坝上高原近90年以来降水变化趋势

根据史料和降水量资料，建立了自１９００年以来坝上高原旱涝级别（５级）序列，并对其进行了周期分析和趋势分析。结果表明，坝上高原降水变化具有明显的４２年和９年周期，自６０年代初以来该区进入干旱少雨阶段，并将持续到本世纪末下世纪初。此外，还有一些短周期，如４－５年和２－３年等，因而，在今后１０年内，干旱和少雨仍将持续，土地沙漠化也将继续发展。

THE TENDENCY OF PRECIPITATION VARIATION IN THE PAST MINE DECADES IN BASHANG HIGHLAND

Based on historical documents and precipitation data the sequence of drought-waterlogg1ng class from 1900 onwards in the Bashang highland was established;the periodicity and the variation tendency of precipitation were analysed.The analytcal results showed that the precipitation in Bashang highland has an obvious 42-year and 9-year periedicities.Since 1960s the region has entered into the rain-deficient poriod and this will continue to the beginning of next century. In addition,there were also some short periedicities,e. g.2-3- year and 4-5- year periodicities. Therefore,in the next 10 years the area will continue to experience drought and rain- deficient climate and the desertification will continue to develop.