Long-term trends in observed and MERRA-2 reanalysis temperatures: Between the Atacama Desert and the Andes

Anthropogenic greenhouse gas emissions impact the occurrence and intensity of unusual temperatures. This paper analyzes trends in annual time series of maximum (TX), minimum (TN), and mean (TM) temperatures recorded at meteorological stations of the Servicio Nacional Meteorológico e Hidrológico of Peru (SENAMHI) and those obtained through NASA’s MERRA-2 reanalysis (Modern Era Retrospective Analysis for Research and Applications, Version 2); as well as temperature-derived climate change indices in the Tacna region, Peru, between 1964 and 2013. Trends were determined by manually applying the Mann Kendall test (significance level of 0.05). Similarly, to quantify trend slopes, Sen’s slope estimator was applied with a 95 % confidence interval. These slopes are more representative than those obtained using linear regression. At the SENAMHI stations located in the Atacama Desert (Calana, Sama Grande and Locumba), the observed temperature series: daytime (TX), nighttime (TN), and mean (TM), showed an upward trend. In contrast, the MERRA-2 temperature series showed no trend. In the Andes Mountain Range satation (Tarata), statistically significant upward (+0.062 °C/year) and downward (−0.057 °C/year) trends were recorded for the observed TX and TN temperatures, respectively. Daytime extreme hot events (TXx, TX90p) showed statistically significant increasing trends at all stations, except Calana. Nighttime extreme cold temperatures (TNn) showed statistically significant upward trends in the Atacama Desert, while in the Andes they showed a statistically significant downward trend. These findings suggest warming in the Atacama Desert, while in the Andes, temperatures increase very rapidly during the day and decrease at a slightly slower rate at night. Practical implications In this study, we found differences in temperature trends between the Atacama Desert and the Andes mountain range in the Tacna region of Peru. Along the coast, the upward trend in daytime (TX) and nighttime (TN) temperatures increases evapotranspiration and water demand. In the Andes, the greater difference between TX and TN can affect snowmelt and runoff patterns. The results suggest impacts on the hydrological cycle. Furthermore, the upward trend in daytime temperatures in the Andes Mountains Range (+0.062 °C yr -1 ) suggests a greater risk of glacial retreat, which requires greater control and monitoring of Andean snow-capped mountains and glaciers. These findings could be useful for improving water balance models and estimating water availability for irrigation, which would improve the efficiency of water resource management. Since the Tacna region shares watersheds with Chile and Bolivia, data and studies from Tacna are also valuable for cross-border cooperation. The creation of observation and early warning systems between the three countries would strengthen sustainable water management and ecosystem conservation. Peru is a country with significant agricultural activity and rich biodiversity; therefore, the climate services derived from this study have great potential for application in the country and others with similar climatic conditions. Therefore, agricultural production decisions should be based on evidence (climate change indices) that allow for the definition of agroclimatic thresholds. For example, the growing season length (GSL), which is the number of days with climatic conditions (TM > 5 °C) favorable for plant growth. When TM < 5 °C, the growth of most plants stops or slows. In the Atacama Desert, the increase in the number of days with temperatures above 25 °C (summer days, SU) and the increased frequency of warm waves can alter crop phenology. Specifically, by accelerating the stages of germination, flowering, fruiting and ripening (earlier phenology), because the crops meet their thermal energy needs (degrees of temperature-day) more quickly. These results can be used to develop a temperature calendar, cultivate more resilient varieties, or modify planting and harvesting dates. However, in the Andes Mountains Range, the decrease in minimum nighttime temperatures increases the risk of frost days (FD). FD and TNn indices are essential for feeding agricultural forecasting systems, allowing producers to protect their crops or agricultural practices. The presence of extreme weather events during critical crop phases exposes them to conditions to which they are not adapted. For example, flowering coinciding with a frost or a heat wave. Studies such as the one presented here, which combine in-situ temperature observations with a global reanalysis model, open up new opportunities to improve meteorological services and models with feedback from input data. This study reveals that the MERRA-2 model tends to underestimate observed temperatures by 1–3 °C, which will allow for fine-tuning of model algorithms and improve their accuracy. Furthermore, the trends shared with neighboring Andean countries (northern Chile and eastern Bolivia) justify the establishment or creation of Andean and cross-border cooperation mechanisms for climate monitoring and information sharing between their meteorological services and institutions conducting climate research. Governments can use these results and the methodology developed in this study to support climate change adaptation and mitigation policies. The study also contributes to connecting the scientific community with society, transforming complex information into accessible climate services for authorities, farmers, and the community at large. Daytime warming and the increase in hot nights in the Atacama Desert pose a direct risk to human health. For example, dehydration, heatstroke, fatigue, and sleep loss are increasingly common consequences. Climate services derived from this study can support the development of biometeorological warnings targeting the most vulnerable populations, as well as preventive health programs aligned with heat wave predictions. Taken together, this research not only expands knowledge about the temporal behavior of temperature in southern Peru but also translates climate science into practical tools for society. Its results contribute significantly to adaptation, food security, health risks, water and energy use, and promote informed participation in climate policy. At a time when climate change is redefining the limits of life in arid and Andean ecosystems, studies like this are essential for transforming scientific information into climate services that promote resilience and societal well-being.