Changes in Regional Hydroclimatology and Water Resources on Seasonal to Interannual and Decade‐to‐Century Timescales

Abstract

Precipitation, runoff, snowpack, and other elements of the hydrologic cycle respond to climate change on many different timescales. Responses are typically regional rather than local and are linked to large‐scale features of the general circulation of the atmosphere. Changes in regional hydroclimatology are important to water resources in most parts of the world, but especially in arid and semiarid regions that are often plagued by chronic shortfalls of water. Instrumental records of precipitation and streamflow indicate that changes on decadal‐and‐longer timescales have been large enough to be of practical importance, and paleoclimatic records suggest that even larger changes have occurred over the past few centuries. Tree‐ring records are perhaps the most useful of the paleoclimatic resources for extracting hydroclimatic estimates with annual resolution. Paleolimnological data has also figured prominently in pointing out possible large changes in regional hydroclimatology prior to the start of the tree‐ring record. In North America, multiple types of proxy records suggest low‐frequency variance in runoff may have been amplified about 500 years ago, with associated multidecadal periods of drought and wetness.