ABSTRACT

The response of the Maroon reservoir in southwest Iran is modeled to evaluate possible impacts of 21st century climate change. Projections of 3 CMIP5 General Circulation Models (GCMs) were investigated using 2 Representative Concentration Pathways (RCP4.5 and RCP8.5), which respectively represent low/medium and high greenhouse gas emission scenarios. The raw GCM projections are statistically bias-corrected to provide boundary conditions for the 3-dimensional Aquatic Ecosystem Model (AEM3D). A new overturn bias analysis method was developed to evaluate possible bias in the GCM predictors during the observational (historic) period and determined it to be negligible. The modeling results, quantified by the analysis of various limnological parameters (onset and length of mixing and stratification periods, hypolimnion and epilimnion thickness and temperature, Brunt-Väisälä frequency, and Schmidt stability) indicate for RCP4.5 a continuous reduction in winter mixing and complete suppression of mixing by the end of the 21st century, implying a switch from monomictic to weakly oligomictic behavior. Under RCP8.5, the behavior transition occurs abruptly in the late 2050s in the form of a tipping point, followed by intermittent oligomictic behavior and transition to permanent stratification (thermal meromixis) within a decade. The change in behavior occurs because the surface and mixing temperatures significantly increase due to climate warming, whereas the hypolimnion is less affected, partly because of milder warming of cold winter river inflows (underflow) and strengthening stratification. The climate change-induced tipping point for the thermal regime of Maroon reservoir might serve as an indicator of changes in other warm monomictic systems.

摘要

对伊朗西南部 Maroon 水库的响应进行建模，以评估 21 世纪气候变化的可能影响。使用 2 个代表性浓度路径（RCP4.5 和 RCP8.5）研究了 3 个 CMIP5 总循环模型 (GCM) 的预测，它们分别代表了低/中和高温室气体排放情景。原始 GCM 预测经过统计偏差校正，为 3 维水生生态系统模型 (AEM3D) 提供边界条件。开发了一种新的翻转偏差分析方法来评估观测（历史）期间 GCM 预测变量中可能存在的偏差，并将其确定为可以忽略不计。通过分析各种湖沼学参数（混合和分层期的开始和长度，下层和上层厚度和温度、Brunt-Väisälä 频率和施密特稳定性）表明 RCP4.5 冬季混合的持续减少和到 21 世纪末混合的完全抑制，这意味着从单一性向弱寡聚性行为的转变。在 RCP8.5 下，行为转变在 2050 年代后期以临界点的形式突然发生，随后是间歇性寡聚行为，并在十年内转变为永久分层（热分离）。行为发生变化的原因是由于气候变暖，地表和混合温度显着升高，而下层水温受到的影响较小，部分原因是冬季寒冷的河流流入（底流）温和升温和加强分层。