Articles | Volume 21, issue 10
Hydrol. Earth Syst. Sci., 21, 5263–5272, 2017

Special issue: The World Meteorological Organization Solid Precipitation...

Hydrol. Earth Syst. Sci., 21, 5263–5272, 2017

Research article 19 Oct 2017

Research article | 19 Oct 2017

Measuring precipitation with a geolysimeter

Craig D. Smith1, Garth van der Kamp2, Lauren Arnold1, and Randy Schmidt2 Craig D. Smith et al.
  • 1Environment and Climate Change Canada, Climate Research Division, Saskatoon, S7N 3H5, Canada
  • 2Environment and Climate Change Canada, Watershed Hydrology and Ecology Research Division, Saskatoon, S7N 3H5, Canada

Abstract. Using the relationship between measured groundwater pressures in deep observation wells and total surface loading, a geological weighing lysimeter (geolysimeter) has the capability of measuring precipitation event totals independently of conventional precipitation gauge observations. Correlations between groundwater pressure change and event precipitation were observed at a co-located site near Duck Lake, SK, over a multi-year and multi-season period. Correlation coefficients (r2) varied from 0.99 for rainfall to 0.94 for snowfall. The geolysimeter was shown to underestimate rainfall by 7 % while overestimating snowfall by 9 % as compared to the unadjusted gauge precipitation. It is speculated that the underestimation of rainfall is due to unmeasured run-off and evapotranspiration within the response area of the geolysimeter during larger rainfall events, while the overestimation of snow is at least partially due to the systematic undercatch common to most precipitation gauges due to wind. Using recently developed transfer functions from the World Meteorological Organization's (WMO) Solid Precipitation Intercomparison Experiment (SPICE), bias adjustments were applied to the Alter-shielded, Geonor T-200B precipitation gauge measurements of snowfall to mitigate wind-induced errors. The bias between the gauge and geolysimeter measurements was reduced to 3 %. This suggests that the geolysimeter is capable of accurately measuring solid precipitation and can be used as an independent and representative reference of true precipitation.

Short summary
This research provides an example of how groundwater pressures measured in deep observation wells can be used as a reliable estimate, and perhaps as a reference, for event-based precipitation. Changes in loading at the surface due to the weight of precipitation are transferred to the groundwater formation and can be measured in the observation well. Correlations in precipitation measurements made with the geolysimeter and the co-located sheltered precipitation gauge are high.