# Extreme Droughs in the Peruvian Amazon Region (2000-2024)
## 4 Discussion  
The droughs of 2004-05 and 2009-10, classified in this paper as extreme, had been previously considered as two of the most severe of the century, as well as the 2022-23 and 2023-24 droughs. The 2015-2016 drought, which has been considered the longest in this century for the entire Amazon basin [1; 9; 13; 24; 31], is classified here as moderate for the  
Figure 10: Average annual cycles of three energy fluxes and the bulk Bowen ratio from ERA5 data for Northeast Loreto (LOR1), Ucayali (UCA), and Madre de Dios (MD). Upper row: sensible heat flow (sshf). Second row: latent heat flow (shlf) Third row: solar surface net radiation (ssr). Lower row: bulk Bowen ratio. Column 1: LOR1. Column 2: UCA. Column 3: MD. The curves refer to the averages for extreme drought (ExD) and the climatology (CLIM). Peruvian Amazon region, with a lesser impact. Another drought period, also classified as moderate in Table 3, was found in 2006-2007, with high values of MCWD in the two observational datasets. This period had not been classified as a drought before, probably because of its local character and because it had not been cited as having an important effect on river hydrology [13]. [PERSON] et al., 2022 [1], found the Peruvian territory covered by moderate drought and some regions, mainly in the northern Loreto region, with local severe and extreme drought, but they only evaluated the distribution of the relative MCWD index and only for the pre-determined years considered as extreme droughs for all the basin. In this paper, we have evaluated the absolute MCWD indices, which allowed us to clarify the more severe impact of the drought on the southern areas of the region and the importance of this situation for the Andes-Amazon transition region. The comparison between the spatial distribution of MCWD for these droughs for the different rainfall datasets is shown in Figure 7. In the estimation of MSWEP, the 2004-05 and 2009-10 thoughts show the greatest high threshold area in the Andes-Amazon transition region, but in 2023-24, most of Loreto was covered by drought conditions, followed by 2022-23. Even if the general pattern is similar, significant differences arise in the spatial distribution of MCWD across the datasets. The ERA5 estimation shows that higher MCWD values are mainly concentrated in UCA and MD, except in 2022-23, when these areas extend to all the regions of Loreto and MOY. CHIRPS and MSWEP show high MCWD areas also in the Andes-Amazon transition region bordering the Andes Cordillera and show unusual drought conditions in Loreto in 2022-23. This result is consistent with extreme dry and warm conditions observed in northern Amazonia during the austral winter and spring of 2023 [2; 59]. The annual cycle of radiation near the Earth's surface depends on cloud cover and is therefore related to precipitation and drought. As a result of the interaction of solar radiation with the atmosphere, the surface is heated by a net positive radiation balance during the day and cooled by a negative radiation balance at night, and the surface temperature, which is the result of the radiative balance, oscillates almost between a minimum at dawn and a maximum in the afternoon. Under rainforest conditions, the daily net radiation balance is positive, and the average daily temperature is determined by the balance of daily mean surface energy, which involves not only the short- and long-wave radiation components but also heat transfers to the atmosphere. On the other hand, the magnitude of the diurnal temperature range is related to factors such as the nature of the underlying surface, vegetation, and water phase changes, which depend on climatological conditions. The rate of increase in soil temperature during the day depends on the latent and sensible heat fluxes. On a humid surface, because of frequent and abundant rains, the latent heat flux related to evaporation prevails and the warming is lower, while on a dry surface, sensible heat prevails, and the warming is greater [60].