En 1892, se difundió la primera observación documentada de la corriente costera “El Niño”, denominada por aquel entonces: “Contracorriente marítima en Paita y Pacasmayo” (Carranza, 1892) y donde se intentaba explicar las lluvias torrenciales acaecidas en 1891. Un siglo y cuarto después, aun continúa el reto de poder comprender el efecto de este fenómeno sobre las lluvias a diferentes escalas de espacio y tiempo, especialmente en regiones del planeta como la Vertiente del Pacífico Peruano (VPP), donde sus efectos son experimentados frecuentemente. En el presente artículo se responde a preguntas comunes sobre la distribución de las lluvias en la VPP y el impacto del Fenómeno El Niño o ENSO (El Niño Oscilación del Sur en inglés), basándose en una revisión del estado del arte en la temática, las metodologías y los nuevos aportes.

The Peruvian Andes are a hotspot of vulnerabilities to impacts in water resources due to the propensity for water stress, the highly unpredictable weather, the sensitivity of glaciers, and the socio-economic vulnerability of its population. In this context, we selected the Vilcanota-Urubamba catchment in Southern Peru for addressing these challenges aiming at our objectives within a particular hydrological high-mountain context in the tropical Andes: a) Develop a fully-distributed, physically-based glacier surface energy balance model that allows for a realistic representation of glacier dynamics in glacier melt projections; b) Design and implement a glacio-hydrological monitoring and data collection approach to quantify non-glacial contributions to water resources and the impact of catchments interventions; c) Mapping of human water use at high spatiotemporal resolution and determining ...

Water resources availability in the southern Andes of Peru is being affected by glacier and snow retreat. This problem is already perceived in the Vilcanota river basin, where hydro-climatological information is scarce. In this particular mountain context, any water plan represents a great challenge. To cope with these limitations, we propose to assess the space-time consistency of 10 satellite-based precipitation products (CMORPH–CRT v.1, CMORPH–BLD v.1, CHIRP v.2, CHIRPS v.2, GSMaP v.6, GSMaP correction, MSWEP v.2.1, PERSIANN, PERSIANN–CDR, TRMM 3B42) with 25 rain gauge stations in order to select the best product that represents the variability in the Vilcanota basin. For this purpose, through a direct evaluation of sensitivity analysis via the GR4J parsimonious hydrological model over the basin. GSMap v.6, TRMM 3B42 and CHIRPS were selected to represent rainfall spatial variabi...

This study provides for the-first-time a water availability analysis at drainage and basin-scale in Peru. Using new gridded datasets of precipitation and temperature, along with six global actual evapotranspiration estimations from remote sensing products, the vulnerability of water resources due to climate change is evaluated. This is addressed under a bottom-up approach and probabilistic Budyko framework that enables us to measure the associated uncertainty. First, to select an adequate estimation of long-term actual evapotranspiration, we compared at basin-scale the remote sensing products with long-term actual evapotranspiration inferred from a waterbalance (precipitation minus discharge) and deterministic Budyko (aridity and evaporative index relationship). Later, the probabilistic Budyko is calibrated using the adequated remote-sensed actual evapotranspiration and is cross-validate...

Land use and land cover (LULC) changes in the Piura River Basin, Peru, were analyzed from 2001 to 2022 using global MODIS and ESA-CCI datasets harmonized into six major land cover classes (Forest, Non-Forest Vegetation, Cropland, Bare Soil, Water and Urban) for comparative analysis. Pearson correlation analyses with hydroclimatic variables, including precipitation (PP), maximum (Tx) and minimum (Tn) temperatures, and El Niño Southern Oscillation (ENSO) indices (Eastern Pacific, Central Pacific, and Coastal El Niño), complemented the intensity analysis to explore environmental drivers. The analyses focused on the lower-middle and upper basin regions during wet (December-May) and dry (June-November) seasons. MODIS detected more dynamic LULC transitions, with 32.8% of pixels showing changes, compared to 6.8% detected by the ESA-CCI product. These differences reflect the distinct sensitivi...

This research assesses present (2009-2016) and future (until 2100) levels of water security taking into consideration socioeconomic and climate change scenarios using the WEAP (Water Evaluation and Planning) tool for Semidistributed hydrological modeling. The study area covers the VilcanotaUrubamba basin in the southern Peruvian Andes and presents a complex water demand context as a glacier-fed system. This study also further explores the importance of incorporating science and policy within a broader study of water security. As a result, it is expected to deliver high spatial resolution water demand maps and adaptation strategies for stakeholders. This research is part of the RAHU project as a new multidisciplinary collaboration between UK and Peruvian scientists.

Surface water resources in Peru are heterogeneously distributed in three drainage areas (Pacific, Titicaca, and Atlantic), and their quantification is relevant for planning in economic activities such as water supply and agriculture. However, their continuous monitoring at national scale becomes difficult due to the low stream gauges density and short streamflow records. The aim of this work is to generate a database of simulated monthly streamflows at a national scale from January 1981 to December 2016, applying the parsimonious GR2M model in a semi-distributed approach, under a parameter regionalization scheme. For this, 3594 sub-basins (~300 km2) located in the three drainage areas were tested. These sub-basins were first grouped in 14 calibration regions based on a sensitivity analysis of the runoff ratio (RR) and runoff variability (RV) indexes derived from the GR2M outputs. The mod...

In regions with limited precipitation information, like Peru, many studies rely on precipitation data derived from satellite products (SPP) and model reanalysis. These products provide near-real-time information and offer global spatial coverage, making them attractive for various applications. However, it is essential to consider their uncertainties when conducting hydrological simulations, especially in a key region like the Pacific drainage (Pd), where 56% of the Peruvian population resides (including the capital, Lima). This study, for the first time, assessed the performance of two bottom-up Satellite-based Precipitation Products (SPP), GPM + SM2RAIN and SM2RAIN-ASCAT, and one top-down approach SPP, ERA5-Land, for runoff simulation in the Pacific drainage of Peru. Hydrological modeling was conducted on 30 basins distributed across the Pd, which were grouped into 5 regions (I–V, or...

This article identifies homogeneous precipitation regions in Ecuador and their relationship to the El Niño-Southern Oscillation (ENSO), using monthly records from 215 rain stations for the 1968–2014 period. A k-means clustering analysis was used to divide the study area into k regions based on monthly and annual precipitation variables and geographic location (latitude, longitude, and altitude). The robustness of each cluster was evaluated using the “silhouette” coefficient. The groupings were then validated using the regional vector method (RVM). Twenty-two regions of homogeneous precipitation were identified. Seven regions are related to regional climate processes on the Pacific coast (unimodal precipitation). Two regions in the western foothills of the Andes show significant orographic rainfall. Eight regions in the inter-Andean region present a bimodal precipitation regime cha...

Soil moisture content can be used to predict drought impact on agricultural yield better than precipitation. Remote sensing is viable source of soil moisture data in instrument-scarce areas. However, space-based soil moisture estimates lack suitability for daily and high-resolution agricultural, hydrological, and environmental applications. This study aimed to assess the potential of the random forest machine learning technique to enhance the spatial resolution of remote soil moisture products from the SMAP satellite. Models were built using random forest for spatial downscaling of SMAP-L3-E, then visually and statistically evaluated for disaggregation quality. The impact of topography, soil properties, and precipitation on the downscaled soil moisture was examined. The relationship between downscaled soil moisture and in-situ soil moisture was analyzed. The results indicate that the pro...

Se identificaron regiones homogéneas de precipitación en el Ecuador y su relación con el fenómeno de El Niño, utilizando registros de 215 estaciones pluviométricas a escala mensual para el periodo 1968-2014. Los datos se sometieron a un análisis de K-means y, posteriormente, fueron validados con el método del vector regional (MVR). Los resultados permitieron identificar 22 regiones: siete regiones relacionadas con procesos climáticos regionales en la costa del Pacífico (precipitación unimodal); dos regiones con precipitaciones orográficas significativas en las estribaciones occidentales de los Andes; ocho regiones ubicadas en zona interandina, caracterizadas por una reducción de la precipitación de norte a sur, de variabilidad local y régimen de precipitación bimodal. En la zona amazónica, se identificaron cinco regiones: tres ubicadas en los flancos externos de la cordi...

The watershed hydrologic conditions in the Madre de Dios (MDD) Basin in the Peruvian Amazon have been irreversibly impacted by deforestation and changes in land cover. These changes have also had detrimental effects on the geomorphology, water quality, and aquatic habitat within the basin. However, there is a scarcity of hydrological modeling studies in this area, primarily due to the limited availability of hydrometeorological data. The primary objective of this study was to examine how deforestation impacts the hydrological conditions in the MDD Basin. By implementing the Soil and Water Assessment Tool (SWAT) model, this study determined that replacing 12% of the evergreen broadleaf forest area with bare land resulted in a significant increase in surface runoff, by 38% monthly, a 1% annual reduction of evapotranspiration, and an average monthly streamflow increase of 12%. Changes in sp...

Quantification of the surface water offer is crucial for its management. In Peru, the low spatial density of hydrometric stations makes this task challenging. This work aims to evaluate the hydrological performance of a monthly water balance model in Peru using precipitation and evapotranspiration data from the high-resolution meteorological PISCO dataset, which has been developed by the National Service of Meteorology and Hydrology of Peru (SENAMHI). A regionalization approach based on Fourier Amplitude Sensitivity Testing (FAST) of the rainfall-runoff (RR) and runoff variability (RV) indices defined 14 calibration regions nationwide. Next, the GR2M model was used at a semi-distributed scale in 3594 sub-basins and river streams to simulate monthly discharges from January 1981 to March 2020. Model performance was evaluated using the Kling–Gupta efficiency (KGE), square root transferred...

The watershed hydrologic conditions in the Madre de Dios (MDD) Basin in the Peruvian Amazon have been irreversibly impacted by deforestation and changes in land cover. These changes have also had detrimental effects on the geomorphology, water quality, and aquatic habitat within the basin. However, there is a scarcity of hydrological modeling studies in this area, primarily due to the limited availability of hydrometeorological data. The primary objective of this study was to examine how deforestation impacts the hydrological conditions in the MDD Basin. By implementing the Soil and Water Assessment Tool (SWAT) model, this study determined that replacing 12% of the evergreen broadleaf forest area with bare land resulted in a significant increase in surface runoff, by 38% monthly, a 1% annual reduction of evapotranspiration, and an average monthly streamflow increase of 12%. Changes in sp...

Water is an essential resource for social and economic development. The availability of this resource is constantly threatened by the rapid increase in its demand. This research assesses current (2010–2016), short- (2017–2040), middle- (2041–2070), and long-term (2071–2099) levels of water security considering socio-economic and climate change scenarios using the Water Evaluation and Planning System (WEAP) in Vilcanota-Urubamba (VUB) catchment. The streamflow data of the Pisac hydrometric station were used to calibrate (1987–2006) and validate (2007–2016) the WEAP Model applied to the VUB region. The Nash Sutcliffe efficiency values were 0.60 and 0.84 for calibration and validation, respectively. Different scenarios were generated for socio-economic factors (population growth and increased irrigation efficiency) and the impact of climate change to evaluate their effect on the...

Gridded high-resolution climate datasets are increasingly important for a wide range of modelling applications. Here we present PISCOt (v1.2), a novel high spatial resolution (0.01°) dataset of daily air temperature for entire Peru (1981–2020). The dataset development involves four main steps: (i) quality control; (ii) gap-filling; (iii) homogenisation of weather stations, and (iv) spatial interpolation using additional data, a revised calculation sequence and an enhanced version control. This improved methodological framework enables capturing complex spatial variability of maximum and minimum air temperature at a more accurate scale compared to other existing datasets (e.g. PISCOt v1.1, ERA5-Land, TerraClimate, CHIRTS). PISCOt performs well with mean absolute errors of 1.4 °C and 1.2 °C for maximum and minimum air temperature, respectively. For the first time, PISCOt v1.2 adeq...

This study investigates the applicability of Satellite Precipitation Products (SPPs) in near real-time for the simulation of sub-daily runoff in the Vilcanota River basin, located in the southeastern Andes of Peru. The data from rain gauge stations are used to evaluate the quality of Integrated Multi-satellite Retrievals for GPM–Early (IMERG-E), Global Satellite Mapping of Precipitation– Near Real-Time (GSMaP-NRT), Climate Prediction Center Morphing Method (CMORPH), and HydroEstimator (HE) at the pixel-station level; and these SPPs are used as meteorological inputs for the hourly hydrological modeling. The GR4H model is calibrated with the hydrometric station of the longest record, and model simulations are also verified at one station upstream and two stations downstream of the calibration point. Comparing the sub-daily precipitation data observed, the results show that the IMERG-E ...

The relationship between El Niño Southern Oscillation (ENSO) and precipitation along the Peruvian Pacific coast is investigated over 1964–2011 on the basis of a variety of indices accounting for the different types of El Niño events and atmospheric and oceanographic manifestations of the interannual variability in the tropical Pacific. We show the existence of fluctuations in the ENSO/precipitation relationship at decadal timescales that are associated with the ENSO property changes over the recent decades. Several indices are considered in order to discriminate the influence of the two types of El Niño, namely, the eastern Pacific El Niño and the central Pacific El Niño, as well as the influence of large-scale atmospheric variability associated to the Madden and Julian Oscillation, and of regional oceanic conditions. Three main periods are identified that correspond to the interl...

Hydrological hazards related to flash floods (FF) in Peru have caused many economic and human life losses in recent years. In this context, developing complete early warning systems against FF is necessary to cope impacts. For this purpose, hydrological and hydraulic models coupled to numerical weather models (NWM) that provide forecasts are generally used. In this sense, the National Meteorological and Hydrological Service of Peru (SENAMHI) has launched the ANDES initiative (Operational Forecasting System for Flash Floods of SENAMHI in English) to support FF events.

In Ecuador and Peru, geochemical information from Pacific coastal rivers is limited and scarce. Here, we present an unedited database of major element concentrations from five HYBAM observatory stations monitored monthly between 4 and 10 years, and the discrete sampling of 23 Andean rivers distributed along the climate gradient of the Ecuadorian and Peruvian Pacific coasts. Concentration (C) vs. discharge (Q) relationships of the five monitored basins exhibit a clear dilution behavior for evaporites and/or pyrite solutes, while the solute concentrations delivered by other endmembers are less variable. Spatially, the annual specific fluxes for total dissolved solids (TDS), Ca²⁺, HCO₃, K+, Mg²⁺, and SiO₂ are controlled on the first order by runoff variability, while Cl, Na⁺ and SO₄² are controlled by the occurrence of evaporites and/or pyrite. The entire Pacific basin in Ecu...