# Extreme Droughs in the Peruvian Amazon Region (2000-2024)
###### Abstract
La Nina was associated with dry conditions in southwestern Amazonia during the onset of the 2022-23 hydrologic year (HY), including the South American Altiplano [16; 17], while El Nino and warm conditions in the tropical North Atlantic were linked to drought in central and northern Amazonia during the austral winter and spring of 2023 [2]. This event also occurred during a widespread anomalous warming over the worldwide ocean, primarily driven by the El Nino event [18]. Several authors have raised the question of the possible link between droughts in Amazonia and global warming [19; 20; 21; 22]; evaluations of the intensity and the characteristics of these droughts have been developed [9; 11; 13; 23; 24; 25], and their impact has been discussed [26; 27; 28; 29]. [PERSON] et al. (2007) [26] proposed the application of the Maximum Cumulative Water Deficit index to the evaluation of drought conditions in the Amazon basin. They used MCWD to study the impact of droughts on the Amazon forest, demonstrating its effectiveness in capturing the cumulative effects of water deficits on vegetation. This index has also been used in several other works and has proved to be a valuable tool for investigating droughts in the Amazon basin due to its ability to capture the cumulative water stress experienced by ecosystems over time and to its relationship with tree mortality ([PERSON] et al. 2009 [30]; [PERSON] et al. 2011 [31]). MCWD has been shown to correlate strongly with ecological responses in the Amazon basin, such as reduced photosynthetic activity, increased tree mortality, and higher fire susceptibility. This makes it a more reliable indicator of drought impacts on tropical forests than other indices, such as SPEI, which is very useful from a climatological or hydrological point of view but does not always align as closely with ecological outcomes in the Amazon due to its standardization and lack of focus on cumulative deficits [32; 33]. [PERSON] et al. (2022) [1] selected several precipitation and evapotranspiration datasets to evaluate these droughts and their effects, studying the possible influence of the different manifestations of El Nino and the warming of the Atlantic surface on their development. They used precipitation data from several sources, including those derived from satellite-based radar measurements, global observations, general circulation models, and atmospheric reanalysis. To evaluate the severity of droughs and their spatial extent, they applied several indices, highlighting the convenience and simplicity of using the maximum cumulative water deficit index (MCWD). All these works have been focused on the whole Amazon Basin, including in some cases part of Peru as one of the subregions, so that the general conclusions are not necessarily valid for the Peruvian Amazon, where particular climate conditions exist, such as in the transition between the forest and the Andes mountains, known as the Andes-Amazon transition region [13; 34; 35]. Additionally, [PERSON] et al., 2022 [1] considered a standardized variant of the MCWD index, in relative terms, which does not allow the assessment of the drought stress on the forests in the different regions of Peru. The present work is aimed at evaluating the severity and spatial extension of the most extreme droughs in the Peruvian Amazon region throughout the XXI century using the MCWD index in absolute terms to answer the question about the degree of manifestation of the drought phenomenon in the Peruvian Amazon basin in the first 24 years of the present century. In addition, we provide a regional approach, highlighting the different expressions of drought in areas characterized by different annual rainfall cycles and the impacts on water deficit and surface energy fluxes. The study period extended from 2000 to 2024, during which four extreme droughs have been reported for the entire Amazon basin, but the degree of influence on the Peruvian territory has not been conclusive.