Testing and Development of Transfer Functions for Weighing Precipitation Gauges in WMO-SPICE

Abstract

Weighing precipitation gauges are used widely for the measurement of all forms of precipitation, and are typically more accurate than tipping-bucket precipitation gauges. This is especially true for the measurement of solid precipitation; however, weighing precipitation gauge measurements must still be adjusted for undercatch in snowy, windy conditions. In WMO-SPICE (World Meteorological Organization Solid Precipitation InterComparison Experiment), different types of weighing precipitation gauges and shields were compared, and adjustments were determined for the undercatch of solid precipitation caused by wind. For the various combinations of gauges and shields, adjustments using both new and previously existing transfer functions were evaluated. For most of the gauge and shield combinations, previously derived transfer functions were found to perform as well as those more recently derived. This indicates that wind shield type (or lack thereof) is more important in determining the magnitude of wind-induced undercatch than the type of weighing precipitation gauge. It also demonstrates the potential for widespread use of the previously developed transfer functions. Another overarching result was that, in general, the more effective shields, which were associated with smaller unadjusted errors, also produced more accurate measurements after adjustment. This indicates that although transfer functions can effectively reduce measurement biases, effective wind shielding is still required for the most accurate measurement of solid precipitation.

Adjustment of measurement errors to reconcile precipitation distribution in the high‐altitude Indus basin

“…A large part of precipitation in the high‐altitude Indus basin falls as snow, which is more susceptible to under‐catch even at moderate wind speeds. The largest corrections were found for wind‐induced under‐catch of solid precipitation, which is in line with the results of previous studies (e.g., Legates and Willmott, ; Goodison et al, ; Adam and Lettenmaier, ; Michelson, ; Ye et al, ; Yang et al, ; Chen et al, ; Wolff et al, ; Kochendorfer et al, ; Kochendorfer et al, ). However, liquid precipitation under‐catch, wetting loss and trace precipitation loss are also important, particularly in low‐altitude and relatively dry areas.…”

“…Hence, its accuracy is essential as errors in precipitation estimates may translate into major changes in the water budget of a particular region. However in many areas, precipitation measurements are still subject to significant errors and a large uncertainty (Kochendorfer et al, ; Kochendorfer et al, ) often leading to a substantial underestimation of the actual precipitation. The situation is particularly serious in the high‐altitude Indus basin where biased distribution and lack of the observed data further worsen the problem.…”

Correction of precipitation measurement for weighing precipitation gauges in a glacierized basin in the Tianshan Mountains

“…The tenfold cross-validation reported by Kochendorfer et al (2018) was applied in this paper. Here, 90% of the data were used to derive the functional coefficients, which were then tested on the remaining 10% of the data.…”