农田灌溉对气候的影响研究综述

过去200年全球灌溉农田面积迅速扩张,灌溉对气候的影响逐渐受到世界各国研究者的关注。回顾了过去有关灌溉对气候的影响研究,归纳了前人的研究手段,指出了目前研究中存在的问题和困难,并提出了未来灌溉对气候的影响研究应该注重如下几个方面:1)同时利用观测数据分析方法和模型模拟研究方法进行灌溉对区域气候的影响,并将两者的结果进行对比分析,以求做到互相验证;2)对于缺乏地面观测数据或者地面数据受其他因素(比如:城市化)影响大的区域,建议利用遥感观测数据进行灌溉对地表参数的影响研究;3)注意对灌溉四大属性(灌溉位置、灌水量、灌溉方式和灌溉时间)的精确模拟,可以考虑耦合气候模型和作物模型进行模拟研究,并注意区分灌溉旱地和灌溉水田。4)提倡利用多模式集合的方式研究灌溉对区域气候的影响,以减少灌溉对气候影响(强度和方向)模拟结果的不确定性;5)未来也应该考虑模拟灌溉和气候变化间的互馈影响。

Impact of Irrigation on Climate

Irrigation is one of the most important land management techniques used to grow crops in dry areas and increase food production. The use of agricultural irrigation has grown rapidly over the past 200 years. In theory, an agricultural irrigation system can impact climate in several ways, both directly and indirectly. Excessive evapotranspiration (ET) resulting from irrigation in an agricultural system increases water vapor in the atmosphere. Water vapor is the most dominant greenhouse gas, and it amplifies the warming effect of increased atmospheric levels of carbon dioxide. This is regarded as a positive feedback in our climate system. Some reports have linked water vapor to changes in convection and precipitation patterns. ET also brings about changes in the land surface energy partition, and it cools the land surface and reduces the near-surface air temperature. Irrigation also increases soil moisture, which can modify the radiative properties of the soil (such as its albedo), control the partitioning of the heat flux, impact land surface processes, and influence the regional climate system. The tremendous increase in irrigated areas and the potential impact of irrigation on climate may have contributed to the formation of the current climate system, and it has the potential to influence our future climate system as well. Hence, it is important to explore the impact of irrigation on the near-surface climate. Such information can improve our understanding of how human activities affect climate. It can also be used to guide policies aimed at mitigating or adapting to climate change, and it can help build a precise model to project the future impact of irrigation on climate systems and irrigation requirements under future scenarios. As a result, researchers from all over the world have been focusing more attention on the impacts of irrigation on climate. So far, there have been a number of reports on the impact of irrigation on near-surface air temperature, energy fluxes, groundwater, water vapor, and precipitation based on climate observations and modeling studies. This paper reviewed the published studies on the impact of irrigation on climate, summarized the methods used by previous researchers, identified the shortcomings of current studies and the challenges of studying the impact of irrigation on climate, and finally we made suggestions regarding the directions of future research. First, a comprehensive evaluation method needs to be developed in which evidence from both observational studies (remote sensing and meteorological measurement) and modeling studies can validate each other. Second, remote sensing observation is a promising tool since it can provide land parameter information on a large scale, including soil moisture, albedo, land surface temperature, vegetation cover, and so on. It could be a valid method to determine the impact of irrigation on the local surface climate, especially in those regions where direct observations are limited or obscured by other factors, such as urbanization. Third, to avoid overestimating or underestimating the impact of irrigation, the modeling study should reflect reality as much as possible, taking into account such factors as irrigation patterns (spray irrigation, flood irrigation, or drop irrigation), rate, location, and time. Combining a crop growth model with a climate model could be a promising solution. Fourth, simulating the impact of irrigation on climate by using multiple-model ensembles can eliminate the uncertainties in the simulation results obtained from a simulation that uses only one model. Fifth, the interaction between irrigation and climate needs to be explored in future research.