We examined the usefulness of a paddy field dam for flood mitigation during extreme storm events, probably induced by effects of future climate change, at a small paddy field catchment. First, after validating the developed rainfall runoff model with a drainage control function by paddy field dam, we confirmed the runoff control effects of a paddy field dam for Typhoon Hagibis in 2019. Then, paddy field dam effects on runoff control were evaluated under climate change conditions by application of current and future projected rainfall data. The paddy field dam installation was estimated to lower the maximum drainage channel water depth by 0.10 m to 0.16 m and to delay the emergence of runoff peak by 60 min during Typhoon Hagibis. Simulation results showed that the paddy field dam did not necessarily perform in terms of the current paddy levee height. In fact, for current and future climatic rainfall data estimated at the four sites in the Abukuma River Basin, results show that overflow from the paddy levee occurred because of the rapid increase in water depth in paddy fields resulting from runoff control. By contrast, a paddy field dam might reduce the rapid rise in the drainage channel water depth and reduce the risk of flooding, even under future climatic rainfall conditions, by raising the paddy levee height to a maximum of 0.42 m to prevent overflow. In conclusion, paddy field dams can be effective for climate change adaptation in conjunction with raising of the paddy levee height.

　How do China and India present official information related to climate change to international society? These countries hold the most important key to how economically developing countries should approach climate change issues. Regarding the effects of climate change on water resources in such countries, the paper presents analyses of the National Communications and Biennial Update Report submitted to the Secretariat under the United Nations Framework Convention on Climate Change. These reports explain details of the tight water supply and demand situations in China and India exacerbated by population growth and economic development, which is worsened further by climate change. Floods and droughts exert the greatest effects of climate change on water resources. Both countries are appealing to the international community with specific figures. Water resource data were once considered confidential information and were given careful handling. However, the background of active disclosure of information by both countries is fulfillment of the responsibilities of economically developing countries under the treaty. With historical responsibility, one might infer that economically developed countries intend to meet such promises.

　Over the past twenty years, vast amounts of quantitative and qualitative information have been created on climate change and its impact on society. However, various issues still remain until such information can be widely utilized by national and local governments and enterprises. Here, the authors, who have long been involved in research on climate projection and impact assessment, discussed various obstacles that are currently seen and clues to the solution. As a result, the communities of climate projection, impact assessment, and users have their own premises and expectations for other communities, hence there is a gap between them. For the solution, it is important to collaborate among the communities of climate projection, impact assessment, and users. Specifically, it was shown that it is necessary to improve mutual information exchange and coordination before the information is created, and to develop the institution and facilities for realizing it.