# Evaluating CHIRPS and ERA5 for Long-Term Runoff Modelling with SWAT in Alpine Headwaters
## 3 Results
### Performance Evaluation Using Gauge Observations
\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}{_mean w_} & \multicolumn{3}{c}{_mean c c c_} & **Cold** & & \\ \hline (**H**) & & & Elev.3 & Elev.2 & Elev.1 & Elev.3 & Elev.2 & Elev.1 & Elev.3 & Elev.2 & Elev.1 & Elev.3 & Elev.2 & Elev.1 \\ \hline \(P\) & OBS & 1022 & 1266 & 945 & 807 & 674 & 811 & 634 & 550 & 348 & 456 & 312 & 257 \\ (mm) & CHIRPS & 1175 & 1273 & 1085 & 1207 & 775 & 868 & 710 & 765 & 400 & 405 & 375 & 443 \\  & ERA5 & 1397 & 1537 & 1314 & 1354 & 878 & 976 & 825 & 838 & 519 & 561 & 490 & 516 \\ _PB_ & CHIRPS & 1578 & **157** & **507s** & **155** & **77s** & **125** & **399s** & **155** & **-11\%** & 20\%** & **72\%** \\  & ERA5 & 37\% & 21\% & 39\% & 68\% & 30\% & 20\% & 30\% & 52\% & 49\% & 23\% & 57\% & 101\% \\ \hline _MAE_ & CHIRPS & 258 & **221** & **215** & **401** & **156** & **106** & **164** & **215** & **134** & 145 & **99** & **186** \\  & ERA5 & 376 & 271 & 369 & 547 & 208 & 171 & 195 & 288 & 176 & **114** & 181 & 258 \\ \hline _RMAE_ & CHIRPS & 25\% & **17\%** & **23\%** & **50\%** & **23\%** & **13\%** & **26\%** & **39\%** & 39\% & 32\% & **32\%** & **72\%** \\  & ERA5 & 37\% & 21\% & 39\% & 68\% & 31\% & 21\% & 31\% & 52\% & 51\% & **25\%** & 58\% & 101\% \\ \hline (**V**) & & & & b1 Sill & & & b1 Sill & & & b2 & & & b1 Sill & & \\ \hline \(P\) & OBS & 1022 & 1050 & 966 & 1048 & 674 & 665 & 662 & 694 & 348 & 385 & 304 & 354 \\ (mm) & CHIRPS & 1175 & 1018 & 982 & 1525 & 775 & 694 & 650 & 980 & 400 & 324 & 332 & 545 \\  & ERA5 & 1397 & 1471 & 1224 & 1497 & 878 & 931 & 775 & 928 & 519 & 540 & 449 & 569 \\ \hline _PB_ & CHIRPS & 25\% & -3\% & **2\%** & 45\% & 15\% & 4\% & -2\% & 41\% & 15\% & -16\% & 9\% & 54\% \\  & ERA5 & 37\% & 40\% & 27\% & **43\%** & 30\% & 40\% & 17\% & **34\%** & 49\% & 40\% & 48\% & 61\% \\ \hline _MAE_ & CHIRPS & 258 & **197** & **101** & 477 & **156** & **79** & **102** & 287 & **134** & **135** & 68 & **199** \\ (mm) & ERA5 & 37\% & 421 & 258 & **449** & 208 & 265 & 122 & **236** & 176 & 162 & 149 & 216 \\ \hline _RMAE_ & CHIRPS & 25\% & **19\%** & **10\%** & 45\% & 23\% & **12\%** & **15\%** & 41\% & 39\% & 35\% & **22\%** & **56\%** \\  & ERA5 & 37\% & 40\% & 27\% & **43\%** & 31\% & 40\% & 18\% & 34\% & 51\% & 42\% & 49\% & 61\% \\ \hline _Monthly_ & _mcm_ & **Jan** & **Feh** & **Mar** & **Apr** & **May** & **Jun** & **Jul** & **Aug** & **Sep** & **Oct** & **Nov** & **Dec** \\ \hline \(P\) & OBS & 85 & 42 & 36 & 55 & 66 & 89 & 124 & 140 & 129 & 94 & 97 & 95 & 54 \\ (mm) & CHIRPS & 98 & 52 & 51 & 62 & 78 & 148 & 130 & 147 & 134 & 115 & 101 & 95 & 63 \\  & ERA5 & 116 & 64 & 61 & 91 & 105 & 133 & 169 & 1 The results show that CHIRPS exhibits a lower bias and ERA5 a higher correlation for precipitation amounts. CHIRPS performs better in catchments b1 and b2, whereas ERA5 outperforms CHIRPS in catchment b3. Both CHIRPS and ERA5 show poorer estimates at lower elevations and during the cold season. The observed trends in annual precipitation in the period 1991-2018 are uniformly positive in all catchments and at all elevation bands (Table 11). The seasonal precipitation trends are generally positive and statistically significant but show an alternating strength in the vertical bands and between the catchments. While gauge b1_SS (at 1235 m a.s.l.) shows a strongly positive trend in the warm season and a negative trend in the cold season (\(TP_{num}=+43\) mm \(10\mathrm{y}^{-1}\) vs. \(TP_{cold}=-4\) mm \(10\mathrm{y}^{-1}\)), gauge b2_TO (at similar elevation, 1219 m a.s.l.) shows a contrasting trends, a strongly negative trend in the warm season and a positive trend in the cold season (\(TP_{num}=-24\) mm \(10\mathrm{y}^{-1}\) vs. \(TP_{cold}=+18\) mm \(10\mathrm{y}^{-1}\)). The observed seasonal trends also vary between catchments. The \(TP_{num}\) is positive in catchments b1 Sill and b3 Isel but negative in catchment b2 Drava. The \(TP_{cold}\) is positive in all catchments but much stronger in catchment b2 Drava.