Seasonal forecasts of the summer 2016 Yangtze River basin rainfall

TL;DR

This paper demonstrates the successful application of a dynamical seasonal forecast system to predict the 2016 Yangtze River basin rainfall, aiding flood management and decision-making.

Contribution

It presents a simple methodology for real-time seasonal forecasting based on historical relationships, validated with the 2016 El Niño event.

Findings

Heavy rainfall forecasted accurately in May-June-July

Low rainfall in August was correctly predicted

Forecasts increased confidence among decision-makers

Abstract

The Yangtze River has been subject to heavy flooding throughout history, and in recent times severe floods such as those in 1998 have resulted in heavy loss of life and livelihoods. Dams along the river help to manage flood waters, and are important sources of electricity for the region. Being able to forecast high-impact events at long lead times therefore has enormous potential benefit. Recent improvements in seasonal forecasting mean that dynamical climate models can start to be used directly for operational services. The teleconnection from El Ni\~no to Yangtze River basin rainfall meant that the strong El Ni\~no in winter 2015/2016 provided a valuable opportunity to test the application of a dynamical forecast system. This paper therefore presents a case study of a real time seasonal forecast for the Yangtze River basin, building on previous work demonstrating the retrospective skill of such a forecast. A simple forecasting methodology is presented, in which the forecast probabilities are derived from the historical relationship between hindcast and observations. Its performance for 2016 is discussed. The heavy rainfall in the May-June-July period was correctly forecast well in advance. August saw anomalously low rainfall, and the forecasts for the June-July-August period correctly showed closer to average levels. The forecasts contributed to the confidence of decision-makers across the Yangtze River basin. Trials of climate services such as this help to promote appropriate use of seasonal forecasts, and highlight areas for future improvements.