# Extreme Droughs in the Peruvian Amazon Region (2000-2024)
## 3 Results
### Determination of Drought Periods  
To determine the drought periods characteristic of the Peruvian Amazon region and their extension and intensity in different parts of the region, we evaluated the areal average MCWD from 2000 to 2024 for each of the study areas (Figure 4). Figure 4: Annual MCWD for the hydrologic years of the period 2000–2024 for the six study areas defined in Figure 1 and Table 2. (**A**). Precipitation and evaporation from ERA5. (**B**). Precipitation from MSWEP and evaporation from ERA5. (**C**). Precipitation from CHIRPS and evaporation from ERA5. The color lines in the legend refer to the different study areas. LOR1, LOR2, and LOR3 refer to the three study areas in the Loreto region. MOY refers to Moyobamba, UCA to Ucayali, and MD to Madre de Dios study areas. Figure 3: Annual cycle of the water deficit (WD) in the different study areas as estimated from different precipitation (Pr) and evapotranspiration (Et) datasets. (**A**). ERA5. (**B**). MSWEP (**C**). CHIRPS. The identification of drought periods was carried out based on the MCWD index, calculated from the different data sources, wherein important differences were found across the precipitation datasets. Figure 4 shows the record of the index value for every hydrological year of the study period, calculated after averaging the values of MCWD on the grid points of each study area. The lines in different colors represent the different study areas. For instance, following ERA5 (Figure 4A), the higher values of the record for most of the period were obtained by MD, followed by UCA, and the greatest peaks were obtained for MD in 2009-10 and for LOR3 in 2023-24. LOR1, LOR2, and MOY show relatively low values for this database. UCA shows clearly the highest MCWD record for MSWEP (Figure 4B), followed by MD, but for the second half of the period, MD is not much higher than LOR3 and MOY. In this case, the higher peaks are for 2023-24 and for 2004-05. The CHIRPSf (Figure 4C) record shows again that UCA has the highest record, followed by LOR3 and MD, and peaking in 2022-23 in the case of UCA and 2006-07 in the case of LOR3. The threshold values were considered as close to those obtained by [1] from the distribution functions of their relative MCWD values to make possible the intercomparison of results and considering the evaluations of [30]. Based on this, the value of 30 mm is considered as threshold 1, the lower threshold, corresponding to weak drought near to normal conditions; the middle (threshold 2) is 110 mm, corresponding to mild drought conditions, which, according to [31], may be associated with tree mortality for more vulnerable species; an intermediate-higher threshold (threshold 3) is 140 mm, where more species may become vulnerable; and a higher threshold of 200 mm (threshold 4) has been considered to show up in the most severe drought regions. It has to be emphasized that the effect of drought conditions in a specific location depends not only on MCWD but also on the water table depth of the soil and on the types of trees [54], underlining the dependence of the MCWD threshold effect on tree mortality and the difference in the effect of different thresholds in forest trees and palms, which are much more resilient. The most relevant aspect of the MCWD index series is its high temporal variability, with peaks in the dry years for the given region, as well as across regions, with the largest MCWD values in the southern areas (UCA and MD), followed by MOY and LOR3 further north, while the water deficit is not so stressful in the LOR1 and LOR2 regions, with climatologically higher precipitation. For each of the datasets, the average MCWD, including all the study areas, is shown in Figure 5. The HYs with greater average MSWD are not the same for every dataset. Considering the four higher MCWD values for each dataset, according to ERA5 (Figure 5A), the higher average MCWD corresponds to 2023-24, 2022-23, 2015-2016, and 2009-2010, while for MSWEP (Figure 5B), they correspond to 2023-24, 2004-05, 2009-10, and 2006-07.