## 1 Introduction  
### _Watersheds_, _Demographics_, and _Geographical Diversity of Peru's Territory_  
Peru is one of the most diverse countries on the planet, and its geography allows it to have 70% of the planet's ecosystems. This is how this country, in simple terms, has three geographic units: coast, Sierra, and jungle [1]. The coast corresponds to the entire geographic area near the Pacific Ocean, which is mainly a dry climate and desert territory,which goes from north to south. Then there is the Sierra, which corresponds to the Andean zone where the Andes Mountain range is located, an area full of valleys and high mountains from the north to south of the country. Finally, there is the jungle zone, which corresponds to the Amazon territory, full of vegetation covered by forests and large plains, where high rainfall is recorded throughout the year [2].  
In these three main geographic areas, there are a large number of hydrographic basins, where the orography of these territories allows for the development of the water cycle or hydrological cycle, allowing water to transform into its three basic phases: gaseous in the ocean, rivers, and lakes, snow on the summit of the Andes, and liquid in the beds of springs, ravines, streams, lakes, wetlands, and rivers. This is how there are a significant number of riverbeds throughout the territory that connect these coastal, mountain, and jungle areas. Some of the main rivers in the coastal area that we can highlight are the Rimac River, the Chillon River, and the Canete River, among others. On the other hand, some of the main rivers in the Sierra area are the Huallaga River, the Apurimac River, and the Vilcanota River, among others. Finally, in the jungle area, the main rivers are the Amazon River, the Ucayali River, and the Madre de Dios River, among others [3; 4].  
The territory of Peru was populated by indigenous peoples who built their first human settlements in strategic places to cope with the impacts of climate change such as floods, droughs, and frosts, as well as the effects of earthquakes. Some of the indigenous peoples who inhabited Peru in its beginnings include the (i) Caral Culture (the oldest in South America), (ii) Moche Culture, (iii) Chimu Culture, (iv) Tia Huanaco Culture, (v) Nazca Culture, and (vi) Inca Culture, among others [3; 4]. The arrival of the Spanish in Peru brought about many changes in the original human settlements, where mainly new towns and larger cities were built near the banks of rivers for the purpose of exploiting minerals and metals such as gold and silver and not placing emphasis on avoiding damage from the impact of extreme hydrometeorological events. This is how many of the contemporary towns and cities of Peru are in the coast, Sierra, and jungle areas, where to reach them, provide for the transportation of people and goods/merchandise, and promote services, connectivity is achieved by a network of roads and bridges that allow for crossing the channels of the main rivers (see Figure 1). Some of the main cities in the coast area in Peru include (i) Lima, (ii) Trujillo, and (iii) Chiclayo, among others. Some of the main cities in the Sierra area include (i) Huaraz, (ii) Arequipa, and (iii) Cusco, among others. Some of the main cities in the jungle area include (i) Iquitos, (ii) Pucallpa, and (iii) Puerto Maldonado.  
Figure 1: Typical landscape of watershed in Peru.