SGER: Seasonal Cycle of Drought in Coupled Climate Models and its Implication for the Hydro-ecosystem

这是气候变率和可预测性计划（CLIVAR）试点项目DRICOMP下的一笔拨款，该项目是干旱耦合模式项目的一部分，重点是对干旱机制进行初步探索，因为它们在全球气候模型的输出中有所体现，并试图评估这些模型在模拟干旱方面的可靠性。这项研究探讨了如果揭示了干旱的季节周期，就能更好地理解干旱的严重程度这一假设的含义。例如，干旱发生在旱季的影响比发生在雨季的影响更大。研究人员将在对总降水变化的典型分析之外，利用新获得的耦合模式比对项目3 （CMIP3）模式探索降水变化的季节周期。将对20世纪的控制气候模拟进行分析，并与观测结果进行比较，初步评估其季节周期及其年平均值的真实性。在这样做的过程中，将会发展出一个区域相关的标准，可能对评估预测的气候变化有用。然后，利用所有存档模式对20世纪至未来的降水变化进行分析。它们的季节周期，特别是旱季行为将得到强调，具有较强信号的区域将按季节进行分类，从而初步了解未来干旱的可能性和机制。重点将放在三个地区：密西西比盆地、萨赫勒地区和亚马逊地区，这三个地区代表了三种不同的气候制度，对经济和环境都具有重要意义。典型CMIP3模式预估的未来降水、温度、土壤湿度和其他相关变量的变化将用于驱动陆地表面和动态植被耦合模式VEGAS。因此，将评估生态系统和水循环对不同季节周期特征变化的敏感性。模拟的土壤湿度和植被状态将与传统的干旱指数（如降水异常、Palmer干旱严重指数（PDSI）和标准化降水指数（SPI））进行比较。这些分析可能有助于回答一个重要的问题，即传统的干旱指数在描述和预测水文生态系统的未来变化方面是否足够。这些研究的更广泛影响在于它对评估气候变暖时干旱风险的贡献。该项目将涉及一名研究生，并将为她/他提供一个月的支持。

This is a grant under a Climate Variability and Predictability (CLIVAR) Program pilot project called DRICOMP, for the Drought in Coupled Models Project, which focuses on making initial explorations into the mechanisms of drought as they are represented in the output of global climate models and on attempting to assess the reliability of these models in simulating drought.This research explores implications of the hypothesis that the severity of drought is better understood if its seasonal cycle is revealed. For example, the impact of a drought is greater when it occurs during the dry season than during the wet season. The investigators will explore the seasonal cycles of precipitation changes in the newly available Coupled Model Intercomparison Project 3 (CMIP3) models, going beyond the typical analysis of total precipitation change. The 20th century control climate simulations will be analyzed and compared with observations, in an initial effort to assess the realism of their seasonal cycles as well as their annual means. In doing so, a region-dependent criterion will be developed that may be useful for evaluating predicted climate change. Then, precipitation changes from the 20th century to the future from all the archived models will be analyzed. Their seasonal cycles, especially the dry season behaviors, will be emphasized, and regions with more robust signals will be classified by seasons, providing initial insights into the likelihood and the mechanisms of future droughts. The focus will be on three regions: the Mississippi basin, the Sahel, and the Amazon, which represent three distinct climatic regimes and which have great economic and environmental significance. The projected future changes in precipitation, temperature, soil moisture and other relevant variables from representative CMIP3 models will be used to drive a coupled land-surface and dynamic vegetation model, VEGAS. The ecosystem and water cycle sensitivity to different characteristic changes in seasonal cycles will thus be assessed. The simulated soil moisture and vegetation state will be compared to traditional drought indices such as the precipitation anomaly, the Palmer Drought Severity Index (PDSI), and the Standardized Precipitation Index (SPI). These analyses may help answer the important question of how adequate are the traditional drought indices for the purposes of characterizing and predicting future changes in the hydro-ecosystem. Broader impacts of the studies are in its contribution to assessing the risk of drought in a warmer climate. The project will involve a graduate student and will provide her/him with one month of support.