ABSTRACT
Rain gauges should have a sharp edge near the vertical sides (inside) to minimize rain splash (drops are either in or out). It should have a funnel with a small hole to minimize evaporation losses. Sides and funnel should be smooth, hydrophobic material to minimize loss due to wetting of the surfaces conducting water. Standard height in the U.S. is about 75 cm (30 inches). In winter, the funnel is typically removed so snow doesn’t accumulate on the funnel. Some gauges are heated in winter to melt and measure snow, but this causes some evaporation losses. Biggest issue is wind, as the turbulence causes undercatch. Most common shields to minimize this problem are Alter shield (strips of metal hanging around the perimeter) and Nipher shield (like the opening of a tuba). It latter will cause over catch in rain and hail. Ideal location is in a forest opening to minimize wind effects. Gauge should be located at a distance that is twice the height of the nearest object, which is an angle of 30 degrees from the top of the object (i.e., 60 m from a 30-m tall tree). If necessary, an angle of 45 degrees is acceptable. Wind effects can be minimized by installing the opening of the gauge at or near ground level, but this makes it harder to service and more susceptible to materials falling into the gauge and possible clogging it, for example, leaves.
