A History of Hydroclimatology

The science of hydroclimatology has undergone a long history of development from the speculative ideas of the ancient Greeks, to the theoretical reasoning of late Renaissance scholars, to the beginning of quantification with the basic collection of needed data in the 17th and 18th centuries, and finally to the expansion of observing networks to a near-global coverage in the last century. The development of the concept of potential evapotranspiration and its use in a climatic water budget by Thornthwaite in the middle of the twentieth century has provided a significant merging of basic hydroclimatic data to achieve useful estimates of such factors as moisture storage in the soil, water deficit, streamflow, groundwater recharge, and evapotranspiration on a daily, weekly, or monthly basis. These hydroclimatic factors have great utility in a variety of applied studies. Recent developments in hydroclimatology have involved improving data-gathering networks, achieving new understanding of the reliability and accuracy of hydroclimatic data, development of computer programs to manipulate basic hydro-climatic data, and the preparation of global distributions of different hydroclimatic factors. Significant challenges lie ahead but the field is now in a position to answer those challenges with scientific knowledge based on improved global measurements and sound theoretical reasoning. [Key words: hydroclimatology, history of climatology, water budget, moisture factor in climate.]