RII Track-4:NSF: Amplification of drought effects on vegetation by anthropogenic warming

干旱是世界上损失最大的自然灾害之一，对社会和生态系统造成严重破坏。人为造成的变暖增加了大气的“干燥”，在所有其他条件相同的情况下，增加了植物和土壤表面的蒸发率，这反过来又增加了土壤水分的流失，增加了自然发生的降水不足。干旱降低了植物的光合作用和生产力，包括在自然和农业生态系统中，但人类引起的生态变化在多大程度上放大了干旱对植物生产力的影响仍不清楚。EPSCoR RII Track-4：NSF Fellowship将结合联合收割机最先进的卫星和地面植物观测与观测和模拟的气候数据，研究过去世纪气候变化对植物造成的干旱影响有多大，特别关注最近两次严重干旱期间自然与人为影响的相对贡献：2012-2015年加州干旱和2012年中西部干旱。该项目将提高我们对干旱对地球生态系统的影响因气候变化而放大的程度的认识，还将通过培训一名博士后研究人员和为爱荷华州大学的课程开发新的与气候变化有关的实验室练习，提高教育成果。人为变暖通过热引起的蒸发需求增加，加剧了自然降水不足，使土壤进一步干燥，植被受到压力。干旱频率和严重程度的人为增加可能会对生态系统功能，包括光合作用和植物生长（“初级生产”）产生巨大影响，但这种影响仍然没有得到很好的控制。虽然干旱明显降低了植被健康和初级生产力，但自然变异和人为强迫的相对作用仍然未知。以2012-2015年加州和2012年中西部严重干旱为案例研究，该项目将量化干旱导致的初级生产损失中直接归因于人为气候变化的比例，包括归因于特定的气候驱动因素（温度、蒸汽压不足、土壤湿度和太阳辐射）。这一提议的主要假设是，由于较高的温度和蒸发需求对气孔导度和光合作用的直接负面影响，人为因素对干旱引起的初级生产损失的贡献甚至大于人为因素对土壤水分损失的贡献。将使用最先进的遥感技术（例如，太阳诱发叶绿素荧光）和气候变化归因方法。本研究的最终目标是开发一个经验性的“全球变化生态学”归因框架，该框架将可移植到其他生态系统和气候变化的其他影响，包括以下各项─重点关注气候变化对全国初级生产变化的影响的工作。该奖项反映了NSF的法定使命，并通过利用基金会的知识价值和更广泛的评估被认为值得支持影响审查标准。

Droughts are among the world’s costliest natural disasters, causing severe damage to both social and ecological systems. Human-caused warming increases the “dryness” of the atmosphere and, all other things being equal, increases evaporation rates from plant and soil surfaces, which in turn increases the loss of soil moisture and worsens naturally occurring precipitation deficits. Drought reduces the photosynthesis and productivity of plants, including in both natural and agricultural ecosystems, but the extent to which human-caused ecological change has amplified the effects of drought on plant productivity still remains unclear. This EPSCoR RII Track-4:NSF Fellowship will combine state-of-the-art satellite and ground-based plant observations with observed and modeled climate data to examine how much the past century of climate change has worsened drought effects on plants, focusing specifically on the relative contributions of natural- vs. human-caused effects during two recent severe droughts: the 2012-2015 California drought and the 2012 Midwest drought. The project will improve our understanding of the extent to which the effects of drought on Earth’s ecosystems are amplified by climate change, and it will also improve educational outcomes through training of a postdoctoral researcher and development of new climate change-related laboratory exercises for courses at the University of Iowa.Droughts are among the world’s costliest natural disasters, causing severe damage to both social and ecological systems. Anthropogenic warming exacerbates natural precipitation deficits through heat-induced increases in evaporative demand, which further dries soils and stresses vegetation. Anthropogenic increases in the frequency and severity of droughts likely exert large, but still poorly constrained, impacts on ecosystem function, including photosynthesis and growth of plants (“primary production”). While drought clearly reduces vegetation health and primary production, the relative contributions of natural variability and anthropogenic forcing remain unknown. Using the severe 2012-2015 California and 2012 Midwest droughts as case studies, this project will quantify the proportion of drought-induced primary production loss that was directly attributable to anthropogenic climate change, including attribution to specific climatic drivers (temperature, vapor pressure deficit, soil moisture, and solar radiation). The primary hypothesis of this proposal is that anthropogenic contributions to drought-induced loss of primary production were even greater than anthropogenic contributions to loss of soil moisture due to the direct negative effects of higher temperatures and evaporative demand on stomatal conductance and photosynthesis. This hypothesis will be tested using state-of-the-art remote sensing techniques (e.g., solar-induced chlorophyll fluorescence) and climate change attribution methods. The ultimate goal of this research is to develop an empirical “global change ecology” attribution framework that will be portable to other ecological systems and other impacts of climate change, including follow-up work focused on the effects of climate change on nationwide changes in primary production.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.