Hiroki Okachi

Hydroclimatic extremes are intensifying, escalating risks to ecosystems, infrastructure, and vulnerable communities. Rapid technological innovation and scientific discovery offer powerful tools to address these challenges, yet a gap remains between hydroclimate knowledge production and its use in decision‐making. Bridging this divide requires democratizing hydroclimate science through expanded participation in research design and implementation, as well as in the distribution of recognition, resources, and decision power. Democratizing science can foster outcomes that are (a) more credible, through transparency and integration of decision‐maker perspectives; (b) more just, through fair distribution of research opportunities, resources, recognition, and decision power; and (c) more resilient, by strengthening the capacity of communities and institutions to adapt, learn, and recover from climate pressures. Drawing on insights from the 2024 Global Energy and Water EXchanges (GEWEX) Early Career Researcher Workshop, which gathered participants from 19 countries across disciplines, we outline pathways toward more democratic hydroclimate science grounded in diverse participation and shared leadership. We highlight three priorities: building trust through co‐production, improving the usability of hydroclimate information, and promoting responsible research and innovation in emerging technologies. Case studies illustrate how early‐ and mid‐career researchers and practitioners are advancing these priorities and modeling practices that connect innovation with equity. Achieving lasting and effective change requires research and funding institutions to recognize and support collaborative leadership, and to value relevance and accountability alongside technical excellence. Strengthening such democratic frameworks can help ensure that hydroclimate science advances more just research practices and supports the resilience of the communities it serves.

Hydroclimatic extremes are intensifying, escalating risks to ecosystems, infrastructure, and vulnerable communities. Rapid technological innovation and scientific discovery offer powerful tools to address these challenges, yet a gap remains between hydroclimate knowledge production and its use in decision-making. Bridging this divide requires democratizing hydroclimate science through expanded participation in research design and implementation, as well as in the distribution of recognition, resources, and decision power. Democratizing science can foster outcomes that are (1) more credible, through transparency and integration of decision-maker perspectives; (2) more just, through fair distribution of research opportunities, resources, recognition, and decision power; and (3) more resilient, by strengthening the capacity of communities and institutions to adapt, learn, and recover from climate pressures. Drawing on insights from the 2024 Global Energy and Water EXchanges (GEWEX) Early Career Researcher Workshop, which gathered participants from 19 countries and across disciplines, we outline pathways toward more democratic hydroclimate science grounded in diverse participation and shared leadership. We highlight three priorities: building trust through co-production, improving the usability of hydroclimate information, and promoting ethical use of emerging technologies. Case studies illustrate how early- and mid-career researchers and practitioners are advancing these priorities and modeling practices that connect innovation with equity. Achieving lasting and effective change requires research and funding institutions to recognize and support collaborative leadership, and to value relevance and accountability alongside technical excellence. Strengthening such democratic frameworks can help ensure that hydroclimate science advances more just research practices and supports the resilience of the communities it serves.

海面砕波飛沫は海上での降雨観測において降雨の中に混在しうるものであり，さらに，内陸における塩害被害，降雨発生要因となる海塩粒子をもたらすものとしての意味を有する．本研究ではディスドロメータを用いた野外での海面砕波飛沫の観測を実施し，得られた粒径分布から風速の関数としての粒径分布式を提案した．同式の提案により，降雨観測時に混在しうる飛沫量の推定や塩害被害及び降雨発生要因となる海塩粒子の元となる飛沫量の推定が可能となった．

The effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and seasonality. Over the ocean, small rain and large sea spray droplets co-exist in the same diameter size class (0.072 to 1000 mm); hence, sea spray creates uncertainty when seeking to characterize the drop size distribution (DSD) of rain droplets over the ocean. We measured droplet sizes at a marine tower using a state-of-the-art optical disdrometer, a tipping-bucket rain gauge, a wind anemometer, and a time-lapse camera, over a period that included typhoon Krosa of 2019. The number of rain droplets of diameter less than 1 mm increased monotonically as the horizontal wind speed became stronger. Thus, the shape parameter μ of the Ulbrich distribution decreased. This decreasing trend can be recognized as an increase in sea spray. During no-rainfall hours (indicated by rain gauges on the ocean tower and nearby land), sea spray DSDs were obtained at various horizontal wind speeds. Furthermore, the proportions of sea spray to rainfall at different rainfall intensities and horizontal wind speeds were determined; at a horizontal wind speed of 16 to 20 m s⁻¹, the average sea spray proportions were 82.7%, 19.1%, and 5.3% during total rainfall periods of 2.1 mm h⁻¹, 8.9 mm h⁻¹, and 32.1 mm h⁻¹, respectively. Representation of sea spray DSDs, as well as rainfall DSDs, is a key element of calculating real rainfall intensities over the open ocean.