# Comparison of GPM IMERG and TRMM 3B43 Products over Cyprus
## 4 Results and Discussion
### Influence of Elevation on Satellite Precipitation Products
TRMM exhibited lower RMSE and MAE values than those of GPM in the elevation ranges 0-300 m and >600 m and higher values in the elevation range 300-600 m.  
The monthly and annual spatio-temporal variations of bias for both satellite precipitation products for the study period are presented in Figures 8 and 9, respectively, while the corresponding seasonal spatio-temporal variation is presented in Figure 10. It is clear that both SP products underestimate precipitation in higher elevation areas and overestimate in areas with lower elevation fluctuations. The underestimation is more evident in the winter. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **All Annual** & **2014** & **2015** & **2016** & **2017** & **2018** \\ \hline \multirow{2}{*}{\% of gauge} & 107.7 & 119.2 & 125.5 & 106.4 & 85.9 & 107.8 \\  & (85.9–135.0) & (91.9–166.8) & (86.7–182.6) & (77.4–139.3) & (61.6–131.8) & (82.5–160.7) \\ \hline \multirow{2}{*}{correlation} & 0.92 & \multicolumn{6}{c}{Elevation: 0–300 m (13 cells)} \\  & (0.84–0.96) & \multicolumn{6}{c}{} \\ \hline \multirow{2}{*}{\% of gauge} & 78.0 & 83.1 & 99.3 & 74.8 & 68.1 & 60.6 \\  & (67.3–99.6) & (73.8–102.6) & (83.9–122.1) & (61.1–106.9) & (51.9–91.3) & (52.6–66.7) \\ \hline \multirow{2}{*}{correlation} & 0.92 & \multicolumn{6}{c}{Elevation: 300–600 m (4 cells)} \\  & (0.88–0.94) & \multicolumn{6}{c}{} \\ \hline \multirow{2}{*}{\% of gauge} & 65.6 & 74.1 & 77.3 & 57.2 & 63.1 & 56.5 \\  & (61.4–69.8) & (72.1–76.1) & (75.9–78.7) & (51.2–63.1) & (57.2–69.0) & (52.6–60.5) \\ \hline \multirow{2}{*}{correlation} & 0.94 & \multicolumn{6}{c}{Elevation: \(>\)600 m (2 cells)} \\  & (0.93–0.94) & \multicolumn{6}{c}{} \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Annual rBias and Pearson correlation coefficient performance for TRMM data according to elevation (the range of values is given in parentheses). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Elevation (m)** & \multicolumn{2}{c}{**Bias (mm/month)**} & \multicolumn{2}{c}{**RMSE (mm/month)**} & \multicolumn{2}{c}{**MAE (mm/month)**} \\ \hline  & _GPM_ & _TRMM_ & _GPM_ & _TRMM_ & _GPM_ & _TRMM_ \\ \hline \multirow{2}{*}{0–300} & 5.8 & 1.5 & 19.6 & 17.2 & 13.2 & 11.0 \\  & (\(-\)5.2–13.0) & (\(-\)5.8–7.7) & (14.7–28.6) & (11.6–25.1) & (10.2–17.2) & (9.0–14.3) \\ \hline \multirow{2}{*}{300–600} & \(-\)3.9 & \(-\)10.2 & 23.1 & 24.5 & 14.3 & 15.3 \\  & (\(-\)17.0–8.1) & (\(-\)15.8—0.1) & (15.4–42.1) & (13.4–30.0) & (10.3–21.8) & (8.7–18.0) \\ \hline \multirow{2}{*}{\(>\)600} & \(-\)16.5 & \(-\)17.8 & 35.4 & 33.0 & 21.5 & 21.0 \\  & (\(-\)31.8—8.7) & (\(-\)21.5—14.1) & (23.2–55.0) & (28.7–37.2) & (15.0–35.5) & (17.7–24.3) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Metrics (Bias, RMSE, MAE) performance for GMP and TRMM monthly data according to elevation (the range of values is given in parentheses). Figure 8: Monthly bias for both precipitation products for the study period: (**a**) TRMM and (**b**) GPM. Figure 10: Cont. Figure 9: Annual bias for both precipitation products for the study period: (**a**) TRMM and (**b**) GPM. These findings are in agreement with previous studies reported in the literature [45; 46; 47; 48; 49; 50]. The performance of both SP products could be due to the products themselves and to topography. Both satellite precipitation products combine data from both satellite sensors and ground gauges. Since data from only one gauge station are used in mountainous areas in Cyprus, while three are located in rather flat areas, the accuracy of satellite precipitation products may be affect. [PERSON] and [PERSON] [51] and [PERSON] et al. [52] also reported that the accuracy of satellite precipitation products in high mountainous areas in west China could be attributed to the sparse gauge network. Moreover, estimated differences could be also attributed to the differences of the rainfall process, which is rather complicated in mountainous areas than in low altitude areas due to the influence of topography.