## 4 Results
### Evaluation of Changing Trends and Abrupt Transition:  
Figure 9 presents the annual trends of precipitation products and observed data for Punjab region obtained by the MK and Theil-Sen approach. The trend plots are arranged as A and B with respect to GB and SB products during the study periods 1979-2017 and 2003-2017, respectively. The results indicated that, the annual observed precipitation revealed the insignificant positive trend during the periods 1979-2017 and 2003-2017 with the rate of 1.12 and 5.5 mm/decade, respectively. All of the GB and SB products exhibited the non-significant positive trend with the different scale of overestimation, except for CRU, CPC, and UDel products, which indicates the insignificant trend with the magnitude of 0.05, \(-\)1.38, and \(-\)0.06 mm/decade, respectively. These products are relatively less accurate to detect the observed precipitation trend. Though, GPCC and TRMM products outperformed other datasets in terms of trends magnitude with the rate of 1.29 and 5.53 mm/decade, which is quite close to the magnitude of observed precipitation. The range of overestimation was higher in SB products, which could be due to the shorter time period. The highest increasing trend was indicated by APHRODITE product followed by GSMap and PERSIANN products as compared with the observed precipitation trend. Overall, the performance of GPCC and TRMM precipitation products showed better agreement in terms of trend detection when compared with the observed precipitation. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**GPPs** & **Annual** & **Winter-Monsoon** & **Summer-Monsoon** \\ \hline CRU & 1.19 & 1.24 & 1.17 \\ GPCC & 1.18 & 1.31 & 1.15 \\ APHRODITE & 1.61 & 1.48 & 1.71 \\ CPC & 1.53 & 1.47 & 1.57 \\ UDel & 1.20 & 1.33 & 1.38 \\ TRMM & 0.99 & 0.84 & 1.06 \\ CHIRPS & 1.34 & 1.37 & 1.3 \\ GSMap & 1.05 & 0.61 & 2.33 \\ PERSIANN-CDR & 1.01 & 0.92 & 1.08 \\ PERSIANN-CCS & 1.01 & 0.72 & 1.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Annual and seasonal correction factors for each GPPs over Punjab region. The abrupt changes in climate data series revealed the transition of climate from one state to another due to some external factors, which activates a change to new state at a rate determined by the climate system [74; 75]. The Sequential Mann-Kendall (SQMK) test was applied for the evaluation and comparison of different precipitation products with observed data over the Punjab region. The retrograde and progressive series were attained at 0.05 significance level. The comparative evaluation of GB and SB precipitation products with reference data using the SQMK test with the confidence interval of 95% during the study periods 1979-2017 and 2003-2017 over the Punjab region are shown in Figure 10. The results indicate that the GPCC and TRMM products exhibited a similar pattern and mutation points as compared with reference data series. However, the other products also showed the similar fluctuated pattern in progressive series as compared with the reference data, yet they failed to capture the exact temporal mutation changes. The major fluctuations in the reference data series were detected during the period of 1984-1985 (negative), 1988-1989 (positive), 1998-1999 (negative), and 2005-2006 (positive). Moreover, the reference data showed the multiple turning points in progressive data series during the whole study Period. However, the gentle increase in the precipitation trend has been observed with no significant breakpoint during the period 2005-2017. All of the GB and SB products indicated the similar pattern of variability in progressive series. However, the TRMM product showed the best agreement as compared with the reference data series during this period over the Punjab region. The inter-annual and multi-decadal temporal abrupt changes in precipitation data series depicted a large fluctuation in precipitation over the targeted region during the whole study period.