中文摘要：

根据关中地区30个气象站41年的气象资料,采用FAO推荐的Penman-Monteith公式计算参考作物蒸发蒸腾量（ET0）,分析了陕西关中地区ET0的变化及原因,结果表明,从长期来看,关中地区ET0在减少趋势的基础上表现出周期性变化,从阶段性来看,1980年之前和之后则主要表现为增加趋势。关中地区年内ET0的最大值在1980年前主要出现在6月,1980年以后则主要出现在6月和7月,且以7月为多;1980年后5～8月ET0所占比值在减少,但仍在全年中占50%以上。关中地区平均气温、最高气温和最低气温表现为增加趋势,风速、日照时数和相对湿度表现为减少趋势。关中地区ET0与平均气温、最高气温和最低气温表现为不显著正相关,与风速和日照时数表现为显著正相关,与水汽压表现为显著负相关,与年降水量表现为不显著负相关,近一半地区的ET0与年蒸发量显著正相关。对关中地区ET0影响显著的气象因子的顺序为：风速〉日照时数〉水汽压〉年蒸发量。即风速和日照时数的减少趋势是引起关中地区ET0降低趋势的主要原因。

英文摘要：

Changes of reference crop evapotranspiration （ET0） and its causes were analyzed by the computed ET0 using Penman-Monteith equation which was recommended by FAO according to weather data of 41 years for 30 weather stations in Guanzhong Region of Shaanxi Province（Central Shaanxi Plain）. The results show that ET0 presents periodical changes based on decreasing trend in the long term and increasing trend before and after 1980 respectively, in the short term. The maximum ET0 appeared on June before 1980 and on June and July after 1980. ET0 percentage between May and August in a year after 1980 is less than the one before 1980, but still is over 50%. The tendencies for mean, maximum and minimum temperature are to increase and those for wind speed, sunlight hours and relative humidity are to decrease. ET0 is related positively to wind speed, sunlight hours insignificantly, and is related negatively to water vapor insignificantly. The influence capacity of weather factors on ET0 is as follows ： wind speed〉sunlight hours〉water vapor〉yearly evaporation. The decline trend of ET0 is mainly caused by the decrease of wind speed and sunlight hours.