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Comparison of Gridded Rainfall Estimates with Gauge Rainfall during the South-West Monsoon Period in the Wet-Zone of Sri Lanka

Malinda Millangoda

In this day and age, multiple numbers of gridded rainfall estimates are available. These estimates are used in diverse fields of interests including meteorological and climatic studies. Considering, meteorology and climate studies, rainfall estimates are used to monitor hydro meteorological hazards and for agricultural purposes. The most commonly used and the most reliable way of monitoring rainfall are to use rainfall gauges. However, this could be a costly affair considering the equipment, maintenance and training required to run such a rainfall gauge network. Moreover, it is also difficult to cover a large area of land with point rainfall gauges. In this background, estimated gridded rainfall products are used in analysing rainfall which will give a homogenous rainfall dataset which could be easily arranged and used in data analysis and studies. In this comparison, Climate Hazards Group Infrared Precipitation with Station data (CHIRPS), Global Precipitation Climatology Centre (GPCC) and European Centre for Medium Range Weather Forecast (ECMWF) ERA-5 reanalysis data is compared with gauge rainfall data of the gauge network maintained by the Department of Meteorology, Sri Lanka. Multiple statistical parameters such as Correlation Coefficient (CC), Root Mean Square Error (RSME) and bias values were used in determining what source of rainfall estimate data better represents the observed rainfall over Sri Lanka during the south-west monsoon period. This study revealed that GPCC rainfall data of resolution (0.25° x 0.25°) best represents the gauge rainfall data for the selected points.