Temporal trends in United States dew point temperatures

Abstract

In this study, hourly data for the 1951–1990 period for 178 stations in the coterminous United States were used to establish temporal trends in dew point temperature. Although the data had been quality controlled previously (Robinson, 1998. Monthly variations of dew point temperatures in the coterminous United States. International Journal of Climatology 18: 1539–1556), comparisons of values between nearby stations suggested that instrumental changes, combined with locational changes, may have modified the results by as much as 1°C during the 40‐year period. Nevertheless, seasonally averaged results indicated an increase over much of the area, of slightly over 1°C/100 years in spring and autumn, slightly less than this in summer. Winter displayed a drying of over 1°C/100 years. When only the 1961–1990 period was considered, the patterns were similar and trends increased by approximately 1–2°C/100 years, except in autumn, which displayed a slight drying. Analyses for specific stations indicated periods of both increasing and decreasing Td, the change between them varying with observation hour. No single change point was common over a wide area, although January commonly indicated maximum values early in the period in the east and west, and much later in the north‐central portion. Rates of increase were generally higher in daytime than at night, especially in summer. Investigation of the inter‐decadal differences in dew point, as a function of wind conditions, indicated that changes during calm conditions were commonly similar in magnitude to that of the overall average changes, suggesting an important role for the local hydrologic cycle in driving changes. Other inter‐decadal changes could be attributed to the changes in the frequency and moisture content of invading air‐streams. This was particularly clear for the changes in north–south flow in the interior. Copyright © 2000 Royal Meteorological Society

A critical overview of pan evaporation trends over the last 50 years

“…This is similar for other meteorological variables. For example, rates of dew point temperature increase were 0.42 • C/100a for a 1951-1990 dataset, but 2.16 • C/100a for a 1961-1990 dataset (Robinson 2000). Hutchinson et al (2005) reported that the 1970s dominated the period of declining pan evaporation in Australia but that in the mid-1990s there was a switch to a continental average increasing pan evaporation trend.…”

“…However, this does not imply that the dew point must also be increasing faster than average temperature. The overall dew point for 178 stations in USA in the last 50 years has been increased by 0.42 • C/100 year (Robinson 2000). But it is "attributed to a range of changes, from changes in the frequency of the various 'air mass' types influencing a station, to changes in the intensity of one or more these air masses, and to changes in the local vertical exchanges of energy and moisture" (Robinson 2000).…”

“…The overall dew point for 178 stations in USA in the last 50 years has been increased by 0.42 • C/100 year (Robinson 2000). But it is "attributed to a range of changes, from changes in the frequency of the various 'air mass' types influencing a station, to changes in the intensity of one or more these air masses, and to changes in the local vertical exchanges of energy and moisture" (Robinson 2000). The increase of dew point could be the result of higher humidity, which is partly caused by changes in evaporation rate (Robinson 2000), because dew point temperature is a function of specific humidity and atmospheric pressure (Gaffen and Ross 1999).…”

“…But it is "attributed to a range of changes, from changes in the frequency of the various 'air mass' types influencing a station, to changes in the intensity of one or more these air masses, and to changes in the local vertical exchanges of energy and moisture" (Robinson 2000). The increase of dew point could be the result of higher humidity, which is partly caused by changes in evaporation rate (Robinson 2000), because dew point temperature is a function of specific humidity and atmospheric pressure (Gaffen and Ross 1999). As these changes are different from station to station, the dew points can be increasing at one station and decreasing at another, or increasing in a season and decrease in another (Robinson 2000).…”

“…The increase of dew point could be the result of higher humidity, which is partly caused by changes in evaporation rate (Robinson 2000), because dew point temperature is a function of specific humidity and atmospheric pressure (Gaffen and Ross 1999). As these changes are different from station to station, the dew points can be increasing at one station and decreasing at another, or increasing in a season and decrease in another (Robinson 2000). The national average unweighted 178 station values indicate the dew point temperature increase by 1.44 • C/100a, 0.63 • C/100a, 1.43 • C/100a, and −1.82 • C/100a for the spring, summer, autumn, and winter seasons, respectively during 1951-1990 period (Robinson 2000).…”