Abstract
Drought is the most expensive natural hazard and one of the deadliest. While drought propagation through standardised indices has been extensively studied at the regional scale, global scale drought propagation, and particularly quantifying the space and time variability, is still a challenging task. Quantifying the space time variability is crucial to understand how droughts have changed globally in order to cope with their impacts. In particular, better understanding of the propagation of drought through the climate, vegetation and hydrological subsystems can improve decision making and preparedness. This study maps spatial temporal drought propagation through different subsystems at the global scale over the last decades. The standardised precipitation index (SPI) based on the gamma distribution, the standardised precipitation evapotranspiration index (SPEI) based on the log-logistic distribution, the standardised vegetation index (SVI) based on z-scores, and the standardised runoff index (SRI) based on empirical runoff probabilities were quantified. Additionally, drought characteristics, including duration, severity and intensity were estimated. Propagation combined the delay in response in the subsystems using drought characteristics, and trends in time were analysed. All these were calculated at 0.05 to 0.25 arc degree pixels. In general, drought propagates rapidly to the response in runoff and streamflow, and a with longer delay in the vegetation. However, this response varies spatially across the globe and depending on the observation scale, and amplifies progressively in duration and severity across large regions from the meteorological to the agricultural/ecological and hydrologic subsystems, while attenuating in intensity. Significant differences exist between major Köppen climate groups in drought characteristics and propagation. Patterns show intensification of drought severity and propagation affecting vegetation and hydrology in regions of southern South America, Australia, and South West Africa.
Highlights
Drought corresponds to a sequence of climate events triggered by ocean or atmospheric circulation conditions which results in rainfall deficits (Zargar et al, 2011; Yuan et al, 2017), leading to a landscape imbalance between water supply and demand (Ault, 2020)
Large drought episodes have occurred in different regions and have received different names, such as the millennium drought that occurred in Australia between 2001 and 2009 (Van Dijk et al, 2013) or the megadrought that has affected Chile since 2010 (Garreaud et al, 2020)
Atmospheric/oceanic circulation cycles strongly impact the development of dry/wet conditions, leading to interannual/ interdecadal climate variability (Vicente-Serrano et al, 2011). Some examples of this are the El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), or the Indian Ocean Dipole (IOD), which all cause an oscillation in surface ocean temperatures (Mantua and Hare, 2002; Xiao et al, 2015)
Summary
Drought corresponds to a sequence of climate events triggered by ocean or atmospheric circulation conditions which results in rainfall deficits (Zargar et al, 2011; Yuan et al, 2017), leading to a landscape imbalance between water supply and demand (Ault, 2020). Atmospheric/oceanic circulation cycles strongly impact the development of dry/wet conditions, leading to interannual/ interdecadal climate variability (Vicente-Serrano et al, 2011). Like the Subtropical Ridge (STR) or the North Atlantic Oscillation (NAO), are mainly driven by atmospheric conditions that affect the atmospheric pressure at sea level (Hurrell et al, 2003; Grose et al, 2015) All these cycles strongly impact weather conditions across different time scales. Anthropogenic impacts on the interannual climate variability as part of “climate change” are still difficult to quantify He and Li (2019) identified an overall increase in the interannual variability of rainfall associated with climate change across all longitudes between latitudes 20°S–50°N, while Zhu (2013) estimated an overall increase in rainfall intensities across the United States. Climate change has decreased rainfall in Mediterranean regions, and an increase in temperatures is expected to increase evaporative demand, reduce snowfall and increase the ablation of glaciers, the soil water deficit and runoff, leading to an increase in drought risk and severity (Cook et al, 2018)
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