Extended-range forecasting of Chinese summer surface air temperature and heat waves

Because of growing demand from agricultural planning, power management and activity scheduling, extended-range (5–30-day lead) forecasting of summer surface air temperature (SAT) and heat waves over China is carried out in the present study via spatial–temporal projection models (STPMs). Based on the training data during 1960–1999, the predictability sources are found to propagate from Europe, Northeast Asia, and the tropical Pacific, to influence the intraseasonal 10–80 day SAT over China. STPMs are therefore constructed using the projection domains, which are determined by these previous predictability sources. For the independent forecast period (2000–2013), the STPMs can reproduce EOF-filtered 30–80 day SAT at all lead times of 5–30 days over most part of China, and observed 30–80 and 10–80 day SAT at 25–30 days over eastern China. Significant pattern correlation coefficients account for more than 50% of total forecasts at all 5–30-day lead times against EOF-filtered and observed 30–80 day SAT, and at a 20-day lead time against observed 10–80 day SAT. The STPMs perform poorly in reproducing 10–30 day SAT. Forecasting for the first two modes of 10–30 day SAT only shows useful skill within a 15-day lead time. Forecasting for the third mode of 10–30 day SAT is useless after a 10-day lead time. The forecasted heat waves over China are determined by the reconstructed SAT which is the summation of the forecasted 10–80 day SAT and the lower frequency (longer than 80-day) climatological SAT. Over a large part of China, the STPMs can forecast more than 30% of heat waves within a 15-day lead time. In general, the STPMs demonstrate the promising skill for extended-range forecasting of Chinese summer SAT and heat waves.