Regionalization on the basis of the properties of hydro-meteorological data helps in identifying the regions reflecting the similar characteristics which could be useful in designing hydrological structures as well as planning and management of water resources of the region. In this study, rainfall data of northeast India were utilized for calculation of extreme precipitation indices as suggested by expert team on climate change detection and monitoring. Trend analysis of the indices was carried out using Mann-Kendall nonparametric test, and Sen's slope estimator was used for calculating the magnitude of trend. Further fuzzy c-means method was used for clustering of the selected stations on the basis of six parameters of all these precipitation indices, i.e., latitude, longitude, mean, standard deviation, minimum value and maximum value. Three cluster validity indices, namely fuzzy performance index, modified partition entropy and cluster separation index were used for selecting the optimum cluster numbers. Analysis shows insignificant trend for the indices like consecutive dry days and consecutive wet days, whereas maximum 1-day precipitation (R1 day) and maximum 5-day precipitation (R5 day) are not showing any clear trend. It is observed that the number of rainy days is decreasing followed by increasing 1-day precipitation. Cluster analysis of the precipitation indices shows five major clusters for most of the indices.
Pan evaporative changes are one of the key components of water resources management of a basin under changing climate and anthropogenic-induced warming. This study was undertaken for trans-boundary Godavari River (India) to identify trends through the Mann-Kendall (MK) test after removing the effect of significant lag-1 serial correlation from the climatic time-series by pre-whitening in pan evaporation (Epan) and in the probable causative meteorological parameters responsible for evaporative climatic changes in a large basin. Further, the Pettitt's test was applied on Epan time series for estimating the change point year of Epan to find out the effective year when the change in pattern started reflecting in the time-series. At seasonal (monthly) time scales, statistically significant decreasing trends in Epan were witnessed in pre-monsoon season (in the months of March, April and May) over all the seven sites of the Godavari basin. Four sites witnessed statistically significant increasing trends in Tmin (Tmax) in July (December) and in monsoon (post monsoon) season in the basin. Statistically significant decreasing (increasing) trends in wind speed (relative humidity) in pre-monsoon and in month of March at these seven sites support the observed decline in the evaporative demand in the basin leading to possible enhancement in the total yield of the basin. Results of stepwise regression analysis showed that wind speed followed by relative humidity was found to be two main causative parameters of the observed decline in the Epan under the warmer environments in the basin. Pettitt's test shows year 1991-1992 to be the probable year of change in the Epan in the Godavari river basin.
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