# Evaluating CHIRPS and ERA5 for Long-Term Runoff Modelling with SWAT in Alpine Headwaters
## 3 Results
### Performance Evaluation Using Hydrological Model
The model results show that the alternating \(TP\) performance in the pilot catchments is followed by alternating \(TQ\) performance. The CHIRPS shows a lower uncertainty than ERA5 in catchment b1 with underestimated annual \(TP\) and \(TQ\) (\(PB\_TP=-5\%\), \(PB\_TQ=-14\%\)), while the ERA5 shows a lower uncertainty than CHIRPS in catchment b3 with overestimated annual \(TP\) and \(TQ\) (\(PB\_TP=18\%\), \(PB\_TQ=26\%\)). When compared to the \(TQ\) generated with measured precipitation (MEAS), both GPPs generate a lower annual \(TQ\) uncertainty than the \(TQ\) generated with the measured precipitation (MEAS) in catchment b1 (\(PB\_TQ=-13\%\) CHIRPS, \(-25\%\) ERA5, \(-41\%\) MEAS) and in catchment b2 (\(PB\_TQ=35\%\) CHIRPS, \(27\%\) ERA5, \(44\%\) MEAS). The CHIRPS-generated \(TQ\) bias is consistent with the \(TP\) bias for the annual and warm season trend (\(B\_TP<0\) and \(B\_TQ<0\) in b1; \(B\_TP>0\) and \(B\_TQ>0\) in b3) and for the cold season trend in b3 (\(B\_TP<0\) and \(B\_TQ<0\)). The ERA5 generates inconsistent bias between \(TQ\) and \(TP\) for the annual and warm season trend in b1 (\(B\_TP>0\) and \(B\_TQ<0\)). For the seasonal time step, both GPPs generate a higher \(TQ\) uncertainty in the warm season (\(MAE\_TQ_{warm}=13.5\) mm \(10\)y\({}^{-1}\) CHIRPS, \(16.7\) mm \(10\)y\({}^{-1}\) ERA5) than in the cold season (\(MAE\_TQ_{cold}=3.8\) mm \(10\)y\({}^{-1}\) CHIRPS, \(6.0\) mm \(10\)y\({}^{-1}\) ERA5), which is consistent with a higher \(TP\) error in the warm season (\(MAE\_TP_{warm}=38\) mm \(10\)y\({}^{-1}\) CHIRPS, \(25\) mm \(10\)y\({}^{-1}\) ERA5) than in the cold season  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline
**Matrix** & **Product** & **mean \(a\)** & **Annual** & \multicolumn{3}{c|}{ \begin{tabular}{c} **mean** \\ **tr** \\ \end{tabular}  } & \multicolumn{3}{c|}{ \begin{tabular}{c} **norm** \\ **tr** \\ \end{tabular}  } & \multicolumn{3}{c|}{ \begin{tabular}{c} **norm** \\ **tr** \end{tabular}  } & \multicolumn{3}{c|}{ \begin{tabular}{c} **Cold** \\ **m** \\ \end{tabular}  } & \multicolumn{3}{c}{\ \begin{tabular}{c} **mean** \\ **m** \\ \end{tabular}  } & \multicolumn{3}{c}{ \begin{tabular}{c} **Monthly** \\ \end{tabular}  } \\ \hline \multicolumn{2}{c}{} & **outlet** & \multicolumn{3}{c|}{b1. JNN} & b3.1 LE & \multicolumn{3}{c|}{b1. JNN} & b3.1 LE & \multicolumn{3}{c|}{b1. JNN} & b3.1 LE \\ \hline \(TQ\) & OBS & _40.2_ & 30.4 & 50.0 & _19.8_ & 9.9 & _29.6_ & (? )20.5 & _(? )20.6_ & _(? )20.3_ & _3.4_ & _2.6_ & _4.2_ \\ \((\)mm\(10)^{-1}\()\) & CHIRPS & (\(\star\))46.9 & 26.3 & (? )67.5 & (\(\star\))30.2 & 6.8 & (\(\star\))53.6 & (\(\star\))16.7 & 19.5 & (\(\star\))13.9 & _3.9_ & _2.2_ & _5.6_ \\ ERA5 & _43.2_ & 22.9 & 63.6 & _24.1_ & \(-\)2.5 & _50.6_ & _19.2_ & _25.4_ & _13.0_ & _3.6_ & _1.9_ & _5.3_ \\ MEAS & _(\(\star\))44.9_ & 18.1 & (? )71.8 & (\(\star\))27.9 & 4.0 & (? )51.8 & _17.0_ & 14.0 & 19.9 & _3.7_ & _1.5_ & _6.0_ \\ \hline \(B\) & CHIRPS & _6.7_ & _4.0_ & 17.5 & _10.4_ & _-3.1_ & 24.0 & _-3.8_ & _-1.1_ & _-6.4_ & _0.5_ & _-0.4_ & _1.4_ \\ \((\)mm\(10)^{-1}\()\) & ERA5 & _3.0_ & \(-\)7.5 & 13.6 & _4.3_ & \(-\)12.4 & 21.0 & \(-\)1.3 & _4.7_ & _-7.3_ & _0.2_ & \(-\)0.7_ & _1.1_ \\ MEAS & _4.7_ & \(-\)12.3 & 21.8 & _8.2_ & \(-\)5.9 & 22.2 & \(-\)3.5 & \(-\)6.6 & \(-\)0.4 & _0.4_ & \(-\)11.1 & _1.8_ \\ \hline \(PB\) & CHIRPS & \(\star\)17.5 & \(\star\)18.5 & 35.7 & 35.7 & **-31.5** & **51.5** & \(-\)18.5 & \(-\)**32.5** & **10.5** & \(-\)**15.5** & **34.5** \\ ERA5 & _8.8_ & \(-\)25.7 & 27.5 & 22.7 & \(_MAE_TPcold_ = 24 mm 10y\({}^{-1}\) CHIRPS, 16 mm 10y\({}^{-1}\) ERA5). CHIRPS generates a somewhat lower _TQ_ uncertainty than ERA5 in both the warm and cold seasons. When compared to the _TQ_ generated with measured precipitation (MEAS), both GPPs generate a lower seasonal _TQ_ uncertainty than the _TQ_ with the measured precipitation (MEAS) in the warm season (CHIRPS in b1, ERA5 in b3) and in the cold season (CHIRPS in b1).