(Adds details on 2022, quotes) MADRID, Oct 25 (Reuters) - Relatively high inflation rates are likely to prevail in Spain over coming months although their underlying causes are mainly transitory, Bank of Spain Governor Pablo Hernandez de Cos said on Monday. A surge in energy prices could last through the winter as demand generally increases because of cold weather while oil and gas storage levels are relatively low, he said. De Cos warned, however, that the longer the transitory inflation pressure lasts, the likelier high inflation will become persistent. “All these elements introduce a noticeable level of uncertainty about the duration of the current episode of rising costs of production,” he said in a presentation to the budget committee in parliament. The effects of higher inflation are already reflected in the yields demanded by investors on Spanish 10-year government bonds, which have risen to 0.5% as of Friday from 0% at the beginning of the year, he said. Nevertheless, de Cos said, the general perception is that the European Central Bank will keep its expansive tone for a “dilated period of time”. He added that current supply chain disruptions, higher energy prices and other recent developments are likely to prompt a “significant downward” revision of the bank’s estimate for Spain’s economic growth in 2021 due to be updated in December. The Bank of Spain last month raised its growth forecast for this year by 0.1 percentage points to 6.3%, though a few days later the National Statistics Institute revised second-quarter growth sharply lower to 1.1% from an original 2.8%. De Cos said then the bank would have to update its outlook to take the revision into account. The growth outlook for 2022, which the bank had recently raised to 5.9%, could also be revised downward in December, de he said, though it is “less clear” than for 2021. (Reporting by Jessica Jones and Inti Landauro, editing by Andrew Cawthorne and Mark Heinrich)