Needs of GCOS and GTOS for hydrological observations were discussed in a number of presentations, starting from the opening addresses of representatives of the two Global Observing Systems. However, during the meeting, several speakers recognized that GTOS had many data needs that had not yet been developed, hence the meeting concentrated on those variables that were required by the climate community.
The meeting decided to divide the hydrological variables of interest to global observing systems into two groups of variables which were each considered by a subgroup of participants. The first subgroup, chaired by Mr Cilhar, dealt with precipitation, both a real and point, evapotranspiration, snow cover area and snow water equivalent. The responsibility of the second subgroup, chaired by Mr Bonell, was to consider surface water - discharge and runoff, surface water storage flux, freshwater flux to oceans, biogeochemical material transport to oceans and groundwater storage fluxes. In addition, it was found necessary to consider the lake and river freeze-up and break-up. The chairman of the meeting presented the subgroup with a questionnaire covering a number of aspects germane to items 4 to 7 of the agenda. This is attached as Annex 7. In responding to the questionnaire, participants assessed each of the hydrological variables compiled in the report of the GCOS/GTOS Terrestrial Observation Panel and, where necessary, suggested additional variables. The meeting also analyzed the accuracy specification. The results of deliberations for each variable considered are compiled in Annex 8.
The meeting stressed the importance of precipitation as the output process from meteorological and climatological systems and the input process to hydrological system. Due to the cross-cutting nature of precipitation it was proposed that precipitation should be considered as both a meteorological and a hydrological variable. As snow and ice are also hydrological elements, it was decided to include also relevant considerations of these elements.
The meeting noted that the use of two variables - surface water discharge and runoff is confusing. Since the word runoff, as used in the literature, has a number of different meanings, it was recommended that discharge be the only variable listed.
