it is emptied more than once per 24hours. Analysis of the daily rainfall and evaporation readings in areas with regular heavy rainfall events shows that almost without fail, on days with rainfall in excess of 30mm (203mm Rain Gauge) the daily evaporation is spuriously higher than other days in the same month where conditions more receptive to evaporation prevailed. The most common and obvious error is in daily rainfall events of >55mm (203mm rain gauge) where the Class A Evaporation pan will likely overflow. The less obvious, and therefore more concerning, is the influence of heavy or intense rainfall causing spuriously high daily evaporation totals without obvious overflow. Sunken Colorado pan The sunken Colorado pan is square, 0.92 m (3 ft) on a side and 0.46 m (18 in.) deep and made of unpainted galvanized iron. As the name suggests, it is buried in the ground to within about 5 cm (2 in.) of its rim. Evaporation from a Sunken Colorado Pan can be compared with a Class A pan using conversion constants. The pan coefficient, on an annual basis, is about 0.8. Symons Pan / Tank The Symons Pan / Tank is a standard instrument of the UK Met Office. It is a steel container 1.83 m (6 ft) on a side and 0.61 m (2 ft) deep, sunk into the ground with an above-ground rim of 0.076 - 0.1 m (3 - 4 in.) and is painted black internally. Its evaporation rate is lower than the Class A pan and conversion factors must be used. Decreasing Trend of Pan Evaporation Over the last 50 or so years, pan evaporation has been carefully monitored. For decades, pan evaporation measurements were not analyzed critically for long term trends. But in the 1990s scientists reported that the rate of evaporation was falling. According to data, the downward trend had been observed all over the world except in a few places where it has increased. It is currently theorized that, all other things being equal, as the global climate warms evaporation would increase proportionately and as a result, the hydrological cycle in its most general sense is bound to accelerate. The downward trend of pan evaporation has since also been linked to a phenomenon called global dimming. In 2005 Wild et al. and Pinker et al. found that the "dimming" trend had reversed since about 1990. Other theories suggest that measurements have