Abstract
In this study rainfall is calculated from Tropical Rainfall Measuring Mission (TRMM) Version 6 (V6) 3B42 datasets and calibrated with reference to the observed daily rainfall by rain-gauge collected at 15 locations over Nepal during 1998-2007. In monthly, seasonal and annual scales TRMM estimated rainfalls follow the similar distribution of historical patterns obtained from the rain-gauge data. Rainfall is large in the Southern parts of the country, especially in the Central Nepal. Day-to-day rainfall comparison shows that TRMM derived trend is very similar to the observed data but TRMM usually underestimates rainfall on many days with some exceptions of overestimation on some days. The correlation coefficient of rainfalls between TRMM and rain-gauge data is obtained about 0.71. TRMM can measure about 65.39% of surface rainfall in Nepal. After using calibration factors obtained through regression expression the TRMM estimated rainfall over Nepal becomes about 99.91% of observed data. TRMM detection of rainy days is poor over Nepal; it can approximately detect, under-detect and over-detect by 19%, 72% and 9% of stations respectively. False alarm rate, probability of detection, threat score and skill score are calculated as 0.30, 0.68, 0.53 and 0.55 respectively. Finally, TRMM data can be utilized in measuring mountainous rainfall over Nepal but exact amount of rainfall has to be calculated with the help of adjustment factors obtained through calibration procedure. This preliminary work is the preparation of utilization of Global Precipitation Measurement (GPM) data to be commencing in 2013.
Highlights
One of the most interesting aspects of weather is rainfall, and its variance from one place to another
The Tropical Rainfall Measuring Mission (TRMM) data can provide a better distribution of rainfall in mountainous region because it observes from upper side and covers wide area
Rainfall collected at 15 stations over Nepal by the Department of Hydrology and Meteorology (DHM) are utilized in calibration of TRMM rainfall during 1998-2007
Summary
One of the most interesting aspects of weather is rainfall, and its variance from one place to another. In the present work estimation of rainfall at upland region by Tropical Rainfall Measuring Mission (TRMM) data is focused on over Nepal as a pilot study. The rainfall amounts can vary significantly within a small distance. There are two basic effects on precipitation caused by mountains. There is the "orographic" effect and the "rain shadow" effect.
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