For the targeted use of irrigation water and early tactical decisions regarding fleet management, water resource planning, and crop management measures to adapt to an impending dry period, a web-based early warning system is being developed based on daily, temporal-spatial high-resolution simulation of crop growth and yield formation with an agroecosystem model (MONICA). These simulations incorporate short- and medium-term weather forecasts as well as real-time soil moisture data via an assimilation algorithm. Threshold values developed in the project for evaluating the intensity of an approaching drought define individual warning levels. Scenarios for irrigation applications (optimal application, deficit irrigation) integrated into the early warning system make it easier for irrigating farms to derive an individual strategy for the optimal use of available resources. Decision-makers at regional level benefit from indications of withdrawal peaks for holding water reserves or preparing withdrawal bans.