The trajectory of land surface wetness is one of the most consequential unknowns in the Arctic climate system. The present analysis is intended to (1) document seasonal and interannual variations of surface moisture fluxes, (2) clarify the drivers of P-ET variations among Arctic vegetative types, and (3) evaluate the effects of wildfire disturbance on ET. The analysis is based on field measurements from sites in boreal forest and tundra ecosystems of Alaska. The surface moisture budget at boreal forest sites in permafrost areas generally shows a moisture deficit in late spring and early summer, followed by a moisture surplus from late summer into autumn. The annual net P-ET is generally positive but can vary interannually by more than an order of magnitude. The primary drivers of variations in evapotranspiration over weekly to monthly timescales are radiative fluxes, air temperature, relative humidity and wind speed. Overall, the ET at forest sites shows a stronger dependence on relative humidity and wind speed, while ET at tundra sites shows the stronger dependence on air temperature. These differences imply that tundra sites are more temperature-limited and forest sites are more humidity-dependent. Relative to a nearby unburned site, a burned forest site in interior Alaska shows an increase in ET for nearly a decade following the fire, while the recovery time for ET at a burned tundra site is only about three years.

地表湿度的轨迹是北极气候系统中最重要的未知数之一。本分析旨在 (1) 记录地表水分通量的季节性和年际变化，(2) 阐明北极植物类型之间 P-ET 变化的驱动因素，以及 (3) 评估野火干扰对 ET 的影响。该分析基于阿拉斯加北方森林和苔原生态系统中的现场测量结果。多年冻土地区北方森林地表水分收支通常在春末夏初表现出水分亏缺，然后从夏末到秋季水分盈余。年度净 P-ET 通常为正，但年际变化可能超过一个数量级。每周到每月时间尺度上蒸发蒸腾量变化的主要驱动因素是辐射通量、气温、相对湿度和风速。总体而言，森林站点的 ET 对相对湿度和风速的依赖性更强，而苔原站点的 ET 对气温的依赖性更强。这些差异意味着苔原场地更受温度限制，森林场地更依赖湿度。相对于附近未烧毁的场地，阿拉斯加内陆的一个被烧毁的森林场地在火灾后近十年内显示出 ET 增加，而在一个被烧毁的苔原场地的 ET 恢复时间只有大约三年。而苔原地区的 ET 对气温的依赖性更强。这些差异意味着苔原场地更受温度限制，森林场地更依赖湿度。相对于附近未烧毁的场地，阿拉斯加内陆的一个被烧毁的森林场地在火灾后近十年内显示出 ET 增加，而在一个被烧毁的苔原场地的 ET 恢复时间只有大约三年。而苔原地区的 ET 对气温的依赖性更强。这些差异意味着苔原场地更受温度限制，森林场地更依赖湿度。相对于附近未烧毁的场地，阿拉斯加内陆的一个被烧毁的森林场地在火灾发生后近十年内显示出 ET 增加，而在一个被烧毁的苔原场地的 ET 恢复时间只有大约三年。