Measuring precipitation with a geolysimeter

Craig D Smith,Garth Van Der Kamp,Lauren Arnold,Randy Schmidt

doi:10.5194/hess-21-5263-2017

Craig D Smith, Garth Van Der Kamp + Show 2 more

Open Access

https://doi.org/10.5194/hess-21-5263-2017

Copy DOI

Abstract

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.

Highlights

It is well recognized that it is difficult to accurately measure solid precipitation with an accumulating precipitation gauge on account of the systematic undercatch due to wind (e.g. Sevruk et al, 1991; Goodison et al, 1998; Kochendorfer et al, 2017a)
The World Meteorological Organization (WMO) recommended that a double fence intercomparison reference (DFIR) be accepted as the standard for the measurement of solid precipitation (Goodison et al, 1998)
This study presents a novel approach for using measurements of groundwater pressure in deep observation wells as an indirect method for recording precipitation events

Summary

Introduction

It is well recognized that it is difficult to accurately measure solid precipitation with an accumulating precipitation gauge on account of the systematic undercatch due to wind (e.g. Sevruk et al, 1991; Goodison et al, 1998; Kochendorfer et al, 2017a). The World Meteorological Organization’s (WMO) Solid Precipitation Intercomparison Experiment (SPICE) as described by Nitu et al (2012) and Rasmussen et al (2012) has recently documented similar results, with Alter-shielded and unshielded gauges undercatching snowfall by an average of ∼ 40 and ∼ 60 % respectively at gauge height wind speeds of 5 m s−1 (Kochendorfer et al, 2017a) This undercatch represents a large error in precipitation measurement, especially in cold regions, and could have a significant impact on water resource forecasting, climate trend analysis, and hydrological model initialization and validation (Barnett et al, 2005; Pomeroy et al, 2007).

Objectives

Methods

Results

Discussion

Conclusion