利用中国新疆地区1960-2005年109个设有蒸发皿蒸发观测的常规气象站资料,并结合不同驱动场和不同陆面模式的模拟结果,对蒸发皿蒸发及模拟的实际蒸发的年、各个季节的变化及其它们的相互联系进行了详细的分析和讨论。结果发现,在过去的46年里,年蒸发皿蒸发总体上都表现为明显的下降趋势,而实际蒸发在总体上显著上升,与蒸发皿蒸发的变化趋势相反。在80年代中后期,蒸发皿蒸发、实际蒸发和降水的转折点(1986年)一致,进一步说就是无论在转折点的前后,降水增加的转折性变化与模拟的实际蒸发的转折性增加变化一致,而与蒸发皿蒸发减小的转折性变化相反,这表明,在新疆地区,蒸发皿蒸发和实际蒸散之间具有相反的变化关系,这支持Brutsaert and Parlange提出的蒸发皿蒸发和实际蒸散之间具有互补相关关系(变化趋势相反)的理论。分析气温、降水、湿度、云量和日照时数等环境变量的变化趋势发现:降水、云量等表征大气中水分特征的变量表现为明显的上升趋势,这也间接的证明了蒸发皿蒸发和实际蒸散之间存在相反的关系,而与各个环境变量之间相关系数的分析则表明,气温日较差、风速、低云量和降水是与蒸发皿蒸发和实际蒸发关系最紧密的环境因子,它们的变化可能是导致蒸发皿蒸发和蒸散量变化的原因。
基于DEM数据和土壤分类、土壤属性、土地利用分类、植被属性和观测气象数据,利用分布式水文模型SWAT(Soiland Water Assessment Tool),对陕西区域进行了土壤湿度模拟和检验.模拟土壤湿度与实际观测土壤湿度的对比分析表明:SWAT较好的模拟了区域土壤湿度的变化特点及其长期趋势,且对多气候类型及复杂地形区域的土壤含水量时空变化有较强的模拟能力;表层土壤湿度在植被状况好的陕南地区和地形性降水明显的秦岭山地等区域量值较大,而深层土壤湿度较大值出现在河流及平原地区;1951～2004年土壤湿度变化总体上不同深度的土壤湿度均呈下降趋势,深层下降趋势较表层表现更明显,秦岭以北地区比以南地区表现更明显;土壤干化趋势的强度深层大于表层,秦岭以北地区大于以南地区,土壤干化(土壤湿度减小的趋势)的范围深层亦大于表层,且多分布于秦岭以北地区.与NCEP和ERA40再分析土壤湿度数据对比分析表明,SWAT模拟的土壤湿度日变化、月和年平均值的变化趋势均优于NCEP和ERA40的土壤湿度变化趋势.
In this study, the Palmer Drought Severity Index （PDSI） was used to analyze the average and extreme dry/wet states of Asia and North America from 1953 to 2003. The results indicate that the two continents underwent drying trends during this period. Compared with North America, Asia showed more severe drought trends. However, more significant and regular seasonal variation for drought was found in North America. The driest regions in Asia were located in the northern region of China, Mongolia, and eastern mid-Siberian plateau. Most regions in central North America were relatively wetter than other regions. The northern and southwestern regions of North America, as well as the Atlantic and Pacific coastal areas, experienced the most drought during this period. A sharp increase of the drought area and the number of extreme drought events took place from 1997 to 2003 in both Asia and North America. Severe drought events were more likely to occur during the summer on both continents. Asia had the most extreme drought events during July, but North America reached its highest drought frequency from June to September. In Asia, a persistent increasing trend of extreme drought emerged throughout the studied period. However, a more complex evolution of drought emerged in North America： a decreasing trend appeared before the mid-1960s and an increasing trend appeared after the late 1970s. A relatively steady dry/wet status was observed between the mid-1960s and the late 1970s. The role of exceptional, extreme drought events with respect to the La Nin？a event was considered during 1997–2003.
