**1. Introduction**

Precipitation is an important variable for hydrological, agricultural, industrial and energy systems [1]. It has a grea<sup>t</sup> impact on people's lives and the control of the hydrological cycle, as well as fluctuations that affect water resources management, environmental planning and disaster mitigation [2,3]. Its utility is fundamental as an input to hydrological models, meteorological models and climate models [4,5]. The most accurate precipitation measurements are those taken directly with a rain gauge [6]. However, the availability of such data are limited to the few areas where weather stations have been installed [7].

Climatological and hydrometeorological applications of SPPs have been significantly improved with the appearance of the GPM IMERG [8]. The IMERG combines data from the GPM constellations of satellites to estimate precipitation over most of the earth's surface which lacks terrestrial rain gauges, and offers three runs to meet different users' latency and accuracy requirements, including IMERG Early (IMERG-E), IMERG Late (IMERG-L) and IMERG Final (IMERG-F) [9], which has led many researchers to consider using the IMERG and evaluate its performance.

In recent years, the use of SPPs from IMERG have shown promise in detecting precipitation on different time scales. For example, in mainland China, an evaluation of monthly precipitation products of IMERG and TRMM 3B43 [10] was carried out; in Brazil [11], IMERG grid-level evaluation was conducted at various spatial and temporal scales; in Thailand [12], a hydrological evaluation and application of TRMM and GPM precipitation products in a tropical monsoon basin was conducted; and a comprehensive evalua-

**Citation:** Quispe, L.A.; Paxi, E.; Lujano, E. Evaluation of GPM IMERG Performance Over the Lake Titicaca Basin at Different Time Scales. *Environ. Sci. Proc.* **2023**, *25*, 65. https://doi.org/10.3390/ECWS-7-14324

Academic Editor: Athanasios Loukas

Published: 3 April 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

tion of GPM IMERG and MRMS with hourly ground observations was conducted across Canada [13]. Additionally, [14] evaluated GPM IMERG, TMPA 3B42, and ERA-Interim in different topographic and climatic conditions in Iran; in Singapore [15], GPM and TRMM precipitation products were evaluated; [16] compared satellite precipitation products GPM IMERG, TMPA 3B42, and PERSIANN-CDR over Malaysia; [17] focused on a complete comparison of GPM IMERG with nine satellites and reanalysis datasets; while a first validation of IMERG over Spain is presented in [18]. The [19] developed a precipitation dataset through simultaneous use of IMERG, synoptic measurements, and automatic rain gauge measurements in the Philippines; [20] evaluated and compared daily precipitation of GPM and TRMM products over the Mekong River basin; in China [21], an evaluation of the IMERG version 05B precipitation product was conducted and compared with the IMERG version 04A at hourly and daily scales; in Myanmar, TRMM and GPM precipitation products were used for sub-daily scale flood simulations in a sparsely gauged river basin [22]; and a comprehensive evaluation of the latest IMERG and GSMaP precipitation products of the GPM era was conducted in mainland China [23]. Although the GPM IMERG SPP has been used in hydrological modeling in the LTB [24], its performance has not ye<sup>t</sup> been evaluated at different time scales.

Taking the aforementioned studies into account, the objective of this research is to evaluate the performance of the GPM IMERG at different time scales in the lake Titicaca basin, its importance in improving the understanding of climate variability and its impact on flood risk management, hydrological modeling, and hydroclimatic studies. The hypothesis is that the quality and accuracy of GPM IMERG precipitation estimates vary at different time scales in the LTB.

### **2. Materials and Methods**

### *2.1. Study Area*

The LTB is located in southern Peru (Puno department) and west Bolivia (La Paz department) (Figure 1). It is a part of the Titicaca hydrographic region and the Titicaca-Desaguadero-Poopó-Salar of Coipasa (TDPS) endorheic system, bordered by the eastern and western mountain ranges. It covers an approximate area of 53,919.1 km2. According to the digital elevation model (DEM), its average altitude is 4190.2 m.s.a.l., with a maximum altitude of 6397 m.s.a.l. and a minimum altitude of 3758 m.s.a.l. Most of the LTB has a flat topography, with a mean slope of 13.7%. The mean annual precipitation is 683.3 mm; 59.5% of the annual precipitation occurs in austral summer, 2.3% in winter and 22.1% and 16.1% in the transition periods from wet to dry (autumn) and from dry to wet (spring), respectively.

**Figure 1.** Location of LTB with weather stations in relation to South America.

### *2.2. Cartographic Information*

The DEM was generated by NASA's Shuttle Radar Topography Mission (SRTM) at a spatial resolution of ~90 m, and was obtained from the Google Earth Engine (GEE) platform (https://earthengine.google.com/, accessed on 16 September 2022), Image ID CGIAR/SRTM90\_V4 [25].

### *2.3. Rain Gauge Measurements*

Rain gauge measurements were obtained from the Servicio Nacional de Meteorología e Hidrología (SENAMHI) Perú, considering a total of 33 meteorological stations. Moreover, from the Servicio Nacional de Meteorología e Hidrología (SENAMHI) Bolivia, five weather stations within the LTB were considered (Figure 1). The total number of weather stations considered was 38, with a daily recording period from 1 January 2003 to 31 December 2016.

### *2.4. GPM IMERG Satellite Precipitation Products*

In this research, the GPM IMERG SPPs (IMERG-E, L and F) version 6 (V06) were evaluated. GPM produces precipitation data with a temporal resolution of up to 30 min, spatial resolution of 0.1◦ × 0.1◦ (latitude 60◦ N-S) and in three executions (IMERG-E, -L and -F), cohosted by the National Aeronautics and Space Administration (NASA) and Japan Aerospace Exploration Agency (JAXA). In sequence, IMERG-E and L are near real-time data with a delay of 4 hours and 14 hours after observation time respectively, however, IMERG-F has a delay of 3.5 months [9]. The IMERG-E can be used when rapid responses are required, such as possible flood or landslide warnings, while the IMERG-L can be used for agricultural forecasting or drought monitoring [26].

GPM IMERG V06 data were obtained from the National Aeronautics and Space Administration (NASA) GIOVANNI online (Web) server (https://giovanni.gsfc.nasa.gov/ giovanni/, accessed on 20 October 2022). The data were collected for the same period as the rain gauge measurements.
