A comparative study of historical droughts over Texas, USA and Murray-Darling Basin, Australia: Factors influencing initialization and cessation

Water availability and food security are tightly coupled on a global scale. The occurrence of drought puts this balance at risk due to reductions in dryland farming production and water allocations to irrigated agriculture. Improved understanding of drought initiation and cessation would therefore be beneficial for drought planning and management. The study objective was to determine factors affecting drought initiation and cessation over the past century in two climatologically similar regions that represent net agricultural exporters; south central U.S. (Texas) and southeast Australia (Murray Darling Basin, MDB). Drought indices included the Standardized Precipitation Index (SPI, 1900-2014) for meteorological drought, the Normalized Difference Vegetation Index (NDVI, 1981-2014) for agricultural drought, and the Streamflow Drought Index (SDI, 1930-2014) for hydrological drought. Results show that meteorological drought tends to develop gradually over a period of up to six months, with agricultural drought developing shortly thereafter (within one month) in both regions. Evidence of hydrological drought was observed within one month (Texas) and within four months (MDB) on average after meteorological drought was established. Further, droughts appear to cease more quickly than they initiate over Texas, whereas rates of drought initiation and cessation are similar over the MDB. Drought breaking rainfall in Texas is generally a result of a southward shift in the Polar Jet Stream or a low-pressure trough over central North America, whereas drought cessation in the MDB is typically associated with a monsoon trough or low-pressure system in the Tasman Sea/Great Australian Bight. Improved knowledge of the climate mechanisms controlling the onset and termination of drought periods should enhance drought forecasts and improve drought management practices, particularly in regions where water security is a primary objective.