中文摘要：

裸沙表面的蒸发虽然是一个物理问题，但对于沙地植被演替的初始阶段非常重要。目前存在的地表蒸发的机理性模型大多是瞬时或者短时期的，而年尺度以上的蒸发量与降水和蒸发驱动下的土壤水分系统的状态变化及其对蒸发过程的反馈密切相关。一些估算毛乌素年蒸发量的实验结果之间分歧很大且缺乏准确的机理性解释。该文利用生态系统模型中的土壤水分运动和蒸发模块计算了毛乌素裸沙丘从日到年际尺度的实际蒸发量，发展了一个以单次降雨量和降雨频率为驱动因素的降雨-蒸发模型对年蒸发量进行简单的估算，并研究了年蒸发量对降雨格局的响应。结果表明毛乌素裸沙丘的多年平均蒸发量为166mm，占多年平均降雨量的56％。虽然研究区1959～1992年降雨总量无显著变化趋势，但是裸沙丘斑块的实际蒸发量呈现较明显的增加趋势（1．30mm·a^-1）。小降雨事件对蒸发量贡献的显著增加（0．69mm·a^-1）是导致实际蒸发量增大的重要原因。大强度降雨事件的频度和雨量对降雨总量的贡献要远高于对蒸发总量的贡献，小于12mm的降雨事件在年际比较稳定，很大程度上保证了年蒸发量100mm左右的基数值。这些因素使得年蒸发量的变异程度小于年降雨量的变异程度。由于降雨格局的年际变化会对蒸发量产生直接的影响，降雨-蒸发模型可以相对有效地预测年度蒸发量，而用年降雨量预测年蒸发量误差较大。

英文摘要：

Aims Annual or long-term actual evaporation and its response to precipitation pattern are poorly known. Our alms are to estimate average annual surface evaporation of bare sand dunes and explore the relationship between precipitation pattern and annual evaporation variance. Methods Based on a meta-analysis of previous experiments, we used a process-based model to calculate the evaporation （EV） of bare sand dunes in Maowusu from day to multiyear scales. We also developed a simple Rainfall-EV model driven by amount and frequency of rainfalls, by which we explored the relationship between intensify of rainfall events and variance of annual evaporation. Important findings The process-based model yielded reasonable short-term evaporation pattern after rainfalls and accumulative evaporation. The long-term average of evaporation from 1959 to 1992 is 166 mm, accounting for 56 % of annual precipitation. Although there is no significant change of annual precipitation, the actual evaporation increased significantly with a tendency of 1.30 mm·a^-1. We suggested the significant increase （0.69 mm·a^-1） of small rainfall events （ 〈5 mm） was the dominant reason of the increase of annual actual evaporation. The frequencies and amounts of strong rainfall contributed more to annual precipitation than annual evaporation, while weak rainfall events （ 〈 12 mm） kept relatively constant among years, providing about 100 mm evaporation. These resulted in less variance of annual evaporation than precipitation. Since the precipitation pattern among years apparently will influence annual evaporation, the simple Rainfall-EV model is able to predict annual evaporation effectively.