Abstract
Spatially compounding droughts over multiple regions pose amplifying pressures on the global food system, the reinsurance industry, and the global economy. Using observations and climate model simulations, we analyze the influence of various natural Ocean variability modes on the likelihood, extent, and severity of compound droughts across ten regions that have similar precipitation seasonality and cover important breadbaskets and vulnerable populations. Although a majority of compound droughts are associated with El Niños, a positive Indian Ocean Dipole, and cold phases of the Atlantic Niño and Tropical North Atlantic (TNA) can substantially modulate their characteristics. Cold TNA conditions have the largest amplifying effect on El Niño-related compound droughts. While the probability of compound droughts is ~3 times higher during El Niño conditions relative to neutral conditions, it is ~7 times higher when cold TNA and El Niño conditions co-occur. The probability of widespread and severe compound droughts is also amplified by a factor of ~3 and ~2.5 during these co-occurring modes relative to El Niño conditions alone. Our analysis demonstrates that co-occurrences of these modes result in widespread precipitation deficits across the tropics by inducing anomalous subsidence, and reducing lower-level moisture convergence over the study regions. Our results emphasize the need for considering interactions within the larger climate system in characterizing compound drought risks rather than focusing on teleconnections from individual modes. Understanding the physical drivers and characteristics of compound droughts has important implications for predicting their occurrence and characterizing their impacts on interconnected societal systems.
Highlights
Weather and climate extremes pose substantial risks to people, property, infrastructure, natural resources and ecosystems[1,2,3]
In order to establish the robustness of our findings, we compare our analyses with data from the Climate Prediction Center (CPC; 0.5° × 0.5°) and Climatic Research Unit (CRU; 0.5° × 0.5°), by comparing the Standardized
We find that CPC-based SPI does not capture documented droughts over AMZ71, SAS72 during the record breaking El Niño year 2015, and over SAS73, EAF74, and EAS75 in another well-known El Niño year 2009 (Fig. S9)
Summary
Weather and climate extremes pose substantial risks to people, property, infrastructure, natural resources and ecosystems[1,2,3]. Projected warming is likely to increase the co-occurrence of warm and dry extremes over multiple croplands and pastures[7], and is expected to amplify the risk of synchronous failures across major maize producing regions[12]. Such synchronous shocks could trigger international food price spikes and disrupt trade infrastructure, which could amplify threats to food security[12,13,15], in developing countries, where the population is already more vulnerable and food insecure[16]. Their increasing occurrence and associated losses could limit the profitability of insurance companies, which could have cascading impacts on financial markets and could force companies to increase insurance premiums, reducing insurance affordability and shifting more of the burden of disaster-related losses on governments and individuals[10]
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