1Met Office Hadley Centre, FitzRoy Road, Exeter, UK
2NOAA's National Climatic Data Center, Asheville, NC, USA
3Cooperative Institute for Climate and Satellites North Carolina, NCSU and NOAA's National Climatic Data Center, Asheville, NC, USA
4National Physical Laboratory, Teddington, UK
5Climatic Research Unit, University of East Anglia, Norwich, UK
6Center of Excellence for Climate Change Research/Dept of Meteorology, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, P.O. Box 80234, Jeddah 21589, Saudi Arabia
Abstract. Presented herein is HadISDH: an annually-updated near-global land-surface specific humidity product providing monthly means from 1973 onwards over large scale grids. HadISDH is an update to the land component of HadCRUH utilising the global high resolution land surface station product HadISD as a basis. HadISD, in turn uses an updated version of NOAA's integrated surface database. Intensive automated quality control has been undertaken at the synoptic level, as part of HadISD processing. The data have been subsequently run through the pairwise homogenisation algorithm developed for NCDC's GHCN Monthly temperature product. Uncertainty estimates including station uncertainty and sampling uncertainty are provided at the gridbox spatial scale and monthly time scale.
HadISDH is in good agreement with existing land surface humidity products in periods of overlap. Widespread moistening is shown over the 1973–2011 period. The largest moistening signals are over the tropics with drying over the subtropics, supporting other evidence of an intensified hydrological cycle over recent years. Moistening is detectable with high (95%) confidence over large-scale averages for the globe, Northern Hemisphere and tropics with trends of 0.095 (0.086 to 0.105) g kg−1 per decade, 0.091 (0.08 to 0.103) g kg−1 per decade and 0.147 (0.133 to 0.162) g kg−1 per decade, respectively. No change (0.008 (−0.011 to 0.028) g kg−1 per decade) is detectable in the Southern Hemisphere. When globally averaged, 1998 was the moistest year since records began in 1973, closely followed by 2010, two strong El Niño years.