中国封建王朝长达2133年，经历了六十多个王朝，其中统一的王朝约十一个。这些王朝大多经历相似的过程，由初期的兴盛到末期的衰落，最终被新王朝取代。研究中国古代王朝兴衰可以为当代中国可持续发展及政策制定提供有效的启示。目前各领域学者已从气候变化等角度解释了朝代更替的现象，但王朝兴衰的根本原因仍是具有争议的科学问题。

本文在此背景下，选取人地关系较为简单的中国汉朝时期进行研究。基于系统动力学方法，充分考虑区域间差异，在对古代人地关系进行结构分析后，依据人口、耕地和粮食子系统中各要素间的相互作用，构建中国古代区域人地系统动力学模型，从系统的角度定量模拟研究，解释汉朝兴衰。主要结论如下：

（1）对汉朝时期区域气候与社会不稳定性进行分析，揭示了气候灾害不是造成全国饥荒、汉朝灭亡的根本原因。首先基于中国当代行政区划下六个典型省的气候干旱序列，重建了两汉时期（公元前202年至公元220年）各区域气候灾害指数序列，将其与全国饥荒指数进行相关分析，证明了汉朝时期气候灾害对社会不稳定有重要影响，但区域间差异明显，河南省气候灾害指数与全国饥荒指数相关程度最高，相关系数 ，河南省区域气候对全国社会不稳定性贡献最大。区域气候灾害指数与全国饥荒指数峰值不对应，两汉末期区域气候灾害均非各时期最大值，却引发汉朝的灭亡，由此揭示了气候灾害不是造成全国饥荒、汉朝灭亡的根本原因。

（2）构建中国古代区域人地系统动力学模型，验证了该模型能有效反映中国古代汉朝历史情况。综合考虑气候条件、政府效率、医疗水平、生产技术水平、交通条件等要素的影响，基于系统动力学方法，根据人口、耕地和粮食子系统间的反馈机制建立中国古代区域人地系统动力学模型。对西汉、东汉时期历史情况进行模拟，模型可通过有效性检验，能真实的反映中国古代汉朝人地关系的基本情况。

（3）分别对中国古代区域人地系统动力学模型在汉朝历史情况及不同模拟情景下进行模拟，总结得到政府效率是汉朝灭亡的根本原因。历史情况模拟结果表明汉朝全国尺度的饥荒从未发生，气候灾害导致的粮食短缺不是汉朝灭亡的根本原因；而部分典型区域在汉朝末期出现局部饥荒，低于饥荒临界值，诱发农民起义。通过对模型中相关参数的调控，设置亩产水平提高情景、医疗水平提高情景和政府效率提高情景，并将不同模拟情景结果与历史情况比较。结果表明，亩产水平提高或医疗水平提高时，部分区域的人均粮食供应量仍低于饥荒临界值，依然会发生区域饥荒引发农民起义，最终导致汉朝的灭亡；政府效率提高时，粮食运输状况良好，区域的粮食短缺可通过政府组织高效的粮食运输得到缓解，人均粮食供应量均不会低于饥荒临界值，不会发生区域的粮食安全隐患导致的汉朝灭亡。因此我们认为政府效率是导致汉朝灭亡的根本原因。

Chinese feudal dynasty lasted for 2133 years and experienced more than 60 dynasties, including about 11 unified dynasties. Most of these dynasties experienced a similar process, from the initial prosperity to the final decline, and finally replaced by the new dynasty. The study of the collapse of ancient Chinese dynasties can provide effective enlightenment for contemporary Chinese sustainable development and policy-making. At present, scholars in various fields have explained the phenomenon of dynasty cycle from climate change, but the fundamental of the collapse of the dynasty is still a controversial scientific issue.

In this context, the paper studyed the Han dynasty in which the human-land relationship was relatively simple. Using the method of system dynamics and having considered the regional differences, we built the ancient Chinese regional human-land system dynamics model based on the interactions among different factors in the population, cultivated land and also food subsystem after a structural analysis of the ancient human-land system. From the viewpoint of this system, we explained the collapse of the Han dynasty by quantitative simulation. The main conclusions are as follows:

(1) After analyzing the regional climate and social instability in the Han dynasty, the result shows that climate disasters were not the fundamental cause of the nationwide famine or the collapse of Han Dynasty. Firstly, based on the drought series of six nowaday relevant provinces, we rebuild the climate disaster index series of those regions in the Han dynasty (202B.C.- 220A.D.) and compare it with the index of nationwide famine. The result shows that climate disasters had a significant impact on social instability. The impact differed from each other in different regions, and the climate disaster index of Henan province was the most correlated with the nationwide famine index, the correlation coefficient was 0.1377, so Henan province contributed the most in the instability of the country. The peak of regional climate disaster index doesn’t correspond to the peak of nationwide famine. The regional climate disaster index in the late Han dynasty doesn’t reach its maximum value in different periods, either. However, Han dynasty still came to an end. This can prove that climate disasters were not the fundamental cause of the downfall of the Han dynasty.

(2) By building an ancient Chinese regional human-land system dynamics model, we can simulate the real situation in Han dynasty. Having taken into account of factors such as climate conditions, government efficiency, medical level, production technology and traffic conditions, we then develop the model based on system dynamics method and the feedback mechanism between population, cultivated land and food systems. This model is able to simulate the real situation in Western Han dynasty and Eastern Han dynasty, and reflect the basic situation of human-land relationship in Han dynasty by means of validity test.