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Delineation of homogeneous reference evapotranspiration (ET0) regions is essential for different applications in hydro‐meteorology. In conventional regionalization approaches, lumped (time‐invariant) statistics such as mean, median or interquartile range of different hydrometeorological variables are often considered as attributes to delineate regions. Information on temporal dynamics of those variables is not utilized (as it is lost in lumped statistics), which if accounted could yield better regions. To address this, a new regionalization approach is presented in fuzzy framework in this Part 1 of a two‐part series. In the proposed approach, information on temporal dynamics of predictor climate variables influencing ET0 is used for regionalization, and the delineated regions are subsequently validated for homogeneity using the predictand (ET0) related information. Effectiveness of the approach is demonstrated through a case study on India, which yielded 18 regions. They are shown to be statistically more homogeneous in ET0 when compared to the existing agro‐ecological zones and regions formed using global fuzzy c‐means clustering method. The homogeneous ET0 regions were found to be different from homogeneous actual evapotranspiration (ETa) regions delineated over India using the fuzzy dynamic clustering approach. Various applications of the homogeneous ET0 regions formed using the proposed approach are presented in Part 2 of this series. [ABSTRACT FROM AUTHOR]

Geostationary satellites provide measurements over a wider geographical area with high temporal sampling, while microwave measurements are more accurate but sparse. For continuous monitoring of the Indian monsoon, geostationary platform would be ideal. In this study, INSAT ( Indian National Satellite) Multi-spectral Rainfall Algorithm ( IMSRA) has been used for the estimation of rainfall from Kalpana-1 very high resolution radiometer ( VHRR) measurements. IMSRA benefits from the relative advantages of infrared and microwave sensors and is operational at the India Meteorological Department ( IMD). In this paper, rainfall is estimated over India at meteorological sub-divisional scale during the south-west monsoon season of 2009 using Kalpana-1 satellite measurements. This is the first experimental attempt to generate meteorological sub-divisional scale rainfall maps using Kalpana-1 satellite measurements. The rainfall maps for the south-west monsoon season over the Indian land region are successfully utilised as a space input for the drought monitoring of the year 2009. The results have been compared with the IMD gauge-based accumulated rainfall maps at monthly and seasonal time scales. The qualitative comparison suggests that rainfall maps generated using the present methodology is in good agreement with the IMD rainfall maps. The quantitative comparison of the sub-divisional monthly accumulated rainfall shows a correlation of 0.77 and standard error of 71 mm over the non-orographic regions, whereas a correlation of 0.60 and standard error of 117 mm is observed over the orographic regions. The present study shows that Kalpana-1 satellite-based rainfall estimates ( IMSRA technique) can act as a complementary tool for the monsoon monitoring over the Indian meteorological sub-divisions and can be used for various meteorological and hydrological applications. [ABSTRACT FROM AUTHOR]