**5. Conclusions**

An evaluation of the monthly and annual IMERG and TRMM 3B43 product estimates with corresponding rain-gauges data over Cyprus for the period April 2014 to June 2018 was performed. Based on the analysis presented, it is found that, overall, both monthly satellite product estimates and rain gauge data presented a very good agreement; however, both IMERG and TRMM estimates tend to underestimate precipitation, especially during the rainy season, although, IMERG and rain gauge records seem to exhibit similar temporal patterns. Considering the annual values, we notice that both SP estimates underestimate annual precipitation records, although IMERG estimates are much closer to gauge station records. In terms of statistical scores analysis, it was found that on a monthly and annual basis, a slightly better performance of IMERG for R, Bias and rBias values was noticed, while 3B43 product performed better in terms of RMSE and MAE values. Seasonal analysis showed that both products exhibited a better performance during the rainy (winter) period, followed by autumn and

spring seasons, while both products were able to detect the summer-time precipitation, although with high uncertainty in terms of relative bias values.

In summary, we conclude that although satellite products could be considered as quite accurate estimates of precipitation, indeed, their accuracy is not yet profound, and this issue is open to further elaboration. Nonetheless, IMERG estimates, due to their superiority in terms of spatial and temporal resolution, could serve as an alternative precipitation dataset, where in-situ precipitation records are limited.

The influence of elevation of both SP estimates was considered by grouping rain gauge stations in three categories, with respect to their elevation and it was found that both SP estimates underestimate precipitation with increasing elevation and overestimate it at lower elevations. Thus, it is suggested that one possible improvement would be the prospect of blending the SP data with more in situ data from rain gauges that are distributed evenly over the geographical area of Cyprus and especially in mountainous areas. Furthermore, it would be quite challenging to enhance the retrieval algorithms by implementing elevation correction or adjustment.

Although the results derived from this study are site specific for Cyprus, the methodology adopted could be "transferred" to other regions according to our understanding of how satellite-based precipitation estimates perform over different regions. For example, for study areas with characteristics similar to our area of study, in terms of geographic location, with no very complex topography, the methodology could be applied directly. For other areas, with complex topography or with various climatic zones the methodology should further consider these parameters.

The authors aim to expand their research in this field, by considering an evaluation over Cyprus of the newly released version of IMERG data that expands the SP products into a uniformly processed data set embracing the TRMM-era. The establishment of a uniform TRMM and GPM SP record will broaden the scientific challenges for further research in several meteorological and hydrological applications.

**Author Contributions:** All authors contributed extensively to the work presented in this paper. The manuscript was prepared by A.R. and revised by D.K., F.T. and S.M. D.K. and F.T. provided and analyzed data. All authors discussed the results and implications of the manuscript at all stages. All authors have read and agreed to the published version of the manuscript.

**Funding:** S.M. was supported by the EMME-CARE project that has received funding from the European Union's Horizon 2020 Research and Innovation Programme, under grant agreement no. 856612, as well as matching co-funding by the Government of the Republic of Cyprus.

**Acknowledgments:** The authors acknowledge the provision of the rain gauge data by the Cyprus Department of Meteorology and the provision of the TMPA and IMERG data by the NASA/Goddard Space Flight Center's Mesoscale Atmospheric Processes Laboratory and Precipitation Processing Center, U.S.A., which developed and computed them as a contribution to TRMM and GPM, respectively.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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