『Abstract
　One of the more important questions in hydrology is: if the climate warms in the future, will there be an intensification of the water cycle and, if so, the nature of that intensification? There is considerable interest in this question because an intensification of the water cycle may lead to changes in water-resource availability, an increase in the frequency and intensity of tropical storms, floods, and droughts, and an amplification of warming through the water vapor feedback. Empirical evidence for ongoing intensification of the water cycle would provide additional support for the theoretical framework that links intensification with warming. This paper briefly reviews the current state of science regarding historical trends in hydrologic variables, including precipitation, runoff, tropospheric water vapor, soil moisture, glacier mass balance, evaporation, evapotranspiration, and growing season length. Data are often incomplete in spatial and temporal domains and regional analyses are variable and sometimes contradictory; however, the weight of evidence indicates an ongoing intensification of the water cycle. In contrast to these trends, the empirical evidence to date does not consistently support an increase in the frequency or intensity of tropical storms and floods.

Keywords: Global water cycle; Climate change; Global change; Hydrologic time series; Precipitation; Evaporation; Hydrologic cycle』

『要旨
　水文学でより重要な疑問の一つは次のようである：将来もし気候が暖かくなれば、水循環は強くなるか？　そしてそうならばその強さの性質は？　この疑問にはかなり関心がある、なぜなら水循環の強さは、水資源の利用しやすさの変化、熱帯の嵐・洪水・干ばつの頻度と強度の増大、そして水蒸気フィードバックを通じた温暖化の増幅をもたらすであろうからである。今進んでいる水循環の増大についての経験的な証拠は、温暖化の増大と結びつく理論的な枠組みに新たな支持を与えているのかもしれない。本論文は、降水量・流出量・対流圏水蒸気・土壌水分・氷河質量バランス・蒸発・蒸発散・成長する季節の長さを含む水文的な変数における歴史的傾向に関する科学的な現状を簡単にレビューしている。』

1. Introduction
2. Trends in hydrologic variables
3. Trends in evaporation and evapotranspiration
4. Summary
Acknowledgements
References