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中文摘要：
依据北方农牧交错带46个气象站1961-2012年的逐日气象数据，分析了不同时间尺度下，全区及东北、华北、西北3个子区气温、降水和潜在蒸散量的变化特征，探讨了潜在蒸散量下降的原因，重点验证了研究区是否存在“蒸发悖论”现象。结果表明：①近52a，北方农牧交错带全区气温于1986年发生突变，潜在蒸散量除西北段外，其余均随气温的升高呈下降趋势，整体存在“蒸发悖论”现象；②不同时空尺度，表现出不同的“蒸发悖论”规律：1961-1986年，全区及各子区均存在“蒸发悖论”现象，近26a，仅东北段和华北段存在。春、冬、夏季前26a及秋季后26a存在；③近52a，全区及子区年降水量均呈现下降趋势，夏、秋季降水与潜在蒸散量呈逆向分布的站点分别为37％、63％；④各气象因子中风速的显著上升是影响全区年、季潜在蒸散量下降的主导因素。
英文摘要：
As an estimate of the evaporative demand of the atmosphere, potential evapotranspir- ation has been widely applied in irrigation management and predictions in ungauged basins. In recent years, change trends in ETo and its dominant factors across different regions of the world have been studied. Despite global warming, decreasing trends in ETo have been detected in several countries. Based on the daily meteorological data of 46 meteorological stations in the farming-pastoral ecotone of northern China from 1961 to 2012, we analyzed the variation in temperature, precipitation and potential evapotranspiration at different time scales in the entire region and three sub-zones. We verified the existence of an ＇ evaporation paradox＇ phenomenon in the study area and found that in the past 52 years, temperature experienced mutations in 1986 and potential evapotranspiration decreased as temperature increased in other regions apart from the northwest. The evaporation paradox showed different rules at different spatial and temporal scales： the evaporation paradox existed in the overall region and the sub-region from 1961 to 1986, but only existed in the northeast and northern sections in the last 26 years. The initial 26 years in spring, winter and summer, as well as the later 26 years in autumn showed an evaporation paradox phenomenon. During the last 52 years, annual precipitation showed a downward trend in the entire region and sub-region, and sites where precipitation and potential evapotranspiration exhibit a contrary trend were 37% in summer and 63% in autumn. In terms of the effect of change in meteorological elements to potential evapotranspiration change, a significant increase in wind speed over the past 52 years was the dominant factor leading to a decrease in annual and seasonal potential evapotranspiration in the farming-pastoral ecotone of northem China.
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