Probabilistic Forecasts of Water Shortage Persistence under Central-Pacific El Niño Conditions: Implications for Short-Term Demand Management

Water shortage risk management strategies, such as demand curtailment and/or temporary water supply augmentation, are vital, but their effectiveness depends on accurate monitoring and forecasting of water shortage indicators, robust water restrictions enforcement, and timely public engagement. A key question following a water shortage declaration is, “how long will it persist, and how severe might it become?” The answer is essential for determining whether water shortage measures should be sustained or adjusted. This study fills the gap of integrating the impact of Central Pacific-El Niño on local climate into the operational forecasts of water shortage indicators and provides guidance for regional water shortage management. It aims to address the key question of how long the water shortage event will persist. This study addresses the question by developing predictive water shortage indicators and demonstrates its implementation using a recent water shortage event in the Tampa Bay region, a metropolitan area in southwest Florida. The approach incorporates the Central-Pacific El Niño condition, an important driver of winter rainfall in the region, into stochastic rainfall generation process probabilistic forecasts of two key indicators, a 12-month rolling cumulative rainfall deficit (RCD rainfall) and a 12-month rolling median streamflow deficit (RMD flow), which were made for the upcoming months. These predictions were used to characterize the level of water shortage and guide the duration of media campaigns and public engagements. While demonstrated at a local scale, the proposed methodology has broader applicability for water management in other regions.