overview of the 2010-2015 drought in Texas, as seen from version 1 of our high-resolution drought monitoring products. Such products, based on historical probabilities, are presently much more useful for identifying drought onset than drought termination. The recent shrinkage of drought area within Texas is directly related to improvements in reservoir levels, even though in many parts of the state the reservoirs are rarely full. Ongoing and future planned work involving the high-resolution drought monitoring products will be noted.
Amir AghaKouchak - This presentation outlines a framework for improving seasonal precipitation prediction by combining the national multi-model ensemble (NMME) prediction with a baseline statistical prediction. The statistical model is based on an analog year concept and based on wet-season precipitation and three major indicators of climate variability over the southern US, namely Southern Oscillation Index (SOI), Pacific Decadal Oscillation (PDO), and Multivariate ENSO Index (MEI). The two different prediction methods are combined together using the concept of Expert Advice (EA) algorithm which has been successfully applied to the financial sector. The goal of this methodology is to derive an “ensemble response” that at every time step is equal or better (less error) than the best model relative to historical observations. The preliminary results show substantial improvements in seasonal precipitation predictability in the western United States.