The Pacific slope of Peru is greening, and this is not good news

Newswise — Over the last two decades, the Cavendish Laboratory in Cambridge conducted a thorough examination of satellite data to analyze the changes in vegetation along the Pacific coast of Peru and northern Chile. This region is known for its distinctive and delicate arid and semi-arid ecosystems.

The findings of the study, published in MDPI Remote Sensing, indicate that certain areas have experienced positive vegetation growth, referred to as "greening," while others have displayed negative trends, known as "browning." These changes in vegetation patterns can be attributed to various factors such as agricultural practices, urban development, and alterations in land use.

The most intriguing discovery of the research was a significant greening trend observed in a vast section of the West Slope of the Andes during the same 20-year period. This area, stretching approximately 2000km from Northern Peru to Northern Chile, has witnessed substantial growth in its vegetation over time. Interestingly, the greening trend varies with altitude, leading to distinct vegetation types at different elevations.

The research team comprised mathematicians, geographers, biologists, and earth scientists who utilized satellite imagery from 2000 to 2020 to observe changes in vegetation across the studied region. With 450 data points plotted, they developed a robust mathematical model to filter out artificial variations like cloudy days and seasonal effects. Through rigorous statistical analysis, they focused on areas with significant trends to ensure the validity of their findings.

According to Hugo Lepage, the mathematician from the Cavendish Laboratory and the study's lead author, perfecting the methodology and statistical model took three years. They wanted to ensure that the observed changes were genuinely widespread and not just random fluctuations.

To validate their data, the researchers embarked on multiple field trips, making on-ground observations to confirm their numerical assessments. Their investigations began with a localized study of the impact of mining on local vegetation. Surprisingly, the data indicated that the area was experiencing greening rather than browning. Expanding their focus, they discovered similar greening trends on a larger scale in other regions. Subsequent ground observations aligned with their satellite data, confirming the remarkable greening phenomenon.

The researchers were not only intrigued by the existence of the greening strip but also fascinated by its unexpected characteristics. Eustace Barnes explained that the strip's altitude increases as they move southward, ranging from 170-780 m in northern Peru to 2600-4300 m in the southern part of Peru. This defies intuition, as one would typically expect surface temperatures to decrease with both southward movement and higher elevation.

Equally surprising was the fact that the extensive greening strip did not conform to the climate zones established by the widely-used Köppen-Geiger classification system, which is based on vegetation and serves as an empirical climate classification system. On the other hand, the greening and browning trends observed in the coastal deserts and high Andes align well with this classification.

Hugo Lepage elaborated that the greening strip in northern Peru primarily exists within the climate zone classified as a hot arid desert. However, as they observed the strip further south, it ascended to align mostly with the hot arid steppe zone and ultimately transitioned to the cold arid steppe zone. This discrepancy with the expected climate zones intrigued the researchers.

The findings of this study hold significant implications for environmental management and policymaking in the region. Although the specific cause and consequences of this greening phenomenon remain unknown, any substantial change (30-60% increase in vegetation index) in the vegetation will inevitably impact ecosystems and the environment at large.

According to Barnes, the Pacific slope plays a vital role in supplying water to two-thirds of the country and is also the primary source of Peru's food. With the rapid changes observed in vegetation, water levels, and ecosystems, there will undoubtedly be implications for water and agricultural management and planning.

The researchers are confident that their findings will make a substantial contribution to the scientific community's understanding of the intricate interactions between climate change and the delicate ecosystems in arid and semi-arid environments.

Lepage likened their discovery to a warning sign, akin to the canary in a coal mine. While it may be challenging to prevent changes on such a large scale, being aware of these transformations will enable better planning for the future.

This research was carried out by the Environmental Physics Group led by Prof. Crispin Barnes and funded by Universidad Nacional de Cañete (UNDC), dpto Lima, Peru.