Drought crisis escalates in Peruvian Amazon amid global climate shifts

The Peruvian Amazon is facing a dramatic intensification of drought conditions, with the hydrological years 2022–2023 and 2023–2024 ranking among the most extreme drought events in recent memory. The peer-reviewed research article, titled “Extreme Droughts in the Peruvian Amazon Region (2000–2024)” and published in Water, systematically analyzes two decades of climate data using the Maximum Cumulative Water Deficit (MCWD) index.

Led by Daniel Martínez-Castro and a team of researchers from Peru, France, Cuba, and Italy, the study exposes the alarming escalation of water stress across critical ecosystems in the region.

What is causing these droughts and how are they measured?

To assess the severity of droughts, the study utilizes the MCWD index - an ecological indicator designed to quantify accumulated water stress on vegetation. Unlike standardized drought indices that mask ecological impacts, MCWD offers a clearer link to forest stress and tree mortality. It calculates the deficit when evapotranspiration (Et) surpasses precipitation (Pr), emphasizing periods when vegetation suffers the greatest water scarcity.

The authors combined data from three major precipitation datasets, ERA5, CHIRPS, and MSWEP, with evapotranspiration data from ERA5 to create a comprehensive regional drought assessment. They focused on six distinct areas within the Peruvian Amazon, including northern, central, and southern territories such as Loreto (LOR1, LOR2, LOR3), Moyobamba (MOY), Ucayali (UCA), and Madre de Dios (MD). The results show that central and southern zones, particularly Ucayali and Madre de Dios, have experienced the most severe and recurrent water deficits.

Statistical analysis classified four years as extreme drought events: 2004–05, 2009–10, 2022–23, and 2023–24. Two additional years, 2006–07 and 2015–16, were identified as moderate droughts. Notably, 2023–24 exhibited the highest average MCWD value across datasets (103.7 mm), indicating widespread and severe drought stress. This aligns with earlier findings linking droughts in the Amazon to both El Niño and warming of the tropical North Atlantic, which disrupt regional rainfall patterns.

How widespread and severe are the droughts?

The study's spatial and temporal breakdown reveals alarming trends in drought expansion. While previous research focused broadly on the entire Amazon basin, this analysis zeroes in on Peru’s subregions, uncovering critical disparities. For example, northern Loreto consistently showed lower drought stress due to higher rainfall levels, while southern areas like Ucayali and Madre de Dios were identified as persistent hotspots of extreme drought.

When evaluating the affected area, approximately 80% of the Peruvian Amazon was under at least weak drought conditions (MCWD ≥ 30 mm) during extreme drought years. Up to 20% of the area was classified under the highest drought stress category (MCWD ≥ 200 mm), a level linked to vegetation shifts from rainforest to savanna ecosystems.

Crucially, the 2023–24 drought not only recorded the highest MCWD value but also demonstrated the most widespread coverage of high-stress zones, particularly in central and southern regions. CHIRPS and MSWEP data corroborated that this drought extended deeply into the Andes–Amazon transition zone - areas highly vulnerable due to their unique rainfall patterns and ecological significance.

What are the environmental implications and future directions?

The ecological impact of such extreme droughts is profound. High MCWD levels are associated with increased tree mortality, reduced photosynthesis, and heightened fire susceptibility. The study's evaluation of energy fluxes, such as net solar radiation and the Bowen ratio, indicated a significant departure from climatological norms during extreme droughts. August, the end of the hydrological year, consistently showed peak water deficit and energy stress across affected regions.

Importantly, the research highlights that even short-term variations in evapotranspiration significantly influence MCWD calculations. The team found that using a fixed Et value (commonly 100 mm in earlier studies) underestimates drought severity, reinforcing the importance of dynamic climate modeling for accuracy. Differences of over 20 mm in MCWD estimates were observed when using ERA5 data to capture real-time evapotranspiration variability.

The study also calls attention to the limitations of MCWD. While highly effective at capturing dry-season stress, it does not account for the mitigating effects of heavy rainfall during wet seasons. Mechanisms like groundwater recharge, capillary rise, and plant hydraulic buffering play a crucial role in ecosystem resilience but are not reflected in MCWD metrics alone.

The authors advocate for continued refinement of drought indices and stress the need for expanded in situ measurement networks in the Peruvian Amazon. Given the critical role of this region in global climate regulation and biodiversity conservation, these findings underscore an urgent need for localized drought monitoring and mitigation strategies.