De-convolving the effects of rising atmospheric CO2, solar dimming, and afforestation on usable water and carbon sequestration potential in the Southeastern U.S.

解决大气二氧化碳上升、太阳变暗和造林对美国东南部可用水和碳固存潜力的影响。许多注意力被引导到评估人为二氧化碳排放和气候变化如何影响土壤水分流失和大陆径流。这反映在美国全球变化研究项目（USGCRP）提出的水和碳循环科学计划以及2001年政府间气候变化专门委员会（IPCC）的报告中。最近的一些研究表明，尽管人类及其活动的用水量迅速增加，但整个20世纪大陆径流仍在增加。径流增加的原因仍然是一个有争议的话题，尽管它通常被归因于20世纪降水(P)的增加或蒸散发（ET）的减少。虽然P的增加可以用变暖趋势来解释，但ET的减少，特别是在次大陆尺度上，则更为复杂。ET减少的三种合理解释是：(1)太阳变暗导致的能量和光输入减少，较低的光照水平降低了平均气孔对水蒸气的导度（gc）；(2)大气CO2升高导致的gc降低；(3)土地利用变化导致植被耗水量减少。这三种机制之间的相互作用可以在从生态系统水平到流域到次大陆区域的许多尺度上进行探索。利用生态系统模型和详细的野外实验相结合，我们将研究太阳变暗、大气二氧化碳增加和森林面积增加如何改变美国东南部（SE）的水可用性和生态系统总二氧化碳交换，该地区被认为是美国最具碳固存能力的地区之一。由于过去100年的快速造林（和再造林）和过去50年降水的微小变化，东南地区提供了一个理想的研究案例。该项目的智力价值在于阐明了过去50年来导致全球径流增加的机制，并评估径流时间序列是否包含可识别的气候变化信号。认识到碳固存将在未来的区域和国家政策中发挥越来越大的作用，而水资源目前发挥着主要作用，本项目的更广泛影响是提供科学基础、数据和模型，可以指导土地覆盖类型转换后碳水平衡的生态系统评估。该项目的教育效益是支持两名研究生，为他们提供在测量和模拟生物圈-大气交换率方面的最新技术的独特经验，同时与杜克大学从事水和碳循环的物理和生物科学家组成的广泛跨学科团队进行互动。

Katul0628432De-convolving the effects of rising atmospheric CO2, solar dimming, and afforestation on usable water and carbon sequestration potential in the Southeastern U.S.Much attention is directed to assessing how anthropogenic CO2 emissions and climate change impact soil water losses and continental runoff, as reflected in both the Water and Carbon Cycles Science Plans proposed by United States Global Change Research Program (USGCRP) and the 2001 Intergovernmental Panel on Climate Change (IPCC) report. A number of recent studies suggest that continental runoff increased throughout the 20th century despite a rapid increase in water consumption by humans and their activities. The reason for the increase in runoff remains a subject of debate, though it is commonly attributed to either an increase in precipitation (P) or a decrease in evapotranspiration (ET) over the 20th century. While the increase in P can be explained by warming trends, the reduction in ET, especially at sub-continental scales, is more complex. The three plausible explanations for reductions in ET are: (1) Less energy and light input due to solar dimming with lower light levels reducing mean stomatal conductance to water vapor (gc), (2) lower gc due to elevated atmospheric CO2, and (3) land-use change to vegetation that consumes less water. The interplay between these three mechanisms can be explored on a number of scales ranging from the ecosystem level to watershed to sub-continental region. Using a combination of ecosystem models and detailed field experiments, we will investigate how solar dimming, increases in atmospheric CO2, and increases in forested area alter water availability and gross ecosystem CO2 exchange in the Southeastern (SE) U.S., a region that is considered among the most productive in the U.S. in terms of carbon sequestration. The SE provides an ideal case study due to rapid afforestation (and reforestation) over the past 100 years and the minor change in precipitation over the past 50 years. The project's intellectual merit is to elucidate the mechanisms leading to global runoff increases over the past 50 years, and to assess whether runoff time series contain a discernable signal of climate change. Recognizing that carbon sequestration will play an increasing role in regional and national policy in the future, and that water resources currently play a major role, the broader impact of this project is to contribute the scientific foundation, data, and models that can guide ecosystem valuation for C-H2O tradeoffs upon conversion among land cover types. The educational benefit of the project is to support two graduate students, providing them with a unique experience in the state of the art techniques in measurement and modeling of biosphere-atmosphere exchange rates while interacting with a broad interdisciplinary team of physical and biological scientists working on water and carbon cycling at Duke University.