4.1.2. Spatial Variation

Figure 3 compares the spatial distribution of the four annual continuous evaluation metrics among the SPPs at the monthly scale. The spatial distributions of the CCs varies considerably among the IMERG products, while staying similar between the TMPA products. Topography does not seem to be a significant influencing factor of the CCs, although some stations at higher altitude (station 12 and 13) do have lower CCs in all five SPPs. In terms of RMSEs and MADs; however, topography plays a more eminent role. For all five SPPs, both metrics tend to get larger at higher altitude. In particular, RMSEs and MADs of three stations at high altitude (station 10, 12, and 13) consistently surpass those of the rest stations. In addition, the RBs exhibit a similar spatial pattern among the IMERG products. They all tend to underestimate monthly rainfall more severely at high altitude (e.g., stations 12 and 13). However, for the TMPA products, no clear pattern in the spatial distribution of RB could be observed.

**Figure 3.** Spatial distribution of the annual continuous evaluation metrics at monthly scale: (**a**) *CC*; (**b**) *RMSE*; (**c**) *RB*; and (**d**) *MAD*.

Similar to our study, Milewski et al. [45] also found that elevation was a key factor affecting the accuracy of the TMPA products in Northern Morocco. The CCs of all four TMPA products at the low elevation class (0–500 m) consistently surpassed those at the medium (500–1000 m) and high (>1000 m) elevation classes. Contrary to the CCs, the normalized RMSEs at the low elevation class were consistently smaller.
