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• Proactive drought responses are crucial in a drought vulnerable future. • Antecedent conditions need to be considered in context of anticipated conditions. • We combine rainfall, soil moisture and evapotranspiration data with forecasts for early warning. • Validation efforts found promising accuracy in the drought early warning maps. • Proof-of-concept drought early warning system can aid proactive drought management. Droughts are a cyclical feature of Australia's climate that have compounding impacts on agricultural productivity and the wellbeing of drought-affected communities. Understanding anticipated drought conditions in context of antecedent observations is critical to providing early warning of drought. In this study we paired probabilistic seasonal rainfall forecasts with precipitation, soil moisture and evapotranspiration data that were objectively combined using Principal Component Analysis (PCA). The final Drought Early Warning System (DEWS) maps overlay forecasting information with the multi-variate PCA-weighted maps at 1-, 3- and 6-month timescales over the common period of overlap between all datasets (1982–2018). In this study period, the 1982–1983 Ash Wednesday tinder drought and the 1997–2001 Millennium drought were investigated. We validated PCA-weighted maps with satellite vegetation data and found performance was strongest over the Murray Darling Basin region (R = 0.63, p = 0.009) and poorest over Central interior Australia (insignificant correlations). We also validated PCA-weighted maps using agricultural commodity data from ABARES. Significant negative correlations at 95 %, 99 % and 99.9 % confidence intervals were found between %-Area in drought category and crop cultivation area; export volume/value; crop yield; and rural debt. Our findings indicate that early warning of drought can be categorised by concern – wherein dry antecedent conditions and dry forecasted conditions are of the highest concern. The developed proof-of-concept DEWS contributes to the growing body of proactive drought management research. In a drought vulnerable future, operationalising and communicating drought early warnings will be critical to reducing the harmful impacts of drought on communities, economies, and environments. [ABSTRACT FROM AUTHOR]

Summary: Across southern Australia, a large proportion of urban water supply is sourced from mountainous catchments forested with native eucalypts. Mixed species eucalypt forest (MSEF) is the most common forest type in this region and occurs on relatively dry, fire prone sites, yet factors controlling forest water use and stream flow in response to topography, disturbance and drought are poorly understood. This study investigated the patterns and drivers of water balance over a 4year period in a 1.36km2, MSEF catchment by: quantifying spatial and temporal variability in evapotranspiration (Et ) and its components; evaluating the abiotic, structural and physiological factors controlling water use across the catchment; and testing the effects of antecedent soil water conditions on water fluxes after drought. This was done using a ‘bottom up’ measurement approach that included stream flow and Et (sap flow, interception troughs and evaporation dome) and a simple empirical model of Et to track catchment response to drought. Spatial variability was considerable, with 40% lower rates of Et at an up slope plot compared to mid and bottom slope plots. Tree transpiration was the dominant flux annually and was correlated to reference Et (r 2 =0.35–0.80), implying strong limitation by atmospheric demand across the catchment. Annual Et totals were relatively consistent between years (841±34mm) despite large variation in rainfall (463–1179mmy−1). Annual stream flow represented a very small proportion of the water budget (<2% of rainfall) and showed little recovery from the drought period. The modelling showed that the change in soil water storage following drought was large (up to −330mm) and was responsible for decreased rates of stream flow. These findings show that Et in the MSEF is sensitive to topography and demand limitation and suggests that water yield in this forest type may be particularly sensitive to future climatic change as shown by the sustained effect of drought on catchment water balance. [Copyright &y& Elsevier]

• SPEI/SPI-12 are better predictors of hydrological stores like groundwater (GW). • Influence of global climate teleconnections is better diagnosed with SPEI/SPI-12. • GW loss in Murray Darling Basin occurred about 44% of the time during 2002–2017. • Extreme events (droughts and floods) affect the distribution of surface water extent. • SPEI/SPI-3 are excellent metrics that capture variability in annual crop production. Risk-management solutions that increase opportunities for adaptation plans and resilience to climate change require an understanding of climate change processes and the trickle down effects of droughts and floods on hydrological and socio-economic systems. To guide future expectations about droughts, this study aims to assess large-scale variability of hydrological stores (groundwater, soil moisture, and surface water) and their responses to drought intensities over large semi-arid domains in Australia. Multi-scaled indicators synthesised from in-situ rainfall (SPI-standardised precipitation index), water budget (SPEI-standardised evapotranspiration precipitation index), model (soil moisture-SM), and satellite observations (groundwater storage-GWS, surface water extent-SWE, and terrestrial water storage-TWS) are employed to assess this variability in climatic hotspots identified through statistical rotation. The link between these hotspots and climate modes are diagnosed using gaussian kernel-based SVMR (support vector machine regression), and quantile function of storage (QFS) is used to assess the response of hydrological stores to climate variability. The capability of these indicators to capture impacts of water deficit on agricultural systems is explored by implementing a PLSR (partial least square regression). Results show that (i) drought characteristics and intensities vary greatly across Australia but hotspots of higher drought duration and intensity are predominant in regions below latitude 25 ° S, (ii) hydrological drought indicators (SPEI/SPI-12) are better predictors of hydrological stores such as TWS and GWS, though the latter shows strong but opposite phase relationship with climate data, (iii) influence of climate teleconnections is better diagnosed and predicted with SPEI/SPI-12, and the Murray Darling basin-MDB (r = 0.84 , α = 0.05) and central/east coast (r = 0.80 , 0.79 , α = 0.05) are major teleconnection hotspots, (iv) SM and GWS losses in the MDB occurred 60% and about 44% of the time, respectively, during the 2002 - 2017 period, (v) extreme events (droughts and floods) affect the distribution of SWE, and (vi) meteorological drought indicators (SPEI/SPI-3) are excellent metrics that capture variability in crop production. Choosing appropriate indicators that reflect the response of freshwater ecosystems (including groundwater) to climatic and anthropogenic constraints is part of a key process to guide investments in drought resilience and sustainable management of water resources. [ABSTRACT FROM AUTHOR]