Is the hydrological cycle (evaporation and precipitation) changing?
Overall, land precipitation for the globe has increased by ~2% since 1900, however, precipitation changes have been spatially variable over the last century. Instrumental records show that there has been a general increase in precipitation of about 0.5-1.0%/decade over land in northern mid-high latitudes, except in parts of eastern Russia. However, a decrease of about -0.3%/decade in precipitation has occurred during the 20th century over land in sub-tropical latitudes, though this trend has weakened in recent decades. Due to the difficulty in measuring precipitation, it has been important to constrain these observations by analyzing other related variables. The measured changes in precipitation are consistent with observed changes in streamflow, lake levels, and soil moisture (where data are available and have been analyzed). Northern Hemisphere annual snow cover extent has consistently remained below average since 1987, and has decreased by about 10% since 1966.
Globally-averaged land-based precipitation shows a statistically insignificant upward trend with most of the increase occurring in the first half of the 20th century. Further, precipitation changes have been spatially variable over the last century. On a regional basis increases in annual precipitation have occurred in the higher latitudes of the Northern Hemisphere and southern South America and northern Australia. Decreases have occurred in the tropical region of Africa, and southern Asia. Due to the difficulty in measuring precipitation, it has been important to constrain these observations by analyzing other related variables. The measured changes in precipitation are consistent with observed changes in stream flow, lake levels, and soil moisture (where data are available and have been analyzed).
Globally-averaged land-based precipitation shows a statistically insignificant upward trend with most of the increase occurring in the first half of the 20th century. Further, precipitation changes have been spatially variable over the last century. On a regional basis increases in annual precipitation have occurred in the higher latitudes of the Northern Hemisphere and southern South America and northern Australia. Decreases have occurred in the tropical region of Africa, and southern Asia. Due to the difficulty in measuring precipitation, it has been important to constrain these observations by analyzing other related variables. The measured changes in precipitation are consistent with observed changes in stream flow, lake levels, and soil moisture (where data are available and have been analyzed). Northern Hemisphere snow cover extent has consistently remained below average since 1987, and has decreased by about 10% since 1966. This is mostly due to a decrease in spring and summer s
Is the atmospheric/oceanic circulation changing? Is the climate becoming more variable or extreme? How important are these changes in a longer-term context? Is sea level rising? Can the observed changes be explained by natural variability? www.ncdc.noaa.gov/ol/climate/globalwarming.html OUR PLANET – GLOBAL POSITIONING Global Positioning System enters High School Curriculum – In a joint program between the National Ocean Service’s National Geodetic Survey (NGS) and the American Congress on Surveying and Mapping (ACSM), students at Springbrook High School in Silver Spring, Maryland are learning about global positioning systems (GPS) in a hands-on program for creating highly accurate maps of their school grounds. GPS became a part of the school’s curriculum in 1998 in a program entitled “Information Technology in a Global Society”. This program gives students the opportunity to use computers, telecommunications, and other emerging technologies to gather, analyze, and communicate informati
