Impacts of anthropogenic forcing and internal variability at the watershed scale - going from the daily to the hourly time scale

人类活动对辐射强迫的影响所造成的气候变化现在已经得到了充分的证实。除了预计地表温度上升外，这些变化还将影响水循环的所有主要组成部分，包括各种空间和时间尺度上的降雨变异性和强度。对这些变化的影响的了解主要来自于大气环流和地球系统模型。然而，由于可用计算能力的限制，直到最近，这些模型的输出大多是在每天的时间步长上获得的。因此，次日级别的变化没有得到很好的记录。然而，发布更高分辨率的区域气候模式(无论是否允许对流)表明，人为强迫对短期和强降雨的影响将更大。因此，我们可以预测对小流域的不成比例的影响，这些小流域的水文反应迅速，可与对流降水系统的反应相称。同样，我们还可以预测，与小流域(1000平方公里)夏季秋季降水有关的洪水相比，融雪洪水的影响将会减少。在水文学方面，这些结果指出了对小型农村和城市化流域的重大影响。 人为强迫变化对这些盆地水文的潜在影响一直没有得到很好的研究，主要原因有两个： 1--在北美(以及除少数欧洲国家外的世界大部分地区)没有可靠的次日时间步长的水文气象数据库，无法对这些流域进行足够数量的研究； 2--仍然没有几个气候模型的主要输出(例如温度和降水)可以在次日时间步长获得。 这项研究计划旨在通过使用我们的研究实验室和其他地方开发的工具和方法来填补这一知识空白，以研究气候变化对中小型流域的影响。这些工具和方法将与使用新的数据库和具有高时间和空间分辨率的气候模型的输出相结合，从而能够处理小到中等规模的流域的研究，直至每小时的时间步长及以下。

Climate change resulting from the anthropogenic impact on radiative forcing is now well established. In addition to increases in projected surface temperatures, the changes will affect all major components of the water cycle, including variability and intensity of rainfall at various spatial and temporal scales. The knowledge of the impacts of these changes comes largely from general circulation and earth system models. However, due to the limitations related to the available computing power, the outputs of these models have mostly been available at the daily time-step until recently. Changes at the sub-daily scales are therefore less well documented. Nevertheless, releases of higher-resolution regional climate models (convection-permitting or not) indicate that the impacts of anthropogenic forcing will be greater for short-duration and intense rainfall. We can thus predict a disproportionate impact on small watersheds whose hydrological response is rapid and commensurable with that of convective precipitation systems. Similarly, we can also predict a decrease in the impact of snowmelt related floods to those related to summer fall precipitation over small watersheds (<1000 km2). In hydrology, these results point to major impacts towards small rural and urbanized watersheds. The potential impacts of anthropogenic forcing change on the hydrology of these basins have been poorly studied for two main reasons: 1- There is no reliable hydrometeorological database at sub-daily time steps in North America (as well as in the majority of the world, except for a few European countries) to study these watersheds in sufficient numbers; 2- There are still few climate models whose main outputs (e.g. temperature and precipitation) are available at the sub-daily time steps. This research program specifically aims to fill this knowledge gap by using the tools and methodologies developed within our research laboratory and elsewhere to study the impacts of climate change at the daily time step on small to medium-size watersheds. These tools and methods will be combined with the use of new databases and outputs of climate models with high temporal and spatial resolution to thus be able to tackle the study of small to mdieum-size watersheds up to the hourly time step and below.