LONDON—JPMorgan cuts its fourth quarter growth forecast for China to 4.0 percent quarter-on-quarter from 5.0 percent on Friday, citing the impact of power shortages and the recurrence of COVID-19 clusters hitting consumer spending and services. “Looking back, we have downgraded China’s growth forecasts five times since August,” JPMorgan’s Haibin Zhu said in a note, adding the bank now expected full-year growth of 7.8 percent and 4.7 percent in 2022. “In particular, to smooth out COVID-related volatility, we note that the pace of average annual GDP growth (compared to two years ago) has decelerated notably.”